CN114961668A

CN114961668A - Fracture-type hot dry rock reservoir double-inclined-well segmented regulation and enhanced heat recovery method

Info

Publication number: CN114961668A
Application number: CN202210539039.5A
Authority: CN
Inventors: 陈跃都; 梁卫国
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2022-05-18
Filing date: 2022-05-18
Publication date: 2022-08-30
Anticipated expiration: 2042-05-18
Also published as: CN114961668B

Abstract

The technical field of exploitation and utilization of underground heat energy is a fracture type hot dry rock reservoir double inclined shaft subsection regulation and control reinforced heat extraction method; drilling an inclined injection well and an inclined extraction well in a primary fissure development zone of the dry hot rock, and injecting high-pressure low-temperature fluid into the two wells in a segmented manner from bottom to top in sequence to realize circulating shearing unloading disturbance on the fissure development zone and improve the fracture network fracture communication effect of the reservoir stratum of the dry hot rock; secondly, intelligently regulating and controlling the injection and production well sections, injecting low-temperature liquid into the injection well sections, and extracting the high-temperature liquid subjected to sufficient heat exchange from the production well sections; the invention enables the primary fracture of the reservoir fracture development zone to achieve full crossing-expansion under the combined action of hydraulic pressure shearing and unloading disturbance; the problems that the double-vertical well is large in construction and storage difficulty, small in scale, low in heat convection efficiency and difficult to realize large-area heat energy exploitation are solved.

Description

Fracture-type hot dry rock reservoir double-inclined-well segmented regulation and enhanced heat recovery method

Technical Field

The invention belongs to the technical field of underground heat energy exploitation and utilization, and relates to a fracture-type hot dry rock reservoir double-inclined-well segmented regulation and control reinforced heat recovery method.

Background

Geothermal resources have become a new energy source for intensive research and development in countries of the world due to their characteristics of cleanliness, stable operation and wide spatial distribution. According to the existing form division, geothermal resources can be divided into a hydrothermal type and a dry-hot rock type, wherein the exploitation of dry-hot geothermal is the focus of attention of commercial geothermal exploitation at home and abroad at present and is the development direction of geothermal resource exploitation in the future. However, in the current exploitation process, the fracture communication area of the hot dry rock is low, the water injection cycle is poor, and the thermal breakthrough is serious, which seriously restricts the process of the geothermal exploitation of the hot dry rock. The water injection shearing stimulation technology is used as a technology for artificially modifying a reservoir and increasing the yield, fluid is injected by a ground high-pressure pump, a certain injection process technology and a certain injection program are adopted, a certain pump injection pressure is applied to a thermal reservoir containing a primary fracture, so that a dense primary fracture network generates shearing slippage and is intersected and communicated with a new fracture to form a fracture network, and a dry hot rock geothermal well is usually in crystalline rock (granite), so that the sheared and slipped fracture has quite large self-supporting capacity, the permeability of the reservoir can be enhanced and modified, and then cold water is continuously injected into the primary fracture and the new fracture of the rock, so that the heat energy of the thermal reservoir can be extracted.

At present, the construction and heat recovery of artificial heat reservoirs are generally carried out by adopting single-well water injection, double-vertical-well or double-horizontal-well water injection circulation in deep dry heat rock mining projects at home and abroad. When artificial heat reservoirs are constructed by traditional single-well water injection, double-vertical-well or double-horizontal-well water injection circulation, the fracture length and the sweep range limit the fracture expansion and extension by simply injecting water and fracturing or shearing stimulation, so that a single fracture is easy to form, the sweep range is small, and the artificial heat storage volume and the heat exchange area which are finally formed are difficult to obviously improve. Because of the high-temperature and high-pressure environment of the hot dry rock reservoir, large-volume artificial fracture thermal storage is difficult to build by only depending on a water injection fracturing or water injection shearing stimulation technology, the required pumping pressure is usually too high, the implementation is difficult, the fracture pressure shearing communication area of the mineral reservoir is small, the thermal recovery efficiency is low, and a series of geological disaster problems such as fault slippage, surface subsidence and the like are caused; in addition, in the long-term injection-production stage, since the fluid is more prone to form a dominant channel in a local seepage path, the flow is difficult to form a seepage channel with high density, so that the heat storage is thermally short-circuited, and the heat breakthrough is formed prematurely.

Generally, geothermal mining focuses on three aspects: 1) high injection amount; 2) high heat exchange capacity; 3) high recovery, the first two of which depend on reservoir fracture network development and the latter on wellbore placement and injection-production processes. Therefore, how to design drilling arrangement and injection-production process in the dry hot rock geothermal reservoir by using the natural fracture system and the geothermal characteristics of the dry hot rock reservoir relates to the successful reconstruction and the efficient heat energy exploitation of the dry hot rock reservoir.

Disclosure of Invention

The invention overcomes the defects of the prior art, and provides a fracture-type hot dry rock reservoir double-inclined-well segmented regulation and control reinforced heat recovery method, so as to enhance the permeability of a hot reservoir and realize the efficient extraction of heat energy.

In order to achieve the above object, the present invention is achieved by the following technical solutions.

A fractured dry hot rock reservoir double inclined shaft segmented regulation and enhanced heat recovery method comprises the following steps:

s1: and arranging vertical opposite wells on the surface of the geothermal exploitation area of the dry hot rock, then respectively turning inclined wells to obliquely enter a target thermal reservoir and cementing wells to form an injection well and an extraction well.

S2: and correspondingly segmenting the inclined section of the injection well and the inclined section of the extraction well respectively, and injecting high-pressure low-temperature fluid upwards section by section from the inclined well segment with the lowest elevation of the injection well and the extraction well, wherein the high-pressure low-temperature fluid enters a target thermal reservoir through the perforation on the inclined well segment to perform shearing stimulation so as to gradually form unloading disturbance influence on a reservoir area.

S3: independently sealing each inclined well section of the injection well and the extraction well, starting to inject low-temperature liquid from the inclined well section with the lowest elevation of the injection well and generating sufficient heat exchange with cracks of a dry hot rock reservoir, and extracting through corresponding sections on the extraction well; and then closing the inclined shaft subsection with the lowest elevation, and heating the upper inclined shaft subsection, and repeating the steps of heating layer by layer.

Preferably, the high-pressure low-temperature fluid is injected upwards section by section in the step S2, and the heat extraction process layer by layer in the step S3 is performed repeatedly.

Preferably, the inclined section of the injection well is drilled into the low temperature zone of the target thermal reservoir and the inclined section of the production well is drilled into the high temperature zone of the target thermal reservoir.

Preferably, the inclined sections of the injection well and the extraction well are distributed at equal intervals and are perpendicular to the main fracture direction of the heat storage fracture area, and the inclined section of the extraction well is positioned above the inclined section of the injection well.

Preferably, a monitoring well is arranged between the injection well and the production well, and the monitoring well is provided with a microseismic monitoring device.

Preferably, the high-pressure low-temperature fluid is injected by adopting a constant flow injection mode or a monotonous injection mode or a circulating injection mode.

Preferably, a conduit through which the cryogenic fluid can pass is arranged in the inclined section of the injection well and the inclined section of the production well, the conduit is connected with a perforator, a casing is arranged outside the conduit, and cement is adopted between the casing and the well shaft for cementing.

Preferably, the perforator has a hole on the fracturing side and a plugging structure on the other side.

Preferably, the inclined shaft sections are separated or independently sealed by adopting a packer, and the packer is provided with a temperature sensor and a water pressure sensor and can monitor the temperature and water pressure changes of the fluid in the sections.

Preferably, the temperature sensor and the water pressure sensor of each packer are connected to a ground control platform through signal lines, and the ground control platform is communicated with a host through an interface and is added with a temperature threshold value alarm function.

Preferably, the packer is provided with a control valve for controlling the communication of the packer with the water pressure in the conduit.

Preferably, in the step S2, during multiple cycles, the ground control platform measures and feeds back the temperature of the packer in each segment, judges the temperature through a temperature threshold, flexibly adjusts a control valve of the packer through a controller, controls the sealing water pressure in the packer, and completes the intelligent control of the opening/closing state of the packer.

Preferably, the high-pressure low-temperature fluid is water or hydrochloric acid or supercritical CO ₂ 。

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, the injection and production wells are subjected to high-pressure low-temperature fluid shear stimulation in stages from bottom to top, so that shear unloading disturbance on a fracture development zone is realized, effective volume stress in high-pressure fracture thermal storage is released, and the opening degree and length of a fracture in a reservoir are increased, thereby effectively improving the fracture network fracturing communication effect of the dry hot rock reservoir.

Meanwhile, by dynamically and intelligently regulating the injection-production well subsection, the reduction of the heat production efficiency caused by the premature heat breakthrough generated by a single injection-production path can be avoided, and the heat recovery of the exploited subsection is facilitated, so that the aim of rapidly exploiting the geothermal heat from the deep dry heat rock reservoir layer on a large scale is fulfilled, and the requirements of crack-type heat storage commercial development and geological environment regulation are met.

Drawings

FIG. 1 is a schematic diagram of a double slant well segmented regulation enhanced heat recovery system.

Fig. 2 is a schematic view of the construction of the injection and production well section of the present invention.

FIG. 3 is a diagram of the sectional water injection shearing pressure relief permeability improvement effect of the double slant well.

FIG. 4 is a diagram of a sensor control circuit for packer setting.

The reference numbers illustrate:

1-an injection well; 2, producing a well; 3-a monitoring well; 4-fault; 5-a deviated well section; 6-segmenting the inclined shaft; 7-high temperature resistant water pressure expansion type metal packer; 8-water injection shearing pressure relief disturbance area; 9-magma reservoir; 10-dry hot rock mining the reservoir; 11-primary fissure development zone; 12-cement; 13-a sleeve; 14-a catheter; 15-injection holes; 16-a perforator; 17-hydraulic fracture; 18-injection well first section; 19-an injection well second section; 20-injection well third section; 21-injection well fourth section; 22-injection well fifth subsection; 23-a first section of the production well; 24-a production well second section; 25-producing well third section; 26-producing well fourth section; 27-producing well fifth subsection; 28-a temperature sensor; 29-water pressure sensor; 30-a control valve; 31-a ground control platform; 32-a controller.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail with reference to the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solution of the present invention is described in detail below with reference to the embodiments and the drawings, but the scope of protection is not limited thereto.

The embodiment discloses a fractured dry hot rock reservoir double inclined shaft segmented regulation and enhanced heat recovery method, which comprises the following steps:

a dry hot rock exploitation reservoir 10 with the burial depth of 2000m-3000m is selected as a development area, the heat storage temperature is 200-300 ℃, and the deep magma reservoir 9 is mainly formed through the heat convection effect in a fault 4, as shown in figure 1. 3 wells are arranged on the ground, the wells comprise a group of vertical counter wells (an injection well 1 and a production well 2) and a monitoring well 3, the ground distance of the counter wells is 50m, and microseismic monitoring equipment is arranged in the monitoring well 3 and used for positioning and representing fracture development in the water injection shearing pressure relief process.

Each well is drilled into a hot dry rock producing reservoir 10 and simultaneously a casing 13 is lowered, the casing 13 and the wall of the well are cemented with cement 12.

The method comprises the following specific steps:

1) the method comprises the steps of determining the main crack orientation of a primary crack development zone 11 of a thermal reservoir by using an imaging logging means, then drilling one of vertical opposite wells into a thermal storage low-temperature zone in an inclined mode to form an injection well 1, drilling the other one of the vertical opposite wells into a thermal storage high-temperature zone in an inclined mode to form a production well 2, simultaneously putting a casing 13 into the casing, completing the well by using cement 12, performing lateral drilling in the vertical well, drilling the injection well into the thermal storage low-temperature zone, drilling the production well into the thermal storage high-temperature zone, and thus avoiding the risk of collapse when the injection well is drilled into the high-temperature zone, being beneficial to well wall maintenance and simultaneously not influencing the heat production.

As shown in FIG. 2, wherein the injection well 1 is below the production well 2, the vertical distance between the two wells is 300- & lt 500 & gt. After the injection well 1 and the inclined well part 5 at the lower part of the production well 2 enter a dry hot rock reservoir, a conduit 14 capable of passing low-temperature fluid and a high-temperature-resistant hydraulic expansion type metal packer 7 are put in for packing the annular space of the conduit 14 and a casing 13. The conduit 14 is connected to a perforating gun 16 which leaves injection holes 15 only on the fracture side, as shown in fig. 2. The high-temperature-resistant hydraulic expansion type metal packer 7 can generate lateral expansion under the action of water pressure, has the elasticity of rubber and metal strength, is not easy to soften and damage under the action of long-term high temperature, can effectively support the inclined shaft to prevent the collapse of a well wall, and can pack the inclined shaft into different sections which are sealed independently. The high-temperature-resistant hydraulic expansion type metal packer 7 is provided with a temperature sensor 28 and a pressure sensor 29, and can monitor the temperature and the water pressure of each section in the fracturing or thermal recovery process, thereby providing feedback for the selection of the injection and recovery process. In addition, the packer is provided with a control valve 30 for controlling the communication of the packer 7 with the water pressure in the conduit 14, which effects the open/closed state of the packer. In addition, the temperature sensor 28 and the water pressure sensor 29 of each packer are connected to a ground control platform 31 through signal wires, the ground control platform 31 is communicated with a host through an interface, and a temperature threshold value alarming function is added, so that the minimum geothermal recoverable temperature of 100 ℃ is used as a threshold temperature.

2) Dividing an injection well 1 and a production well 2 into different inclined well sections 6 according to the length, firstly selecting a first injection well section 18 with the lower height in the injection well 1 as a fracturing section, moving a high-temperature-resistant water pressure expansion type metal packer 7 to two sides of the first injection well section 18 for plugging, then injecting high-pressure cold water into the first injection well section 18 by using a large-displacement injection pump to perform shear stimulation to generate hydraulic fractures 17, simultaneously forming a water injection shear pressure relief disturbance area 8 of a fracture area above the first injection well section 18, then sealing a second injection well section 19 by using a packer to perform high-pressure cold water injection shear stimulation in the same way, then sequentially producing a first well section 23, a second production well section 24, a third injection well section 20, a fourth injection well section 21, a third production well section 25, a fourth production well section 26, an injection well 22 and a fifth production well section 27, and sequentially performing water injection stimulation on the sections of the injection production well from bottom to top, and releasing effective volume stress in the high-pressure fracture thermal storage to enable the primary fracture of the reservoir fracture development zone to achieve full crossing-expansion under hydraulic shear stimulation and unloading disturbance, and then alternately selecting each subsection of the injection and production well for re-circulating fracturing for 4-8 days until a geothermal exploitation channel with strong permeability and large heat exchange area is formed between the two wells.

3) After the well groups are communicated with each other, a plurality of high-temperature water pressure resistant expansion type metal packers 7 are put down into an injection and production well, the inclined well section 6 of the injection well 1 and the inclined well section 6 of the production well 2 are independently sealed, the first section 18 of the injection well is selected as an injection section, the first section 23 of the production well is selected as a production section, cold water with the temperature of 30-50 ℃ is injected with low pump capacity, so that the cold water and fractures of the dry hot rock exploitation reservoir layer 10 are subjected to full heat exchange, meanwhile, a temperature sensor on the packers is used for monitoring the temperature change of the production section, the production section can be opened when the temperature of the production section is higher than 200 ℃, hot water is continuously extracted, and then the high-temperature water or steam after heat exchange is discharged to the ground for steam extraction and power generation.

4) And after 7-10 days of operation, closing the first injection well subsection 18 and the first production well subsection 23, replacing the second injection well subsection 19 as an injection well, replacing the second production well subsection 24 as a production well, and repeatedly carrying out heat recovery.

5) And after 7-10 days of operation, closing the second injection well section 19 and the second extraction well section 24, selecting the third injection well section 20 and the third extraction well section 25 for extraction, and after 7-10 days of operation, closing the third injection well section 20 and the third extraction well section 25, and dynamically regulating and controlling the injection and extraction sections according to the water temperature change of the extraction well in sequence.

6) In the circulating multi-stage injection and production operation process, the ground control platform 31 monitors the temperature change of fluid in the operation stage in real time, if the temperature of the fluid is lower than the minimum geothermal recoverable temperature by 100 ℃, the control valve 30 in the stage is opened through the controller 32, the guide pipe 14 and the high-temperature-resistant water pressure expansion type metal packer 7 are communicated, the water pressure in the unloading guide pipe 14 is increased to enable the packer 7 to generate lateral contraction, and the water injection and heat recovery of the stage is stopped; if the temperature of the fluid in the subsection recovers and exceeds the minimum geothermal heat production temperature by 100 ℃, the control valve 30 in the subsection is opened, the water pressure in the unloading guide pipe 14 is increased to enable the packer 7 to generate lateral contraction, the annular space of the guide pipe 14 and the sleeve 13 is sealed, the subsection sealing is realized, and therefore the intelligent control of the opening/closing state of each subsection packer 7 is realized.

In the embodiment, water injection, shearing and pressure relief transformation are sequentially carried out on each section from bottom to top to generate a fracture group distributed along a reservoir, and after main fractures of multiple sections are communicated, injection and production well sections are alternately arranged at intervals for multiple times, so that primary fractures of a reservoir fracture development zone are fully crossed and expanded under hydraulic shearing stimulation and unloading disturbance to form a geothermal exploitation channel with high permeability and large heat exchange area; effectively improving the fracturing and communicating effect of the fracture network of the hot dry rock reservoir. The inclined shaft is transformed by alternately injecting water, shearing and releasing pressure, so that the fracturing transformation effect of a plurality of wells or a group of wells adopted in the prior art can be achieved, the engineering quantity is reduced, and the well wall maintenance frequency is reduced.

And then, a packer is adopted to pack the two inclined wells into different sections which are sealed independently, cold water is injected into a reservoir fracture along an injection well section at a low pump rate, hot water is extracted through a production well section after the cold water and the reservoir generate heat exchange and the temperature is increased, and the injection and extraction sections are alternately arranged at intervals along with the extraction, so that the uniform extraction of the hot dry rock heat storage is realized.

The angle, the length and the number of the lateral drilling holes can be adjusted according to the thickness of the thermal reservoir when the lateral inclined wells are drilled into the thermal reservoir, so that the enhancement and the modification of the thermal reservoir permeability with uneven thickness or irregular distribution and the efficient heat extraction are met, the modification area and the modification volume of the thermal reservoir are increased, the fluid seepage passage of the reservoir is improved, and the hot water yield and the thermal recovery efficiency of a single well are improved.

The large-pump-amount injection fracturing is adopted in the fracturing process, and the low-pump-amount injection fracturing is adopted in the recharging exploitation, so that the low-pump-amount shear fracturing and chemical stimulation can be continued for a long time, the pumping pressure and the pumping scale are small, the stress release process is slow, and the risk of inducing an earthquake can be effectively reduced; cold water is injected with low pump amount, mainly to avoid geological hazards such as fault slippage and the like caused by large flow in the thermal recovery process. The injection mode of the low-temperature fluid can adopt a constant flow injection mode, a monotonous injection mode or a circulating injection mode.

The injection and production well subsection is dynamically regulated and controlled in the heat production stage, the heat production efficiency reduction caused by the premature heat breakthrough generated by a single injection and production path can be avoided, and the heat recovery of the exploited subsection is utilized.

The method can be widely applied to the exploitation of geothermal resources of the hot dry rock with different underground burial depths and different thicknesses, and is particularly suitable for the exploitation of fracture-type geothermal reservoirs with lower permeability. The technical principle can also be used for exploiting and utilizing resources such as shale gas, coal bed gas and the like.

While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A fractured dry hot rock reservoir double inclined shaft segmented regulation and enhanced heat recovery method is characterized by comprising the following steps:

s1: arranging vertical opposite wells on the surface of a dry-hot rock geothermal exploitation area, then respectively inclining a slant well to enter a target thermal reservoir and cementing wells to form an injection well and an extraction well;

s2: correspondingly segmenting the inclined section of the injection well and the inclined section of the extraction well respectively, and injecting high-pressure low-temperature fluid section by section from the inclined well segment with the lowest elevation of the injection well and the extraction well, wherein the high-pressure low-temperature fluid enters a target thermal reservoir through perforations on the inclined well segment to perform shear stimulation so as to gradually form unloading disturbance influence on a reservoir area;

2. The fractured-type hot dry rock reservoir double-inclined-well segmented-regulation enhanced heat recovery method according to claim 1, wherein high-pressure low-temperature fluid is injected upwards section by section in step S2, and the layer-by-layer heat recovery process in step S3 is performed repeatedly.

3. The fractured dry hot rock reservoir bi-deviated well segmented control enhanced heat recovery method according to claim 1, wherein the inclined section of the injection well is drilled into a target hot reservoir low-temperature area, and the inclined section of the production well is drilled into a target hot reservoir high-temperature area.

4. The fracture-type hot dry rock reservoir dual-inclined-well segmented regulation and enhanced heat recovery method as claimed in claim 3, wherein the inclined sections of the injection well and the extraction well are distributed at equal intervals and are perpendicular to the main fracture direction of the hot storage fracture area, and the inclined section of the extraction well is located above the inclined section of the injection well.

5. The fractured-type hot dry rock reservoir double-inclined-well segmented regulation and enhanced heat recovery method according to claim 1, characterized in that a monitoring well is arranged between the injection well and the production well, and the monitoring well is provided with a microseismic monitoring device.

6. The fractured-type hot dry rock reservoir double-inclined-well segmented regulation and enhanced heat recovery method according to claim 1, characterized in that the high-pressure low-temperature fluid is injected in a constant-flow injection mode, a monotonic injection mode or a cyclic injection mode.

7. The fractured-type hot dry rock reservoir double-inclined-well segmented regulation and enhanced heat recovery method according to claim 1, characterized in that a conduit through which a cryogenic fluid can pass is arranged in the inclined section of the injection well and the inclined section of the production well, the conduit is connected with a perforator, a casing is arranged outside the conduit, and cement is adopted for cementing between the casing and the well shaft.

8. The fractured-type hot dry rock reservoir double-inclined-well segmented regulation and enhanced heat recovery method according to claim 7, characterized in that a hole is reserved on the fracturing side of the perforator, and a plugging structure is arranged on the other side of the perforator.

9. The split-type hot dry rock reservoir twin-slant well segmented regulation and enhanced heat recovery method according to claim 1, wherein a packer is used for separating or independently sealing the slant well segments, and the packer is provided with a temperature sensor and a water pressure sensor for monitoring the temperature and water pressure changes of the fluid in each segment; the temperature sensor and the water pressure sensor are connected to a ground control platform through signal lines, and the ground control platform is communicated with the host through an interface.

10. The split-type hot dry rock reservoir twin-slant well segmented control enhanced heat recovery method according to claim 9, wherein the packer is provided with a control valve, and the control valve is used for controlling the communication between the packer and the water pressure in the conduit; the ground control platform judges the temperature according to the temperature measurement feedback of the packer in each section through the temperature threshold value, and controls the sealing water pressure in the packer by adjusting the control valve of the packer through the controller, thereby completing the control of the opening/closing state of the packer.