Method for predicting the effect of mud losses during workover on the pressure of a refracturing operation

Abstract

The present application relates to a kind of methods for predicting the influence of mud loss during workover on repeated fracturing construction pressure, comprising the following steps: S1, based on the principle of equivalent seepage resistance, establish the equivalent permeability prediction model in the seam after heavy mud loss;S2, establish the seepage pressure drop relationship prediction model in the seam before and after heavy mud loss;S3, obtain relevant parameters, and obtain repeated fracturing construction parameters.The method of the present application considers the increase of seepage resistance in the seepage area caused by heavy mud loss during workover, can more accurately predict the repeated fracturing construction pressure, thereby improving the success rate and efficiency of repeated fracturing operation.

Description

Technical Field

[0001] This invention relates to the field of hydraulic fracturing technology, and in particular to a method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations. Background Technology

[0002] In the process of hydraulic fracturing, the construction pressure refers to the relationship curve of the pressure at the bottom of the well or the wellhead over time. By analyzing the construction pressure curve, we can determine the fracture propagation mode and fracture geometric parameters, modify the construction plan, etc., to obtain the optimal support for the fracture and the best economic benefits, thereby achieving the purpose of real-time monitoring and surveillance of the fracture.

[0003] However, in field practice, for old wells that have undergone workover measures, the actual construction pressure obtained on-site during repeated fracturing is generally significantly higher than the predicted construction pressure, making it relatively difficult to add sand on-site and limiting further analysis and diagnosis of the formation and fracture conditions.

[0004] Therefore, there is an urgent need to establish a method to predict the impact of mud loss during well workover on the pressure of repeated fracturing operations, so as to achieve accurate prediction of on-site construction pressure and thus improve the success rate and efficiency of repeated fracturing operations. Summary of the Invention

[0005] To overcome the problems in the prior art, this invention provides a method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations. This method considers the increased seepage resistance in the seepage zone caused by heavy mud loss during well workover, which is more in line with actual conditions and can more accurately predict the pressure of repeated fracturing operations after heavy mud contamination. To achieve the above objective, this invention provides the following solution:

[0006] A method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations includes the following steps:

[0007] S1. Based on the principle of equivalent seepage resistance, establish a prediction model for the equivalent permeability in the crack after heavy mud leakage;

[0008] S2. Establish a predictive model for the relationship between seepage pressure drop in the joint before and after heavy mud leakage;

[0009] S3. Obtain relevant parameters and predict the pressure for repeated fracturing operations.

[0010] A further technical solution is that step S1 also includes...

[0011] S11. Divide the seepage zone within the crack. The seepage zone includes a first zone, a second zone, and a third zone. The first zone is the seepage zone where heavy mud leakage occurs. The second zone is the non-leakage zone along the leading edge of the heavy mud leakage zone in the first zone to the tip of the crack. The third zone is the non-leakage zone along the top of the heavy mud leakage zone in the first zone to the height of the crack.

[0012] S12. Based on the seepage characteristics of the first, second, and third regions, establish a prediction model for the equivalent permeability within the fracture after heavy mud leakage.

[0013] A further technical solution is that step S12 also includes...

[0014] S121. Establish equivalent permeability prediction models for the first and second regions.

[0015]

[0016] Where, k eq 1,2 k represents the equivalent permeability of the first and second regions. mud k represents the penetration rate in the first region. prop R represents the permeability of the non-leaking area. L The proportion of the length of the first region to the length of the crack;

[0017] S122. Establish a prediction model for equivalent permeability within the crack after heavy mud leakage.

[0018]

[0019] A further technical solution is that the seepage pressure drop relationship prediction model in step S2 is:

[0020]

[0021] Among them, △p 漏失后 The seepage pressure drop within the joint after the loss of heavy mud; △p 未漏失 The pressure drop of seepage within the joint before the heavy mud leakage; A is the correction factor.

[0022] A further technical solution is that the correction coefficient is:

[0023] A = a * ln(k) mud )+b

[0024] Where a and b are the fitting parameters.

[0025] A further technical solution is that the method for obtaining the length and height of the first region is as follows:

[0026]

[0027] Among them, L mud H is the length of the first region; mud The height of the first region; V f For the volume of heavy mud leakage; w f The width of the crack.

[0028] A further technical solution is that step 3 also includes obtaining the permeability of the first region based on the relationship between the unobstructed flow rate and permeability before and after well repair.

[0029] A further technical solution is that the relationship between the unobstructed flow rate and permeability before and after well workover in step 3 is as follows:

[0030]

[0031] q aof修井前 q represents the unobstructed flow rate before well repair; aof修井后 This refers to the unobstructed flow rate after well repair.

[0032] On the other hand, the present invention provides a system for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations, comprising the following modules:

[0033] An equivalent permeability prediction module is provided, which establishes an equivalent permeability prediction model for the fracture after heavy mud leakage based on the principle of equivalent seepage resistance.

[0034] A seepage pressure drop prediction module is used to establish a seepage pressure drop prediction model in the joint before and after heavy mud leakage;

[0035] A repetitive fracturing pressure prediction module is used to acquire relevant parameters and predict the repetitive fracturing pressure.

[0036] On the other hand, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, when the processor executes the computer program, it implements the steps of the above-mentioned method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations.

[0037] On the other hand, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that, when the computer program is executed by a processor, it implements the steps of the above-described method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations.

[0038] The present invention has the following advantages: The present invention takes into account the increase in seepage resistance in the seepage zone caused by heavy mud loss during well workover, and provides a method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations, which can more accurately predict the construction pressure, thereby improving the success rate and efficiency of repeated fracturing operations. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram illustrating the division of the flow area within the joint after heavy mud leakage in an embodiment of the present invention;

[0041] Figure 2 This is a curve showing the relationship between the correction coefficient and the permeability ratio in an embodiment of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The purpose of this invention is to provide a method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations. To make the above-mentioned objectives, features and advantages of this invention more apparent and understandable, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] This invention provides a method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations, comprising the following steps:

[0045] S1. Based on the principle of equivalent seepage resistance, a prediction model for the equivalent permeability in the fracture after heavy mud leakage is established.

[0046] In repeated fracturing, when existing fractures are not plugged, the target of the repeated treatment is the existing underground fractures. Due to heavy mud loss, the flow channels near the wellbore decrease, and the flow resistance increases, leading to increased construction pressure. To analyze this phenomenon, the fractures from the initial treatment are selected for analysis, and the seepage zone after leakage is delineated. For example... Figure 1 As shown, considering that heavy mud has leaked into the cracks from the initial repair, the length of the leakage area is L.mud The height of the leakage area is H mud In this invention, the leakage area is also referred to as the first area. In addition to the heavy mud leakage area, there is also a non-leakage portion from the crack tip to the mud front edge (i.e., the second area), and a non-leakage portion above the mud leakage area (i.e., the third area).

[0047] like Figure 1 As shown, the proportions of the heavy mud loss area to the crack length and height are defined as R, respectively. L and R H The formula is as follows:

[0048]

[0049]

[0050] The region where heavy mud leakage occurs is defined as the first region, with a permeability of k1, which can also be written as k mud The region from the leading edge of the heavy mud to the tip of the joint is defined as the second region, with a permeability of k2. The upper region without mud is defined as the third region, with a permeability of k3. Since both the second and third regions are areas of heavy mud where the proppant is located that are not contaminated, their permeability can both be written as k. prop Based on the total pressure difference, the equivalent permeability of the first and second regions can be derived.

[0051]

[0052] Based on the fact that the two regions have the same total flow, the equivalent penetration rates for the first, second, and third regions can be derived as follows:

[0053]

[0054] Where, k prop k represents the initial permeability of the proppant sand pile. mud The permeability of the heavily contaminated mud area.

[0055] S2. Establish a predictive model for the relationship between seepage pressure drop in the joint before and after heavy mud leakage.

[0056] for Figure 1 In the three seepage zones, under the same discharge rate and the same fluid injection, the relationship between the flow pressure difference and the permeability of the flowing medium is as follows:

[0057]

[0058] During fracture propagation, the pressure at the fracture tip is low. The pressure difference in the above formula reflects the pressure relationship at the fracture inlet at the bottom of the well, which is the construction pressure relationship. From this formula, it can be seen that when there is no mud leakage, the fracturing pressure is the initial construction pressure during the initial fracturing operation, which is also the construction pressure predicted in the fracturing design scheme. When mud leakage occurs, due to heavy mud contamination, the permeability k of the first zone decreases. mud Less than the original fracture permeability k prop This also generates additional flow resistance, resulting in higher construction pressure during repeated modifications and greater permeability damage caused by mud contamination.

[0059] S3. Obtain relevant parameters and predict the pressure for repeated fracturing operations.

[0060] Predicting the construction pressure after mud loss requires obtaining the equivalent permeability of the fractures after mud loss. Since laboratory experiments cannot fully simulate downhole conditions, this invention proposes an approximate calculation method for this parameter. In engineering, wells with heavy mud loss can obtain the unobstructed flow rate after initial workover and the unobstructed flow rate after well repair. The main difference between the two is caused by mud loss. Therefore, assuming that the ratio between the two is the ratio between the mud contamination zone and the original permeability, the permeability of the mud contamination zone can be obtained, i.e.:

[0061]

[0062] Since it is difficult to obtain the specific value of the proppant sand pile permeability in practice, but the method established in this invention uses different parameter values, the specific absolute value does not need to be input, only the ratio is needed. Therefore, in the calculation, the proppant sand pile permeability k can be taken. prop Since k is 1, it is a dimensionless parameter. Therefore, the calculated k... mud It is the permeability of the part where the mud is after mud contamination. Then, based on the formula of the three seepage zones, the equivalent permeability of the entire crack is calculated considering the presence of mud, which enables the calculation and prediction of construction pressure.

[0063] When applying the construction pressure prediction method proposed in this invention to certain areas, it is necessary to correct the calculation results of the theoretical formula. Through multiple field tests and analyses, a formula for the correction coefficient was established using the permeability after mud contamination.

[0064] In one embodiment, the prediction method for the correction coefficient is as follows:

[0065] A = 0.1022ln(k) mud +1.1308

[0066] Using the above formula, the predicted construction pressure can be corrected, and then the increase in construction pressure caused by mud loss can be calculated based on the calculated construction pressure. Since the correction data comes from data under a certain discharge rate, when calculating the increase in construction pressure using the method of this invention, it is necessary to input the construction pressure under the discharge rate corresponding to the normal gradient.

[0067] Calculation Example

[0068] A prediction was made based on a specific case study of a certain block. Using data from previous well operations, the reservoir thickness H and lost mud volume V of heavily mud-contaminated wells during well workover were statistically analyzed. f The unobstructed flow rate before and after well workover are calculated. Based on these two values, the unobstructed flow rate after workover is divided by the unobstructed flow rate before workover to obtain the desired result. The relevant parameters adopted are shown in Table 1.

[0069] Table 1 Basic Parameters

[0070]

[0071] Based on the simulation results of artificial cracks in the block, the crack width is set, assuming that heavy mud leaks out simultaneously in both the crack length and crack height directions, and that the leakage distances are equal. The leakage amount V can then be used as a basis for calculation. f and the width of the artificial crack w f The intrusion length L was calculated based on the principle of volume conservation. mud and intrusion height H mud :

[0072]

[0073] With a leakage volume of 13m 3 Taking a crack width of 0.006m as an example, the calculated L mud =H mud =46.55m.

[0074] Using the intrusion height H mud and the length of intrusion L mud R can be calculated using formulas (4-23) and (4-24). L and R H Taking the fracture height as equal to the reservoir thickness, i.e., 93m, R is calculated. L =R H =0.5.

[0075] The permeability k of the proppant sand pile can be taken. prop The value is 1, which is a dimensionless parameter obtained from the previous steps. The calculated k mud, which is the permeability of the part where the mud was located (the first area) after mud contamination, also known as k. mud =0.37.

[0076] The pressure increase after considering mud loss can be calculated based on the relationship between the seepage pressure drop in the joint before and after the heavy mud loss.

[0077] Since the formula calculation results require correction based on field data, it is necessary to collect construction pressure data for wells with prior mud leakage under different discharge rates. This data will be used to correct the formula calculation results and obtain data for different... The correction factor is as follows. Taking this block as an example, The relationship with the correction is as follows: Figure 2 As shown.

[0078] Multiplying the predicted construction pressure obtained in the above steps by the correction factor A yields a construction pressure prediction value that more closely approximates the actual situation. Based on the prediction result for a specific displacement, the increase in the prediction result is obtained, for example, 3m³. 3 The construction pressure at a displacement of [displacement rate] / min without mud loss is 83.8 MPa. Considering mud loss, the pressure becomes 109.17 MPa. Therefore, the increase in construction pressure is 109.17 - 83.8 = 25.37 MPa. 25.37 is the increase in construction pressure caused by mud loss. The predicted pressure at other displacement rates can be obtained by adding this value.

[0079]

[0080] This invention addresses the issue of heavy mud leakage into the artificial fractures created during the initial well workover. The resulting retention of heavy mud within these fractures, compared to the initial absence of heavy mud, reduces the flow space for the fracturing fluid in subsequent fracturing operations. This increases flow resistance and significantly raises the pressure required for repeated fracturing. Compared to existing technologies, this invention allows for more accurate prediction of the fracturing pressure, thereby improving the success rate and efficiency of repeated fracturing operations.

[0081] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations, characterized in that, Includes the following steps: S1. Based on the principle of equivalent seepage resistance, establish a prediction model for the equivalent permeability in the crack after heavy mud leakage; Step S1 includes: S11. Divide the seepage zone within the crack. The seepage zone includes a first zone, a second zone, and a third zone. The first zone is the seepage zone where heavy mud leakage occurs. The second zone is the non-leakage zone along the leading edge of the heavy mud leakage zone in the first zone to the tip of the crack. The third zone is the non-leakage zone along the top of the heavy mud leakage zone in the first zone to the height of the crack. S12. Based on the seepage characteristics of the first, second, and third regions, establish a prediction model for the equivalent permeability within the cracks after heavy mud leakage. S121. Establish an equivalent permeability prediction model for the first and second regions; ； Where, k eq 1,2 k represents the equivalent permeability of the first and second regions. mud k represents the penetration rate in the first region. prop R represents the permeability of the non-leaking area. L The proportion of the length of the first region to the length of the crack; S122. Establish a prediction model for the equivalent permeability within the fracture after heavy mud leakage; ； S2. Establish a predictive model for the relationship between seepage pressure drop in the joint before and after heavy mud leakage; The seepage pressure drop relationship prediction model in step S2 is as follows: ； Among them, △p 漏失后 The seepage pressure drop within the joint after the loss of heavy mud; △p 未漏失 The pressure drop of seepage within the joint before the heavy mud leakage; A is the correction factor; S3. Obtain relevant parameters and predict the pressure for repeated fracturing operations.

2. The method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations according to claim 1, wherein the correction coefficient is: A=a*ln(k mud )+b; in, a and b are the fitting parameters.

3. The method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations according to claim 1, wherein the method for obtaining the length and height of the first region is as follows: ； in, L mud H is the length of the first region; mud The height of the first region; V f For the volume of heavy mud leakage; w f The width of the crack.

4. The method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations according to claim 1, wherein step 3 further includes obtaining the permeability of the first region based on the relationship between the unobstructed flow rate and permeability before and after well workover.

5. The method for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations according to claim 4, wherein the relationship between the unobstructed flow rate and permeability before and after well workover in step 3 is as follows: 。 6. A system for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations, based on the method according to any one of claims 1 to 5, characterized in that, Includes the following modules: An equivalent permeability prediction module is provided, which establishes an equivalent permeability prediction model for the fracture after heavy mud leakage based on the principle of equivalent seepage resistance. A seepage pressure drop prediction module is used to establish a seepage pressure drop prediction model in the joint before and after heavy mud leakage; A repetitive fracturing pressure prediction module is used to acquire relevant parameters and predict the repetitive fracturing pressure.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5 for predicting the impact of mud loss during well workover on the pressure of repeated fracturing operations.

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