RU2758828C1 - Hydraulic fracturing fluid based on highly mineralized water, method for its preparation and method for processing the formation with its use - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: invention relates to the field of oil and gas production. Hydraulic fracturing fluid based on highly mineralized water contains components in the following ratio, wt. %: gel-forming agent 0.2-0.5, crosslinking agent 0.2-0.4, crosslinking stabilizer 0.04-0.3, destructor 0.02-0.14, demulsifier 0.01-0.2, biocide 0.001-0.005, highly mineralized water the rest, while the ratio of the crosslinking agent to the gel-forming agent ranges from 0.6:1 to 1.0:1, to the crosslinking stabilizer from 1.3:1 to 5.6:1, to the destructor from 3.5:1 to 13.0:1. The method for preparing hydraulic fracturing fluid consists in the fact that, when mixing, a biocide is added to highly mineralized water, then a gel-forming agent is added, a gel-forming agent is hydrated and a demulsifier and a destructor are introduced into the resulting linear gel, then a crosslinking agent is added, a crosslinking stabilizer is introduced simultaneously or after adding the crosslinking agent. The method for processing the formation includes hydraulic fracturing using hydraulic fracturing fluid based on highly mineralized water.

EFFECT: ensuring the possibility of regulating the stability time of the liquid during the necessary period for the operation at high temperatures and its subsequent complete disintegration, simplifying and improving the efficiency and eco-friendliness of the processing method.

36 cl, 9 dwg, 2 tbl

Description

The invention relates to the field of oil and gas production, in particular to the technological compositions used to increase the permeability of productive formations through hydraulic fracturing (HF), and can be used to prepare a hydraulic fracturing fluid using alternative water sources, such as saline bottom water, a mixture of bottom and fresh water, stratal and other waters.

Hydraulic fracturing is one of the most effective technologies for intensification of production and injection wells. The hydraulic fracturing method has many technological solutions due to the characteristics of a particular object. The most important factor in the success of a hydraulic fracturing procedure is the quality of the fracturing fluid. Hydraulic fracturing fluids should have sufficient dynamic viscosity to create high conductivity fractures, have low filtration leaks into the formation, ensure a minimum decrease in the permeability of the treated formation, ensure low friction pressure losses in pipes, have sufficient thermal stability and high shear stability during the fracturing period, easily be removed from the formation after processing (including as a result of destruction), be processable in preparation and storage in field conditions, have low corrosive activity, be environmentally friendly and safe to use, and have a relatively low cost.

The use of a quality fluid is one of the key elements for a successful hydraulic fracturing operation. For effective hydration of natural polymer, the water temperature must be at least 25-30 ° C, therefore, the water used is preheated, which increases the cost of hydraulic fracturing operations. In most cases, the mixing liquid is fresh water. In connection with the general tendency to reduce costs, currently the world is looking for opportunities to use saline waters for hydraulic fracturing fluids, which will lead to a decrease in the cost of produced hydrocarbons by minimizing the costs of water treatment, delivery and storage.

Produced waters, for example, from the Cenomanian aquifers, as well as produced water after separation from hydrocarbon raw materials have a temperature of 30-50 ° C and are a potential source for the preparation of fracturing fluids. The use of produced and produced water can significantly reduce the time of hydraulic fracturing operations and reduce the cost of hydrocarbon production, due to the absence of the need for water heating and additional preparation, transportation and storage.

However, formation and produced water contains a large amount of ions of iron, chlorine, boron, magnesium, calcium, carbonates, other elements and compounds, oil products, suspended particles, which negatively affect the performance of standard hydraulic fracturing fluids, leading to the absence or incomplete hydration. polymer, premature crosslinking of a linear gel, weak crosslinking, up to its absence, and sometimes to the effect of crosslinking (syneresis), poor recovery and insufficient temperature stability.

The physicochemical properties of reservoir and produced water depend on many different factors, such as the geological structure of the reservoir, mineralogical composition, chemical processes that took place during sedimentation, the type of hydrocarbons, vital activity and types of microorganisms, reservoir temperature and pressure. The produced water contains suspended particles and various water-soluble compounds, which are a mixture of organic and inorganic compounds. Some compounds are present in the formation water, others appear during the development and implementation of various geological and technical measures, but the water sources are characterized by high mineralization. The salinity of formation and bottom water can vary in the range from several milligrams to tens and hundreds of grams per liter, with the main effect on salinity is provided by sodium and chlorine ions and slightly less potassium, calcium and magnesium.

Cenomanian water of Western Siberia is mostly used in oil production in reservoir pressure maintenance systems, because is better suited for this than the river water of the region due to its superior performance and related chemical composition. Such water has a total mineralization of up to 20 g / l, mainly due to chloride salts.

The currently used guar-based fluid compositions are very sensitive to the quality of the water used, namely to the content of iron, calcium and magnesium ions, boron, etc. in it, which makes it impossible to use bottom and formation waters without preliminary and costly preparation. To maintain the stability of the resulting polymer when using mineralized water, the content of the gelling agent in the composition of the liquid is increased. Another way that allows the use of saline water in the composition of the hydraulic fracturing fluid is the use of special additives (stabilizers, buffers and auxiliary components), which make it possible to neutralize the negative effect of ions and pollutants present in the water.

It is known [L.A. Magadova Development of water-based and hydrocarbon-based fracturing fluids and technologies for their application to improve the process of hydraulic fracturing. Ph.D. thesis abstract 2007] that the introduction of water-soluble amino alcohols into the composition of a guar-based liquid with a borate crosslinker makes it possible to obtain highly structured gels using mineralized water containing monovalent and multivalent cations. However, this source does not indicate the ratios at which the viscosity will be maintained for the required time and the subsequent destruction of the fluid to remove it from the formation.

A solution is known (patent CN 104877658, publ. 02.09.2015, IPC: C09K 8/68), which uses a 6-component composition of hydraulic fracturing fluid based on GPG (hydroxypropyl guar) with a load from 0.2 to 0.4 wt. %, efficient at a total mineralization of water 10-100 g / l. The common features of the known and claimed hydraulic fracturing fluid and the method of its preparation are the use of a gelling agent (modified guar), a demulsifier, a bactericide, a crosslinker. However, the absence of a destructor and the contents of the components presented in the known technical solution do not provide a liquid that maintains the required viscosity for the required time and with subsequent destruction for removal from the formation. Also, the stability and effectiveness of the known fluid is ensured only when a modified guar is used.

It is known to use modified guar polymers as gelling agents, which is described in the patent (patent CN 103215024, publ. 20.01.2016, IPC: C09K 8/68). Common features of the known and claimed fluid for hydraulic fracturing and the method of its preparation are the use of a thickener (gelling agent), a crosslinker and a demulsifier in the composition of a thickener (gelling agent). However, the absence of a destructor, a biocide, with the specified amount of a crosslinker does not provide a stable fracturing fluid simultaneously with the required viscosity and subsequent disintegration within the required time and controlled decomposition time for successful withdrawal from the formation, as well as regulation of the stability time.

It is also worth noting that the hydraulic fracturing fluids presented in patents CN 104877658 and CN 103215024 are developed on the basis of only modified natural polymers, namely GPG and carboxymethylhydroxypropyl guar. Such polymers are more stable for use with saline waters, but have an increased cost compared to unmodified guar gum due to the complicated and more expensive production technology.

For the possibility of using highly mineralized waters, technical solutions are also known for the development of new compositions of crosslinkers (patent CN 103497753, publ. 08.01.2014, IPC: C09K 8/68, C07F 7/00; patent CN 103497754, published 02.03.2016, IPC: C09K 8/68), for example, based on zirconium-containing and boron-containing components and binders, which are applicable for crosslinking linear polysaccharide gels prepared in waters with high salinity (about 20 g / l). Common features with the claimed hydraulic fracturing fluid and the method of its preparation are the use of a gelling agent, a crosslinker. However, modified guar gum is used as gelling agents, which in combination with an unconventional crosslinker leads to a high cost of the system and the synthesis of specialized crosslinkers. At the same time, the possibility of ensuring simultaneously the stability of the hydraulic fracturing fluid and its disintegration during a specific time is not indicated.

Information on the use of a buffer composition based on amino alcohol in the composition of a hydraulic fracturing fluid based on a guar gelling agent on the Cenomanian water of Western Siberia fields is known from the source [SPE 131729. Effective hydraulic fracturing using formation water from Western Siberia. A. Fedorov, D-K Fu, K. Mullen et al. 2010.], in which, in addition to the buffer, a dry borate crosslinker and a stabilizer-complexing agent are used, which is the sodium salt of ethylenediaminetetraacetic acid (EDTA). A feature of this system is the use of an organic borate crosslinker. However, the known system has a low temperature stability (up to 70 ° C) and a high cost of some components, which can make their use economically unprofitable, and the possibility of simultaneously ensuring the stability of the fracturing fluid and its disintegration during a specific time is not indicated.

The known method (patent CN 103740355, publ. 04/23/2014, IPC: C09K 8/68), in which it is proposed to use a system of pH buffers to improve the parameters of crosslinking in hydraulic fracturing fluids on borate-crosslinkable natural polymers using produced water. In the present examples of the invention, the hydration of the guar polymer is 60 minutes, which is a long period for reaching an acceptable viscosity. Also, to stabilize the crosslinking, it is preferable to use diethylenetriamine (DEET) at dosages of 3-5 l / m ^3, which increases the cost of the proposed system. The common features of the known and claimed invention are the use of a gelling agent and a crosslinker in the composition of a hydraulic fracturing fluid and a method for its preparation. However, due to the fact that the liquid does not include a destructor, this leads to the impossibility of regulating the time of destruction of the crosslinked gel and ensuring the disintegration of the liquid to remove it from the formation within the required time.

The known composition of a polysaccharide gel for hydraulic fracturing (patent RU 2173772, publ. 09/20/2001, IPC: E21B 43/26), which contains fresh or mineralized water, polysaccharide thickener, boron crosslinker, diethanolamine and an oxidizing component taken from the group consisting of persulfate ammonium, persulfates, percarbonates and perborates of alkali metals, characterized in that it additionally contains a quaternary ammonium compound catamine AB or a water repellant neftenol GF. As a polysaccharide thickener, it is proposed to use guar, modified guar or a mixture of guars, namely, standard guar and modified - hydroxypropyl guar (HPG), which is a more stable polymer for mineralized waters. The effective operation of the system is also shown on formation water with a total content of divalent calcium and magnesium ions up to 1000 mg / l. Common features are the use of a gelling agent (guar or modified guar), a crosslinker (for example, a borate type), a destructor (persulfate) in the composition of a liquid and in its preparation. However, the known composition and preparation method do not in all cases provide the required liquid viscosity, and the minimum disintegration time is 6 hours.

The destructor is rarely used in the composition of hydraulic fracturing fluids in highly mineralized waters due to the fact that the ions present in the waters reduce the viscosity of the polymer. Such a decrease in viscosity is uncontrollable and does not provide complete destruction of the polymer for its successful removal from the formation after hydraulic fracturing. In order to destroy the fracturing fluid and remove it from the formation, the use of a destructor is required, however, the use of a destructor even in low concentrations, as also indicated in patent RU 2173772, at temperatures above 60 ℃ has an avalanche-like character and does not allow for a controlled stability time of the hydraulic fracturing fluid. At the same time, due to the fact that fracturing operations are carried out at elevated temperatures, fracturing fluids must simultaneously have stability at high temperatures without losing viscosity for a time sufficient for fracturing operations and at the same time break down with a significant decrease in viscosity to remove from the reservoir. Thus, determining the composition of a hydraulic fracturing fluid that meets all the specified requirements is a non-trivial task.

The closest analogue (prototype) of a fluid for hydraulic fracturing and a method for its preparation is a technical solution (patent CN 102757778, publ. 04.06.2014, IPC: IPC: C09K 8/68), in which the fluid for hydraulic fracturing on highly mineralized water includes a thickener, a crosslinker, a destructor , stabilizer, demulsifier, bactericide. Common features of the known and claimed liquid and the method of its preparation are the use of components: thickener (gelling agent), crosslinker, destructor, demulsifier, bactericide. In this case, the known ranges of the content of the crosslinker, the thickener are included in the claimed ranges.

However, the known solution uses the content of the destructor, biocide and demulsifier, which, as a result, does not provide the ratio of components at which the fracturing fluid will simultaneously maintain stability (viscosity at least 400 cP) at a temperature of 90 ℃ and completely disintegrate within the required time, as well as not the possibility of regulating the liquid stability time is provided.

There is a known method of treating a formation (patent RU 2377403, publ. 09/10/2008, IPC: E21B 43/26, E21B 43/267, C09K 8/68, C09K 8/80), which includes obtaining a thickened fluid for treating a formation containing an aqueous solution single salt and a crosslinked thickener, bringing a portion of the subterranean formation into contact with a thickened treatment fluid to create or augment one or more faults therein. Common features of the known and claimed methods of treatment of a formation is to carry out hydraulic fracturing using a fluid that includes a crosslinked thickener and water containing salts. However, in the known method, the aqueous solution is a solution of one salt, and the content and ratios of the components do not ensure the simultaneous preservation of the viscosity of the fluid and its complete disintegration for the required time, which leads to the complexity and decrease in the efficiency of the formation treatment method due to the complex removal of fluid after hydraulic fracturing. ...

The closest analogue (prototype) of the formation treatment method is one of the well treatment methods by hydraulic fracturing (RU 2689940, publ. 05/29/2019, IPC: E21B 43/267, C09K 8/68), which includes the formation of a well treatment fluid when mixing ingredients, including an aqueous fluid, a thickener, a crosslinker and other components (for various variants of the method), treatment of the well with the obtained fluids, while dialdehyde is used, which, as a result of conversion into a diacid, ensures the destruction of the thickener. The common features of the claimed and known methods are treatment of a well with hydraulic fracturing using a fluid that contains a thickener, a crosslinker, an agent that provides the destruction of the thickener (destructor), as well as produced water for one of the variants of the known method. However, the known method does not indicate the ratios at which the complete breakdown of the fracturing fluid will be ensured after the required time for withdrawal from the formation, while the conversion of dialdehyde to diacid may be complicated by the content of various ions in the water composition, which will not allow to ensure the exact ratios of the crosslinker, gel-forming an agent and an agent that ensures the destruction of the thickener, to ensure the required stability time of the hydraulic fracturing fluid and the time of its complete disintegration, as well as their regulation. As a result, there is no increase in the efficiency, controllability of the formation treatment (hydraulic fracturing) method and reducing the time required for hydraulic fracturing.

The task of the proposed technical solution is to improve the manufacturability and environmental safety of oil production processes by using saline waters, such as bottom water, a mixture of bottom and fresh water, formation waters, including Cenomanian and other waters, to obtain a hydraulic fracturing fluid with the required functional characteristics, such as the temperature stability of the system, resistance to dynamic loads, the absence of stable emulsions when interacting with the formation fluid, sufficient bearing capacity, and others, without additional operations for the preparation, heating and transportation of water.

The technical result for the hydraulic fracturing fluid and the method for its preparation consists in obtaining a fluid for hydraulic fracturing on highly mineralized water with a composition that simultaneously maintains the optimal viscosity for hydraulic fracturing operations (at least 400 cP) for the time required for hydraulic fracturing (from 60 to 150 minutes, preferably 100 to 120 minutes) at temperatures up to 90 ℃ inclusive and followed by complete fracturing fluid disintegration (viscosity loss below 10 cP) after 600 minutes or less, preferably after 200 minutes, which improves the efficiency of fracturing fluid removal. For the method of preparing a fluid for hydraulic fracturing, the technical result is also to provide the possibility of adjusting the fluid stability time by changing the amount of components in the stated ranges of ratios without losing properties.

The technical result for the method of treating the formation using the claimed fluid is to provide the possibility of regulating the time of hydraulic fracturing operations, as well as to simplify and increase the efficiency and environmental friendliness of the method of treating the formation by using highly mineralized water, since eliminates the need for additional preparation (heating), transportation and storage of water, provides the ability to control the stability time of the hydraulic fracturing fluid, as well as its complete disintegration after the completion of hydraulic fracturing, as a result of which the remaining fluid is easily removed from the formation.

The technical result is achieved due to the fact that the fluid for hydraulic fracturing of formation on highly mineralized water includes a gelling agent, a crosslinker, a crosslink stabilizer, a destructor, a demulsifier, a biocide, while the content of the components is, wt%: gelling agent from 0.2 to 0.5 , crosslinker from 0.2 to 0.4, crosslinker from 0.04 to 0.3, destructor from 0.02 to 0.14, demulsifier from 0.01 to 0.2, biocide from 0.001 to 0.005, highly mineralized water - the rest, while the ratio of the crosslinker to the gelling agent is from 0.6: 1 to 1.0: 1, to the crosslinking stabilizer from 1.3: 1 to 5.6: 1, to the destructor from 3.5: 1 to 13 , 0: 1.

Due to the specifics of the composition of mineralized waters, which include bottom and formation waters, namely the high content of calcium, magnesium and other elements, crosslinking with classical, in particular borate, crosslinkers can be difficult or absent altogether. The crosslinking stabilizer is used for the formation of highly structured crosslinked gels with increased temperature stability, and also performs incl. the role of a pH buffer, as for the effective passage of the linear gel crosslinking operation, the pH value of the system should be maintained in the range of 8-10. The introduction of a destructor into the composition of the fracturing fluid in the stated range is necessary to ensure fluid breakdown (i.e., a decrease in viscosity to 10 cP or lower) after the completion of the fracturing operation and for its successful removal from the formation.

Within the scope of the claimed invention, a lower content of the crosslink stabilizer relative to the crosslinker is used in comparison with the prior art. A decrease in the amount of a crosslink stabilizer relative to a crosslinker (i.e., an increase in the ratio of the concentration of a crosslinker to a crosslinker stabilizer) should lead to a decrease in the temperature stability of the resulting liquid and a decrease in the crosslinking efficiency of a linear gel. In this case, the claimed invention, on the contrary, provides a high temperature stability of the obtained gel (maintaining the viscosity above 400 cP at a shear rate of 100 s ^-1 for at least 60 minutes at a temperature of 90 ℃). This confirms that when using the claimed ratios of the components, a structure is formed in which the crosslinked gel has a high viscosity, but at the same time does not reach the degree of swelling, which provides the possibility of thermal movement and breaking of bonds between molecules. At the same time, it is known from the prior art (for example, patent CN 102757778) that the use of even low values of the concentration of the destructor in the composition of the fracturing fluid (0.0017%) leads to instability of the gel at a temperature of 70 ℃ already after 60 minutes. It would be expected that an increase in the concentration of the destructor in the claimed invention and an increase in temperature to 90 ℃ would lead to a significant reduction in the stability time and viscosity. However, as a result of the formation of the structure of the crosslinked gel obtained using the ratios claimed in the invention, a uniform interaction with the destructor occurs, which ensures the preservation of viscosity even at high temperatures (90 ℃) from 60 to 150 minutes and the subsequent destruction of the crosslinked gel with a decrease in viscosity to 10 cP or below.

A decrease in the concentration of the destructor below the declared value, as well as an increase in the concentration of the crosslink stabilizer above the declared value, taking into account the specifics of using highly mineralized water, will lead to incomplete breakdown of the fracturing fluid. An increase in the concentration of the destructor above the declared value and a decrease in the crosslinking stabilizer below the declared value will lead to a decrease in the stability of the fracturing fluid.

Thus, the ratio of the crosslinker to the crosslink stabilizer and to the destructor in the stated ranges provides both the stability of the liquid (retention of its viscosity, thermal stability) and its subsequent disintegration during the required time. The stability time of the fracturing fluid should be from 60 to 150 minutes, preferably from 100 to 140 minutes, while the disintegration time should not exceed 600 minutes, preferably about 200 minutes.

The content of the gelling agent in the stated ranges is known in the art to be optimal for providing the viscosity of the fracturing fluid, which ensures the success of fracturing operations. Modified polymers used as a gelling agent, as more resistant to the presence of ions in the water used, are preferably used in the range from 0.2 to 0.4 wt%, for unmodified polymers it is preferable to use an increased content - from 0.3 to 0, 5 wt%. An increase in the content of the gelling agent above the stated ranges will lead to excessive contamination of the formation and decrease in permeability, which is impractical from a practical and economic point of view.

A decrease in the amount of crosslinker will lead to a decrease in viscosity, an increase in syneresis and a decrease in fluid stability. The stated ratios of the crosslinker to the gelling agent ensure the formation of a crosslinked gel of the required viscosity (not less than 400 cP) in a wide range of water salinity.

The addition of a biocide is mandatory because in the mixing waters, in most cases, microorganisms are present that can feed on natural polymers, which negatively affects the hydration parameters - the viscosity of the aqueous solution and the rate of the polymer viscosity increase. The amount of biocide is the optimal amount for the stated limits of the gelling agent, which ensures the preservation of the polymer structure with different concentrations of bacteria in the water used and does not affect the properties of the fracturing fluid. A decrease in the amount of biocide will not ensure the preservation of the polymer structure under the influence of the bacteria contained, an increase in the amount of biocide may affect the properties of the fracturing fluid, depending on the composition of the substance used as a biocide.

The demulsifier avoids the formation of stable emulsions of the fracturing fluid when interacting with the formation fluid during fracturing, as well as after fracturing. The introduction of a demulsifier in the stated ranges does not affect the properties of the fracturing fluid. A decrease in the amount of demulsifier will lead to the formation of emulsions, an increase in the content of demulsifier can affect the properties of the fracturing fluid, depending on the composition of the demulsifier used.

Within the framework of the claimed invention, highly mineralized water is understood as a product, reservoir or a mixture of product and fresh water with a salinity of 3 g / l to 20 g / l.

The gelling agent can be selected from the group that includes guar gum, modified guar gum, xanthan gum, a mixture of the above components, another naturally occurring polymer that is functionally suitable to obtain a linear gel with sufficient initial viscosity and is crosslinkable by known types of crosslinkers on borate and other bases. The commercial form of the polymer can be dry or liquid, for example, in the form of a suspension in hydrocarbon solvents.

As a crosslinker, it is preferable to use a borate crosslinker, including in the form of a suspension. The use of crosslinkers of a different nature and in alternative forms capable of binding a linear polymer into a crosslinked form is applicable.

The crosslinking stabilizer can be selected from the group of alcohols and amino alcohols, preferably methyl alcohol, glycerol, ethylene glycol, monoethanolamine, diethanolamine, triethanolamine, diethanoltriamine, or mixtures thereof.

The destructor can be an oxidizing type destructor based on ammonium persulfate, organic peroxides, or another known destructor for use in fracturing fluids.

The demulsifier is a mixture of surfactants based on ethoxylated fatty alcohols, the biocide is potassium sorbate.

When the content of bicarbonate ions in the water is more than 500 mg / l, the hydraulic fracturing fluid may additionally contain the products of the interaction of the linear gel stabilizer and bicarbonate ions. The concentration of the interaction products of the linear gel stabilizer and bicarbonate ions can be no more than 0.3 wt%.

The linear gel stabilizer can be selected from the group of water-soluble organic and inorganic salts and acids, preferably citric acid, acetic acid, formic acid and their salts, oxyethylene diphosphonic acid, nitrilotrimethylphosphonic acid, sodium gluconate, sodium lignosulfonate, sodium salts thereof, ethylenediaminetetras acid ...

Highly mineralized water fracturing fluid may additionally contain a chelating agent (additive) at a concentration of not more than 0.2 wt%. The chelating agent can be selected from the group of water-soluble organic and inorganic salts, (but not limited to) sodium salt of hydroxyethylene diphosphonic acid, trisodium salt of nitrilotriacetic acid, N, N-bis (carboxymethyl) -L-glutamate tetrasodium, salts of diethylenetriamine pentaacetic acid , or mixtures thereof. The addition of the chelating agent can be carried out together with or instead of the linear gel stabilizer, or at another point in the process of preparing the fracturing fluid, but preferably before the moment of crosslinking. The form of the additive can be dry or liquid, it is possible to combine it with another additive of hydraulic fracturing fluid. The use of this additive in the composition of a hydraulic fracturing fluid prepared in saline water is due to the high content of multivalent metal cations in water (up to 1000 mg / l), which negatively affect the quality of the crosslinked gel, when interacting with which the chelating agent binds the corresponding metal into an inactive form.

A clay stabilizer can be additionally added to the composition of the liquid in a concentration of not more than 0.2 wt%, for example, in the case of work on reservoirs with a high content of clay minerals. There are no special requirements for these components in the framework of this invention. It should be noted that in some cases, for example, with increased salinity of the waters used, the properties of the treated formations and other factors, the addition of these components is not necessary, therefore, preliminary tests must be carried out and, based on their results, before carrying out hydraulic fracturing works, it is concluded that what components should be added.

Water can be characterized by a bicarbonate ion content up to 1700 mg / l, calcium and magnesium ions up to 1000 mg / l, iron (total) up to 14 mg / l, boron up to 12 mg / l, chlorine ion up to 10500 mg / l, a value pH = 5 - 8, total mineralization up to 20.0 g / l.

In the case of using the technology at elevated temperatures of the treated formations, the liquid can include high-temperature stabilizers, for example, sodium thiosulfate in an amount of up to 0.2 wt. %.

The technical result is also achieved when using a method for preparing a fluid for hydraulic fracturing on highly mineralized water, in which, while stirring, a biocide from 0.001 to 0.005 wt.% Is added to highly mineralized water, then a gelling agent from 0.2 to 0.5 wt.% Is added, hydration of the gelling agent and introduce into the obtained linear gel a demulsifier in an amount of 0.01 to 0.2 wt% and a destructor in an amount of 0.02 wt% to 0.14 wt%, then a crosslinker is added in an amount of 0, 2 to 0.4 wt.%, Together or after adding a crosslinker, a crosslink stabilizer is introduced in an amount of 0.04 to 0.3 wt%, while the ratio of crosslinker to gelling agent is 0.6: 1 to 1.0: 1, to a crosslink stabilizer from 1.3: 1 to 5.6: 1, to a destructor from 3.5: 1 to 13.0: 1.

The technical result is achieved as a result of the successive dissolution of the claimed components in the indicated amounts in highly mineralized water.

The addition of the crosslink stabilizer occurs together either immediately after the addition of the crosslinker, or after the funnel is closed. After the addition, the linear gel is crosslinked (or the funnel is closed, depending on the moment of loading, and then complete crosslinking). To reduce the amount of added components and optimize the cost of fracturing, a crosslink stabilizer can be added to the crosslinker.

Before adding the gelling agent, it is additionally possible to introduce a linear gel stabilizer in an amount of up to 0.3 wt%. The linear gel stabilizer is added to the water before the gelling agent until a pH value of 5-6 is reached.

It is preferable that the pH of the linear gel with the addition of the remaining components is 6-8, and the crosslinking stabilizer is added together or after the addition of the crosslinker.

The technical result of regulating the stability time is achieved by changing the content of the components in the stated ranges, within which the stability of the crosslinked gel is maintained and its subsequent disintegration is ensured.

Before adding the gelling agent to the water, a chelating agent may additionally be added in an amount of up to 0.2 wt%. The chelating agent can be selected from the group of water-soluble organic and inorganic salts, preferably sodium salt of oxyethylene diphosphonic acid, trisodium salt of nitrilotriacetic acid, N, N-bis (carboxymethyl) -L-tetrasodium glutamate, diethylenetriamine pentaacetic acid salts or their gluconate ...

Highly mineralized water can be produced water, a mixture of produced and fresh water, or stratal (Cenomanian) water with a total salinity of up to 20 g / l.

The gelling agent can be selected from the group that includes guar gum, modified guar gum, xanthan gum, a mixture of the above components, another naturally occurring polymer that is functionally suitable to obtain a linear gel with sufficient initial viscosity and is crosslinkable by known types of crosslinkers on borate and other bases.

The crosslinking stabilizer can be selected from the group of alcohols and amino alcohols, preferably methyl alcohol, glycerol, ethylene glycol, monoethanolamine, diethanolamine, triethanolamine, diethanoltriamine, or mixtures thereof.

The crosslinker can be a borate crosslinker.

The destructor can be an oxidizing type destructor based on ammonium persulfate or organic peroxides. The demulsifier can be a mixture of surfactants based on ethoxylated fatty alcohols. The biocide can be potassium sorbate.

The linear gel stabilizer can be selected from the group of water-soluble organic and inorganic salts and acids, preferably citric acid, acetic acid, formic acid and their salts, oxyethylene diphosphonic acid, nitrilotrimethylphosphonic acid, sodium gluconate, sodium lignosulfonate, sodium salts thereof, ethylenediaminetetras acid ...

A clay stabilizer can be additionally added to the composition of the liquid in a concentration of not more than 0.2 wt%, for example, in the case of work on reservoirs with a high content of clay minerals.

Water can be characterized by a bicarbonate ion content up to 1700 mg / l, calcium and magnesium ions up to 1000 mg / l, iron (total) up to 14 mg / l, boron up to 12 mg / l, chlorine ion up to 10500 mg / l, a value pH = 5 - 8, total mineralization up to 20.0 g / l.

The application of the described method is possible in the temperature range (but not limited to) 60-120 ° C, however, in the case of elevated temperatures, it is recommended to use high-temperature stabilizers, for example, sodium thiosulfate.

The choice of additives for liquids in saline waters is preferably determined individually, based on the composition of a particular source and depending on the performance characteristics to be obtained.

The technical result for the method of treatment of the formation is to simplify and increase efficiency and environmental friendliness.

The technical result is achieved by implementing a method for treating a formation, which includes hydraulic fracturing using the claimed fluid for hydraulic fracturing on highly mineralized water.

The technical result is achieved due to the fact that

- the use of highly mineralized water in the composition of the hydraulic fracturing fluid eliminates the need for additional preparation (heating), transportation and storage of water;

- the composition of the hydraulic fracturing fluid provides the ability to control the stability time of the hydraulic fracturing fluid, as well as its complete disintegration after the completion of hydraulic fracturing, as a result of which the remaining fluid is easily removed from the formation.

In this connection, the process of preparing for formation treatment (hydraulic fracturing) is simplified, the time of hydraulic fracturing is controlled, and the process of cleaning the formation from hydraulic fracturing fluid is simplified, the degree of contamination of the formation and formation fluid with components that are part of the hydraulic fracturing fluid is reduced.

Figure 1 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 1 in table 2.

Figure 2 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 2 in table 2.

Figure 3 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 3 in table 2.

Figure 4 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 4 in table 2.

Figure 5 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 5 in table 2.

Figure 6 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 6 in table 2.

Figure 7 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 7 in table 2.

Figure 8 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 8 in table 2.

Figure 9 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is shown for example 9 in table 2.

In this case, 1 is the change in the temperature of the fluid for hydraulic fracturing in time, 2 is the change in the viscosity of the fluid for hydraulic fracturing in time.

The examples below serve to illustrate the invention, but should not be construed as limiting the invention.

To conduct tests for the preparation of hydraulic fracturing fluid, we used production, mixed and formation waters taken from real sources.

The compositions of the waters used are shown in Table 1.

Table 1. Water composition.

Water No. 1 2 3 4 5 6 7 Content of main components Cl ^- , mg / dm ³ 1400 1600 10400 2800 9800 2300 4400 Na ⁺ , K ⁺ (total), mg / dm ³ 1202 1322 6155 2000 6200 2130 4230 Ca ²⁺ , mg / dm ³ 120 66 410 260 450 210 850 Mg ²⁺ , mg / dm ³ twenty eighteen 110 13 110 twenty 90 HCO ₃ ^- , mg / dm ³ 600 810 190 870 160 710 1350 Total mineralization, mg / dm ³ 3250 3862 17343 6500 17200 5420 10320

In all used water compositions, the iron content is less than 8.0 mg / dm ³ , sulfate ions - less than 200 mg / dm ³ .

To prepare the hydraulic fracturing fluid, chemical additives manufactured by Nika-Petrotek LLC were used. In general, the process of preparation of hydraulic fracturing fluid (in laboratory conditions) is carried out as follows.

A biocide (PT BIO, TU 20.59.42-010-29191682-2017) is added to the mineralized water with stirring, if necessary, depending on the composition of the water, a linear gel stabilizer is added containing more than 50 wt% citric acid as an active component (PT PHS, TU 20.59.42-052-29191682-2020), a chelating agent based on the sodium salt of oxyethylene diphosphonic acid (PT CHS, TU 20.59.42-054-29191682-2020) until complete dissolution. After that, a gelling agent is introduced into the solution with stirring at a rotational speed of the blades of an overhead stirrer (for example, Waring) of about 1500 rpm. Hydration is carried out within 20 minutes. Table 2 shows examples of using the dry form of guar gum (PT WG 7000F, TU 20.59.42-001-29191682-2017) - examples 1 - 4, 7 - 9, guar gum-based suspensions with a guar gum content of 50% - example 5 (PT GS 7000, TU TU 20.59.42-002-29191682-2017), as well as a biopolymer composition based on guar and xanthan gum - example 6 (DPS, TU 20.59.42-056-29191682-2020)

A demulsifier (PT NE, TU 20.59.42-008-29191682-2017 - surfactant based on oxyethylated fatty acids), a destructor (PT OBP-5, TU 20.59.42-004-29191682-2017 - based on organic peroxides, examples 1-5, 7-9; PT HT Cap, TU 20.59.42-023-29191682-2017 - based on ammonium persulfate, example 6) with stirring. Next, a borate crosslinker (PT BCD grade B, TU 20.59.42-003-29191682-2017) is added to the system, after the introduction of which the rotation speed is increased to about 2500 rpm.

Then, with stirring, a crosslinking stabilizer based on ethylene glycol and diethanolamine (PT XLS, TU 20.59.42-053-29191682-2020) is added. Next, the fluid sample was tested on a rheometer. The rheological profile of a fracturing fluid characterizes thermal stability, its ability to maintain basic viscosity with minimal loss in time at bottomhole temperature, as well as the time of complete disintegration.

The contents of the components and their ratios for various compositions of the hydraulic fracturing fluid are presented in Table 2, while, respectively, c / g is the ratio of the crosslinker and the gelling agent, c / cc is the crosslinker and crosslink stabilizer, c / d is the crosslinker and the destructor.

Table 2. Compositions of fracturing fluid.

No. Water No. Linear gel stabilizer,% Biocide,% Gelling agent,% Demulsifier,% Chelating agent,% Stapler,% Crosslinking stabilizer,% Destructor,% Ratios
s / s, s / ss, s / d 1 1 0.0 0.002 0.36 0.2 0.0 0.28 0.2 0.05 0.778: 1; 1.4: 1; 5.6: 1 2 2 0.14 0.002 0.36 0.2 0.025 0.28 0.1 0.05 0.778: 1; 2.8: 1; 5.6: 1 3 3 0.0 0.002 0.36 0.2 0.0 0.3 0.2 0.05 0.833: 1; 1.5: 1; 6: 1 4 3 0.0 0.002 0.36 0.2 0.0 0.26 0.2 0.02 0.772: 1; 1.3: 1; 13: 1 5 4 0.1 0.002 0.75 0.2 0.1 0.3 0.1 0.05 0.833: 1; 3: 1; 6: 1 6 5 0.025 0.002 0.36 0.2 0.025 0.28 0.05 0.04 0.778: 1; 5.6: 1; 7: 1 7 6 0.14 0.002 0.36 0.2 0.025 0.22 0.05 0.05 0.611: 1; 4.4: 1; 4.4: 1 eight 7 0.1 0.005 0.36 0.2 0.15 0.35 0.15 0.1 0.972: 1; 2.33: 1; 3.5: 1 nine 4 0 0.002 0.36 0.2 0 0.32 0.1 0.05 0.889: 1: 3.2: 1: 6.4: 1

As can be seen from Figures 1-9, all the obtained fracturing fluids maintain a viscosity above 400 cP for more than 60 minutes (Fig. 1 shows that the stability at 90 ° C is about 80 minutes, on 2 and 3 graphs - 100, on Fig. 4 and 5 - 120, in Fig. 6 - 90). After the specified time, the gel breaks down and the viscosity of the liquid drops. Liquid breakdown, i.e. viscosity drops below 10 cP for most formulations occurs in 200 minutes or less. The maximum liquid disintegration time corresponds to the maximum amount of crosslinker to the destructor (figure 4).

To control the stability time, the content of the gelling agent and / or the crosslinker and / or the destructor is changed within the stated ratios. So, according to the rheological profile in figure 2, it can be seen that an increase in the ratio of the crosslinker to the crosslink stabilizer leads to an increase in the viscosity retention time. As well as increasing the ratio of crosslinker to gelling agent (Figure 3). Reducing the ratio of crosslinker to destructor also leads to a significant increase in viscosity stability time (Figure 4). However, it should be borne in mind that in this case (the extreme declared ratio of the crosslinker to the destructor), the time for the complete disintegration of the fracturing fluid can also increase up to 600 minutes. Long viscosity retention time of the liquid is also ensured by increasing the amount of gelling agent and crosslinking stabilizer as compared to the crosslinker (Fig. 5). From the presented figures it can be seen that hydraulic fracturing fluids retain thermal stability for the required time at a temperature of 90 ℃.

The described examples of the compositions indicated in table 2, and the figures, which show the change in viscosity, illustrate several embodiments of the composition of the liquid and the method of its preparation depending on the composition of real waters and are not intended to limit the scope of the invention. According to the data obtained, all the obtained fluid compositions on real saline waters have sufficient stability and can be used to prepare a hydraulic fracturing fluid, and the data presented are illustrative and confirming the possibility of smoothing the negative effect of ions and pollutants present in the water, the decomposition of the hydraulic fracturing fluid, which will make it easy remove it after fracturing operations, as well as the ability to adjust the fluid stability time. The presented examples also confirm the achievement of the technical result for the formation treatment method (simplification and improvement of efficiency and environmental friendliness), which is ensured through the use of highly mineralized water, leveling the negative effect of ions contained in it, and also by ensuring the stability of the fluid for hydraulic fracturing (preservation viscosity) at high temperatures and subsequent breakdown of the fracturing fluid, ensuring its successful removal from the formation

Thus, the presented examples confirm the achievement of the technical result for the hydraulic fracturing fluid, the method for its preparation and the method of treating the formation with its use, which is achieved due to the declared content of the components and the ratios of the crosslinker to the gelling agent, crosslink stabilizer and destructor.

Claims (38)

1. A fluid for hydraulic fracturing based on highly mineralized water, including a gelling agent, a crosslinker, a crosslinker stabilizer, a destructor, a demulsifier, a biocide, the content of the components being, wt%: gelling agent 0.2-0.5 stapler 0.2-0.4 stitching stabilizer 0.04-0.3 destructor 0.02-0.14 demulsifier 0.01-0.2 biocide 0.001-0.005 highly mineralized water rest, the ratio of the crosslinker to the gelling agent is from 0.6: 1 to 1.0: 1, to the crosslinker from 1.3: 1 to 5.6: 1, to the destructor from 3.5: 1 to 13.0: 1. 2. A fluid for hydraulic fracturing based on highly saline water according to claim 1, in which the highly saline water is produced water, or a mixture of produced and fresh water, or reservoir Cenomanian water with a total salinity of 3 g / l to 20 g / l. 3. The highly mineralized water fracturing fluid according to claim 1, wherein the gelling agent is selected from the group consisting of guar gum, modified guar gum, xanthan gum, a mixture of the above components. 4. The highly mineralized water fracturing fluid according to claim 1, wherein the crosslinking stabilizer is selected from the group of alcohols and amino alcohols, preferably methyl alcohol, glycerol, ethylene glycol, monoethanolamine, diethanolamine, triethanolamine, diethanoltriamine, or mixtures thereof. 5. The highly mineralized water fracturing fluid according to claim 1, wherein the crosslinker is a borate crosslinker. 6. The highly mineralized water fracturing fluid according to claim 1, wherein the destructor is an oxidizing type destructor based on ammonium persulfate. 7. The highly mineralized water fracturing fluid according to claim 1, wherein the demulsifier is a surfactant based on ethoxylated fatty acids. 8. The highly mineralized water fracturing fluid of claim 1, wherein the biocide is potassium sorbate. 9. The fluid for hydraulic fracturing based on highly mineralized water according to claim 1, which, when the content of bicarbonate ions in the water is more than 500 mg / l, additionally contains the products of the interaction of the linear gel stabilizer and bicarbonate ions. 10. The highly mineralized water fracturing fluid according to claim 9, in which the concentration of the interaction products of the linear gel stabilizer and hydrocarbonate ions is not more than 0.3 wt%. 11. The highly mineralized water fracturing fluid according to claim 9, wherein the linear gel stabilizer is selected from the group of water-soluble organic and inorganic salts and acids, preferably citric acid, acetic acid, formic acid and their salts, hydroxyethylene diphosphonic acid, nitrilotrimethylphosphonic acid , sodium gluconate, sodium lignosulfonate, sodium salts of ethylenediaminetetraacetic acid, or mixtures thereof. 12. The highly mineralized water fracturing fluid according to claim 1, additionally containing a chelating agent in a concentration of not more than 0.2 wt%. 13. The highly mineralized water fracturing fluid according to claim 12, wherein the chelating agent is selected from the group of water-soluble organic and inorganic salts, preferably hydroxyethylene diphosphonic acid sodium salt, nitrilotriacetic acid trisodium salt, N, N-bis (carboxymethyl) -L β-tetrasodium glutamate, diethylenetriamine pentaacetic acid salt, sodium gluconate, or mixtures thereof. 14. The highly mineralized water fracturing fluid according to claim 1, which additionally contains a clay stabilizer in a concentration of not more than 0.2 wt%. 15. The fluid for hydraulic fracturing on highly mineralized water according to claim 2, in which the water is characterized by the content of bicarbonate ion up to 1700 mg / l, calcium and magnesium ions up to 1000 mg / l, iron (total) up to 14 mg / l, boron up to 12 mg / l, chlorine ion up to 10500 mg / l, pH value = 5-8, total mineralization up to 20.0 g / l. 16. The highly mineralized water fracturing fluid according to claim 1, which further comprises a high-temperature stabilizer with a concentration of not more than 0.3 wt%. 17. The highly mineralized water fracturing fluid of claim 16, wherein the high temperature stabilizer is sodium thiosulfate. 18. A method for preparing a fluid for hydraulic fracturing, in which a biocide from 0.001 to 0.005 wt.% Is added with stirring to highly mineralized water, then a gelling agent from 0.2 to 0.5 wt.% Is added, the gelling agent is hydrated and introduced into the resulting linear gel demulsifier in an amount from 0.01 to 0.2 wt.% and a destructor in an amount from 0.02 wt.% to 0.14 wt. %, then add a crosslinker in an amount of 0.2 to 0.4 wt. %, together or after adding a crosslinker, a crosslinker is introduced in an amount of 0.04 to 0.3 wt%, while the ratio of crosslinker to gelling agent is from 0.6: 1 to 1.0: 1, to a crosslinker from 1 , 3: 1 to 5.6: 1, to a destructor from 3.5: 1 to 13.0: 1. 19. A method for preparing a fracturing fluid according to claim 18, wherein before adding the gelling agent, a linear gel stabilizer is additionally introduced in an amount of up to 0.3 wt%. 20. A method for preparing a fracturing fluid according to claim 19, wherein a linear gel stabilizer is added until a pH value of 5 to 6 is reached. 21. A method for preparing a fracturing fluid according to claim 19, wherein the linear gel stabilizer is selected from the group of water-soluble organic and inorganic salts and acids, preferably citric acid, acetic acid, formic acid and their salts, oxyethylene diphosphonic acid, nitrilotrimethylphosphonic acid, sodium gluconate, sodium lignosulfonate, sodium salts of ethylenediaminetetraacetic acid, or mixtures thereof. 22. A method for preparing a fracturing fluid according to claim 18, wherein a chelating agent is additionally introduced in an amount of up to 0.2 wt% before adding a gelling agent. 23. A method for preparing a fracturing fluid according to claim 22, wherein the chelating agent is selected from the group of water-soluble organic and inorganic salts, preferably sodium salt of oxyethylene diphosphonic acid, trisodium salt of nitrilotriacetic acid, N, N-bis (carboxymethyl) -L- tetrasodium glutamate, diethylenetriamine pentaacetic acid salts, sodium gluconate, or mixtures thereof. 24. A method for preparing a fracturing fluid according to claim 18, wherein the linear gel has a pH of 6 to 8. 25. A method of preparing a fluid for hydraulic fracturing according to claim 18, in which the highly mineralized water is produced water, a mixture of produced and fresh water, or reservoir Cenomanian water with a total salinity of up to 20 g / l. 26. A method for preparing a fracturing fluid according to claim 18, wherein the gelling agent is selected from the group consisting of guar gum, modified guar gum, xanthan gum, and a mixture of the above components. 27. A method for preparing a fracturing fluid according to claim 18, wherein the crosslinking stabilizer is selected from the group of alcohols and amino alcohols, preferably methyl alcohol, glycerol, ethylene glycol, monoethanolamine, diethanolamine, triethanolamine, diethanoltriamine, or mixtures thereof. 28. A method for preparing a fracturing fluid according to claim 18, wherein the crosslinker is a borate crosslinker. 29. A method for preparing a fracturing fluid according to claim 18, wherein the destructor is an oxidizing type destructor based on organic peroxides. 30. A method for preparing a fracturing fluid according to claim 18, wherein the demulsifier is a mixture of surfactants based on ethoxylated fatty alcohols. 31. A method for preparing a fracturing fluid according to claim 18, wherein the biocide is potassium sorbate. 32. A method for preparing a fracturing fluid according to claim 18, in which, after obtaining a linear gel, a clay stabilizer is additionally introduced in a concentration of not more than 0.2 wt%. 33. A method of preparation of a fluid for hydraulic fracturing according to claim 18, in which water is characterized by a content of bicarbonate ion up to 1700 mg / l, calcium and magnesium ions up to 1000 mg / l, total iron up to 14 mg / l, boron up to 12 mg / l, chlorine ion up to 10500 mg / l, pH value = 5-8, total mineralization up to 20.0 g / l. 34. A method for preparing a fracturing fluid according to claim 18, wherein high-temperature stabilizers with a concentration of not more than 0.3 wt% are additionally introduced. 35. A method for preparing a fracturing fluid according to claim 34, wherein the high-temperature stabilizer is sodium thiosulfate. 36. A method of treating a formation using a highly saline water fracturing fluid, which includes performing hydraulic fracturing using a highly saline water fracturing fluid according to any one of claims. 1-17.

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