A calculation method for wormhole growth and skin coefficient during acidizing pump injection

Abstract

The present invention discloses a method for calculating wormhole growth and skin coefficient during the acidizing pumping process, including calculating the maximum pumping displacement that can be achieved by surface equipment without breaking the reservoir; comparing the maximum pumping displacement that can be achieved by the surface equipment to determine the maximum pumping displacement of the acidizing operation; calculating the acid absorption amount and acid absorption pressure of each discrete section, and iteratively optimizing the actual pumping displacement of the current pumping stage; calculating the wormhole length, total wormhole length, skin coefficient generated by wormhole growth, and skin coefficient of each discrete section of the reservoir after the pumping time of the current stage is completed; optimizing the pumping program of the entire acidizing operation based on the total acid amount of the acidizing operation, and calculating the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir after the acidizing operation is completed. The present invention adjusts the acid pumping displacement of the reservoir by reducing the wormhole growth and skin coefficient, and can accurately characterize the heterogeneous profile of wormhole development, skin coefficient, and acid absorption caused by reservoir heterogeneity.

Description

Technical Field

[0001] The invention relates to the field of carbonate reservoir acidification transformation, and in particular to a method for calculating wormhole growth and skin coefficient in an acidification pumping process. Background Art

[0002] Acidizing is one of the most effective methods for increasing production and improving efficiency in carbonate reservoirs. Its goal is to remove reservoir contamination near the wellbore and restore reservoir flow capacity. Acidizing requires maximizing the acid injection rate without compressing the reservoir, encouraging continuous acid loss deep into the reservoir. This not only dissolves the acid-soluble minerals in the reservoir matrix, but also dissolves the acid-soluble minerals in the pores and any external plugging minerals. The depth of acid loss through the reservoir is measured by wormhole length, and the degree of improvement in reservoir flow capacity is measured by the skin coefficient. Furthermore, with continued acid injection, wormhole growth and the dynamic changes in the skin coefficient improve reservoir flow capacity. Increasing the critical acid absorption rate and injection rate further promotes wormhole growth and reduces the skin coefficient. Therefore, accurately calculating the dynamic changes in wormhole growth and skin coefficient during acid injection is crucial for adjusting the acid injection rate and enhancing the effectiveness of the reservoir.

[0003] Currently, the maximum pumping rate during acidizing operations is primarily determined by the initial physical characteristics of the reservoir and the surface pumping capacity. This ignores the fact that the ultimate acid absorption rate continuously increases during the dynamic improvement of the reservoir's flow capacity, resulting in insufficient surface pumping rates and inadequate reservoir stimulation. Furthermore, simulations of wormhole growth and skin coefficient reduction typically assume the reservoir is homogeneous. This fails to fully reflect the uneven growth of wormholes and the differences between the acid absorption profile and the skin coefficient profile caused by reservoir heterogeneity, making it difficult to accurately guide the design and optimization of acidizing processes.

[0004] Therefore, a method for calculating wormhole growth and skin coefficient during the acidizing pumping process is needed, which can adjust the acid pumping rate of the reservoir by reducing the growth of wormholes and the skin coefficient, and can accurately characterize the heterogeneous profile of wormhole development, skin coefficient and acid absorption caused by reservoir heterogeneity. Summary of the Invention

[0005] The present invention aims to provide a method for calculating wormhole growth and skin coefficient during the acidizing pumping process, which is used to dynamically calculate the growth of wormholes and the reduction of skin coefficient during the acidizing pumping process and fully reflect the uneven growth of wormholes caused by reservoir heterogeneity and the difference between the acid absorption profile and the skin coefficient profile of the reservoir, thereby providing a basis for the design and optimization of carbonate reservoir acidizing technology.

[0006] In order to achieve the above-mentioned object of the invention, the present invention is implemented through the following technical solutions:

[0007] A method for calculating wormhole growth and skin coefficient during acidizing pump injection comprises the following steps:

[0008] S1. Calculate the maximum pumping rate that the surface equipment can achieve without breaking the reservoir, based on the reservoir fracture pressure, construction string, and acid parameters.

[0009] S2. Calculate the maximum acid absorption rate and the maximum pumping rate that the reservoir can achieve based on its heterogeneous physical parameters, compare them, and determine the maximum pumping rate for acidizing operations;

[0010] S3. Calculate the actual pumping rate for the current pumping phase based on the maximum pumping rate for acidizing operation;

[0011] S4. Calculate the wormhole length, total wormhole length, skin coefficient generated by wormhole growth, and skin coefficient of the reservoir after the completion of the current stage of pumping and the actual pumping rate of the acidizing operation;

[0012] S5. Based on the total acid volume of the acidizing operation, optimize the pumping procedure of the entire acidizing operation and calculate the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir after the acidizing operation is completed.

[0013] In one embodiment, the step S1 further comprises the following steps:

[0014] S11. Given the initial value of the pump injection rate Q, calculate the Reynolds number N for the acid flow in the construction string. R And calculate the friction resistance ΔP along the construction string;

[0015] S12. Given a reservoir with a fracture pressure of P f , calculate the required pumping pressure P under the current pumping displacement sur ;

[0016] S13. Given the construction pressure limit of ground equipment is P limit , determine the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation q-max .

[0017] In one embodiment, the step S11 calculates the Reynolds number N of the acid solution flow in the construction string using the following formula: R And calculate the friction resistance ΔP along the construction string:

[0018]

[0019] Where: N R is the Reynolds number, dimensionless; Q is the pump displacement, m 3 / min;ρ a is the density of acid solution, Kg / m3 ;μ a is the viscosity of the acid solution, mPa·s; d p is the diameter of the construction pipe, m;

[0020]

[0021] Where: ΔP is the friction resistance along the construction string, MPa; f is the drag reduction rate of the acid fluid, dimensionless; L p is the length of the construction string, m;

[0022] The step S12 uses the following formula to calculate the required pumping pressure P under the current pumping displacement: sur :

[0023] P sur =ΔP+P f -9.8×10 -6 ρ a L p

[0024] Where, P sur is the pumping pressure required at the current pumping displacement, MPa; P f is the fracture pressure of the reservoir, MPa;

[0025] The step S13 compares the construction pressure limit P limit and pumping pressure P sur The size of the pumping displacement determines the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation. q-max .

[0026] In one embodiment, step S2 further comprises the following steps:

[0027] S21. Based on the logging interpretation results of the reservoir, the reservoir is discretized, the heterogeneous physical parameters of each discrete segment are defined, and the comprehensive reservoir coefficient k of the reservoir is calculated. t h t and comprehensive skin factor S t ;

[0028] S22. Determine the maximum pumping rate for acidizing operation.

[0029] In one embodiment, the step S21 defines the heterogeneous physical parameter of each discrete segment as the thickness h i , permeability k i and skin factor S i In step S21, the comprehensive reservoir coefficient k of the reservoir is calculated using the following formula: t h t and comprehensive skin factor S t :

[0030]

[0031] Where S i is the skin coefficient of each discrete segment of the reservoir, dimensionless, i = 1, 2, ······n; k i is the permeability of each discrete segment of the reservoir, mD; h i is the thickness of each discrete segment of the reservoir, m; where i = 1, 2, ······n, H is the reservoir thickness, m;

[0032] The step S22 determines the maximum pumping rate of the acidizing operation using the following formula:

[0033] First, calculate the maximum acid absorption and displacement capacity Q that the reservoir can achieve by the following formula: ab-max :

[0034]

[0035] Where Q ab-max is the maximum acid absorption and displacement that the reservoir can achieve, m 3 / min; P e is the reservoir pressure, MPa; P f is the fracture pressure of the reservoir, MPa; r e is the oil leakage area of acidizing well, m 2 ; r w is the wellbore radius, m;

[0036] Then, by comparing the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation, q-max and the maximum acid absorption and displacement capacity Q that the reservoir can achieve ab-max , determine the maximum pumping displacement for acidizing construction.

[0037] In one embodiment, step S3 calculates the actual pumping displacement of the current pumping stage by the following steps:

[0038] S31. Given the initial value of the pumping displacement in the current pumping stage, Q T The acid absorption pressure P of each discrete section of the reservoir at the current pumping rate is obtained by the calculation result of step 21 and the following formula: i :

[0039]

[0040] S32. Substitute the acid absorption pressure Pi obtained in step S31 into the following formula to recalculate the acid absorption amount Q of each discrete segment of the reservoir: i and the theoretical acid absorption capacity of the entire reservoir Q' T :

[0041]

[0042] S33. Comparison Q T With Q' T If the difference is within 10%, then Q T is the actual pumping displacement of the current pumping stage; if the difference is greater than 10%, then Q T =Q' T Repeat steps S31 and S32 until the difference between the two is within 10%, which greatly optimizes the actual pumping displacement in the current pumping stage.

[0043] In one embodiment, step S4 further comprises the following steps:

[0044] S41. Acid absorption amount Q obtained according to step S31 and step S32 i , calculate the radial flow rate V of each discrete segment of the reservoir under the current pumping rate i ;

[0045] S42. Calculate the wormhole growth rate V for each discrete segment of the reservoir based on the wormhole growth effectiveness factor and the wormhole growth rate factor. wh-i After the current stage of pumping time is completed, calculate the length of the wormhole R in each discrete section of the reservoir. wh-i and the total length of the wormhole R T-wh ;

[0046] S43. Calculate the skin coefficient S of each discrete segment of the reservoir after the current stage of pumping time is completed. i .

[0047] In one embodiment, step S41 calculates the radial flow rate V of each discrete segment of the reservoir at the current pumping rate using the following formula: i :

[0048]

[0049] Where V i is the radial flow rate of each discrete segment of the reservoir, cm / min; R i is the radial equivalent radius of each discrete segment of the reservoir, m. When in the first stage of pumping displacement, R i =r w ;φ i is the porosity of each discrete segment of the reservoir, a decimal;

[0050] The step S42 calculates the wormhole growth rate V of each discrete segment of the reservoir using the following formula: wh-i :

[0051] V wh-i =W eff ·V i 2 / 3 Wb

[0052] Where V wh-i is the wormhole growth rate of each discrete section of the reservoir, cm / min; W eff is the effective factor of wormhole growth obtained by fitting the acid core flow test, (cm / min) 1 / 3 ; Wb is the wormhole growth rate factor obtained by fitting the acid core flow test, (cm / min) -2 ;

[0053] The length R of the wormhole growing in each discrete section of the reservoir is calculated using the following formula: wh-i :

[0054] R wh-i =10·V wh-i

[0055] Where, is the length of wormholes grown in each discrete section of the reservoir after the current stage of pumping time is completed, cm;

[0056] The total length R of wormholes in each discrete section of the reservoir is calculated using the following formula: T-wh :

[0057] R T-wh =R T-wh +R wh-i , where after the first stage of pumping time is completed, R T-wh =R wh-i , the equivalent radius of each discrete segment of the reservoir will be updated to R i =R i +R wh-i :

[0058] The step S43 calculates the skin coefficient S of each discrete segment of the reservoir using the following formula: i :

[0059] S i =S i +S wh-i ,in

[0060] Where S wh-i It is the dimensionless negative skin coefficient generated by wormhole growth in each discrete segment of the reservoir after the current stage of pumping time is completed.

[0061] In one embodiment, step S5 further comprises the following steps:

[0062] S51. Calculate the total acid volume for acidizing based on the expected acidizing penetration depth;

[0063] S52. After each stage of pumping is completed, calculate the total amount of acid pumped into the reservoir;

[0064] S53. After each stage of pumping is completed, based on the updated skin coefficient of each discrete segment of the reservoir, repeat step S2 to calculate the maximum acid absorption and displacement Q that the reservoir can achieve after completing the current stage of pumping time. ab-max ;

[0065] S54. By comparing the results obtained in step S51 to step S53, the initial value of the pumping time and pumping displacement of the next pumping stage is determined;

[0066] S55. Calculate the initial value of the pumping time and pumping displacement obtained in step S54, repeat step S3, and calculate the actual pumping displacement of the current pumping stage;

[0067] S56. Repeat step S4 to calculate the length of wormholes grown in each discrete segment of the reservoir, the total length of wormholes, the skin coefficient generated by wormhole growth, and the skin coefficient after the pumping time of this stage is completed;

[0068] S57. Repeat steps S51 to S56. After all pumping stages are completed, the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir are calculated.

[0069] In one embodiment, the step S51 calculates the total acid amount of the acidizing operation using the following formula:

[0070]

[0071] Where Q total is the total acid volume of acidizing construction, m3; r p is the expected acidizing penetration depth, m;

[0072] The step S52 calculates the total amount of acid pumped into the reservoir using the following formula:

[0073] Q T-inj =Q T-inj +10·Q T , where the total amount of acid pumped into the reservoir after the first stage of pumping time is: Q T-inj =10·Q T .

[0074] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0075] First, the dynamic changes of heterogeneous physical parameters during the acidizing process were analyzed, and the maximum pumping rate of acidizing construction at different pumping stages was obtained. Second, the acidizing construction pumping procedure was optimized, and the wormhole development length profile, skin coefficient profile, and acid absorption profile obtained were more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0077] Figure 1 Schematic diagram of the flow chart of the method for calculating wormhole growth and skin coefficient during the acid pumping process according to an embodiment of the present application;

[0078] Figure 2 This is the wormhole length profile after all acid injection stages are completed in the embodiment of this application;

[0079] Figure 3 The skin coefficient profile of the acid solution after all pumping stages are completed in the embodiment of the present application;

[0080] Figure 4 This is the acid absorption profile after all the acid pumping stages of the embodiment of the present application are completed. DETAILED DESCRIPTION

[0081] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0082] In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not necessarily required to practice the present invention. In other embodiments, well-known structures, circuits, materials, or methods are not described in detail to avoid obscuring the present invention.

[0083] Throughout this specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combinations and / or subcombinations. Furthermore, it will be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes only and are not necessarily drawn to scale. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0084] In the description of the present invention, the terms "front", "back", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0085] The present invention will be further described below with reference to the accompanying drawings and examples.

[0086] like Figures 1 to 4 As shown, a method for calculating wormhole growth and skin coefficient during acidizing pump injection includes the following steps:

[0087] S1. Calculate the maximum pumping rate that the surface equipment can achieve without breaking the reservoir, based on the reservoir fracture pressure, construction string, and acid parameters.

[0088] Step S1 further includes the following steps:

[0089] S11. Given the initial value of the pump injection rate Q, calculate the Reynolds number N for the acid flow in the construction string. R :

[0090]

[0091] Where: N R is the Reynolds number, dimensionless; Q is the pump displacement, m 3 / min;ρ a is the density of acid solution, Kg / m 3 ;μ a is the viscosity of the acid solution, mPa·s; d p is the diameter of the construction pipe, m;

[0092] Based on turbulence theory and combined with the drag reduction coefficient of acid fluid, the friction resistance ΔP along the construction string is calculated:

[0093]

[0094] Where: ΔP is the friction resistance along the construction string, MPa; f is the drag reduction rate of the acid fluid, dimensionless; L p is the length of the construction pipe string, m.

[0095] S12. Given a reservoir with a fracture pressure of P f , calculate the required pumping pressure P under the current pumping displacement sur ;

[0096] P sur =ΔP+P f-9.8×10 -6 ρ a L p

[0097] Where, P sur is the pumping pressure required at the current pumping displacement, MPa; P f is the fracture pressure of the reservoir, MPa.

[0098] S13. Given the construction pressure limit of ground equipment is P limit Then assume that the initial calculation value of the pump displacement is Q = 1m 3 / min, when P sur <P limit In this embodiment, 0.2m 3 / min is a step to gradually increase the pump displacement, or 0.1m 3 / min or 0.3m 3 / min is a step to gradually increase the pumping displacement. In the subsequent iterative calculation, let Q = Q + 0.2, iteratively calculate steps S11 and S12 until P sur ≥P limit Stop the iterative calculation. At this point, the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation can be determined. q-max Results

[0099] S2. Compare the maximum acid absorption displacement of the reservoir and the maximum pumping displacement obtained in step S1 based on the heterogeneous physical parameters of the reservoir to determine the maximum pumping displacement of the acidizing operation;

[0100] Step S2 further includes the following steps:

[0101] S21. Based on the logging interpretation results of the reservoir, the reservoir is discretized, the heterogeneous physical parameters of each discrete segment are defined, and the comprehensive reservoir coefficient k of the reservoir is calculated. t h t and comprehensive skin factor S t ;

[0102]

[0103] Where S i is the skin coefficient of each discrete segment of the reservoir, dimensionless, i = 1, 2, ······n; k i is the permeability of each discrete segment of the reservoir, mD; h i is the thickness of each discrete segment of the reservoir, m; where i = 1, 2, ······n, H is the reservoir thickness, m;

[0104] S22. Determine the maximum pumping rate for acidizing operation;

[0105] First, use Darcy's formula to calculate the maximum acid absorption and displacement Q that the reservoir can achieve. ab-max :

[0106]

[0107] Where Q ab-max is the maximum acid absorption and displacement that the reservoir can achieve, m 3 / min; P e is the reservoir pressure, MPa; P f is the fracture pressure of the reservoir, MPa; r e is the oil leakage area of acidizing well, m 2 ; r w is the wellbore radius, m;

[0108] Then, by comparing the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation, q-max and the maximum acid absorption and displacement capacity Q that the reservoir can achieve ab-max If Q ab-max ≤Q q-max , with Q ab-max As the maximum pumping displacement of acidizing operation, otherwise take Q q-max As the maximum pumping displacement for acidizing construction.

[0109] S3. Using the maximum pumping displacement obtained in step S2, calculate the actual pumping displacement of the current pumping stage;

[0110] Step S3 further includes the following steps:

[0111] S31. Given the initial value of the pumping displacement in the current pumping stage, Q T (In this embodiment, the initial value of the pumping displacement calculation for the first stage is set to one-fourth of the maximum pumping displacement of the acidizing operation in the initial state). Substituting the calculation results of step S21 and step S22 into the following formula, the acid absorption pressure P of each discrete segment of the reservoir under the current pumping displacement is obtained. i :

[0112]

[0113] S32. Substitute the acid absorption pressure Pi obtained in step S31 into the following formula to recalculate the acid absorption amount Q of each discrete segment of the reservoir: i and the theoretical acid absorption capacity of the entire reservoir Q' T :

[0114]

[0115] S33. Comparison Q T With Q' TIf the difference is within 10%, then Q T is the actual pumping displacement of the current pumping stage; if the difference is greater than 10%, then Q T =Q' T Repeat steps S31 and S32 until the difference between the two is within 10%, which greatly optimizes the actual pumping displacement of the current pumping stage.

[0116] S4. Calculate the wormhole length, total wormhole length, skin coefficient generated by wormhole growth, and skin coefficient of the reservoir after the completion of the current stage of pumping and the actual pumping rate of the acidizing operation;

[0117] Step S4 further includes the following steps:

[0118] S41. Acid absorption amount Q obtained according to step S3 i and the actual pumping rate, calculate the radial flow rate V of each discrete segment of the reservoir under the current pumping rate i ;

[0119]

[0120] Where V i is the radial flow rate of each discrete segment of the reservoir, cm / min; R i is the radial equivalent radius of each discrete segment of the reservoir, m. When in the first stage of pumping displacement, R i =r w ;φ i is the porosity of each discrete segment of the reservoir, a decimal;

[0121] S42. Calculate the wormhole growth rate V for each discrete segment of the reservoir based on the wormhole growth effectiveness factor and the wormhole growth rate factor. wh-i After the current stage of pumping time is completed, calculate the length of the wormhole R in each discrete section of the reservoir. wh-i and the total length of the wormhole R T-wh ;

[0122] First calculate the wormhole growth rate V of each discrete section of the reservoir under the current pumping rate wh-i :

[0123] V wh-i =W eff ·V i 2 / 3 W b

[0124] Where V wh-i is the wormhole growth rate of each discrete section of the reservoir, cm / min; W eff is the effective factor of wormhole growth obtained by fitting the acid core flow test, (cm / min)1 / 3 ;W b is the wormhole growth rate factor obtained by fitting the acid core flow test, (cm / min) -2 ;

[0125] Then, set the pumping time of each stage of pumping displacement to 10 minutes, and use the following formula to calculate the wormhole length R of each discrete section of the reservoir after the current stage of pumping time is completed: wh-i :

[0126] R wh-i =10·V wh-i

[0127] Where R wh-i The length of wormholes grown in each discrete segment of the reservoir after the current stage of pumping time is completed, cm.

[0128] In addition, after the current stage of pumping time is completed, in order to improve the accuracy of the equivalent radius of each discrete segment of the reservoir in the subsequent steps, the equivalent radius of each discrete segment of the reservoir in the subsequent steps will be corrected to: R i =R i +R wh-i Similarly, during the first stage of pumping, the total length of wormholes in each discrete section of the reservoir is: R T-wh =R T-wh +R wh-i After the first stage of pumping is completed, the total length of the wormhole in the subsequent pumping stage is corrected to R T-wh =R wh-i .

[0129] S43. Calculate the skin coefficient S of each discrete segment of the reservoir after the current stage of pumping time is completed. i

[0130] In this example, since the reservoir permeability after wormhole growth is an order of magnitude different from the original permeability, the negative skin coefficient generated by wormhole growth in each discrete segment of the reservoir after the current pumping time is completed is first calculated using the following formula. This is used to correct the skin coefficient of each discrete segment of the reservoir to improve its accuracy:

[0131]

[0132] Where S wh-i It is the dimensionless negative skin coefficient generated by wormhole growth in each discrete segment of the reservoir after the current stage of pumping time is completed.

[0133] After the current stage of pumping is completed, the skin coefficient of each discrete segment of the reservoir during the subsequent stage of pumping can be obtained as: S i =S i +S wh-i .

[0134] S5. Based on the total acid volume of the acidizing operation, optimize the pumping procedure of the entire acidizing operation and calculate the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir after the acidizing operation is completed.

[0135] Step S5 further includes the following steps:

[0136] S51. Calculate the total acid volume for acidizing according to the expected acidizing penetration depth:

[0137]

[0138] Where Q total is the total acid volume of acidizing construction, m3; r p is the expected acidizing penetration depth, m

[0139] S52. After each stage of pumping is completed, calculate the total amount of acid pumped into the reservoir;

[0140] Q T-inj =Q T-inj +10·Q T , where the total amount of acid pumped into the reservoir after the first stage of pumping time is: Q T-inj =10·Q T .

[0141] S53. After each stage of pumping is completed, based on the updated skin coefficient of each discrete segment of the reservoir, repeat step S2 to calculate the maximum acid absorption and displacement Q that the reservoir can achieve after completing the current stage of pumping time. ab-max ;

[0142] S54. By comparing the results obtained in step S51 to step S53, the initial value of the pumping time and pumping displacement of the next pumping stage is determined;

[0143] If Q T-inj <Q total And Q T +1.5≤min[Q ab-max ,Q q-max ], then the initial value of the next stage pump displacement is set as: Q T =Q T +1.5, acidizing operation is not completed yet, and the next stage of pumping begins;

[0144] If Q T-inj <Q total And Q T +1.5≥min[Q ab-max ,Q q-max ], then the next stage is set as the last stage of pumping, and the initial value of the last stage of pumping displacement is: Q T=min[Q ab-max ,Q q-max ], the last stage of pumping time is min, acidizing operation is not completed and enters the next stage of pumping;

[0145] If Q T-inj ≥Q total , acidizing construction is completed.

[0146] S55. Calculate the initial value of the pumping time and pumping displacement obtained in step S54, repeat step S3, and calculate the actual pumping displacement of the current pumping stage;

[0147] S56. Repeat step S4 to calculate the length of wormholes grown in each discrete segment of the reservoir, the total length of wormholes, the skin coefficient generated by wormhole growth, and the skin coefficient after the pumping time of this stage is completed;

[0148] S57. Repeat steps S51 to S56. After all pumping stages are completed, the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir are calculated.

[0149] Example calculation

[0150] Step S1: Collect the reservoir fracture pressure, construction string and acid parameters of the target acidizing well and obtain: the acidizing reservoir section is 2450-2550m, a total of 100m, the string length is 2500m, the string diameter is 0.076m, the acid viscosity is 8mPa·s, and the acid viscosity is 1000kg / m 3 , the acid fluid resistance reduction rate is 70%, the reservoir fracture pressure is 50MPa, and the construction limit pressure is 72MPa.

[0151] Assume that the initial calculation value of pump displacement is Q = 1m 3 / min, at 0.2m 3 / min is a step to gradually increase the pumping displacement. Through steps S11 to S13, it is calculated that the maximum pumping displacement that the ground equipment can achieve without breaking the formation is 7.0m 3 / min.

[0152] Step S2: Collect the reservoir logging interpretation results of the target acidized well. If it is shown that the reservoir is divided into 10 small layers, the reservoir is discretized into 10 segments. The heterogeneous physical parameters of each discrete segment are as follows:

[0153] Table 1 Heterogeneous physical parameters of each discrete segment of the reservoir

[0154] Reservoir number Thickness, m Permeability, mD Skin Factor 1 12 10 8 2 8 5 5 3 6 3 4 4 10 12 9 5 5 10 6 6 17 4 10 7 18 10 13 8 6 5 6 9 13 8 10 10 5 6 7

[0155] The calculations in steps S21 and S22 show that the maximum acid absorption and displacement that the reservoir can achieve is 4.5m 3 / min, it is judged that the maximum pumping rate of acidizing operation in the initial state of the reservoir is 4.5m 3 / min.

[0156] Step S3: Set the initial value of the pumping displacement calculation for the first stage to one-fourth of the maximum pumping displacement of the acidizing operation in the initial state, that is, 1.125m 3 / min. Through iterative calculation from step S31 to step S33, the actual pumping displacement in the first stage is 1.21m 3 / min.

[0157] In step S4, based on the actual pumping displacement of the first stage, the length of the wormholes grown in each discrete section of the reservoir, the total length of the wormholes, the skin coefficient generated by the wormhole growth, and the skin coefficient are calculated through steps S41 to S43 after the pumping time of the current stage is completed. The calculation results are as follows:

[0158] Table 2 Discrete segment wormhole and skin coefficient after the first stage of pumping time

[0159] Reservoir number Growing wormhole length, cm Total length of wormhole mD Skin coefficient generated by wormhole growth Skin Factor 1 15.98 15.98 -0.64 7.36 2 11.82 11.82 -0.51 4.49 3 11.08 11.08 -0.48 3.52 4 18.18 18.18 -0.70 8.30 5 17.49 17.49 -0.68 5.32 6 11.68 11.68 -0.50 9.50 7 18.03 18.03 -0.70 12.30 8 12.10 12.10 -0.52 5.48 9 16.25 16.25 -0.65 9.35 10 14.78 14.78 -0.60 6.40

[0160] Step S5: Set the expected acidizing penetration depth to 2m. The total acid volume of the acidizing operation is calculated to be 279.8m through steps S51 and S52. 3 The total amount of acid pumped into the reservoir is 121m 3 .

[0161] According to Q T-inj <Q total And Q T +1.5≤min[Q ab-max ,Q q-max ], the initial value of the second stage pumping displacement is 2.71m 3 / min, repeat step S2 to obtain the second stage limit pumping displacement Q q-max and the maximum acid absorption and displacement capacity Q that the reservoir can achieve ab-max Repeat step S3 to calculate the actual pumping displacement of this stage to be 3.24m 3 / min, repeat step S4, and obtain the calculation results of the wormhole length, total wormhole length and skin coefficient of each discrete segment of the reservoir after the second stage of pumping time is completed as follows:

[0162] Table 3 Discrete segment wormhole and skin coefficient after the second stage of pumping time

[0163] Reservoir number Growing wormhole length, cm Total length of wormhole mD Skin coefficient generated by wormhole growth Skin Factor 1 19.08 35.06 -1.09 6.27 2 18.40 30.22 -0.99 3.50 3 18.73 29.81 -0.98 2.53 4 21.41 39.59 -1.17 7.13 5 24.09 41.58 -1.20 4.11 6 15.53 27.20 -0.93 8.57 7 19.58 37.61 -1.14 11.16 8 19.65 31.75 -1.02 4.46 9 20.80 37.05 -1.13 8.23 10 22.23 37.01 -1.12 5.27

[0164] After the second stage of pumping is completed, the calculation of the third stage and subsequent stages is continued until Q T-inj≥Q total According to the parameters of this embodiment, the sixth stage is the last stage of pumping, and the last stage of pumping time is 9.33 minutes.

[0165] After all the pumping stages are completed, the wormhole development length profile, skin coefficient profile and acid absorption profile of the entire reservoir are shown in Table 4. After each pumping stage is completed, the length of the wormholes grown is as follows: Figure 1 As shown in the figure, the skin coefficient generated by wormhole growth is as follows Figure 2 As shown, the acid absorption of each discrete segment is as follows Figure 3 shown.

[0166] Table 4 Parameters of wormhole development length profile, skin coefficient profile and acid absorption profile of the entire reservoir

[0167] Reservoir number Length of wormhole development, cm Skin Factor <![CDATA[Acid absorption profile, m 3 > 1 102.89 -0.45 40.32 2 94.61 -2.90 18.28 3 95.41 -3.87 9.35 4 112.63 0.09 42.44 5 124.11 -3.19 23.68 6 79.36 2.65 22.46 7 102.16 4.41 54.28 8 96.21 -2.01 14.84 9 104.21 1.44 39.54 10 108.61 -1.61 14.61

[0168] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calculating wormhole growth and skin coefficient during acidification pump injection, characterized in that: The following steps are involved: S1. Calculate the maximum pumping rate that the surface equipment can achieve without breaking the reservoir, based on the reservoir fracture pressure, construction string, and acid parameters. S2. Calculate the maximum acid absorption rate and the maximum pumping rate that the reservoir can achieve based on the heterogeneous physical parameters of the reservoir, compare them, and determine the maximum pumping rate for acidizing operation; S3. Calculate the actual pumping rate for the current pumping phase based on the maximum pumping rate for acidizing operation; S4. Calculate, based on the pumping time and actual pumping rate of the current acidizing operation, the wormhole length, total wormhole length, negative skin coefficient generated by wormhole growth, and skin coefficient of the reservoir after the completion of the current pumping time; S5. Based on the total acid volume of the acidizing operation, optimize the pumping procedure of the entire acidizing operation and calculate the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir after the acidizing operation is completed.

2. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 1, characterized in that: The step S1 further comprises the following steps: S11. Given the initial value of the pump injection rate Q, calculate the Reynolds number N for the acid flow in the construction string. R And calculate the friction resistance ΔP along the construction string; S12. Given a reservoir with a fracture pressure of P f , calculate the required pumping pressure P under the current pumping displacement sur ; S13. Given the construction pressure limit of ground equipment is P limit , determine the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation q-max .

3. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 2, characterized in that: The step S11 calculates the Reynolds number N of the acid solution flow in the construction string using the following formula R And calculate the friction resistance ΔP along the construction string: Where: N R is the Reynolds number, dimensionless; Q is the pump displacement, m 3 / min;ρ a is the density of acid solution, Kg / m 3 ;μ a is the viscosity of the acid solution, mPa·s; d p is the diameter of the construction pipe, m; Where: ΔP is the friction resistance along the construction string, MPa; f is the drag reduction rate of the acid fluid, dimensionless; L p is the length of the construction string, m; The step S12 uses the following formula to calculate the required pumping pressure P under the current pumping displacement: sur : P sur =ΔP+P f -9.8×10 -6 r a L p Where, P sur is the pumping pressure required at the current pumping displacement, MPa; P f is the fracture pressure of the reservoir, MPa; The step S13 compares the construction pressure limit P limit and pumping pressure P sur The size of the pumping displacement determines the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation. q-max .

4. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 1, characterized in that: The step S2 further comprises the following steps: S21. Based on the logging interpretation results of the reservoir, the reservoir is discretized and the heterogeneous physical parameters of each discrete segment are defined. The heterogeneous physical parameters include the thickness h i , permeability k i and skin factor S i , the comprehensive skin coefficient S of the reservoir is calculated by the formula t and comprehensive reservoir coefficient k t h t ; in, Where S i is the skin coefficient of each discrete segment of the reservoir, dimensionless, i = 1, 2, ······n; k i is the permeability of each discrete segment of the reservoir, mD; h i is the thickness of each discrete segment of the reservoir, m; where i = 1, 2, ······n, H is the reservoir thickness, m; S22. Use the following formula to determine the maximum pumping rate for acidizing: First, calculate the maximum acid absorption rate Q that the reservoir can achieve using the following formula: ab-max , Where Q ab-max is the maximum acid absorption and displacement that the reservoir can achieve, m 3 / min; P e is the reservoir pressure, MPa; P f is the fracture pressure of the reservoir, MPa; r e is the oil leakage area of acidizing well, m 2 ; r w is the wellbore radius, m; μ a is the acid viscosity, mPa·s, and then the maximum pumping displacement Q that the surface equipment can achieve without breaking the formation is compared. q-max and the maximum acid absorption and displacement capacity Q that the reservoir can achieve ab-max The smaller value shall be taken as the maximum pumping displacement of acidizing construction.

5. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 4, characterized in that: The step S3 calculates the actual pumping displacement of the current pumping stage by the following steps: S31. Given the initial value of the pumping displacement in the current pumping stage, Q T The acid absorption pressure P of each discrete section of the reservoir at the current pumping rate is obtained by the calculation result of step S21 and the following formula: i : S32. Substitute the acid absorption pressure Pi obtained in step S31 into the following formula to recalculate the acid absorption amount Q of each discrete segment of the reservoir: i and the theoretical acid absorption capacity of the entire reservoir Q' T : S33. Comparison Q T With Q' T If the difference is within 10%, then Q T is the actual pumping displacement of the current pumping stage; if the difference is greater than 10%, then Q T =Q' T Repeat steps S31 and S32 until the difference between the two is within 10%.

6. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 5, characterized in that: The step S4 further comprises the following steps: S41. Acid absorption amount Q obtained according to step S31 and step S32 i , calculate the radial flow rate V of each discrete segment of the reservoir under the current pumping rate i ; S42. Calculate the wormhole growth rate V for each discrete segment of the reservoir based on the wormhole growth effectiveness factor and the wormhole growth rate factor. wh-i After the current stage of pumping time is completed, calculate the length of the wormhole R in each discrete section of the reservoir. wh-i and the total length of the wormhole R T-wh ; S43. Calculate the skin coefficient S of each discrete segment of the reservoir after the current stage of pumping time is completed. i .

7. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 6, characterized in that: The step S41 calculates the radial flow rate V of each discrete segment of the reservoir at the current pumping rate using the following formula: i : Where V i is the radial flow rate of each discrete segment of the reservoir, cm / min; R i is the radial equivalent radius of each discrete segment of the reservoir, m. When in the first stage of pumping displacement, R i =r w ;φ i is the porosity of each discrete segment of the reservoir, a decimal; The step S42 calculates the wormhole growth rate V of each discrete segment of the reservoir using the following formula: wh-i : V wh-i =W eff ·V i 2 / 3 ·W b Where V wh-i is the wormhole growth rate of each discrete section of the reservoir, cm / min; W eff is the effective factor of wormhole growth obtained by fitting the acid core flow test, (cm / min) 1 / 3 ;W b is the wormhole growth rate factor obtained by fitting the acid core flow test, (cm / min) -2 ; The length R of the wormhole growing in each discrete section of the reservoir is calculated using the following formula: wh-i : R wh-i =10 V wh-i Where R wh-i The length of wormholes grown in each discrete segment of the reservoir after the current stage of pumping time is completed, cm; The total length R of wormholes in each discrete section of the reservoir is calculated using the following formula: T-wh : R T-wh =R T-wh +R wh-i , where after the first stage of pumping time is completed, R T-wh =R wh-i , the equivalent radius of each discrete segment of the reservoir will be updated to R i =R i +R wh-i : The step S43 calculates the skin coefficient S of each discrete segment of the reservoir using the following formula: i : S i =S i +S wh-i ,in Where S wh-i It is the dimensionless negative skin coefficient generated by wormhole growth in each discrete segment of the reservoir after the current stage of pumping time is completed.

8. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 7, characterized in that: The step S5 further comprises the following steps: S51. Calculate the total acid volume for acidizing based on the expected acidizing penetration depth; S52. After each stage of pumping is completed, calculate the total amount of acid pumped into the reservoir; S53. After each stage of pumping is completed, based on the updated skin coefficient of each discrete segment of the reservoir, repeat step S2 to calculate the maximum acid absorption and displacement Q that the reservoir can achieve after completing the current stage of pumping time. ab-max ; S54. By comparing the results obtained in step S51 to step S53, the initial value of the pumping time and pumping displacement of the next pumping stage is determined; S55. Calculate the initial value of the pumping time and pumping displacement obtained in step S54, repeat step S3, and calculate the actual pumping displacement of the current pumping stage; S56. Repeat step S4 to calculate the length of wormholes grown in each discrete segment of the reservoir after the pumping time of this stage is completed, the total length of wormholes, the negative skin coefficient and the skin coefficient generated by the wormhole growth; S57. Repeat steps S51 to S56. After all pumping stages are completed, the wormhole development length profile, skin coefficient profile, and acid absorption profile of the entire reservoir are calculated.

9. The method for calculating wormhole growth and skin coefficient during acidification pump injection according to claim 8, characterized in that: The step S51 calculates the total acid amount of the acidification operation using the following formula: Where Q total is the total acid volume of acidizing construction, m 3 ; r p is the expected acidizing penetration depth, m; The step S52 calculates the total amount of acid pumped into the reservoir using the following formula: Q T-inj =Q T-inj +10·Q T , where the total amount of acid pumped into the reservoir after the first stage of pumping time is: Q T-inj =10·Q T .

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