Ultra-deep crack type carbonate rock acidification acid injection discharge capacity optimization method

Abstract

The invention discloses an ultra-deep fractured carbonate rock acidification acid injection discharge capacity optimization method, which comprises the following steps: S1, obtaining the width of a natural fracture according to the elevation distribution of the natural fracture of an underground rock core, and obtaining the width of the coarsened natural fracture after discretization; s2, constructing a model considering fracture normal deformation, and correcting the roughened natural fracture width; s3, constructing a temperature-hydraulic-chemical three-field coupling acid etching hydraulic fracture model, and calculating the acid etching fracture width based on the fracture width obtained in the step S2 after the normal deformation of the fracture is considered; and S4, carrying out simulation calculation under different acid injection rate conditions, and preferably selecting the acid injection displacement according to the dimensionless comprehensive transformation coefficient. According to the method, the influence of closed stress and multiple heat effects is considered when the acid etching process of the ultra-deep fractured carbonate rock is simulated, and the influence of the effective action distance of acid liquor and the width of an acid etching seam on the transformation effect can be quantitatively and comprehensively considered when the acid injection displacement is optimized; and a means is provided for the design of an acid fracturing transformation scheme of the ultra-deep crack type carbonate reservoir.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploitation and geothermal development, and particularly relates to an acidizing injection displacement optimization method for super-deep fractured carbonate rock. BACKGROUND

[0002] Taking the 10,000-meter deep well represented by Shengdi No. 1, Shengdichuanke No. 1 and Shengditake No. 1, the exploration and development of carbonate rock oil and gas reservoirs in China has entered the 10,000-meter deep stage. Super-deep carbonate rock reservoirs have the characteristics of deep burial (>6000m), developed natural fractures and high closure stress (>50MPa). When acidizing and fracturing these reservoirs, the acid liquid is often difficult to press open the rock matrix to form artificial fractures due to the limitation of the pressure-bearing capacity of the current wellhead device (≤140MPa), and is more likely to flow along the natural fractures with smaller flow resistance.

[0003] Numerical simulation is the main means for optimizing the acidizing injection displacement, but for the above-mentioned super-deep carbonate rock reservoirs, the conventional acid etching model has the following limitations: (1) unable to capture the normal deformation characteristics of the fractures under the action of closure stress; (2) difficult to represent the acid-rock reaction characteristics in high-temperature environment. In addition, the effective action distance of the acid liquid and the acid-etched fracture width jointly determine the modification effect of acidizing and fracturing, but the current evaluation method usually only considers one of the parameters, and there is still a lack of a quantitative evaluation system that can comprehensively reflect the coupling effect of the two. SUMMARY

[0004] In view of the above problems, the present application aims to provide an acidizing injection displacement optimization method for super-deep fractured carbonate rock, which establishes an acid etching model coupling closure stress and multiple thermal effects, can take into account the effective action distance of the acid liquid and the acid-etched fracture width for comprehensive modification effect evaluation, and provides a means for optimization design of acidizing and fracturing modification scheme for super-deep fractured carbonate rock reservoirs.

[0005] The technical scheme of the present application is as follows:

[0006] In the first aspect, the present application provides an acidizing injection displacement optimization method for super-deep fractured carbonate rock, comprising the following steps:

[0007] S1: obtaining the natural fracture width b according to the natural fracture elevation distribution of the downhole core, and obtaining the roughened natural fracture width b after discretizing the fracture surface; ini ;

[0008] S2: constructing a fracture normal deformation model, and correcting the roughened natural fracture width b ini ;

[0009] S3: constructing a temperature-hydraulic-chemical three-field coupled acid etching hydraulic fracture model, and obtaining the fracture width b considering the fracture normal deformation based on step S2.c Calculate the acid etching seam width b a ;

[0010] S4: carry out simulation calculation under different acid injection rates, and optimize acid injection displacement according to the dimensionless comprehensive reconstruction coefficient.

[0011] Preferably, step S1 comprises the following steps:

[0012] S11: process the full-diameter core taken from the well of the target layer with developed natural fractures into a plunger core along the extension direction of the natural fractures, and the size of the plunger core is 5.0 cm in length and 2.5 cm in diameter;

[0013] S12: split the plunger core into two half-plunger cores with similar shapes along the natural fractures;

[0014] S13: use a three-dimensional laser device to obtain the elevation distributions h1 and h2 of the two half-plunger cores, respectively;

[0015] S14: according to the elevations h1 and h2, reconstruct the natural fracture width b by using a single-point touch method, and the calculation formula is:

[0016] (1)

[0017] In the formula, h m is the maximum value of h1+h2, cm;

[0018] S15: discretize the fracture surface into a structured grid system with a size of δ, and coarsen the natural fracture width b obtained in step S14 to b ini .

[0019] Preferably, in step S15, the natural fracture width b is coarsened to b ini by using a grid area weighted average method, and the formula is:

[0020]

[0021] In the formula, n g is the number of grids before coarsening, and b ini is the natural fracture width after coarsening.

[0022] Preferably, step S2 comprises the following steps:

[0023] S21: obtain basic parameters, and the basic parameters include formation parameters, acid liquid parameters, and acid injection parameters;

[0024] S22: calculate the protrusion height L 0 in the coarsened grid system, and the calculation formula is:

[0025]

[0026] wherein L 0 is the height of the asperity, D0 is the maximum value of the natural fracture after roughening, D0 = max{b ini};

[0027] S23: Calculate the distance D between the fracture surfaces, assuming that the fracture surfaces are under the action of the closure stress σ c , the normal displacement d, then the distance D between the fracture surfaces satisfies:

[0028]

[0029] wherein D is the distance between the fracture surfaces, d is the normal displacement of the fracture surface under the action of the closure stress σ c ;

[0030] S24: After calculating the normal displacement d of the fracture surface under the action of the closure stress σ c , the number of contact asperities n and the elastic deformation ΔL i satisfy the following formula and are considered as contact asperities:

[0031]

[0032] Based on the height L 0 of the asperity, the elastic deformation is calculated according to the initial Hooke's law:

[0033]

[0034] wherein ΔL is the elastic deformation; f is the force borne by the contact asperity, N; i is the serial number of the contact asperity; L 0 is the height of the asperity; E is the rock modulus of the rock, GPa; a is the area of the grid, cm 2 ;

[0035] S25: Calculate the deformation W i of the fracture surface, and the deformation W i is considered as the contribution of all contact asperities, so W i satisfies:

[0036]

[0037] wherein W i is the deformation of the fracture surface, w ij is the contribution of the contact asperity j to the deformation of the fracture surface at i, which is calculated by the following formula:

[0038]

[0039] where v is the Poisson's ratio of the rock; r is the distance between the centers of the two contacting asperities i and j, cm; θ is the polar angle from the contact center;

[0040] In addition, the contribution of the contacting asperity i to the deformation of the fracture surface at i, w ii The calculation method is as follows:

[0041]

[0042] S26: Calculate the force f c experienced by each contacting asperity under the closing stress σ i ; for a certain contacting asperity i, the distance D between the fracture surfaces and the deformation of the fracture surface at i, W i , are equal to the height L0 i - ΔL i of the contacting asperity i after elastic deformation, that is:

[0043]

[0044] S27: Determine whether the force f i satisfies the stress balance, and the determination method is as follows:

[0045]

[0046] where A a is the fracture surface area, cm 2 ; ε1 is the error threshold set by the model calculation;

[0047] S28: If the stress balance is not satisfied, it means that d does not meet the requirements, and d needs to be re-assumed and steps S22-S26 are repeated; if the stress balance is satisfied, the fracture width b c after considering the normal deformation of the fracture is calculated, and the calculation formula is as follows:

[0048]

[0049] Preferably, step S3 comprises the following steps:

[0050] S31: Calculate the fluid pressure P and the flow velocity v c distribution according to the fracture width b l after considering the normal deformation of the fracture, and the calculation formula is as follows:

[0051]

[0052] where vx , v y is the flow velocity of the acid liquid along the length and width directions of the fracture, cm / s; l is the filtration rate of the acid liquid along the width direction of the fracture, cm / s;

[0053] wherein, v x , v y is calculated by the following formula:

[0054]

[0055] wherein, μ is the viscosity of the acid liquid, mPa·s;

[0056] v l is calculated by the following formula:

[0057]

[0058] wherein, k m is the permeability of the rock matrix, D; P e is the formation pressure, atm; h l is the thickness of the plug core, cm; P is the fluid pressure in the fracture, atm;

[0059] S32: the concentration distribution C of the acid liquid in the fracture is calculated, and the specific formula is:

[0060]

[0061]

[0062] wherein, m is the grid number adjacent to the center cell i (m≠i); ΔL m is the height difference between the protrusion i and its adjacent protrusion m, cm; δ is the size of the grid i, cm; R s is the acid-rock reaction rate, g / (s·cm 2 ); is the acid-rock reaction rate in the grid m, g / (s·cm 2 );

[0063] R s and are calculated by the following formula:

[0064]

[0065] wherein, T f is the temperature in the fracture, ℃; R is the molar gas constant, 8.314 J / (mol·℃).

[0066] S33: Calculate the temperature T in the fracture f and the temperature T of the filtration zone d distribution, and the specific formula is:

[0067]

[0068] In the formula, ρ f is the acid density, g / cm 3 ; c f is the specific heat capacity of the acid, J / (g·℃); k f is the thermal conductivity of the acid, W / (cm·℃); N u is the Nusselt number; K ef is the effective thermal conductivity, J / (g·℃); (cρ) ef is the effective value of specific heat capacity and density deposition, J / (cm 3 ·℃) ;

[0069] K ef and (cρ) ef are calculated as follows:

[0070]

[0071] In the formula, ρ r is the rock density, g / cm 3 ; c r is the specific heat capacity of the rock, J / (g·℃);

[0072] The calculation formula of F and D in formula (19) is:

[0073]

[0074]

[0075] In the formula, φ is the rock porosity;

[0076] S34: Calculate the acid-etched fracture width b a at the current time step, and the calculation method is:

[0077]

[0078] In the formula, β is the dissolution capacity of the acid; η is the ratio of the filtration acid participating in the acid-rock reaction; Δt is the time step, s;

[0079] S35: Determine whether the acid injection is finished, if not, b a b ini , repeat steps S2-S3; if the acid injection is finished, b a at this time is the final acid etched fracture width.

[0080] Preferably, step S4 comprises the following steps:

[0081] S41: Based on the established model, repeat steps S2-S3 to carry out simulation under different acid injection rates to obtain the final acid etched fracture morphology under different acid injection rates;

[0082] S42: Calculate the fracture closure degree b p , the calculation method is:

[0083]

[0084] In the formula, b a0 is the acid etched fracture width without considering the closure stress, cm; b ac is the acid etched fracture width considering the closure stress, cm;

[0085] S43: Calculate the acid breakthrough rate v b , the calculation method is:

[0086]

[0087] In the formula, L is the length of the rock plate, cm; l is the effective action distance of acid, cm; t a is the total acid injection time, min; t b is the acid breakthrough time, min;

[0088] S44: Calculate the dimensionless comprehensive reconstruction coefficient, the calculation method is:

[0089]

[0090] In the formula, w is the width of the piston core, cm; Q is the construction displacement, m 3 / min;

[0091] S45: Optimize the acid injection displacement according to the dimensionless comprehensive reconstruction coefficient, draw the relationship curve of the dimensionless reconstruction coefficient and the acid injection displacement q, that is, C s =f(q), the acid injection displacement corresponding to the maximum dimensionless reconstruction coefficient is the optimal acid injection displacement q a , that is:

[0092]

[0093] The preferred acid injection rate q is determined by the similarity criterion a converted into the field-scale acid injection rate Q.

[0094] Preferably, the injection rate conversion formula in step S45 is:

[0095]

[0096] where h is the field design fracture height, cm; b is the field design average fracture width, cm; b is the simulation average fracture width, cm; n is the flow state index of the acid liquid. f is the field design fracture height, cm; b r is the field design average fracture width, cm; b ac is the simulation average fracture width, cm; n f is the flow state index of the acid liquid.

[0097] In a second aspect, the present application provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method of any of the above when executing the computer program.

[0098] In a third aspect, the present application provides a computer readable storage medium, comprising:

[0099] The computer readable storage medium stores a computer program, and the computer program is executed by the processor to implement the method of any of the above.

[0100] In a fourth aspect, the present application further provides a computer program product, comprising a computer program, and the computer program is executed by the processor to implement the method of any of the above.

[0101] Compared with the prior art, the present application has the beneficial effects that the present application provides an acid injection rate optimization method for super-deep fracture type carbonate rock acidification, which establishes an acid etching model coupling closure stress and multiple thermal effects, and optimizes the acid injection rate according to the acid etching morphology of the fracture, and the method provided by the present application can take into account the effective action distance of the acid liquid and the comprehensive reconstruction effect evaluation of the acid etching fracture width, and provides a means for optimization design of the super-deep fracture type carbonate rock reservoir acidification and fracturing reconstruction scheme. BRIEF DESCRIPTION OF DRAWINGS

[0102] Figure 1 is the field design fracture height, cm; b

[0103] Figure 2 is the field design fracture height, cm; b 3 is the field design fracture height, cm; b

[0104] Figure 3The variation law of the acid injection displacement in the embodiment of the present application with the dimensionless comprehensive reconstruction coefficient. DETAILED DESCRIPTION

[0105] The core of the present application is to provide an acid injection displacement optimization method for super-deep fracture type carbonate rock acidification, which establishes an acid etching model coupling closed stress and multiple thermal effects, and can take into account the comprehensive reconstruction effect evaluation of acid liquid effective action distance and acid etching fracture width.

[0106] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0107] In order to solve the defect that only one parameter of acid liquid effective action distance and acid etching fracture width is considered in the evaluation of the reconstruction effect of acidification fracturing in the prior art, the present application constructs an acid etching model coupling closed stress and multiple thermal effects, taking into account the influence of acid liquid effective action distance and acid etching fracture width, and provides an acid injection displacement optimization method for super-deep fracture type carbonate rock acidification, including the following steps:

[0108] S1: obtaining the natural fracture width b according to the natural fracture elevation distribution of the downhole core, and obtaining the roughened natural fracture width b after discretizing the fracture surface ini ;

[0109] The step S1 includes:

[0110] S11: processing the downhole full-diameter core taken from the target layer developing natural fractures into a plunger core along the extension direction of the natural fractures, and the size of the plunger core is 5.0 cm long*2.5 cm in diameter;

[0111] S12: splitting the plunger core into two half-plunger cores with similar shapes along the natural fractures;

[0112] S13: acquiring the elevation distributions h1 and h2 of the two half-plunger cores respectively by using a three-dimensional laser device;

[0113] S14: reconstructing the natural fracture width b according to the elevations h1 and h2 by using a single-point touch method, and the calculation formula is:

[0114] (1)

[0115] In the formula, h m is the maximum value of h1+h2, cm;

[0116] S15: discretize the fracture surface into a structured grid system with size δ, and coarsen the natural fracture width b obtained in step S14 into b ini ;

[0117] In step S15, the natural fracture width b is coarsened into b by using the grid area weighted average method ini , and the formula is:

[0118] (2)

[0119] In the formula, n g is the number of grids before coarsening, and b ini is the natural fracture width after coarsening.

[0120] S2: build a fracture normal deformation model considering the coarsened natural fracture width b ini ;

[0121] Step S2 includes:

[0122] S21: obtain basic parameters, including formation parameters, acid parameters, and acid injection parameters;

[0123] S22: calculate the height L 0 of the protrusion in the coarsened grid system, and the calculation formula is:

[0124] (3)

[0125] In the formula, L 0 is the height of the protrusion, D0 is the maximum value of the coarsened natural fracture, D0 = max{b ini};

[0126] S23: calculate the distance D between the fracture surfaces, assuming that the normal displacement d of the fracture surface under the action of the closure stress σ c , then the distance D between the fracture surfaces satisfies:

[0127] (4)

[0128] In the formula, D is the distance between the fracture surfaces, and d is the normal displacement of the fracture surface under the action of the closure stress σ c ;

[0129] S24: after calculating the normal displacement d of the fracture surface under the action of the closure stress σ c , the number n of contact protrusions and the elastic deformation ΔL i satisfy the following formula, which can be regarded as a contact protrusion:

[0130] (5)

[0131] Based on the height L0 , which is calculated from the initial Hooke's law of elastic deformation:

[0132] (6)

[0133] where ΔL is the elastic deformation; f is the force on the contact asperity, N; i is the asperity number; L 0 is the asperity height; E is the rock modulus of the rock, GPa; a is the area of the grid, cm 2 ;

[0134] S25: Calculate the deformation W of the fracture surface i distribution, W i is considered as the contribution of all contact asperities, and thus W i satisfies:

[0135] (7)

[0136] where W i is the deformation of the fracture surface, w ij is the contribution of the contact asperity j to the deformation of the fracture surface at i, which is calculated by the following formula:

[0137] (8)

[0138] where v is the Poisson's ratio of the rock; r is the distance between the centers of the contact asperities j and i, cm; θ is the polar angle from the contact center.

[0139] In addition, the contribution of the contact asperity i to the deformation of the fracture surface at i, w ii is calculated by:

[0140] (9)

[0141] S26: Calculate the force f c exerted on each contact asperity under the closing stress σ i ; for a certain contact asperity i, the distance D between the fracture surfaces and the sum of the deformations W i of the fracture surfaces at i should be equal to the height L0 i of the contact asperity i after elastic deformation - ΔL i , that is:

[0142] (10)

[0143] where D and L0 i are known quantities, and the unknown quantities W i and ΔL i are known from formulas (7), (8), and (5), which are all linear functions of f i ; therefore, by simultaneously listing the above formulas for n contact asperities, the following equation about fi n x n linear equations, the Gauss-Seidel iteration method is used to solve the equation group, and the force f c experienced by each contact protrusion under the closed stress σ i ;

[0144] S27: whether f i satisfies stress balance, the judgment method is:

[0145] (11)

[0146] A a is the fracture surface area, cm 2 ; ε1 is the model calculation error threshold;

[0147] S28: if the stress balance is not satisfied, it means that d does not meet the requirements, and it is necessary to re-hypothesize d and repeat steps S22-S26; if the stress balance is satisfied, the crack width b c after considering the normal deformation of the crack is calculated, and the calculation formula is:

[0148] (12)

[0149] S3: build a temperature-hydraulic-chemical three-field coupled acid etching hydraulic fracture model, based on the crack width b c after considering the normal deformation of the crack obtained in step S2, the acid etching crack width b a is calculated;

[0150] wherein, step S3 comprises:

[0151] S31: according to the crack width b c after considering the normal deformation of the crack, the pressure P and the flow velocity distribution are calculated, and the calculation formula is:

[0152] (13)

[0153] v x , v y is the flow velocity of the acid along the crack length and crack width direction, respectively, cm / s; v l is the filtration rate of the acid along the crack width direction, cm / s;

[0154] wherein, v x , v y are calculated by the following formula:

[0155] (14)

[0156] μ is the viscosity of the acid, mPa·s;

[0157] v lThe calculation method of is as follows:

[0158] (15)

[0159] In the formula, k m is the permeability of the rock matrix, D; P e is the formation pressure, atm; h l is the thickness of the core plug, cm; P is the fluid pressure in the fracture, atm;

[0160] S32: The concentration distribution C of the acid liquid in the fracture is calculated, and the specific formula is as follows:

[0161] (16)

[0162] (17)

[0163] In the formula, m is the grid number adjacent to the central cell i (m≠i); is the height difference between the protrusion i and the adjacent protrusion m, cm; δ is the size of the grid i, cm; R s is the acid-rock reaction rate, g / (s·cm 2 ); is the acid-rock reaction rate in the grid m, g / (s·cm 2 );

[0164] and The calculation method of is as follows:

[0165] (18)

[0166] In the formula, T f is the temperature in the fracture, ℃; R is the molar gas constant, 8.314 J / (mol·℃);

[0167] S33: The temperature T f in the fracture and the temperature T d distribution of the filter loss zone are calculated, and the specific formula is as follows:

[0168] (19)

[0169] (20)

[0170] In the formula, ρ f is the density of the acid liquid, g / cm 3 ; c f is the specific heat capacity of the acid liquid, J / (g·℃); k f is the thermal conductivity of the acid liquid, W / (cm·℃); N u is the Nusselt number; K efEffective thermal conductivity, J / (g·℃); (cρ) ef Effective value of specific heat capacity and density, J / (cm 3 ·℃);

[0171] K ef and (cρ) ef The calculation method is respectively:

[0172] (21)

[0173] In the formula, ρ r is the rock density, g / cm 3 ; c r is the specific heat capacity of the rock, J / (g·℃);

[0174] The calculation formula of F and D in formula (19) is:

[0175] (22)

[0176] (23)

[0177] In the formula, φ is the porosity of the rock;

[0178] S34: Calculate the acid-etched crack width b a at the current time step, and the calculation method is:

[0179] (24)

[0180] In the formula, β is the dissolution capacity of the acid; η is the ratio of the lost acid participating in the acid-rock reaction; Δt is the time step, s;

[0181] S35: Determine whether the acid injection is finished, if the acid injection is not finished, take b a as b ini of the subsequent time step, repeat steps S2-S3; if the acid injection is finished, b a at this time is the final acid-etched crack width;

[0182] S4: Develop simulation calculation under different acid injection rates, and optimize the acid injection displacement according to the dimensionless comprehensive reconstruction coefficient.

[0183] Specifically, step S4 includes the following steps:

[0184] S41: Based on the established model, repeat steps S2-S3 to develop simulation under different acid injection rates, and obtain the final acid-etched crack morphology under different acid injection rates;

[0185] S42: Calculate the crack closure degree b p , and the calculation method is:

[0186] (25)

[0187] wherein b a0 is the acid-etched fracture width without considering the closure stress, cm; b ac is the acid-etched fracture width considering the closure stress, cm;

[0188] S43: calculating the acid breakthrough rate v b , the calculation method being:

[0189] (26)

[0190] wherein L is the length of the rock plate, cm; l is the effective action distance of the acid, cm; t a is the total acid injection time, min; t b is the acid breakthrough time, min;

[0191] S44: calculating the dimensionless comprehensive reconstruction coefficient, the calculation method being:

[0192] (27)

[0193] wherein w is the width of the piston core, cm; Q is the construction discharge, m 3 / min;

[0194] S45: optimizing the acid injection discharge according to the dimensionless comprehensive reconstruction coefficient, and drawing a relationship curve of the dimensionless reconstruction coefficient and the acid injection discharge q, i.e. C s =f(q), the acid injection discharge corresponding to the maximum dimensionless reconstruction coefficient being the optimized acid injection discharge q a , i.e.

[0195] (28)

[0196] Finally, the optimized acid injection discharge q a is converted into the field-scale acid injection discharge Q through the similarity criterion.

[0197] wherein the discharge conversion formula in step S45 is:

[0198] (29)

[0199] wherein h f is the field design fracture height, cm; b r is the field design average fracture width, cm; b s is the simulation average fracture width, cm; n f is the flow state index of the acid.

[0200] Application Example

[0201] In the application example of the present application, a full-diameter core with natural fractures taken from the Xianxia group in western Sichuan is processed into a plug core (5 cm long x 2.5 cm in diameter) along the extension direction of the natural fractures, as shown in step S1, the plug core is split into two similar half plug cores along the natural fractures, the single-point touch method is used to reconstruct the natural fracture width b, the fracture surface is discretized into a structured grid system with a size of δ = 0.01 cm, and the weighted average method is used to coarsen the natural fracture width b obtained in step S14 to b ini .

[0202] The basic parameters such as formation parameters, acid liquid parameters, acid injection parameters and the like are obtained as shown in Table 1, and are substituted into the model, and the solution process of the super-deep carbonate rock acid etching model considering closure stress as shown in Figure 1 is solved.

[0203] Table 1 Model input parameters

[0204] Parameter Value Parameter Value Acid solution density p f ]]> 1.0 g / cm3 Rock thermal conductivity k r ]]> 0.052 W / (cm·℃) Rock density p r ]]> 2.87 g / cm3 Porosity φ 8% Acid solution solubility β 1.07 Matrix permeability k m ]]> 0.005 μm2 Acid viscosity μ 1.1 mPa·s Acid injection time t a ]]> 30 min Acid initial concentration 20 wt% Nusselt number N u ]]> 4.3 Acid liquid specific heat c f ]]> 4.18 J / (g·℃) Lost acid reaction participation ratio 0.01 Rock specific heat c r ]]> 1.0 J / (g·℃) Formation pressure P e ]]> 800 atm Thermal conductivity k of the acid liquid f ]]> 0.0065 W / (cm·℃) Protrusion radius a 0.05 cm Elastic modulus E 60 GPa Poisson's ratio v 0.3 Acid liquid flow regime index n f ]] 0.5 On-site design joint height h f ]]> 80m On-site design average joint width b r ]]> 0.6 cm closed stress σ c ]]> 50 MPa

[0205] Figure 2 That is, the final acid etching fracture morphology under the acid injection rate of q = 20 cm 3 / min in the application example, Figure 3 is the change rule of the acid injection rate with the dimensionless comprehensive reconstruction coefficient. According to the method provided by the present application, the optimal acid injection rate q a = 20 cm 3 / min corresponding to the maximum dimensionless comprehensive reconstruction coefficient, the average acid etching seam width is 0.4 mm, and the acid injection rate of the field scale is finally calculated to be 2.00 m 3 / min through the Reynolds number similarity criterion, which can be used for the guidance of field construction.

[0206] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for optimizing acid injection and discharge rates in acidizing ultra-deep fractured carbonate rocks, characterized in that, Includes the following steps: S1: Obtain the natural fracture width b based on the elevation distribution of natural fractures in the downhole core. After discretizing the fracture surface, obtain the coarsened natural fracture width b. ini ; S2: Construct a model that considers the deformation of the crack normal, and apply the coarsened natural crack width b. ini Make corrections; S3: Construct a temperature-hydraulic-chemical three-field coupled acid etching hydraulic crack model, based on the crack width b obtained in step S2 after considering the crack normal deformation. c Calculate the acid etching crevices width b a ; S4: Conduct simulation calculations under different acid injection rates, and optimize the acid injection rate based on the dimensionless comprehensive modification coefficient.

2. The method for optimizing acid injection and discharge rates in ultra-deep fractured carbonate rocks according to claim 1, step S1 includes: S11: The full-diameter downhole core with natural fractures taken from the target layer is processed into a plunger core along the direction of the natural fracture extension. The plunger core dimensions are 5.0cm in length and 2.5cm in diameter. S12: The plunger core was split into two similarly shaped semi-plunger cores along a natural fracture. S13: The elevation distributions h1 and h2 of the two semi-plunger cores were obtained using a three-dimensional laser device; S14: Based on elevations h1 and h2, the width b of the natural crack is reconstructed using the single-point contact method. The calculation formula is as follows: In the formula, h m The maximum value of h1+h2 is in cm; S15: Discretize the crack surface into a structured mesh system of size δ, and coarse the natural crack width b obtained in step S14 to b ini .

3. In the method for optimizing the acid injection and discharge rate of ultra-deep fractured carbonate rocks according to claim 2, step S15 uses a grid area weighted average method to coarse the natural fracture width b to b0. ini The formula is: In the formula, n g b is the number of grid cells before coarsening. ini The width of the natural crack is after coarsening.

4. The method for optimizing acid injection and discharge rates in ultra-deep fractured carbonate rocks according to claim 1, step S2 includes: S21: Obtain basic parameters, including formation parameters, acid parameters, and acid injection parameters; S22: Calculate the protrusion height L in the coarsened mesh system. 0 The calculation formula is: Among them, L 0 Where B is the height of the protrusion, and D0 is the maximum value of the coarsened natural crack, D0 = max{b ini }; S23: Calculate the distance D between crack surfaces, assuming the crack surfaces are under the closing stress σ. c Under the action of , the normal displacement d, then the distance D between the crack surfaces satisfies: Where D is the distance between crack surfaces, and d is the distance between crack surfaces under the closing stress σ. c Normal displacement under the action of ; S24: Calculate the crack surface under the closing stress σ c After a normal displacement d under the action of the action, the number of contact protrusions n and the elastic deformation ΔL i A protrusion is considered to be in contact if it satisfies the following formula: Based on the height L of the protrusion 0 Calculated using Hooke's law for initial elastic deformation: In the formula, ΔL is the elastic deformation; f is the force on the contact protrusion, in N; i is the contact protrusion number; L 0 E is the height of the protrusion; E is the rock modulus (GPa); a is the area of ​​the grid (cm²). 2 ; S25: Calculate the deformation W of the crack surface. i Distribution, deformation W i Considering the contributions of all contact protrusions, therefore W i satisfy: In the formula, W i w represents the deformation of the crack surface. ij The contribution of the contact protrusion j to the surface deformation of the crack at location i is calculated by equation (8): In the formula, v is the Poisson's ratio of the rock; r is the distance between the centers of contact protrusions j and i, in cm; θ is the polar angle originating from the contact center. Furthermore, the contribution w of the contact protrusion i to the crack surface deformation at location i ii The calculation method is as follows: S26: Calculate the closure stress σ for each contact protrusion. c Force f under action i For a certain contact protrusion i, the distance D between the crack surfaces and the deformation W of the crack surface at i are related. i The sum equals the height L0 of the contact protrusion i after elastic deformation. i -ΔL i ,Right now: S27: Determine the force f acting on the body. i Whether stress balance is satisfied is determined by the following method: In the formula, A a The crack surface area is in cm². 2 ε1 sets the error threshold for model calculation; S28: If stress balance is not satisfied, it means that d does not meet the requirements, and it is necessary to re-assume d and repeat steps S22-S26; if stress balance is satisfied, then calculate the crack width b after considering the normal deformation of the crack. c The calculation formula is: 。 5. The method for optimizing acid injection and discharge rates in ultra-deep fractured carbonate rocks according to claim 1, step S3 includes the following steps: S31: Based on the crack width b after considering the normal deformation of the crack. c Calculate the pressure P and the flow velocity distribution; S32: Calculate the concentration distribution C of the acid solution within the crack; S33: Calculate the temperature T inside the crack f and the filter loss temperature T d distributed; S34: Calculate the acid etching width b at the current time step. a The calculation method is as follows: In the formula, b a b is the width of the acid-etched crater at the current time step; c To account for the fracture width after normal deformation; β is the dissolving power of the acid; Δt is the time step; C is the concentration distribution of the acid; η is the ratio of the filtered acid to participate in the acid-rock reaction; v l R represents the acid loss rate along the slit width direction. s The acid-rock reaction rate; The acid-rock reaction rate in grid m; The height difference between protrusion i and its adjacent protrusion m; δ is the grid size; ρ r φ represents the rock density; φ represents the rock porosity. S35: Determine whether acid injection has ended. If acid injection has not ended, then set b a b as the subsequent time step ini Repeat steps S2-S3; if acid injection is complete, then b at this point a This determines the final acid etching groove width.

6. The method for optimizing acid injection and discharge rates in ultra-deep fractured carbonate rocks according to claim 1, step S4 includes the following steps: S41: Based on the established model, repeat steps S2-S3 to conduct simulations at different acid injection rates and obtain the final acid etching crack morphology at different acid injection rates. S42: Calculate the degree of crack closure b p The calculation method is as follows: In the formula, b p b represents the degree of crack closure. a0 b. The width of the acid-etched crevices without considering the closing stress; ac The width of the acid etching groove should take into account the closing stress; S43: Calculate the acid breakthrough rate v b The calculation method is as follows: In the formula, v b t is the acid breakthrough rate; L is the rock slab length (cm); l is the effective acid contact distance (cm); t a Total acid injection time, in minutes; t b The acid breakthrough time, in minutes; S44: Calculate the dimensionless comprehensive renovation coefficient. The calculation method is as follows: In the formula, w is the width of the plunger core, in cm; Q is the construction displacement, in m³. 3 / min; S45: Optimize the acid injection rate based on the dimensionless comprehensive modification coefficient, and plot the relationship curve between the dimensionless modification coefficient and the acid injection rate q, i.e., C s =f(q), where the acid injection rate corresponding to the maximum dimensionless modification coefficient is the optimal acid injection rate q. a ,Right now:

7. The method for optimizing the acid injection and discharge rate in ultra-deep fractured carbonate rocks according to claim 6 further includes optimizing the preferred acid injection and discharge rate q using a similarity criterion. a Converting to mine-scale acid injection discharge Q, the discharge conversion formula is: In the formula, h f Design seam height on site; b r Design the average seam width on site; b ac To simulate the average seam width; n f It is the flow index of the acid solution.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method of any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method of any one of claims 1 to 7.

10. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, implements the method of any one of claims 1 to 7.

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