EA043119B1 - METHOD FOR CREATING HIGHLY EFFICIENT GEOTHERMAL WELL STRUCTURES - Google Patents

Description

The field of technology to which the invention belongs

The present invention generally relates to the creation of geothermal well structures, and in particular to methods for changing the permeability of a given geological environment to create highly efficient geothermal well structures with improved thermal and mechanical characteristics, and in addition, with improved working fluids composition.

Prerequisites for the creation of the invention

The extraction of geothermal energy is an attractive idea from an energy point of view, as well as from an environmental point of view, due to the possibility of its reclamation.

Known hitherto technical solutions have focused on problems relating to the permeability of wells, their geometries, working fluids, the configuration of well structures with multiple transverse sections and energy production. Examples of attempts to solve these problems will be discussed below.

The topic of permeability disturbance of the geological environment is covered in the proceedings of the World Geothermal Congress, Melbourne, Australia, April 19-25, 2015, Badalyan et al.

Here, we present a new way to evaluate permeability disturbance in thermal reservoirs. It has long been known that the cause of disturbance of the permeability of the geological environment is the mobilization, migration and straining of fine material of natural reservoirs ... The migration of fine material generated by the speed leads to some decrease in the permeability of the geological environment, resulting in an initial violation of the permeability of the geological environment. The subsequent injection of a low ionic strength aqueous solution increases the electrostatic repulsion force between the clay particles and the sandy surface, causing further mobilization of the particles, which leads to a violation of the permeability of the geological environment. Mobilized fine material with mixed-layer illite-chlorite mineralogical composition causes a decrease in the permeability of the geological environment due to blockage of pore channels.

Fine material migration is one of the most common mechanisms for permeability disturbance in oil and gas wells. Numerous recent publications talk about the deterioration of well quality due to the migration of fine material in geothermal fields.

In Proceedings of the International Conference on Drilling Technology and Subsequent Development of Geothermal Wells, Mechanisms for Permeability Disruption in Primary Permeability Geothermal Wells, Albuquerque, New Mexico, USA, January 21, 1981, Bergosh et al. The summary of their presentation states the following:

Heat-bearing geological media with primary permeability are subject to permeability disturbance during drilling and subsequent development of wells. Permeability disturbances are investigated near the wellbore, which can be caused by the penetration of solid particles and chemical interaction between clay materials of the subsurface, mud filtrates and formation brines. Permeability testing of filtrates of various chemical compositions in sandstone from the East Mesa region shows that permeability is significantly impaired by the flow of formation brines with low salinity. This disturbance is attributed to the processes of cation exchange and cation migration, which undermine the stability of clay structures. The shear action of the fluid dislodges the particles that clog the pore channels, irreversibly reducing the permeability. A test program to study the effects of fluid-borne particles on heat-bearing geological media is ongoing. The final results of these tests will be presented at the conference.

It is clear that the loss of permeability of these thermal fluids has a significant impact on the productivity of the well structure and hence energy recovery.

In the proceedings of the World Geothermal Congress, held from May 28 to June 10, 2000 in Kyushu - Tohoku, Japan, the report Physico-chemical aspects of clay material migration and decrease in injectivity of geothermal clastic reservoirs, Chistyakov (Tchistiakov) summarizes:

The likelihood of a permeability failure can only be assessed with an open mind and interdisciplinary thinking, and not by automatically applying mathematical equations to laboratory test results. We believe that a better understanding of the fundamental physico-chemical principles of stability and migration of clay particles in porous media will help scientists develop better and more efficient use of existing technologies to prevent clay-induced permeability disturbance of geothermal reservoirs.

This document states that the disturbance of the permeability of the geological environment during well drilling is caused by clay material.

In a short lecture course on geothermal developments and geothermal wells organized by GTP at the United Nations University and LaGeo in Santa Tecla, El Salvador, from 11 to 17 May 2012, in the presentation Acidizing geothermal reservoirs to stimulate the flow of Barrios et al.

- 1 043119 (Barrios et al.) note:

There may be siltation of both injection and productive wells, which reduces their productivity and injectivity below their capacity. The main causes of these blockages can be penetration of drilling fluid (mainly bentonite) into microfractures of the formation, ingress of rock fragments or drilling fines during drilling with complete loss of circulation, ingress of large amounts of dissolved solids, re-injection of water with a high potential for precipitation of silica, formation of fine-grained solids displaced by migration of the clay fraction, ingress of amorphous silica fragments from re-injection pipelines during their cooling and heating after service, calcite precipitation in the perforated liner and/or in the perforated production string.

It is only possible to ensure a continuous flow for energy generation by controlling all possible causes of permeability failure. It is well known that the field of geothermal energy uses technologies and practices similar to those used in the oil industry over the past 50 years. Oil and gas wells are similar in terms of scaling and mud fouling problems, and similar techniques can be applied to prevent permeability problems to improve injectivity and productivity for geothermal wells. A cost-effective and widely used solution is to use acids to dissolve deposits and blockages created by solids.

At the Society of Petroleum Engineers conference and exhibition, held from 3 to 5 July 2015 in Budapest, Hungary, in the abstract of the report A new laboratory method for assessing permeability disturbance in geothermal wells, You et al. (You et al.) note:

A new method for assessing permeability in heat-bearing geological media and predicting well productivity decline is presented. The developed laboratory technique aims to determine the deterioration of permeability based on data on the mobilization, migration and straining of fine material in the natural geological environment. Conducted laboratory tests of core flooding with a constant and gradually reduced ionic strength of the solution with the measurement of pressure loss along the length of the core and the accumulated concentration of leached particles. Formation permeability stabilization takes place after numerous porous structures are filled, it can be assumed that the drift of mobilized particles is slow compared to the water carrier. An aqueous solution of low ionic strength increases the electrostatic repulsive forces between clay particles and sand grain surfaces, which contributes to further mobilization of particles and leads to a violation of the permeability of the geological environment. Mixed-layer kaolinite and illite-chlorite clayey rocks are identified by scanning electron microscope analysis and energy dispersive X-ray analysis, and it is these rocks that are primarily responsible for permeability disturbance. With an increase in temperature, the binding of particles was competed by a decrease in the viscosity of the aqueous solution, on the one hand, and a weakening of the electrostatic attraction, on the other. Micromodeling of the mechanical equilibrium of particles of fine material shows that the effect on particle binding of the viscosity of the aqueous solution is dominant. The result is fine material shedding and deterioration of permeability as the temperature rises.

With regard to drilling fluids, many proposals have been made regarding their composition in order to mitigate problems associated with, among other things, strengthening, permeability and compaction of wells. Drilling fluids are also relevant to the above discussion of reservoir permeability disturbance.

US Pat. No. 6,059,036, issued May 9, 2000 to Chatterji et al., discloses methods and compositions for compacting subterranean areas. The text of this patent reads:

The present invention provides improved methods and compositions for compacting subterranean zones and limiting losses of drilling fluid, its flow through the well from one formation to another and/or underground emissions. The proposed method for compacting the underground zone basically contains the following stages:

preparing a viscous, delayed setting sealing composition according to the invention, introducing the sealing composition into the subterranean area to be sealed, and leaving the sealing composition to set as a hardened sealing mass.

The proposed sealing compositions include a water-containing alkali metal silicate, a gelling agent to increase the viscosity of this solution, and a slow-acting polymerization or cross-linking activator of said alkali metal silicate and setting of the sealing composition in the form of a hardened sealing mass.

As mentioned above, where low density sealant compositions are required or where a large cavernous subterranean area is required to be sealed, the sealant composition may be foamed to activate and swell it. The non-foamed and foamed compositions may also include thinners and/or bridging agents to facilitate filling and sealing of the zone.

This document is useful in that it demonstrates the effectiveness of alkali metal silicate compositions in preventing mud losses and in sealing wells in general.

US Pat. No. 7,740,068, issued June 22, 2010 to Ballard, discloses a silicate well fluid and methods for stabilizing unconsolidated subsurfaces. The text of this patent reads:

Advantageously, embodiments of the present invention can provide wellbore treatments or additives that can be used to stabilize the unconsolidated subsurface. The use of solid or pulverized silicate precipitants can slow down the reaction between the silicate and the precipitants or prolong the gel time. Slowing down the reaction can allow the gel components, silicate, and precipitants to more fully penetrate the unconsolidated subsurface before gelation occurs. In addition, if silicate precipitators are used in the form of solid material crushed to micron or submicron sizes, then silicate precipitators have less interference when penetrating into the geological environment.

This document is useful in that it justifies the feasibility of using silicates to stabilize the geological environment.

U.S. Patent No. 8,822,386, issued September 2, 2014 to Quintero et al., discloses drilling fluids containing nanoparticles and methods for using such fluids in drilling, as well as fluids used in well completion. This document further contributes to the body of work relating to drilling fluids and speaks to the benefits of using such fluids in the drilling process. The text of this patent gives further details in this regard.

According to one non-limiting exemplary embodiment of the present invention, a drilling fluid containing nanoparticles is believed to be useful in terms of stabilizing a well during drilling, in particular when driving shale areas that may contain areas that are prone to shedding into the well or contain clay prone to swelling, which is undesirable, in contact with water introduced in the composition of the drilling fluid. As such a drilling fluid, in particular, aqueous drilling fluids such as WBM, non-aqueous drilling fluids such as OBM or SBM, or combinations thereof, namely emulsions, can be used. A surfactant may be used in an amount that ensures the suspended state of the nanoparticles in the drilling fluid. It is assumed that nanoparticles are useful in the composition of such shale stabilizing drilling fluids, which have the property to bind to shale and help to maintain its original state or state as close as possible to the original state, that is, strengthen the wellbore wall. Surface-charged nanoparticles, such as carbon nanotubes, can contribute to this stabilization of the shale. In addition, the small size of the nanoparticles provides them with excellent access to the shale microstructure matrix to hold both the outer and inner surfaces of the clay and minimize damage to its structure.

The use of high-silica hydrous alkali metal silicates as drilling fluids is disclosed in US Pat. No. 9,212,304, issued December 15, 2015 to McDonald. This document is additional evidence in favor of the applicability of such compositions in the oil and gas industry. The text of this patent reads:

The present invention provides a method for stabilizing a wellbore when drilling wells for conventional and unconventional energy sources, including (but not limited to) conventional oil and gas wells, shale gas and oil sands. The method involves the use of a drilling fluid that, among other things, can react with shale to prevent hydration and dispersion, plug microcracks, prevent shale separation, prevent an increase in the proportion of bituminous oil, and enable drilling of depleted zones.

The present invention contemplates the use of larger, more complex polysilicate anions found in high silica hydrous silicates. These high silica hydrous silicates are not conventional commercially available silicates. These polysilicate anions accelerate the precipitation and polymerization reactions to a greater extent than hydrous silicates of standard silica. Higher silicity yields a silicate with lower salinity, which makes the drilling fluid less polluting. To achieve the necessary stabilization of the wellbore, high-silica water-containing silicate can be added to the drilling fluid in a wide range of concentrations. The concentration of soluble silicic anhydride in the drilling fluid can be from 0.25 wt.% to about

- 3 043119 wt.%. As far as pH is concerned, it seems preferable to keep this value above 10.

In the paper High-Temperature Plug Formation with Silicates, presented at the 13th Thermal Fluid Engineering Symposium, held at Stanford University, Stanford, California, Jan. 31-Feb. 2, 2005, Stephen Bauer et al. disclose a method for temporarily plugging certain areas of drilling fluid leakage that are commonly encountered in drilling wells in the oil and gas and geothermal industries. This paper describes a chemistry that utilizes the unique gelling properties of silicates in a cost effective and environmentally friendly manner to form plugs to restrict water inflow into a well by injecting steam into the formation and pouring slurry as the drilling fluid exits. This report does not cover the creation and use of silicate-based drilling fluid for wellbore sealing and the provision of multiple transverse connection channels to create a closed loop geothermal system.

In the application PCT WO 03/106585 in the name of Halliburton Energy Services (Halliburton Energy Services), a method for creating a chemical protective casing is described: Drilling a wellbore is performed with a drilling fluid with a pH in the range of 6 to 10 and containing water, a polymer cationic catalyst, capable of accepting and donating protons, which is adsorbed on unconsolidated clay, shale, sandstone, etc., a water-soluble or water-dispersible polymer that is crosslinkable by a thermosetting resin and becomes hard and viscous upon exposure to the latter, and a water-soluble or water-dispersible thermosetting resin capable of crosslinking said polymer. The drilling fluid is subjected to catalysis and aged, then it is used to consolidate weak zones of the geological environment, thus preventing the collapse of the walls of the well.

This document does not address the creation and use of drilling fluid to seal a wellbore, nor the provision of multiple transverse connection channels to create a closed loop geothermal system, nor the maintenance of a seal over the lifetime of a geothermal system (50 years or more).

With respect to multiple lateral connection technology, an example is US Patent No. 9,512,705 to Halliburton Energy Services, which describes a mechanical multi-channel lateral connection for isolating multiple horizontal wells from the surrounding subsurface. The prior art is characterized by complex and expensive mechanical or cemented joints, the creation of which requires many installation steps. Because of these many steps, it is necessary to interrupt drilling operations, in particular, to retrieve the drill bit and bottomhole block to the surface, or to wait for the cement to set.

Another disadvantage of known multiple lateral communication channel technologies is the reduction in the borehole inner diameter, which makes drilling subsequent lateral channels much more difficult and may require drilling of vertical wells and larger central boreholes.

With regard to well geometries and aspects related to power generation, U.S. Patent No. 6,301,894, issued October 16, 2001 to Halff, discloses a geothermal power plant based on a closed loop underground heat exchanger. This patent focuses on the benefits of generator location, water conservation, water purity and efficiency when using multiple closed loops. This patent does not say anything about technologies for creating efficient wells with a closed loop without the use of casing.

A geothermal system with a closed loop is described in US patent publication No. 20110048005, published on March 3, 2001 on behalf of McHargue. The novel approach is to circulate a drilling fluid (liquid or gas) through a thermally charged subsurface through continuous underground pipelines formed by continuous cemented channels along a path formed by the intersection of two or more wells.

This patent does not say anything about technologies for creating efficient wells with a closed loop without the use of casing.

GreenFire Energy Publication PCT/US/2016/019612 talks about how to extract thermal energy from high-temperature, low-permeability geothermal environments using closed-loop geothermal thermal systems to generate electricity. The text of the post reads:

A method or apparatus for using a fluid in a closed loop downhole system to extract thermal energy from heat-carrying subsurfaces to generate electrical power is/is located within or near high-temperature, low-permeability subsurfaces. In some embodiments of the proposed

- 4 043119 of the invention, a closed loop system may have one or more heat exchange zones, of which at least some may be located in an underground region, the temperature of which is at least 350°C. This subterranean region may be within a plastic zone or within 1000 meters of a plastic zone that has a temperature gradient of at least 80° C. per kilometer of depth.

Some embodiments of the proposed methods for the production of geothermal energy suggest the possibility of having intervals of wells that are not cased with metal pipes, but instead, at such intervals, reservoir rock is used as the walls of the well, compacted with a hardened sealant, and the wall of the well at such intervals is formed by such a hardened substance - a compactor, which in some embodiments of the invention makes the borehole diameter at such intervals larger, and in some cases much larger, than at intervals where the wellbore is cased with metal pipes.

Once the closed loop heat exchange system is installed, a fluid can be circulated through it to heat the latter and generate power with the heated fluid. In particular, the energy extracted from the heat-bearing subsurface environment can be used directly for heat supply, or converted into electrical energy or other useful forms of energy, as is known to those skilled in the art.

In addition to determining the temperature profile and the heat loss recovery profile, the proposed methods make it possible to assess the long-term prospects of the geological environment for the production of geothermal energy based on the temperature profile and the heat loss recovery profile. Such an analysis can be performed by modeling well performance as a function of time, taking into account changes in temperature, heat flow intensity, plasticity of the geological environment in the vicinity of the well, and other parameters over time, in order to assess the change in the amount of energy extracted and the conversion efficiency provided by the system over time. Such an analysis may also be performed to compare different regions of a given subsurface in order to determine one or more suitable locations for the placement of heat exchange circuits.

Embodiments of the present invention disclosed herein relate to apparatus and methods for extracting energy from high temperature impermeable geological media without fractures or pores, natural or stimulated. Contrary to the prevailing consensus that some degree of permeability and hence convection is required for efficient heat transfer and power generation, the inventors of the present invention have found that an impermeable thermal environment can be an efficient and sustainable resource for extracting geothermal energy, in particular for generating electrical energy.

A closed loop geothermal heat exchange system can be placed in a subterranean subterranean environment based on a particular temperature profile and a particular heat loss recovery profile of that subterranean environment. Deployment of a closed loop geothermal heat exchange system may involve drilling, casing, perforating and blasting, cementing, reaming fractured open hole walls, sealing open hole walls, and other drilling and well contouring operations as known to those skilled in the art. This arrangement may include locating the heat exchange zone of the closed loop subsurface system within a plastic zone or a brittle-to-ductile transition zone. In some embodiments of the invention, this arrangement may include or further include placing the heat exchange zone of the closed loop system in the subsurface within the brittle zone, as well as stimulating the brittle zone in the vicinity of the heat exchange zone.

It has been said above: The deployment of a closed loop geothermal heat exchange system may involve drilling, pipe casing, perforating and blasting, cementing, reaming open hole walls with cracks, sealing open hole walls, and other operations related to drilling and completion of the well contour, as is known to the experts.

Nothing is said in this document about methods, sequences, chemistries, or technologies that relate to sealing openholes, maintaining seal over time, and maintaining wellbore integrity.

In the summary of Dry Hot Rocks - A New Source of Geothermal Energy, Energy, Volume 3, Issue 5, October 1978, pages 639-644, Mortensen writes the following:

The project, led by the Los Alamos Research Laboratory, is designed to demonstrate the technical and economic feasibility of extracting energy from dry hot rocks as a geothermal source. The system being tested has two deep boreholes drilled in hot impermeable rock and connected by a hydraulic fracture. In September 1977, the circulation loop was closed for the first time and water circulated in the bottomhole tank and in a pair of 10-megawatt thermal heat exchangers. To evaluate the thermal, chemical and mechanical properties of this energy extraction system, a series of long-term experiments is planned for 1978.

Based on geothermal energy harvesting technologies, Senju et al., in U.S. Patent No. 10,260,778, issued April 16, 2019, claim [c]a way to create a geothermal power plant to extract thermal energy from a hot dry subsurface with low porosity , in which the combined supply and return well (22) is drilled to the first predetermined depth, after which the well is drilled to the second predetermined depth, forming the lower part (22') of the said combined supply and return well, while at the said second predetermined depth, the first reservoir is created zone (8), the lower part (22') of said combined supply and return wells (1') is extended by drilling a well with the same or smaller diameter to a maximum depth, where a second reservoir zone (9) is created, while drilling one or more production wells (P) to create a closed loop between the mentioned first reservoir zone (8) and the second reservoir zone (9), made with the possibility of circulation of the working fluid in it, while in the said combined supply and return well (22, 22') a pipe (5) is installed, and between said first and second collector zones (8, 9) a fluid seal (66) is installed, sealing the annular space (20) between the lower part (22') of said combined supply and return well and said pipe (5) in order to separate the supply and return flows.

Thus, prior to the priority date of the present invention, the prior art is in need of a method for extracting thermal energy from the subsurface that is applicable in creating and maintaining wellbore seals under closed-loop geometries and is efficient for geothermal applications without limitation. type of geological environment, in particular, its permeability.

The present invention solves a number of problems in various fields of technology and uniquely combines the principles to create a new direction in the field of geothermal energy.

Brief description of the invention

One of the objectives of the invention is to provide significant improvements in the technology of creating borehole structures in general, as well as in the field of geothermal energy extraction.

Another objective of the present invention is to provide a method for creating a well structure in a geological environment suitable for extracting geothermal energy, comprising the following steps:

during the drilling process, an irreversible permeability disturbance is caused in the well structure using at least one of the following actions: thermal, mechanical, chemical, biological, and a layer practically impermeable to fluids is created between the well structure and the geological environment.

The use of permeability disruption technologies is a paradoxical solution in the field of drilling wellbores and, in particular, in the field of geothermal energy, depending on the migration of fluid through pores, fractures, etc. The proposed technology, as a first step, involves sealing cracks and other areas of the geological environment facilitating fluid migration.

The present invention provides for the use of destructive techniques to reduce the permeability of the borehole walls to such an extent that in the subsurface the heating of the working fluid intended for heat extraction is carried out only due to the conductive heat transfer from the surrounding rock.

This technology generates the immediate benefit of reducing or eliminating the need for casing and connectors. This alone provides great savings in drilling, and this process accounts for most of the costs associated with the development of geothermal resources.

With regard to another objective of one of the aspects of the implementation of the present invention, it is to provide a method for creating a well structure with an inlet well and an outlet well drilled in a geological environment suitable for extracting geothermal energy, comprising the following steps:

cause an irreversible permeability disturbance for the wellbore extending between said inlet and outlet wells during drilling of this wellbore, using chemical action to create a practically impermeable layer between said wellbore and said geological medium, circulating in said wellbore structure of the chemical composition, capable of causing precipitation on the subsurface with said interlayer to increase the sealing ability and mechanical integrity of this interlayer, and

- 6 043119 carry out the circulation in the compacted wellbore of the working fluid containing an additive that helps maintain the layer to maintain impermeability in the process of circulation of the working fluid in the well structure.

The impermeable layer between the wellbore and the surrounding geological environment is formed due to a special choice of chemical compounds and sequence of operations. The result is an impermeable, self-healing wellbore that, when built into a real surface loop, provides an excellent alternative to geothermal fracturing and casing-in-the-loop geothermal technologies.

Those skilled in the art will appreciate that a wide variety of chemical compositions can be used to form said interlayer. To do this, the composition of the drilling fluid can be used those compounds that form a sediment with the geological environment surrounding the wellbore. For the second treatment, any suitable compound may be used which reacts with any non-precipitated composition remaining after the first treatment. Finally, a working fluid can be selected to circulate in the loop to further respond to the various crevices, cracks, anomalies, etc. that develop over time in the interlayer.

The working fluid is selected to optimize the thermodynamic performance of the geothermal system and improve the mechanical integrity of the wellbore. To ensure this, after completion of drilling, additional operations may be performed to treat the wellbore.

Well structures formed using the technology described here can be made suitable for creating closed loop geothermal systems in a single operation, as opposed to the multi-stage operations required with existing technologies. In addition to a clear reduction in the number of individual operations, a positive economic effect is also provided. This is the main feature of the proposed technology, which puts it much higher than the methods currently used.

From a performance standpoint, measures to address problems that arise during drilling due to irregular or changing conditions must be taken promptly as problems arise. Another essential feature of the proposed technology is its adaptability and flexibility. Since this methodology is based on technologies for creating a well in the geological environment by destroying a reservoir, in which these technologies are in conflict with known technologies, the proposed technology, in the worst case, proposes to make the geological environment suitable for creating a geothermal system with a closed loop, without taking into account permeability or geological structure.

Alternatively, another aspect of the present invention is to provide a method for producing a well in a heat-bearing subsurface for energy recovery, comprising the following steps:

an open hole is drilled in a heat-bearing geological environment, injected into the wellbore active chemicals for chemical reactions to form a fluid-tight interlayer between the wellbore and the geological environment, so that said interlayer also contains unreacted active chemicals, and injected into the wellbore well working fluid capable of reacting with said unreacted active chemicals to further form the interlayer.

As long as there is an effective supply of unreacted active chemicals, the wellbore is capable of self-healing in the event of any interlayer problems. Thus, the working fluid not only removes the thermal energy of the geological environment with maximum operational efficiency, but also ensures the integrity of the interlayer is maintained without requiring a lot of effort and money.

In order to implement the environmentally responsible methods that are set forth here, another goal of one of the embodiments of the present invention is to provide a method for restoring a wellbore, including sections that have undergone hydraulic fracturing, created in the geological environment using hydraulic fracturing technologies, containing the following stages:

the wellbore and the porous space of the areas subjected to hydraulic fracturing are treated with the first chemical composition, which is capable of forming a deposited impermeable layer in these areas, and in order to precipitate possible unreacted residues of the mentioned first chemical composition, this layer is treated with the second chemical composition for its further compaction.

The sealing technologies described here make it possible to both restore and transform geothermal processes based on hydraulic fracturing.

In this regard, another object of one of the embodiments of the present invention is to provide a method for converting an open geothermal system, the geological environment of which has at least one of the following: a fracture, unconsolidated rock, sand, having an inlet well in communication with the possibility of transferring fluid And

- 7 043119 outlet well, into a geothermal well structure with a closed loop, comprising the following stages:

a first chemical composition is introduced that is capable of forming a deposited impermeable layer in the area between said inlet well and outlet well and in said geological environment having at least one of the following: a fracture, unconsolidated rock, sand, thereby providing the creation of a closed loop, including said subsurface having at least one of the following: a discontinuity, unconsolidated rock, sand, and said inlet well, outlet well, and the area therebetween, and to deposit possible unreacted residues of said first chemical composition, treat said interlayer with a second chemical composition for further compaction.

Brief Description of Attached Graphics

In FIG. 1 shows plots of filtrate volume versus time for fluids of various compositions.

In FIG. Figure 2 shows graphs of pressure drop and permeability versus time during core tests for waterflooding with chemically anchored formation, described in example 1.

In FIG. 3 schematically shows a section of a borehole structure with walls that are impermeable in the transverse section between the inlet and outlet wells without casing.

In FIG. 4, a well structure similar to that shown in FIG. 3 is shown with casings on a portion of said transverse section, and the connections to the seal are also illustrated.

In FIG. 5 is a compacted well structure similar to that shown in FIG. 4 is depicted in a discontinuous subsurface with negligible permeability.

In FIG. 6 schematically shows a multi-channel structure of transverse connecting sections of a well structure.

In FIG. 7 is a fragment of the multi-channel structure of the transverse connecting sections sealed with impermeable walls, shown in FIG. 6 is shown schematically on an enlarged scale.

In FIG. 8 is a schematic representation of an alternate configuration geothermal well structure.

In FIG. 9 is a schematic representation of a geothermal well structure according to yet another alternative configuration.

In FIG. 10 schematically depicts a geothermal well structure according to an alternative embodiment.

In FIG. 11 is a schematic representation of a geothermal well structure according to yet another alternative embodiment.

In FIG. 12 is a schematic representation of a geothermal well structure according to yet another alternative embodiment.

In FIG. 13 the geothermal well structure shown in FIG. 12 is shown in plan view.

In FIG. 14 is a schematic representation of a geothermal well structure according to yet another alternative embodiment.

In FIG. 15 is a schematic representation of a geothermal well structure according to yet another alternative embodiment.

In FIG. 16 is a cross-sectional view of a wellbore drilled in a high permeability subsurface, showing the unconverted packing material,

In FIG. 17 in the same view as in FIG. 16 illustrates the transformation of a wellbore impermeability layer after circulating contact with a working fluid.

In FIG. 18 shows a cross-sectional view of a wellbore drilled in a low permeability subsurface and an interlayer between the wellbore and the surrounding subsurface.

In FIG. 19 is a diagram of an embodiment of a power cycle for a geothermal well structure in accordance with the present invention.

In FIG. 20 is a diagram of an alternative to that illustrated in FIG. 19 embodiments of the energy cycle of the geothermal well structure.

In FIG. 22 is a diagram of an integrated geothermal circuit comprising a turbine and generator driven directly by the working fluid of the geothermal system.

In FIG. 23 is a diagram of an alternative embodiment of an integrated geothermal circuit to that illustrated in FIG. 22.

In FIG. 24 shows graphs of the temperature of various working fluids as a function of distance.

In FIG. 25 schematically shows a system of wells connected in a W-shaped configuration or in a loop.

In FIG. 25A is a set of transverse connection wells of the system depicted in

- 8 043119 fig. 25 is shown on an enlarged scale.

In FIG. 26 depicts a well system in accordance with an alternative embodiment to that illustrated in FIG. 25.

In FIG. 27 depicts a well system in accordance with yet another alternative embodiment to that illustrated in FIG. 25.

In FIG. 28 depicts a well system in accordance with yet another alternative embodiment to that illustrated in FIG. 25.

In the accompanying drawings, like elements are given like reference numerals.

The present invention is applicable in the fields of geothermal energy and reclamation of areas of the earth's crust that serve as a source of geothermal energy.

Detailed Description of the Preferred Embodiments of the Invention

Briefly, the present invention relates to the design and technical implementation of well structures, in particular geothermal well structures with a closed loop. The aspect of technical execution includes operations:

i) sealing (impermeability of the walls) of the wellbore during drilling, ii) upon completion of the drilling process, strengthening the seal with a chemical treatment, and iii) then replacing the drilling fluid with a circulating working fluid that enhances and maintains the seal by creating a sealing layer in places of remaining permeability and its recovery in the event of permeability while maintaining the integrity of the wellbore.

The flexibility of this approach allows each of these operations to be applied separately depending on the specific properties of the geological environment, but they are most effective when performed together to create and maintain closed-loop geothermal systems.

The well structure can have a variety of configurations, such as a single U-tube configuration in which the inlet and outlet wells are located on the same piece of land, or a pipe-in-pipe configuration that can be vertical, inclined or horizontal and include a plume of several such well structures, or an L-shaped configuration, etc. These are just examples and the variety of configurations is not limited. Those skilled in the art will be aware of other suitable solutions.

The options mentioned above are particularly effective in creating multiple lateral communication channels downhole systems in which the multiple lateral communication channels are connected to a vertical wellbore, typically a U-tube well structure with multiple horizontal channels connecting a vertical cased inlet well. and a vertical cased outlet well. The use of multiple transverse connecting channels provides several advantages, hitherto unknown in the industry. Namely, the following.

i) To save time and material costs associated with the installation of casing, transverse connection channels can be started, drilled and completed open hole.

ii) When drilling, it is possible to create and seal (tighten) joints in open holes in a single drilling operation. This eliminates complicated mechanical connectors, placing cement in the annulus, drilling out the cement plug or metal sections, multiple deliveries to the surface, and other complexities and costs associated with intricate underground operations that lead to delays in prospective drilling.

iii) Does not reduce the internal diameter, which allows you to drill an unlimited number of transverse connecting channels.

iv) There is no reduction in heat transfer due to the presence of an insulating cement layer or a fixed annulus between the steel casing and the rock.

v) Finally, it was possible to re-enter multiple transverse connection channels with magnetic location equipment to intersect with other transverse wellbores and create a closed well structure with a U-tube configuration.

With regard to compaction during drilling, it can be carried out by adding additives to the drilling fluid itself, which create an irreversible permeability, reducing the latter to zero or lowering it to a negligible level.

Such additives can be biofouling accelerators, such as those used in microbiological enhanced oil recovery methods, or physical particles capable of creating an impermeable clay cake, or chemical bridging agents that react upon contact with and penetration into the subsurface, such as , time curing resins or thermoset resins and epoxies, gels and polymers.

Another way to seal a wellbore while drilling relies on compacting the rock surface by melting the borehole wall at extremely high temperatures, such as with high temperature plasma or a laser drill head.

- 9 043119

The preferred solution is to use chemical bridging agents, such as an alkaline silicate drilling fluid with a pH greater than 10.5, which remains liquid in the wellbore but settles to form a solid after contact with and penetration into the rock. The technical function of the drilling fluid is different in permeable rocks (eg sandstone or fractured rock) and in impermeable rocks such as, for example, tight shales or siltstones. In permeable geological environments, liquid alkaline silicate drilling fluid enters all kinds of flow paths before it reacts and becomes a solid. The resulting solid sediment fills the porous structure and natural fissures in the rock itself and creates a fluid-tight barrier between the wellbore and the subsurface.

In contrast, in rocks with near zero permeability, such as shale, for example, the function of the drilling fluid is not to disturb the permeability, since it does not exist anyway. In these cases, the drilling fluid is used to create a mechanical and chemical barrier between the rock and the wellbore and fill natural cracks, crevices, or chips. The end result is the same: creating a fluid-tight barrier between the wellbore and the subsurface.

Sealant can also be used for cementation of loose sands, to increase the resistance of the formation to compressive loads and to prevent sand from the formation into the well and collapse of the well walls.

As is known, soluble silicates contain three components, namely, silicic anhydride, alkali metal oxide and water. Silicic anhydride (silicon dioxide, SiO2) is the main component of soluble silicates and is stabilized by alkali metal oxide. The alkali metal oxide may be selected from the following group: sodium oxide (Na2O), potassium oxide (K2O), lithium oxide (Li2O). This component is responsible for maintaining the solubility of silicic anhydride.

Suitable silicates include potassium, sodium aluminosilicates. They are available in both liquid and powder form. In the present invention, the use of silicates is desirable, as they are capable of entering into certain types of chemical reactions, in particular, they form a gel (with a sharp decrease in pH), which is a sign of polymerization or thickening of soluble silicate structures to form a water-containing amorphous silicate gel structure. Gelation is caused by a sharp decrease in pH, while the polymerization process begins to proceed quickly at a pH below 10.5.

Another type of reaction that silicates can enter into is the formation of a precipitate in the presence of cations, in particular calcium cations. Precipitation takes place when cross-linking silicate molecules with polyvalent cations (ie Ca ⁺ 2, Mg ⁺ 2, Al ⁺³ , Fe ⁺³ , etc.). These cations are present in the formation fluid, so the result of the interaction of the drilling fluid with the formation fluid is the deposition of a solid in the porous structure.

Another type of reaction that silicates can enter into is dehydration. As water is removed from the liquid silicate, the silicate becomes more and more sticky and viscous until it eventually becomes a vitreous film. Such reactions take place in the near-wellbore environment by mixing the filtrate from the drilling fluid with the fluids present in the matrix.

Silicates may be considered particularly suitable for use in the present invention because they exhibit stability as sealants both in local environmental conditions and at ultra-high temperatures. For example, in foundries, alkali metal silicates and sand are used at temperatures of 650°C and above, and this basic chemical reaction is also used to seal concrete structures at ambient temperature.

In order to maximize fluid penetration into the formation and accelerate the absorption of filtrate into the formation for chemical wellbore sealing, the alkali silicate drilling fluid is formulated to be free of solids and have a low viscosity. For multiple transverse connecting channels, friction is a serious problem, so a lubricant additive is added to the drilling fluid that is compatible with the silicate fluid and does not harm the sealing properties of the drilling fluid.

The concentration of the active alkali metal silicate in the water may be from 0.3 to 10% by weight, preferably from 3 to 6% by weight. The optimal concentration value to some extent depends on the properties of the geological environment, in particular, on the specific composition of the reservoir fluid and its temperature. Higher rock temperatures can cause sediment release to be delayed. Sedimentation also slows down at a low content of polyvalent cations in the reservoir fluid, for example, below 1000 mg/l. Therefore, with an increase in temperature and a decrease in the content of cations in the reservoir fluid, the concentration of alkali metal silicate should be increased.

Another benefit of alkaline silicate drilling mud is the increase in ROP and tool life.

- 10 043119

The physical properties of the combined material of rock and compactor are largely dependent on the rock, but can be adjusted by skillful selection of the properties of the compactor. A heat-conducting additive, for example, graphene nanoparticles, can be added to the drilling fluid, which will ensure high thermal conductivity of the sealant.

The energy output of a closed loop geothermal system can be determined using a thermodynamic well system model consisting of a discretized well system with multiple thermal resistances between the fluid temperature and the far zone temperature of the subsurface. Each discretized segment is energy and mass balanced, with fluid properties and calculations determined by the equation of state. Thermal resistances include rock, binder (cement), steel casing, and resistance to convective heat transfer within the downhole system itself.

As a quantitative example, consider a seven-inch cased and cemented well in contact with a geological environment with a thermal conductivity of 3 Βτ/(μ Κ), thermal resistances after five years of operation for rock, cement, casing, and flow convection in the pipe are respectively 2, 2E-02, 2.1E-03, 2.9E-05 and 5.0E-5. Heat transfer is dominated by radial heat transfer through the rock, compared to which all other thermal resistances can be neglected. With the sealant described here, there are no casing or cement thermal resistances, so the thermal efficiency is about 9% higher than the prior art. Heat transfer can be further improved by increasing the thermal conductivity of the rock and/or sealing material.

To improve the performance of the seal and increase the mechanical integrity, solid particles can be introduced into the alkali silicate sealant, capable of chemically incorporating into and/or bonding with the alkali silicate precipitate. Strengtheners such as exfoliated fly ash, surface-activated graphene and graphene oxide, carbon fibers, etc. can be introduced into the drilling fluid. They can be in a nano- or micro-dispersed state and be chemically associated with precipitated silicic anhydride.

After the initial seal has been created during the drilling process, the integrity of the seal is tested. This is typically done by pressurizing the well structure and monitoring the rate of pressure drawdown if it occurs. Another method consists in end-to-end long-term measurement of the rate of absorption of fluid by the reservoir during the circulation process. In this case, the drilling fluid is removed and replaced with a working fluid, the main purpose of which is to deliver energy to the surface, and in the course of performing regular operations, the rate of absorption of fluid by the formation is measured.

Upon completion of drilling, the seal is essentially created, but there may still be small areas with some permeability, such as fractured zones or high permeability channels, that were not sufficiently sealed during the drilling process. Therefore, the seal may be strengthened by chemical washing or treatment prior to commencement or resumption of normal operation.

When using an alkaline silicate drilling fluid, the latter, as described earlier, reacts with the formation fluid to form a gel and subsequently cures to form a solid and high-strength layer. These reactions occur in the mixing zone of the alkaline silicate drilling fluid with the reservoir fluid. In a high permeability channel or fracture, the drilling fluid may permeate through the subsurface so rapidly that the formation fluid is forced out of the wellbore and the mixing zone is substantially displaced into the subsurface, or the formation fluid may be extremely low in salinity such that the silicate gels, but is not completely deposited.

In such cases, there is partial or thorough compaction deep within the rock, while the near-wellbore space contains unspent or unreacted liquid alkali silicate drilling fluid in the absence of formation fluid with which it could react. Therefore, the purpose of chemical flushing is to pump a chemical treatment agent through the wellbore structure at a pressure sufficient to cause seepage from the wellbore into the near-wellbore zone of the geological environment, to contact with the unconsumed liquid alkaline silicate drilling fluid left after drilling and to cause sedimentation. Suitable agents known in the industry are calcium chloride brine, acids, carbon dioxide (CO2), surfactants, esters.

In another form of seal enhancement, a chemical treatment is pumped through the wellbore structure at a pressure sufficient to cause seepage from the wellbore into the near-wellbore subsurface, said chemical treatment consisting of cement plugs or alkaline silicate shots followed by a reactive chemical treatments such as industry known calcium chloride brine, acids, carbon dioxide (CO ₂ ), surfactants, esters. The two chemical treatments can be pumped alternately multiple times, resulting in significant near-wellbore mixing. To prevent mixing within the wellbore or direct contact, the alkali silicate and chemical portions may be separated from each other by a separator.

With regard to maintaining the seal and integrity of the wellbore during operation, it should be noted that the drilling process in the oil and gas field and geothermal energy requires maintaining the integrity of the wellbore and its partial seal (in the form of a mud cake on the walls of the well) for some time until it is established casing string or hidden string. The integrity of an open hole (before casing or liner is installed) and its partial sealing is achieved by proper techniques and the use of drilling fluid.

In contrast, the present invention requires maintaining open hole seal and wellbore integrity throughout the life of the geothermal system, which is 50 years or more.

In addition to creating a seal during the drilling process and, if necessary, reinforcing the seal with a separate chemical treatment, the working fluid itself plays a critical role in maintaining the seal and integrity of the wellbore. The main function of the working fluid is to transfer energy from the subterranean formation to the surface for direct use, either for conversion into electrical energy or for cooling. Therefore, this working fluid must have physical properties that ensure the transfer of energy and maximum thermodynamic efficiency of the system. For example, this fluid may have at least one property selected from the following group:

a) in order to achieve the maximum temperature difference and maximum heat transfer between the fluid and the surrounding heat-bearing geological environment within the transverse connection channel between the inlet well and the outlet well, has a significantly non-linear enthalpy dependence on temperature at pressures above 10 MPa and temperatures below 180 ° C,

b) has the ability to enter into a reversible pressure-sensitive reaction: endothermic at elevated pressure and exothermic at pressures below said elevated pressure,

c) is a mixture entering into the said transverse connecting channel in an endothermic reaction of chemical absorption,

d) is an aqueous solution of an electrolyte with a solubility depending on temperature and pressure, having a heat-absorbing effect inside said transverse connecting channel,

e) is a water-based fluid containing a composition that reduces drag in turbulent flow,

f) is a supercritical fluid such as carbon dioxide (CO2),

g) is a mixture of ethane and ammonia,

h) has any of the workable combinations of features listed in a) to g).

In addition to achieving maximum thermodynamic efficiency, the working fluid also has many drilling fluid properties, namely:

i) brings solids that may have collected in the wellbore to the surface where they are removed, typically by means of a settling tank, filter or hydraulic centrifugal cleaner, environments, and ii i) maintain the stability and integrity of the wellbore.

According to one embodiment of the invention, the seal is maintained by a working fluid that contains solids and that forms a filter cake on the wellbore walls or bridges and plugs natural fractures. As such particles, carbon fibers, mineral fibers, cellulose fibers, particles of silicon dioxide, fly ash, graphite, graphene, graphene oxide, calcium carbonate, bentonite or other materials known in the industry can be used. Typically, these particles are added in an amount of from 0.5 wt.% to 2.0 wt.% relative to the working fluid, if the latter has an aqueous basis, and in an equivalent volume concentration in the case of other types of working fluids.

When using the alkaline silicate drilling fluid described above, the latter reacts with the formation fluid to form a gel, which subsequently hardens to form a solid and high-strength layer. These reactions take place in the mixing zone of the alkaline-silicate drilling fluid and formation fluid. In a high permeability channel or fracture, the drilling fluid may permeate through the subsurface so rapidly that the formation fluid is forced out of the wellbore and the mixing zone is substantially displaced into the subsurface, or the formation fluid may be extremely low in salinity such that the silicate gels, but is not completely deposited. In such cases, there is partial or thorough compaction deep within the rock, while the near-wellbore space contains unused or unreacted liquid alkali silicate drilling fluid in the absence of formation fluid with which it could react. Therefore, another way to maintain the seal involves the introduction of a reagent, which, after penetrating from the wellbore into the near-wellbore zone of the formation, would contact with the unused liquid alkali silicate drilling fluid left after drilling and cause sedimentation.

In fact, any areas of the well structure where permeability remained after drilling had a significant influx of alkali metal silicate and contain unspent liquid alkali silicate drilling fluid in the near-wellbore zone of the formation. Therefore, the reagent introduced into the working fluid will naturally seal the remaining permeable areas. Calcium chloride brine, acids, carbon dioxide (CO2), surfactants, esters, and other substances known in the art can be used as such a reagent.

In order to maintain the stability and integrity of the wellbore, in addition to sealing the formation, the working fluid may exert sufficient pressure on the subsurface to prevent wellbore breakouts, collapse of rock into the wellbore, and partial formation subsidence. The amount of pressure that the working fluid must exert can be calculated using a complex thermodynamic model of the well structure, which includes an equation of state to account for phase transitions, changes in fluid properties with pressure and temperature, and hydraulic friction losses. If calculated correctly, the working fluid should give the entire downhole system a minimum resistance to compressive loads, either by applying a sufficiently high stress at the top of the inlet well (pressurized working fluid) or by changing the density of the working fluid. Along with other techniques known in the industry, the density of the working fluid can be increased by the addition of weighting agents such as barite, or by using soluble salts.

Another way to maintain wellbore stability is to use a shale inhibitor in the working fluid. Such substances have the property of preventing swelling and rupture of clays and shales and are used as conventional drilling fluid additives. Among others known in the industry, suitable additives of this kind include amine-containing reagents, latexes, aqueous solutions of potassium salts.

The combination of the additives and functions described above results in a working fluid that not only efficiently brings energy to the surface, but also strengthens and maintains the wellbore, eliminates permeability when it occurs, and maintains the stability and integrity of the wellbore, providing preventative measures to preserve the geothermal environment. closed-loop systems in a fluid-tight state.

It is important that sealing additives do not impair the thermodynamic properties of the working fluid. According to one embodiment, the water-based working fluid contains a commercially available anti-corrosion additive at a concentration of from 1 l/m ³ to 10 l/m ³ , potassium bromide at a concentration of from 0.05 l/m ³ to 0.3 l/m ³ , 3 mM to 7 mM cetyltrimethylammonium surfactant, 8 mM to 16 mM sodium salicylate, and 0.5 wt% calcium carbonate solids.

The solution described above provides more than 60% drag reduction in turbulent flow over a temperature range that allows direct geothermal heat supply, which is important for efficient operation from a thermodynamic point of view. It also delivers over 40% recovery as tested by American Petroleum Institute (API) Procedure 13i for shale fineness in hot rolling, reacts with unspent alkali metal silicate to form a strong hard layer, and calcium carbonate particles bridge and plug natural cracks. , eliminating the permeability of the bulk of the rock.

According to another embodiment of the present invention, simply a modified alkaline silicate brine is used as the working fluid.

According to another embodiment of the invention, supercritical carbon dioxide (CO ₂ ) is used as a working fluid, which is especially valuable, since in the field of geothermal energy, in many cases, the thermodynamic efficiency of supercritical carbon dioxide (CO ₂ ) is higher than that of water, and in addition, it is an excellent reagent for converting an alkaline silicate liquid into a strong solid material.

In the following, various mechanisms for the formation of a seal will be described by way of example.

Example 1 Sealing by chemical treatment.

The initial testing of the sealing properties of the silicate system was carried out using a permeability tester for rock models while plugging wells.

Testing with a tester to determine the permeability of rock models:

µm, 3000 mD discs (OFITE) were soaked in a 30% calcium chloride solution from evening to morning (for approximately 16 hours) to completely saturate the pores with brine and create a severe case of formation fluid with which the silicate drilling solution.

- 13 043119

Permeability testing was performed in accordance with OFITE guidelines and American Petroleum Institute (API) Procedure 13i for Laboratory Testing of Drilling Fluids:

0 ml of test fluids, to be described below, were transferred to the well of the permeability tester and placed in the pre-soaked disk device. The drilling fluid was brought into contact with the disk for 45 minutes before the device was pressurized and the test started.

The tests were carried out for 30 minutes at room temperature and a pressure of 500 pounds per square inch (>3.45 MPa).

The volume of the filtrate was recorded after 1, 5, 7.5, 15 and 30 minutes.

In FIG. 2 is a plot of some of the parameters over time that are typical of testing on a quarter inch filter disc (7^=6.35 mm). Passage of the polymer control fluid showed no loss of material in the volume of the filtrate. When silicates of various types were added, the filtration rate was sharply slowed down due to sedimentation. It should be noted that the permeability almost disappeared even in a quarter-inch (7^=6.35 mm) thick disk with a permeability of 3000 mD.

Fluid preparation:

1000 ml of polymer fluid at a concentration of 5 kg/m ³ was prepared by mixing xanthan gum (Kelzan XCD™) with fresh water for approximately 30 minutes using a Silverson mixer at moderate shear.

The control fluid used was the polymer fluid described above.

Formulation A 30 ml of Ecodrill™317, commercially available from PQ Corporation, was mixed with 270 ml of the polymer fluid described above to form 300 ml of 3% active soluble potassium silicate.

Composition B: 30 ml of Ecodrill™ K45, commercially available from PQ Corporation, was mixed with 270 ml of the polymer fluid described above to give 300 ml of 3% (v/v) active soluble silicate.

After the permeability test, the volume of composition A was 273.8 ml, according to the calculations, the fast absorption of the filtrate by the formation was 257 ml, and the static flow rate was 3.2 ml/min; the volume of composition B was equal to 103.8 ml, according to the calculations, the fast absorption of the filtrate by the formation was 103.8 ml, and the static filtration rate was 3.7 ml/min. Calculations were performed according to formulas from API RP 13i.

Tests were also carried out for the hydraulic efficiency of the core, restoration of permeability, and damage to the core. These tests are often carried out to study the effect of a drilling fluid or an additive contained therein on the permeability of a core obtained from a production zone of interest. The goal of such studies is usually to minimize harm or maximize restored permeability. Initial permeability is established and measured by saturating a core sample with formation fluid, oil, or some mixture of formation fluid and oil, and forcing formation fluid(s) through the core under conditions of formation pressure and temperature. Then, a test fluid is injected through the surface of the core for a certain period of time, and the volume of the filtrate, the penetration of the fluid and the thickness of the filtered material can be measured. Then, to determine the degree of change (decrease or increase) in the permeability after the impact of the test fluid in the opposite direction of flow, formation fluid is let in. The aim of this study was to inflict damage to cores through gelation and sedimentation reactions of silicate test fluids with synthetic brine-saturated cores.

Tests for hydraulic efficiency of the core, restoration of permeability, core damage were carried out as follows:

Core samples from Berea sandstone with a permeability of approximately 30 mD were saturated with synthetic brine under reduced pressure and tested using a 3% potassium silicate solution containing 2% of a specialized lubricant additive. Procedures, parameters and test results are set out below.

Procedure.

1) The cores were weighed and pre-saturated with brine for one week at a reduced pressure of 15 inches (381 mm) of mercury.

2) The hydraulic efficiency of the core and its permeability to brine were measured.

3) Potassium silicate mud was stirred and heated to 95°C.

4) Drilling fluid was injected into the core at a constant rate of 3 ml/min.

5) Current control (monitoring) of pressure was carried out.

6) Pressure drop increases exponentially over time to ≈2500 psi (≈17.24 MPa). Fluid breakthrough was observed.

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7) The core did not completely shut off the flow, but there was a loss of 99% permeability.

8) Effluent was collected to determine fluid replacement (depth of penetration).

Options.

Instrument: Chandler formation response tester.

Core Sample: Sandstone, 1.5" x 3.0" (3.81cm x 7.62cm).

Temperature: 95°C.

Test fluid: 3% potassium silicate solution containing 2% lubricant.

Pore volume: 16.76.

Initial brine permeability: 28.32 mD.

Permeability after mud treatment: 0.197 mD.

Permeability reduction: >99%.

Throughput: 3 ml/min.

Brine composition:

sodium chloride (NaCl) 230.303 g, calcium chloride (CaCl ₂ ) 79.054 g, sodium chloride (KCl) 8.346 g, magnesium chloride (VgCl ₂ ) 13.79 g.

Then, to determine the ability of alkaline silicate solutions with a lubricating additive to create a seal and give integrity to the shale samples, the shale was tested for dispersion. The test procedure was in accordance with American Petroleum Institute (API RP) Procedure 13i for hot rolling shale fineness:

A piece of Pyrrhus shale weighing approximately 2 kg was crushed to obtain approximately 900 g of -5/+10 mesh particles (2 mm to 4 mm). The Pyrrhus shale is much more reactive and water receptive than the mature hard shale that is typically present at the depths that geothermal energy deals with. It was chosen as a baseline out of caution, actual mature shale performance would be better.

Said -5/+10 mesh particles (2 mm to 4 mm) were screened through American Society for Testing and Materials (ASTM) sieves using a Ro-Tap® sieve shaker for 2 minutes.

Approximately 10 g of shale was placed in a 250 ml test fluid.

The samples were subjected to rolling for 24 hours at a temperature of 120°C.

After rolling, the samples were poured into a 20 mesh sieve (passes particles no larger than 0.84 mm).

To remove material that could stick to the inner walls, the aging cells were flushed with an inhibited drilling fluid (7% KCl).

All material obtained on a 20 mesh sieve was dried in an oven to constant weight at a temperature of 100°C.

Each sample was then re-sieved and the particle weight of the -5/+10 mesh fraction (2 mm to 4 mm) was recorded.

Test results for fluids of several different compositions are summarized in the table below.

No. p / p Sample Initial weight (g, 2 4 mm) Full weight output (g) Weight output (g, 2 4 mm) % Yield 1 Water 10.025 2.027 0.113 1.1 2 3 vol. % potassium silicate 10.041 9.895 9.799 97.6 3 3 vol. % potassium silicate + 2% lubricant additive 10.007 10.164 9.657 96.5 4 Mineral oil 10.011 9.251 8.501 84.9 5 7% potassium chloride (KCI) 10.054 9.015 7.307 72.7 6 10 l/m ³ amine 10.002 6.961 5.759 57.6 7 Working fluid 10.175 7.102 4.514 44.4

Yields in excess of 97% have been achieved, indicating the excellent sealing and reinforcing capability of this shale. Mineral oil does not react with shale and the mass yield was only 85%. The weight loss is due to mechanical degradation during the rolling process. That's why

- 15 043119 a high yield of 97% indicates that not only chemical compaction takes place, but also an increase in mechanical strength. The shale inhibitor-added working fluid produced a mass recovery of 44%, a significantly higher result than fresh water, which gave only a 1% yield.

Example 2

An aqueous working fluid was tested containing a commercially available anti-corrosion agent, potassium bromide, cetyltrimethylammonium surfactant, sodium salicylate, and calcium carbonate solids at a concentration of 0.5 wt%.

Measurement of pressure drop (due to drag) and characterization of turbulent flow was performed using a 2-inch (5.08 cm) heated flow with a volume of 200 liters. The circuit was equipped with a high shear centrifugal pump (GIW, LCC-M 50-230) and a low shear cavitation type screw pump (Moyno™, 2F090). The maximum Reynolds number (Re) was up to 500,000 and the circuit could operate at a solids volume concentration of 15%. The pressure drop was calibrated with fresh water and compared with the frictional pressure loss at the same working fluid flow rate. In the temperature range suitable for direct heat supply, a 63% reduction in resistance in turbulent flow was achieved.

To test reactivity with respect to near-wellbore unspent alkali metal silicate, Ecodrill™ 317-29.1% active solution of silica (SiO ₂ ) and potassium oxide (K ₂ O) taken in the ratio of SiO ₂ :K ₂ O, equal to 2.5. Sodium hydroxide (NaOH) was used to adjust the pH to 11-12 and this alkaline silicate solution was introduced into the working fluid samples with gentle stirring to obtain solutions with a concentration of 3 vol.% and 1 vol.%. These low concentrations were chosen to carefully represent the alkali silicate drilling fluid left unused in the near-wellbore zone. In each case, the addition of the silicate solution to the working fluid resulted in precipitation and the silicate solidified after 24 hours. These results show that the working fluid strengthens and increases the seal of the wellbore, providing a practical fluid tightness.

To evaluate the ability of the working fluid to maintain the integrity and stability of the wellbore, a modified shale elutriation test was performed. Testing included two consecutive shale elutriation runs with the same sample. First, the sample was hot rolled in a sealant medium as described above, then it was again soaked in the working fluid to determine the mechanical strength and chemical isolation of the shale. After an initial run of elutriation of the shale with a drilling mud sealant, the samples were dried, weighed, immersed in the working fluid chemistry, and rolled for 24 hours.

After rolling, the samples were poured into a 20 mesh sieve (passes particles no larger than 0.84 mm) and all material obtained on a 20 mesh sieve was dried in an oven to constant weight at a temperature of 100°C. Each sample was then re-sieved and the particle weight of the -5/+10 mesh fraction (2 mm to 4 mm) was recorded and compared with the weight of the sample after compaction and drying. Interestingly, the results of multiple runs showed a mass recovery in excess of 96%, indicating an excellent ability of the working fluid to maintain the integrity of the wellbore.

Example 3 - Sealing by machining.

In one embodiment of the present invention, this mechanism can be implemented by introducing solid particles into the drilling fluid that naturally penetrate the pores/fractures to reduce permeability. Such a lost circulation material is referred to as a screening filler.

Said solid particles may be granular, fibrous or flaky material, or a combination of such materials, and may be dispersed in the drilling fluid to the size required to reduce the permeability. The order of suitable sizes can be from nanometers to millimeters.

Abrams' law and optimal packing theory help determine the most suitable materials. Abrams' law states that the particle size of the bridging agent (clotting agent) should be equal to or slightly larger than a third of the average pore size of the corresponding reservoir.

The theory of ideal packing provides a complete distribution of particle sizes, ensuring efficient filling of all cavities, including those created by bridging agents.

The particles may also be sized to penetrate the pores before plugging the pores.

In addition, drilling mud can provide additional plugging of pores and serve as a lost circulation material.

All of these materials can be used to repair borehole leaks after the drilling process is completed. Further displacement of the drilling fluid with a viscosified spacer fluid containing a bridging agent can be accomplished by pumping at a reduced rate through an open hole section to allow the bridging agent to penetrate and plug leaks, if any.

Finally, hard silicates can also be used to provide an effective combined chemo-mechanical mechanism for sealing the formation.

Example 4 Biological Compaction Mechanism

Microbiological EOR is a technology dealing with the selection, cultivation and stimulation of microorganisms for enhanced oil recovery. The pores of most deep geological formations contain anaerobic bacteria. Compared to surface microorganisms, these bacteria receive very little energy and nutrients, so they have very low population densities.

One of the technologies for microbiological enhanced oil recovery involves the treatment of local microbiota with nutrients in order to stimulate their growth for subsequent filling of rock pores with biological material. As nutrients, any suitable substances can be used, but usually include potassium nitrate and monosodium phosphate. With sufficient nutrition and favorable conditions, bacterial growth occurs exponentially, so bacteria can be conditioned to grow and completely fill the pores, making the formation virtually impermeable to fluids.

Another technology provides for the introduction of new microorganisms into the geological environment while simultaneously supplying them with nutrients. Microorganisms can be selected that only grow at a certain temperature and therefore can be activated when introduced into a hot formation.

Any of these technologies can be used with conventional drilling fluid and render the formation substantially fluid-tight and suitable for a closed loop geothermal system.

Example 5 Thermal Sealing Mechanism.

Geological environments differ in chemical composition and therefore have different softening points, although most sedimentary formations melt at or below 1200°C. At the stage of research, development and testing, there are several technologies for penetrating the formation using its thermal disintegration without mechanical contact.

One of the technologies of this kind involves the creation of plasma using electricity or using nuclear energy. This plasma melts the formation, enabling continuous drilling.

Another technology involves the use of a laser, the beam of which is directed at the surface of the rock, the temperature of which rises, and it begins to crumble, break down and then melt.

Another technology involves the use of high-velocity projectiles that release enough energy on impact to raise temperatures by hundreds of degrees.

All these technologies ensure that when drilling porous and permeable rock, it melts, after which it can be cooled and tempered to form a solid, durable barrier that is practically impermeable to fluids.

After the above discussion of the technical details, the following is a description of specific embodiments of the present invention with reference to the accompanying drawings.

In FIG. 1 shows plots of filtrate volume versus time (horizontal axis, square root of time) for fluids of various compositions.

In FIG. Figure 2 shows graphs of pressure drop and permeability versus time during core tests for waterflooding with chemically anchored formation, described in example 1.

In FIG. 3 is a schematic sectional view of a well structure having an inlet well 10 fitted with a wellhead casing 12 for groundwater protection. The intermediate reinforced section 14 of the well is cemented into place as shown in the drawing. All these components and technologies are known in the industry. Extending from the intermediate reinforced section 14 is a transverse section 16, which in this embodiment does not have casing pipes, but is a sealed open hole. The porous structure of the rock surrounding the transverse section 16 is compacted with a compacting agent as described above. This compacted porous structure is indicated by the position 18. The compacted transverse section 16 seamlessly passes into the intermediate cased section 14, which then seamlessly passes into the outlet well 20 equipped with the casing string 12.

In FIG. 4 illustrates an alternative. In this embodiment, the compaction of the transverse portion 16 is variable, resulting in an uncompacted rock surface 22. In this case, given the absence of cementing, casing 24 is used as a protection. This casing 24 thus protects against the adverse effects of the unconsolidated rock surface and maintains the continuity of the circuit from the inlet well 10 to the outlet well 20. This can be used in combination with continuously compacted areas. It depends on the specific properties of the geological environment.

With regard to compacted areas of porous or fractured formations, the compacting agent does not merge with the surface of the rock, but is embedded in it, as described above when considering the example of compaction by chemical treatment. In general, the examples illustrated in FIG. 2 and FIG. 3, refer to hard rocks.

In FIG. 5 illustrates an embodiment in which the well system is in a lower permeability subsurface. As an example of such a geological environment, shale of sedimentary origin or mudstone can be mentioned. In this case, the formation may have occasional gaps, cracks, chips, etc., generally indicated by 26. To provide continuity between the inlet well 10 and the outlet well 20, a chemical lining 28 may be used, which, as shown in the drawing, fills the mentioned gaps, cracks and chips.

In FIG. 6 illustrates a first well structure configuration. In this embodiment, both the inlet well 10 and the outlet well 20 have conventional cased sections 30 connected to the inlets 32 and outlets 34 of the system of the multichannel system 36 of the transverse connecting sections. This system 36 comprises a plurality of transverse wells 16 which, depending on the circumstances, may be partially cased, as shown in FIG. 3 and FIG. 4. Any number of systems 36 can be created in the reservoir 38. This fact is conditionally reflected in the drawing using the notation 6p vertically and horizontally, where p means any number of additional wells in the form of a system 36 or in any other configuration.

The inlet 32 and outlet 34 are connected to the cased portions 30 by a multi-channel connecting structure, which will be detailed in subsequent drawings.

In FIG. 7 illustrates one possible embodiment of a multi-channel interconnect structure. Inlet 32 is connected to a sealed multi-channel connecting structure 40, from which transverse sections 16 extend as its continuation. In order to increase the heat transfer of formation 38, transverse wells 16 are located at a distance from each other (see Fig. 6). transverse wells 16 may be cased as described above with reference to FIGS. 3, fig. 4 and FIG. 5. Outlet 34 of system 36 is provided with the same connection structure (not shown).

In FIG. 8 shows an L-shaped borehole structure, generally designated 42. In this embodiment, the borehole has an extended section 44 with a bottom end 46, with the wellbore uncased and sealed, as in the case of the previously discussed options. An insulated conduit 48 extends within the well for fluid delivery. The angle at which the extended section 44 is located can be chosen at any angle.

In FIG. 9 illustrates a variant with a vertical orientation of the extended portion.

In FIG. 10 illustrates a W-shaped well structure 50. The surface is indicated by 52. In this embodiment, the exit of one well becomes the inlet of another. The direction of flow of the working fluid is shown by arrows. The scheme can be repeated for additional circuits. In this embodiment, the open transverse wells 16 are sealed as described above with reference to the previous drawings, but depending on the nature of the subsurface may have cased sections alternating with simply sealed.

In FIG. 11 illustrates yet another embodiment of a multi-channel system similar to that originally shown in FIG. 3. In this option, the inlet and outlet are at the same wellhead, and the angle at which the multichannel system is made in the reservoir can be any. Transverse wells 16 converge at the bottom end 54.

In FIG. 12 is a side view of a lumped well structure 56 in which an inlet well 10 and an outlet well 20 are located in close proximity. The contour of the flow of fluid through the transverse wells 16 is shown. The designation 12n has the same meaning as the designation 6p in the description of the embodiment illustrated in FIG. 6.

Another variant is illustrated in Fig. 13, where the multi-channel system is shown in top view. Separate transverse wells 16, diverging from a common inlet well 10, extend into a geothermal zone of the subsurface (not shown in this drawing) and, returning, form closed contours, converging at a common outlet well 20. The direction of fluid flow is shown by arrows, while in each individual circuit, the flow may be isolated, or the individual circuits may be daisy-chained. Such a solution presents the advantage that, in a small area, the maximum extraction of heat from the heat-bearing geological medium is ensured.

In FIG. 14 illustrates a solution involving multiple well systems while maintaining the above advantage of the option illustrated in FIG. 13 (small area, maximum recovery).

In FIG. 15 the solution illustrated in FIG. 15 is a multichannel system 50 combined with the well structure shown in FIG. 13. In this embodiment, two separate concentrated well structures 56 can occupy a large area with minimal interference with surface structures while exploiting large underground volumes of the geothermal zone. The direction of flow of the fluid is indicated by arrows, in each individual circuit the flow may be isolated, or the individual circuits may be daisy-chained. The efficiency of the sealing technology described here provides flexibility in implementing these hybrid configurations. This, in turn, allows the production of geothermal energy in a wide range of geological conditions, providing another degree of freedom in the implementation of the methods described here.

In FIG. 16 shows in detail the cross-section of the well, namely its transverse section 16. In this embodiment, the heat-carrying geological environment 38 is highly permeable. For this reason, the sealant is distributed in the porous structure of the rock and in the immediate vicinity of the transverse section 16 of the well area 60 remains unreacted. Further outside this region, the porous structure 18 is compacted, as in the embodiments discussed above.

In FIG. 17 is a cross-sectional view of the same well as in FIG. 16 after being exposed to the working fluid. As a result of this contact, the region of the reservoir surrounding this well became compacted, forming an impermeable layer between the internal volume of the well and the surrounding rock. This provides a particular advantage, since the compacted section 16 of the well is surrounded by an area 60 containing a supply of unreacted sealant material. In the event of damage to the well seal due to seismic or other hazardous activity, the well can maintain the integrity and impermeability of the walls due to self-healing due to the reaction of the working fluid with the said reserve of the sealant. This is clearly a significant benefit in terms of reduced O&M costs over time, justifying the initial capital investment associated with building the well structure.

As for rocks with low or medium permeability, such as granite, mudstone or shale, then they have pores, cracks, cracks, chips, etc. can be filled with a sealant along the periphery of the section 16 of the well with the formation of an impermeable layer in one step without the need for an active working fluid and further processing. Thus, the permeability of the geological environment does not create any problems regarding the applicability of the proposed methods for geothermal energy.

An additional bonus is that the proposed technology can also be extended to areas of reclamation and amelioration. One of the foundations of the proposed methods is an ecological approach to the extraction of geothermal energy, when it is possible to do without hydraulic fracturing, which leads to environmental pollution. Another basis is the use of a truly closed loop system, as opposed to those systems that have been mischaracterized as closed loop systems in the prior art.

The proposed technology provides a highly efficient compaction procedure with the benefits listed above in terms of geothermal energy, therefore it was concluded that this technology is applicable to the restoration of inefficient, unused or otherwise inactive geothermal wells. These wells may be unused or idle due to various problems such as low current production, ineffective hydraulic fracturing, loose formations and associated sand production problems, increased corrosion from formation fluid, washout. Thus, in those cases when retrofitting to a new geothermal system that does not require hydraulic fracturing is impossible, the failed facility is abandoned, taking away casing pipes and other components that are unnecessary here. Or, if they think it possible, they carry out costly and environmentally damaging remedial work, such as hydraulic fracturing, or re-drill entire wells. In light of the fact that reservoir permeability is not an issue, the proposed sealing technology is attractive from a well recovery point of view.

As for the improvement of existing geothermal wells, the very presence of these wells in the application of the proposed technology provides a significant economic advantage, and the proposed technology does not require the use of hydraulic fracturing fluid, which avoids induced seismicity and environmental risks, and allows a facility that was previously considered harmful to the environment , to make an environmentally friendly source of energy with which you can work further.

Further, with reference to the following drawings, other embodiments of the proposed technology will be considered.

In the diagram shown in Fig. 19, the well loop 64 comprises a closed loop system having an inlet well 10 and an outlet well 20 drilled in a subsurface environment, which may be, for example, a geothermal environment, a low permeability rock formation, a sedimentary formation, a volcanogenic formation, or an underburden, which is better characterized as a crystalline rock located under the sedimentary basin (none of this is shown in the drawing).

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Downhole circuit 64 and power cycle 66 are in thermal contact through a heat exchanger 68 which removes heat from the working fluid circulating in a closed subsurface loop 64 to generate power with a generator 70 in power cycle 66. may be, for example, in the range from 80°C to 150°C.

In this embodiment, two different working fluids are used. Details regarding these fluids will be discussed below. By modifying the working fluid used in the downhole circuit, the system can be operated at low temperatures.

In currently used power units, the input temperature of the working fluid of the power cycle in the primary heat exchanger is usually limited to a value above 0°C. By lowering the temperature of this working fluid to below 0° C., it is possible to increase the pressure drop across the turbine. However, in known geothermal projects, there are limitations due to the possible freezing of the fluid and the deposition of salts in it on the other side of the heat exchanger.

The present invention overcomes these limitations by providing a segregated power cycle system in combination with a closed loop well structure.

Fluids can be modified with anti-freeze additives at temperatures below 0°C. Suitable additives which may be mentioned are descalers, anticorrosive agents, friction reducers, antifreezes, cryogens, bactericides, hydrocarbons, alcohols, organic liquids, and combinations of these additives.

A significant advantage of using a specially formulated working fluid in the downhole circuit in combination with a segregated power cycle is that it is unaffected by very low ambient temperatures and thereby facilitates the use of any of the typical power plant cycles (including the organic Rankine cycle, the Viburnum, carbon-supported cycle, Sterling cycle, carbon dioxide transcritical cycle) to increase net power when used with a downhole circuit, as shown in FIG. 19. With this solution, heat is transferred from the first working fluid to the second working fluid when the temperature of the latter is 0°C or lower.

Variations of the segregated loop solution are illustrated in FIG. 20 and FIG. 21.

In FIG. 20 depicts a segregated system including a well loop 12 in thermal contact with two separate heat exchangers 18, each with its own separate generator 22, in parallel. In FIG. 21 shows a similar system with generators connected in series.

An integrated downhole power plant is a closed loop system in which a selected working fluid is circulated in the downhole casing and then fed to a surface turbine, as can be seen in FIG. 22. This system is generally designated 72. This is a system with a single working fluid, rather than a separate working fluid for the downhole circuit and a separate working fluid for the power cycle. The working fluid in this closed circuit can operate in a transcritical cycle, when the fluid is supercritical at a higher operating pressure, and subcritical at a lower operating pressure, or in a fully supercritical cycle, when the fluid remains supercritical even at a lower operating pressure. .

As is known, the transcritical cycle is a thermodynamic cycle in which the working fluid goes through both subcritical and supercritical states. The equipment also includes a cooling device, which in this example is implemented in the form of an air heat exchanger 74, and a turbine 76 with a generator 78. The air heat exchanger 74 serves to cool the working fluid to a temperature exceeding the ambient air temperature by 1 °C to °C. It should also be noted that the working fluid can be cooled to negative temperatures on the Celsius scale. The characteristics of the fluids are shown in FIG. 24.

The driving mechanism in this integrated cycle is a very strong circulating heat exchange (thermosiphon effect), which is enhanced by the difference in density between the inlet vertical well 10 and the outlet vertical well 20. wells 80 heats up and enters the outlet well 20 in a supercritical state, which creates a significant pressure.

The thermosyphon effect can completely eliminate the need for a ground pump during normal operation, which is needed only at start-up. The advantage is that the energy that would be required to operate this pump is saved.

The well circuit uses fluids and mixtures designed to suit the wellbore, depth, length, and ambient temperature. The prior art only discusses the use of fluids such as carbon dioxide or pure hydrocarbons. In the case of a system with

- 20 043119 closed cycle, such as the system according to the invention, the initial costs associated with the complexity of the mixtures used as a fluid, are only a small part of the total economic volumes. Thus, other fluids may be used, such as a fluid having at least one of the properties selected from the following group:

a working fluid for use in extracting thermal energy from a geothermal well structure having an inlet well, an outlet well, and a connecting structure therebetween, said working fluid having at least one of the properties selected from the following group:

a) in order to achieve the maximum temperature difference and maximum heat transfer between the fluid and the surrounding heat-bearing geological environment within the transverse connection channel between the inlet well and the outlet well, has a significantly non-linear enthalpy dependence on temperature at pressures above 10 MPa and temperatures below 180 ° C,

b) has the ability to enter into a reversible pressure-sensitive reaction: endothermic at elevated pressure and exothermic at pressures below said elevated pressure,

c) is a mixture entering into the said transverse connecting channel in an endothermic reaction of chemical absorption,

d) is an aqueous solution of an electrolyte with a solubility depending on temperature and pressure, having a heat-absorbing effect inside said transverse connecting channel,

e) is a water-based fluid containing a composition that reduces drag in turbulent flow,

f) is a supercritical fluid, g) is a mixture of ethane and ammonia,

h) has any of the workable combinations of properties listed in points a) to e).

It has been found that fluids having a substantially non-linear temperature dependence of enthalpy within the cross-sections of the well circuit, and/or having the ability to enter into a reversible pressure-sensitive reaction: endothermic at elevated pressure and exothermic at pressures below said elevated pressure, can significantly increase energy production. This is because the average differential between the temperature of the rock in the well and the temperature of the circulating fluid is increased, causing an increase in heat transfer from the subsurface.

An example of a fluid that can be used in a segregated system is an aqueous sediment-electrolyte solution, the solubility of which depends on temperature, while in the upper part of the inlet well, the water is supersaturated. The suspended state of solid particles is maintained with the help of an anti-scale (anti-flocculating) additive and a turbulent flow regime (similar to drilling fluid). When flowing through the transverse sections, the temperature of the fluid medium increases, as a result of which the solubility of the suspended solid particles also increases. This provides an endothermic process for the solution to absorb the heat of the geological environment (essentially increasing the effective heat capacity of the fluid) when the solid particles are dissolved in water. In a segregated heat-to-electricity heat exchanger, the temperature drops, resulting in an exothermic process in which solid particles come out of solution to release heat.

Examples of fluids useful in the context of the invention include aqueous solutions of substances such as ammonium acetate, ammonium dihydrogen phosphate, ammonium formate, ammonium nitrate, potassium bromide, potassium chloride, potassium formate, potassium hydrogen carbonate, potassium nitrate, acetate sodium, sodium carbonate and monosodium phosphate.

Using only one turbine, it is problematic to ensure efficiency over the entire range of environmental parameters. It has been found that the problem can be solved by using two or more turbines connected in series or in parallel, optimized for different environmental parameters. To maintain high efficiency throughout the cold season throughout the year, a control logic (not shown) automatically moves the fluid to the correct turbine.

Fig. 25 and FIG. 25 A refer to 82 wells daisy chain. In this embodiment of the invention, each localized object 84 includes an injection well 86 connected to a transverse channel system 88 and a production well 90. The continuous well structure thus constructed may be referred to as a U-shaped well structure. Said transverse channels 88 may be implemented as shown in FIG. 3, or otherwise, as described above.

As can be seen in these drawings, each localized object 84 is separate and ingeniously and advantageously connected to nearby ground localized objects 84. The distance between the objects can be, for example, from 3500 m to 6000 m. Of course, it can be different depending on the situation. .

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During operation of the system, the working fluid flows in the injection well 86 of one localized object 84, may pass, for example, through a power plant (not shown) to transfer thermal energy, and then the output stream is directed as an input stream to the injection well 86 of the adjacent localized object 84 The dotted line 92 illustrates this simple or stub transfer of fluid. Not all of the heat is recovered, so the flow to the well 86 of the adjacent localized object is preheated before being injected into the transverse channel 88. The process is repeated on the neighboring localized object 84.

In FIG. 26 illustrates another embodiment of the present invention, which is a well system providing power from 8,000 kW to 12,000 kW. In this embodiment, the individual circuits are connected in a central localized facility 94 to centralize power equipment (not shown) in order to increase power generation and improve efficiency.

In FIG. 27 and FIG. 28 illustrates well systems providing lower power outputs of 4000 kW to 6000 kW (FIG. 27) and 2000 kW to 3000 kW (FIG. 28).

One of the significant advantages of operating a flowline system of wells is the absence of the need for a near-surface return pipeline. When it is required, as is the case in prior art well loop systems, the capital investment exceeds 10% of the total project fixed assets, it may be necessary to negotiate a right-of-way, and as a result there are heat losses with a temperature drop of 3°C and pressure losses, which leads to a decrease in efficiency.

In contrast, with a stub connection, due to the front-to-back connection of the well circuits, there is no need for a near-surface return pipeline. In addition, the paired circuits act as returns to each other so that the pair uses the dissipated heat to preheat the flow discussed above.

Other benefits include increased power generation without destroying the surface (ie without impacting the environment) since everything is in the subsurface and the distance between localized objects 84 is reduced. And if, due to the increased temperature of the preheated feed stream, a shorter transverse channel 88 can be used, the costs are reduced to the same extent.

In the embodiments of the present invention discussed above, wellbores are compacted during drilling according to the technology described above. It should be clear that combinations of wells of any configuration can be used in a daisy chain system. In addition, combinations of any rock intrusion technologies may be used to create wellbores in the daisy chain system, as in any of the other configurations illustrated in the accompanying drawings. In some drawings, symbols are used, consisting of a drawing number with the letter n appended to it. For example, in FIG. 6 there is a zone bearing the designation 6n. This means that any (ie, n-th) number of additional wells can be added to the depicted well, one above the other, or one next to the other, or both, relative to the clearly depicted well. In this case, additional wells can be either of the same or of a different type.

As indicated in the examples discussed above, the present invention is based on the possibility of using a heat-carrying geological environment, regardless of its permeability, and creating effective well structures in it to ensure maximum heat transfer. In combination with high performance working fluids, this gives a remarkable result.

The circulation of the fluid in the well structures can be carried out according to any schemes and in any directions that provide efficiency. This depends in part on the nature of the subsurface, as will be appreciated by those skilled in the art.

Claims (18)

1. A method for creating a well structure with a closed loop in a geological environment suitable for extracting geothermal energy, in which, during drilling, an interlayer is created between the well structure and the geological environment, extending at least between the inlet well and the outlet well of the mentioned contour, for which cause an irreversible violation of the permeability of the well structure, using a sealant circulating in the well system through a drill string located in the well system, while the mentioned sealant is able to enter into chemical reactions with the surrounding rock with the destruction of the latter and the formation of an interlayer, and the said interlayer is fluid-tight and has a thermal conductivity not lower than that of the surrounding rock, and passes the geothermal heat recovery working fluid through the well structure such that the geothermal heat recovery working fluid absorbs - 22 043119 heat of the geological environment by heat transfer due to heat conduction through the formed layer, while at least part of the well structure is not cased, while maintaining the impermeability of the layer for flowing media. 2. The method of claim 1 wherein said sealant circulated in the well system through the drill string comprises the use of an alkali silicate based drilling fluid. 3. The method of claim 2, wherein the alkali silicate drilling fluid contains at least one of the following: potassium, sodium, sodium aluminosilicate. 4. The method of claim 2, wherein the drilling fluid contains alkali metal silicate from 0.3 to 9% by weight in water. 5. The method of claim 4, wherein the drilling fluid contains 3 to 6% by weight alkali metal silicate in water. 6. The method of claim 4, wherein the drilling fluid has a pH of at least 10.5. 7. The method according to any one of claims 1 to 6, further comprising the step of increasing the sealing ability and mechanical integrity associated with the interlayer obtained in the subsequent chemical attack step, wherein the subsequent chemical attack step consists in treating said interlayer with sodium aluminosilicate. 8. The method according to claim 7, wherein the subsequent chemical action step comprises treating the interlayer with at least one of the group: calcium chloride brine, acids, carbon dioxide (CO2), surfactants, esters. 9. The method of claim 7 wherein said chemical attack step comprises treating the resulting interlayer with a compound capable of chemically bonding to said formed interlayer. 10. The method of claim 9 wherein said compound comprises exfoliated fly ash. 11. The method according to claim 9, wherein said compound contains at least one of the following group of substances: surface-activated graphene, graphene oxide, carbon fibers, and mixtures thereof. 12. The method of claim 1, which further comprises circulating in the well structure a working fluid containing an additive to help maintain the interlayer to maintain tightness during operation of the well structure. 13. The method of claim 12, further comprising maintaining the pressure of the working fluid in the well structure at a level sufficient to maintain the integrity of the well structure, if necessary. 14. The method of claim 12 wherein said working fluid includes a non-linear enthalpy versus temperature relationship at pressures above 10 MPa and temperatures below 180° C. to achieve maximum temperature differential and maximum heat transfer between the fluid and the surrounding subsurface. 15. The method of claim 7, further comprising circulating the well structure with a working fluid containing an interlayer maintenance additive to maintain impermeability during operation of the well structure. 16. The method of claim 15, wherein said interlayer maintenance additive is used to self-repair permeability damaged areas of the interlayer. 17. The method of claim 12, wherein said interlayer support additive is used to self-repair permeability damaged areas of the interlayer. 18. The method of claim 12, wherein said interlayer support additive is used to cause the unreacted alkali metal silicate left after drilling to settle.