WO2023035416A1 - Shale gas layer oxidative burst transformation method - Google Patents

Abstract

A shale gas layer oxidative burst transformation method, comprising: performing hydraulic fracturing transformation on a shale gas well to be fractured; and in the hydraulic fracturing process, pumping slickwater A (f), oxidation liquid (e), slickwater containing glue liquid (d), catalytic decomposition liquid (c), and slickwater B (b) in a slug mode in sequence, and integrating shale physical characteristics and chemical thermodynamic properties to provide a fracturing fluid usage and oxidation burst sweep radius calculation formula. According to the method, the methane gas released by the shale gas layer after fracturing by the slick water A (f) is mixed with oxygen generated by the decomposition of hydrogen peroxide in the oxidation solution (e), and the shale gas layer is burst, such that the safe, efficient and damage-free multi-scale yield increasing transformation of hydraulic fractures, explosion fractures and corrosion apertures is achieved.

Description

A shale gas layer oxidation explosion reforming method technical field

The invention relates to a new method for improving production in the technical field of oil and natural gas exploitation, in particular to a method for oxidizing and bursting reforming shale gas layers.

Background technique

Shale reservoirs are generally characterized by tight base blocks and strong heterogeneity. The pore throats of the base blocks are dominated by nanoscale organic pores and intergranular pores of clay minerals. Shale gas seepage resistance is huge, and adsorbed/free gas coexist. The production of shale gas needs to go through the desorption-diffusion-seepage series process. However, the desorption-diffusion process of adsorbed gas in nanopores is slow, and the free gas diffusion-seepage resistance is large, resulting in extremely low shale gas transmission capacity, so effective stimulation is required. technology.

At present, staged hydraulic fracturing of horizontal wells is the main stimulation method for shale oil and gas reservoirs. Hydraulic fracturing breaks the shale base and opens natural fractures at the same time, forming a complex network of artificial fractures inside the gas layer, shortening the flow of gas from matrix pores to Improve the seepage distance of fractures, increase the drainage area, and realize the economic development of shale gas reservoirs. However, the recovery rate of shale gas formations is generally low, and the recovery rate of shale oil and gas formations is far lower than that of conventional oil and gas formations, only about 10% to 16%. The recovery rate of shale gas reservoirs in North America generally ranges from 5% to 20%, especially in the Barnett area, which is only about 10%. From the perspective of long-term development, enhanced oil recovery is an inevitable choice for shale oil and gas development.

Secondly, although the fracture network formed by hydraulic fracturing is conducive to improving the seepage capacity of shale gas layers, it still cannot solve the problem of low gas desorption-diffusion transport capacity in the matrix pores at the far end of the fracture, resulting in a far lower gas supply capacity of the shale matrix The ability of gas transmission in fractures leads to an exponential decline in the production of gas wells at the initial stage of production, shortening the commercial production period, reducing the recovery rate and increasing the development cost.

According to the analysis, the root of improving methane gas production efficiency in shale matrix is to increase the diffusion rate of adsorbed gas and free gas. Due to the tightness of the shale matrix, micro-fractures become the main channels for gas seepage. Therefore, generating more micro-fractures to shorten the diffusion path of methane gas in nanopores is the main idea of hydraulic fracturing stimulation in shale gas formations. Previous studies have shown that compared with hydraulically propped fractures, the unsupported fractures formed by stress disturbance during fracturing have a larger contact area with the shale matrix, and controlling a wider seepage area plays an important role in delaying the rapid production decline of shale gas wells. significance. Therefore, on the basis of hydraulic fracturing, obtaining more unsupported fractures or secondary micro-fractures is one of the important breakthroughs to enhance the effect of fracturing and improve the recovery rate of shale gas.

Contents of the invention

The purpose of the present invention is based on the existing hydraulic fracturing technology, by generating local bursts in the fracturing well section, to realize secondary reconstruction after shale gas lamination, so as to improve the fracture-making efficiency and fracture efficiency of the existing fracturing reconstruction method. Density, complement and enhance the effect of existing fracturing stimulation. The present invention injects slick water A-oxidizing liquid-glue-containing slick water-catalyzed decomposition liquid-slick water B into the fracturing fluid in a slug manner, and decomposes methane gas released by fracturing with slick water A and hydrogen peroxide in the oxidizing liquid The generated oxygen is mixed to induce oxidative bursting, so as to achieve rapid, low-cost, and non-destructive production enhancement transformation effects.

Concrete technical scheme of the present invention is as follows:

A method for reforming shale gas formations by oxidation and explosion, comprising:

Hydraulic fracturing of shale gas wells to be fractured;

In the process of hydraulic fracturing, the sequence of slick water A-oxidizing liquid-glue-containing slick water-catalyzed decomposition liquid-slick water B is pumped in a slug-like flow state.

Wherein, the slick water A is mainly used for hydraulic fracturing to create fractures and release part of methane gas;

The oxidation solution is a mixture of hydrogen peroxide and dilute hydrochloric acid, and the dilute hydrochloric acid is used to prevent hydrogen peroxide from decomposing in the wellbore;

The injection rate of the colloid-containing slick water should be greater than the effective volume of the wellbore to ensure that the hydrogen peroxide in the wellbore completely enters the fracturing fractures, and avoid the catalytic decomposition agent in the catalytic decomposition liquid and the hydrogen peroxide in the oxidizing liquid reacting in the wellbore in advance ;

The catalytic decomposition liquid uses slick water containing a catalytic decomposition agent, and the catalytic decomposition agent includes but is not limited to sodium hydroxide and manganese dioxide;

The slick water B seals off the oxidizing fluid, so that local bursts in shale hydraulic fractures occur away from the end of the wellbore, avoiding damage to the integrity of the wellbore.

As a preferred technical solution, calculate the injection rate of slick water A according to the following formula:

In the formula, V ₁ is the volume of slick water A; α is the loss coefficient, which is 1.0-1.5; D is the outer diameter of the casing; δ is the wall thickness of the casing; h is the well depth; L is the burst point depth; The height of the main fracture in fracturing; W is the width of the main fracture in hydraulic fracturing.

As a preferred technical solution, the oxidizing solution is a mixed solution of hydrogen peroxide and dilute hydrochloric acid.

As a preferred technical solution, the hydrogen peroxide injection quality and the oxidative burst radius are calculated according to the following formula:

In the formula, P _o is the original formation pressure; σ is the tensile strength of rock; φ is the porosity of tight gas layer; r is the sweeping radius of oxidation burst; _R is the ideal gas constant _; T _o is the original formation temperature, K; m is the injected mass of hydrogen peroxide; M _H2O2 is the molar mass of hydrogen peroxide; M _CH4 is the molar mass of methane; C is the specific heat capacity of methane; q is the product The heating value of methane as a gaseous water.

As a preferred technical solution, according to the calculation formula of the hydrogen peroxide injection quality and the oxidative burst sweep radius, given the hydrogen peroxide injection mass m, obtain the unary high-order equation of the oxidative burst sweep radius r, and solve the oxidation burst sweep radius r The one-variable high-degree equation of , obtains the radius r of the oxidation burst;

Alternatively, according to the calculation formula of hydrogen peroxide injection mass and oxidation burst sweep radius, the oxidation burst sweep radius r is given, the unary high-order equation of hydrogen peroxide injection mass m is obtained, and the unary high degree of hydrogen peroxide injection mass m is solved. Subequation equation, get the hydrogen peroxide injected mass m.

As a preferred technical solution, the injection amount of the slick water containing glue is greater than the effective volume of the wellbore.

As preferred technical scheme, calculate the injection rate of slippery water containing glue according to the following formula:

In the formula, _V2 is the volume of slick water containing glue; β is the safety factor, which is 1.0-1.5; D is the outer diameter of the casing; δ is the wall thickness of the casing.

As a preferred technical solution, the catalytic decomposition liquid is prepared by adding a catalytic decomposition agent to slick water, and the catalytic decomposition agent includes but not limited to sodium hydroxide and manganese dioxide.

As a preferred technical solution, calculate the injection amount of the catalytic decomposition liquid according to the following formula:

In the formula, _V4 is the catalytic decomposition liquid; ρ is the density of slick water; m is the injected mass of hydrogen peroxide.

As a preferred technical solution, the slick water B is used to seal off the oxidizing fluid, so that local bursts in shale hydraulic fractures occur away from the end of the wellbore, avoiding damage to the integrity of the wellbore;

Calculate the injection amount of described slick water B according to the following formula:

In the formula, V ₃ is the volume of slick water B; D is the outer diameter of the casing; δ is the wall thickness of the casing; h is the well depth; L is the burst point depth; crack width.

The beneficial effects are:

(1) Increased the density and complexity of the seam network. Based on the artificial fractures formed by hydraulic fracturing, oxidation bursting further increases the fracture density and depth, thereby forming a denser spherical fracture network.

(2) The construction operation is convenient and safe. In the process of hydraulic fracturing, conventional fracturing fluid is slug-injected into the reservoir, and a reasonable fracturing fluid injection volume makes oxidation burst occur in hydraulic fractures far away from the wellbore.

(3) The chemical energy is fully utilized, and the economic cost is low. Combined with the compound effect of high temperature and high pressure generated by combustible gas explosion, the range of oxidation cracking is calculated to provide guidance for process implementation. At the same time, hydrogen peroxide solution is widely used in many links of oil exploration and development, and the price is relatively low, which can effectively control the economy of fracturing and increasing production. cost.

(4) The present invention utilizes hydrogen peroxide to decompose to generate oxygen to induce partial explosion of methane in reservoir fracturing fractures to further transform shale gas layers. The method in the present invention is based on existing hydraulic fracturing shale gas wells without additional drilling , and the required energy comes from the oxygen produced by the decomposition of reservoir hydrocarbon gas and hydrogen peroxide, which reduces the cost of shale oil and gas extraction and further improves the effect of hydraulic fracturing. When comparing the same scale of hydraulic fracturing, oxidation bursting combined with hydraulic fracturing stimulation will be beneficial to increase the stimulated reservoir volume (SRV); and for deeper shale gas reservoirs (>3500m), in the case of poor hydraulic fracturing effect Under the circumstances, the present invention provides a new idea for the effective development of deep shale gas.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the specific embodiments or the prior art. Throughout the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, elements or parts are not necessarily drawn in actual scale.

Fig. 1 is a schematic diagram of the inflow of working fluid in the staged hydraulic fracturing process of a horizontal well in a shale gas layer according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of the process of fracturing fluid inflow and oxygen generation after the first stage of hydraulic fracturing according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of the first-stage shale gas layer oxidation explosion reformation according to an embodiment of the present invention;

In the figure, a-shale gas layer; b-slick water B; c-catalytic decomposition liquid; d-colloid-containing slick water; e-oxidation liquid; f-slick water A; g-bridge plug; h-horizontal well ; i-main hydraulic fracturing fracture; j-oxidation fluid and catalytic decomposition fluid; k-oxidation burst fracture network.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below, obviously, the described embodiments are only some of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relationship between the components in a certain posture (as shown in the drawing). If the specific posture changes, the directional indication will also change accordingly.

In addition, in the present invention, descriptions such as "first", "second" and so on are used for description purposes only, and should not be understood as indicating or implying their relative importance or implicitly indicating the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the invention.

The present invention will be described further in conjunction with accompanying drawing now.

As shown in Figure 1, according to the present invention, a horizontal well in a shale gas layer is subjected to hydraulic fracturing, and the working fluid into the well is injected sequentially in a slug manner, and slick water A (Fig. 1f) is pumped into the early stage for hydraulic fracturing (Fig. 2 ), to create conditions for the subsequent injection of oxidizing fluid (Fig. 2e) and catalytic decomposition fluid (Fig. 2c) to fully contact in the artificial fracturing. decomposition fluid. Then, by pumping slick water B (Fig. 3b) to displace the oxidizing fluid into the fracture, so that the explosion point of oxidation burst is far away from the wellbore. Considering the pumping effect during fracturing, the content of methane in artificial fracturing fractures is constant, when the amount of oxygen produced by the catalytic decomposition of hydrogen peroxide solution reaches the range required for shale oxidation and bursting, the mixed gas of methane and oxygen will deflagrate under high temperature and high pressure, Fracture the shale base block to generate a burst fracture network (Fig. 3K), and realize the secondary stimulation of the reservoir.

Considering that there are differences in the explosion limit of methane mixed with different gases: at normal temperature and pressure, the explosion limit of methane in air is about 5% to 15%; in pure oxygen, the explosion limit of methane is about 5.0% to 61%; Molecular thermal movement is more intense under high pressure. The explosion limit of methane-air mixture at 20MPa and 100℃ is 2.87%-64.40%, and the critical oxygen content of explosion theory can be reduced to 5.74%. Therefore, the ratio value required for methane explosion can be achieved by adjusting the injection amount of hydrogen peroxide.

In the embodiment of the present invention, taking a deep shale gas well in the Longmaxi Formation in the Sichuan Basin as an example, the amount of fracturing fluid required for oxidation and bursting is calculated.

(1) slippery water A

The amount of slick water A is determined according to the location of the burst point and the shape of the hydraulic fracture, and adjusted according to the small-scale fracturing test.

In the formula, V ₁ is the volume of slick water A, m ³ ; α is the loss coefficient, 1.0-1.5; D is the outer diameter of the casing, m; δ is the wall thickness of the casing, m; h is the well depth, m; L is the burst point depth, m; H is the height of the main hydraulic fracture, m; W is the width of the main hydraulic fracture, m.

The outer diameter of the casing is 139.7mm, the wall thickness is 12.7mm, the wellbore is 5100m, the depth of the first burst point is 70m, the height of the main hydraulic fracture is 20m, the width of the main hydraulic fracture is 0.03m, and the amount of slick water A is 164m ³ .

(2) Oxidation liquid and oxidation burst affected range

The oxidizing solution is a mixture of hydrogen peroxide and dilute hydrochloric acid (hydrogen peroxide mass concentration 20%), and the occurrence of oxidative cracking depends on the decomposition of hydrogen peroxide to generate oxygen, and the mixed combustion of oxygen and methane is a two-step reaction. The quality of hydrogen peroxide injection determines the affected area, that is, the radius of the crack network of oxidation burst. The maximum explosion pressure generated when the mixture explodes can be determined according to the relationship between pressure, thermodynamic temperature and molar number, and the injection quality of hydrogen peroxide and the affected area of oxidation burst are calculated. as follows:

In the formula, P _o is the original formation pressure, Pa; σ is the tensile strength of rock, Pa; φ is the porosity of tight gas layer; r is the sweep radius of oxidation burst, Pa; R is the ideal gas constant, 8.314J mol ^-1 K ^-1 ; Z _o is the gas compression factor before oxidation burst; Z _m is the gas compression factor after oxidation burst; T _o is the original formation temperature, K; m is the injected hydrogen peroxide mass, g; M _H2O2 is hydrogen peroxide Molar mass, 34g/mol; M _CH4 is the molar mass of methane, 16g/mol; C is the specific heat capacity of methane, 2.227kJ/(kg K); q is the calorific value of methane when the product is gaseous water, 50200kJ/kg.

According to the above formula, given m, get the one-variable high-order equation of r, and solve it by dichotomy.

In the example, the original formation pressure is 66.8MPa, the tensile strength of the rock after hydration is 6.3MPa, the original formation temperature is 393K, the average porosity is 4.17%, the gas compression factor before and after oxidation burst is 1.2, and the amount of oxidizing solution 5000kg (hydrogen peroxide 1000kg), the radius of oxidation burst is 8.5m.

(3) Slippery water containing glue

The slick water containing colloid is used to squeeze the oxidizing fluid from the wellbore into the formation to prevent the reaction of hydrogen peroxide and the catalyst in the wellbore, and the dosage is 1.2 times the volume of the wellbore.

In the formula, V ₂ is the volume of slick water containing glue, m ³ ; β is the safety factor, taking 1.0 to 1.5.

The parameters are the same as those in slick water A, and the amount of slick water containing glue is 63m ³ .

(4) Catalytic decomposition liquid

The catalytic decomposition liquid uses slick water containing a catalytic decomposition agent, the volume of which is the same as that of the oxidation liquid. The catalytic decomposition agent includes but is not limited to sodium hydroxide and manganese dioxide.

In the formula, V ₄ is the catalytic decomposition liquid, m ³ ; ρ is the density of slick water, kg/m ³ .

The density of slick water is 1000kg/m ³ , and the amount of catalytic decomposition liquid is 5m ³ .

(5) Slippery Water B

Slippery water B is used to displace hydrogen peroxide and catalysts into fractures, avoid oxidation burst from spreading to the wellbore, and protect the integrity of the wellbore.

In the formula, V ₃ is the volume of slick water B, m ³ .

Other parameters are the same as those in slick water A, and the amount of slick water B is 136m ³ .

According to the calculation method provided by the present invention, the total consumption of oxidative burst fracturing fluid is 373m ³ , and an oxidative burst fracture network is generated at 70m on both sides of the wellbore, and the radius of the fracture network is 8.5m.

The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be applied to the foregoing embodiments Modifications to the technical solutions described in the examples, or equivalent replacement of some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention, and they shall cover Within the scope of the claims and description of the present invention.

Claims (10)

1. A method for reforming shale gas formations by oxidation and explosion, characterized in that: comprising:

   Hydraulic fracturing of shale gas wells to be fractured;

   In the process of hydraulic fracturing, the sequence of slick water A-oxidizing liquid-glue-containing slick water-catalyzed decomposition liquid-slick water B is pumped in a slug manner.
2. A method for reforming shale gas layers by oxidative bursting according to claim 1, characterized in that: the injection rate of slick water A is calculated according to the following formula:

   

   In the formula, _V1 is the volume of slick water A; α is the leakage coefficient, which is 1.0-1.5; D is the outer diameter of the casing; δ is the wall thickness of the casing; h is the well depth; is the height of the main fracture; W is the width of the main hydraulic fracture.
3. The method for oxidizing and bursting reforming shale gas formations according to claim 1, characterized in that: the oxidizing solution is a mixed solution of hydrogen peroxide and dilute hydrochloric acid.
4. According to claim 1, a method for reforming shale gas layers by oxidative bursting is characterized in that: the mass of hydrogen peroxide injection and the sweeping radius of oxidative bursting are calculated according to the following formula:

   

   In the formula, P _o is the original formation pressure; σ is the tensile strength of rock; φ is the porosity of tight gas layer; r is the sweeping radius of oxidation burst; _R is the ideal gas constant _; T _o is the original formation temperature, K; m is the injected mass of hydrogen peroxide; M _H2O2 is the molar mass of hydrogen peroxide; M _CH4 is the molar mass of methane; C is the specific heat capacity of methane; q is the product The heating value of methane as a gaseous water.
5. According to claim 4, a method for oxidizing and bursting transformation of shale gas formations is characterized in that: according to the calculation formula of hydrogen peroxide injection quality and oxidation burst radius, given hydrogen peroxide injection mass m, the oxidation burst sweep is obtained The unary high-order equation of the radius r, solving the unary high-order equation of the oxidation burst radius r, to obtain the oxidation burst radius r;

   Alternatively, according to the calculation formula of hydrogen peroxide injection mass and oxidation burst sweep radius, the oxidation burst sweep radius r is given, the unary high-order equation of hydrogen peroxide injection mass m is obtained, and the unary high degree of hydrogen peroxide injection mass m is solved. Subequation equation, get the hydrogen peroxide injected mass m.
6. The oxidative explosion reforming method of shale gas layer according to claim 1, characterized in that: the injection rate of the slick water containing glue is greater than the effective volume of the wellbore.
7. According to claim 1 or 6, a method for oxidizing and bursting reforming shale gas formations is characterized in that: the injection rate of slick water containing glue is calculated according to the following formula:

   

   In the formula, _V2 is the volume of slick water containing glue; β is the safety factor, which is 1.0-1.5; D is the outer diameter of the casing; δ is the wall thickness of the casing.
8. A shale gas layer oxidative explosion reconstruction method according to claim 1, characterized in that: the catalytic decomposition liquid is prepared by adding a catalytic decomposition agent to slick water, and the catalytic decomposition agent includes but is not limited to sodium hydroxide and manganese dioxide.
9. A method for oxidizing and decomposing shale gas layers according to claim 4, characterized in that: the injection amount of the catalytic decomposition liquid is calculated according to the following formula:

   

   In the formula, _V4 is the catalytic decomposition liquid; ρ is the density of slick water; m is the injected mass of hydrogen peroxide.
10. A method for oxidative bursting reconstruction of shale gas layers according to claim 1, characterized in that: the slick water B is used to seal off the oxidizing liquid, so that local bursting in shale hydraulic fractures occurs at the end far away from the wellbore , to avoid damage to the wellbore integrity;

    Calculate the injection amount of described slick water B according to the following formula:

    

    In the formula, V ₃ is the volume of slick water B; D is the outer diameter of the casing; δ is the wall thickness of the casing; h is the well depth; L is the burst point depth; crack width.

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