Method and system for processing shale gas fracturing pump stopping curve

Abstract

The invention relates to the technical field of oil and gas field development, and discloses a method and system for processing a shale gas fracturing pump stopping curve, and the method comprises the steps: calculating an envelope line with a water attack effect part based on an original pump stopping pressure curve, and then processing original pressure data into a plurality of decomposition variables and a residual variable based on the envelope line; the obtained residual variable is regarded as a pressure curve after the water attack effect is eliminated. The problems that the water attack effect cannot be eliminated and the accuracy is low in the prior art are solved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a method and a system for processing a shale gas fracturing pump stop curve. Background Art

[0002] As an important object of well test analysis, pressure curve is widely used in the development of domestic oil and gas fields. By establishing a double logarithmic pressure curve, the original pressure or average formation pressure of the formation can be calculated, and the flow capacity of the fluid in the formation can also be determined. In the process of shale gas development, staged fracturing is often used. Therefore, the pressure change trend after pumping is stopped in each stage of fracturing is equivalent to a micro-injection test, which is of great significance for the evaluation of single-stage post-fracturing of shale gas wells.

[0003] However, when the pump is stopped during fracturing, the injection pressure at the wellhead suddenly drops to zero. The fracturing fluid has inertia and compressibility, and the pressure wave is reflected in the wellbore, producing a strong impact on the casing. At this time, the pump-stop pressure drop is superimposed by the water hammer effect, presenting a sine (cosine) wave shape with a damping effect, which seriously interferes with the smoothness of the pressure curve, and the pump-stop pressure curve cannot be directly used for analysis.

[0004] At present, there is no effective method to eliminate the water hammer effect in the method of shale gas pump shutdown pressure analysis, which is also the main obstacle and difficulty restricting the curve analysis. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a method and system for processing a shale gas fracturing pump stop curve, which solves the problems of the prior art such as failure to eliminate water hammer effect and low accuracy.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] A method for processing a shale gas fracturing pump-off curve, based on the original pump-off pressure curve, calculates an envelope with a water hammer effect, and then processes the original pressure data into a plurality of decomposed variables and a residual variable based on the envelope, and regards the obtained residual variable as a pressure curve after eliminating the water hammer effect.

[0008] As a preferred technical solution, the following steps are included:

[0009] S1, extreme point position calculation: determine the positions of all local extreme points of the original pressure data P(t);

[0010] S2, envelope calculation: calculate the envelope of the pump stop pressure curve;

[0011] S3, decomposition variable calculation: using the original pressure data P(t) and envelope to calculate the decomposition variable;

[0012] S4, residual variable calculation: calculate the residual variable using the decomposed variables;

[0013] S5, pressure curve calculation: output the real pressure curve after removing the water hammer effect.

[0014] As a preferred technical solution, step S1 includes the following steps:

[0015] S11, collecting and arranging gas well construction parameters according to the existing implementation status of the target block;

[0016] S12, extracting the construction data of different fracturing stages of the gas well from the fracturing construction bulletin, extracting the original data of the second point of the single stage construction, and recording the original pressure data as P(t);

[0017] S13, determine the positions of all extreme points of the original pressure data P(t), recorded as S(i); wherein i represents the extreme point number, i≥1 and i is an integer, and S(i) represents the i-th extreme point.

[0018] As a preferred technical solution, in step S2, all extreme points S(i) in P(t) are fitted to obtain the upper envelope H(t) and the lower envelope L(t), and the average values ​​of the upper envelope and the lower envelope are calculated to obtain the mean envelope m(t) of the curve; wherein, m(t) = (H(t) - L(t)) / 2.

[0019] As a preferred technical solution, in step S3, the difference between P(t) and the mean envelope m(t) is calculated, and the difference is recorded as the decomposition variable Δx(t); wherein Δx(t)=P(t)-m(t).

[0020] As a preferred technical solution, step S4 includes the following steps:

[0021] S41, calculate the number of extreme values ​​and zero crossings of Δx(t) in the decomposed variable. When condition 1 is met, the decomposed variable is considered valid and is recorded as C i (t); if condition 1 is not satisfied, let it be P(t), and continue iterating until condition 1 is satisfied and then stop iterating; where condition 1 means: the number of extreme values ​​= the number of zero crossings, or the difference between the number of extreme values ​​and the number of zero crossings is within a set threshold;

[0022] S42, calculate the decomposition variable C twice in a row i The standard deviation of (t) d , if condition 2 is satisfied, the local mean between the upper envelope and the lower envelope is considered to be zero; if condition 2 is not satisfied, let P(t) be, and continue to iterate until condition 2 is satisfied; where condition 2 refers to: S d <Set threshold.

[0023] As a preferred technical solution, in step S5, when condition 1 in step S41 and condition 2 in step S42 are met, the decomposed variable C is output. i (t), and record Δx(t) at this time as r(t); if r(t) is a monotonic function, then output all C i (t) and r(t), end the iteration; otherwise, let r(t) = P(t), and then repeat steps S13 to S42.

[0024] As a preferred technical solution, in step S5,

[0025]

[0026] Where T represents the total time of the original pressure data, C i-1 (t) represents the decomposition variable obtained in the last calculation, C i (t) represents the decomposed variable obtained by the current calculation.

[0027] As a preferred technical solution, in step S13, if the left endpoint and / or the right endpoint of P(t) is not an extreme point, the known pressure data is used to extend the data of the endpoint where P(t) is not an extreme point. The specific method is: extend the real data at the endpoint, and when the extension is greater than the first maximum value or smaller than the first minimum value closest to the endpoint, the extended data is used as the extreme point.

[0028] A system for processing a shale gas fracturing pump stop curve, used to implement a method for processing a shale gas fracturing pump stop curve, comprises the following modules connected in sequence:

[0029] Extreme point position calculation module: used to determine the positions of all local extreme points of the original pressure data P(t);

[0030] Envelope calculation module: used to calculate the envelope of the pump stop pressure curve;

[0031] Decomposition variable calculation module: used to calculate the decomposition variable using the original pressure data P(t) and envelope;

[0032] Residual variable calculation module: used to calculate residual variables using decomposed variables;

[0033] Pressure curve calculation module: used to output the real pressure curve after removing the water hammer effect.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention iteratively filters the pump-off pressure curve by interpolation method, providing as accurate data as possible for pump-off pressure analysis;

[0036] (2) The present invention effectively avoids the interpolation divergence phenomenon caused by the endpoint not being an extreme point through extreme value extension, reduces the calculation error of the interpolation method, and ensures the accuracy of the pressure data. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the fracturing construction curve of a well in the target block;

[0038] Figure 2 This is a pressure curve with water hammer effect after the pump is stopped in a certain well;

[0039] Figure 3 This is the pressure curve 70s after the pump is stopped in the 12th section;

[0040] Figure 4 For Figure 3 The pressure curve after extension;

[0041] Figure 5 It is a schematic diagram of the curves H(t), L(t), and m(t) after interpolation based on the extreme points;

[0042] Figure 6 is the calculated Δx(t) curve;

[0043] Figure 7 It is a schematic diagram of the pressure curve r(t) after filtering. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0045] Example 1

[0046] like Figures 1 to 7 As shown, in order to solve the problems of the prior art, the present invention proposes a method for processing a shale gas fracturing pump-off pressure curve using digital filtering, which can quickly and conveniently eliminate the water hammer effect during pump-off and obtain a relatively stable pump-off pressure curve, so as to realize the post-fracture evaluation of a single-stage shale gas well and improve the applicability of the pump-off pressure drop curve.

[0047] (1) Based on the existing fracturing construction data of a well in the target block, obtain the construction time data of different fracturing stages (such as Figure 1 ):

[0048] (2) Obtain the construction time point data of different fracturing stages of the target well, and extract the original pressure data P(t) containing the water hammer effect from the moment when the displacement is zero (such as Figure 2 ).

[0049] (3) The positions of all local extreme points of the original pressure data P(t) are determined by differential derivative function, which are denoted as S(i) (i=1, 2, 3, ...).

[0050] (4) If the left and right endpoints of P(t) are not extreme points, then use the known data information to extend the data at both ends of P(t). Extend the real data at the left and right ends respectively. When the value of the endpoint is larger than the first maximum value or smaller than the minimum value near the endpoint, the endpoint is treated as an extension point to prevent the signal from falling outside the envelope. Extend the data until the endpoint is approximately an extreme point.

[0051] (5) Use the cubic spline function to fit all the extreme points S(i) after the extension in P(t) to obtain the upper envelope H(t) and L(t) formed by the interpolation of the extreme points. Calculate the average value of the upper and lower envelopes to obtain the mean envelope m(t) of the curve:

[0052] m(t)=(H(t)-L(t)) / 2 (1)

[0053] (6) Calculate the difference between P(t) and the mean envelope m(t), recorded as the decomposition variable Δx(t):

[0054] Δx(t)=P(t)-m(t) (2)

[0055] (7) Calculate the number of extreme values ​​(including maximum and minimum values) and the number of zero crossings in the decomposed variable Δx(t). When these two values ​​are equal or differ by only 1, the decomposed variable Δx(t) is valid and is recorded as C. i (t), if the condition is not met, Δx(t) is set to P(t), and the iteration is continued until the condition 1 is met and the iteration is stopped; wherein the condition 1 means: the number of extreme values ​​= the number of zero crossings, or the difference between the number of extreme values ​​and the number of zero crossings is within the set threshold;

[0056] (8) Calculate the decomposition variable C twice in a row i The standard deviation of (t) d , the standard deviation S d As the stop condition, when the calculated S d <0.2 or 0.3, the local mean between the upper envelope and the lower envelope is considered to be zero. If the stop condition is not met, set Δx(t) to P(t), and continue iterating until the second condition is met; where the second condition refers to: S d <Set threshold;

[0057]

[0058] (9) When the above conditions 1 and 2 are met, the output decomposition variable C i(t), and record Δx(t) at this time as r(t). If r(t) is a monotonic function, then output all C i (t) and r(t), the iteration ends. Otherwise, let r(t) = P(t) and repeat steps (3)-(8).

[0059] (10) After the above cycle, the original pressure data P(t) can be processed into several decomposition variables C i (t) and a residual variable r(t). According to experience, the seepage pressure curve is a monotonic function, so it is believed that r(t) is approximately the real pressure curve after removing the water hammer effect.

[0060]

[0061] By using the existing technical steps, the upper and lower envelopes of the pump stop with water hammer effect are calculated through interpolation method, and filtering processing from high frequency to low frequency is realized to provide more accurate data for pressure curve analysis.

[0062] In the above scheme:

[0063] In formula (1), H(t) is the upper envelope formed by the maximum value points, L(t) is the lower envelope formed by the minimum value points, and m(t) is the mean envelope of the upper and lower envelopes;

[0064] In formula (2), P(t) is the original pressure data, Δx(t) is the difference between the original pressure data P(t) and the mean envelope m(t);

[0065] In formula (3), S d is the standard deviation between two consecutive calculations of the decomposition variable, C i-1 (t) is the decomposition variable obtained in the last calculation, C i (t) is the decomposition variable obtained by the current calculation;

[0066] In formula (4), r(t) is the residual variable obtained after multiple filtering;

[0067] In order to make up for the shortcomings of the prior art, filter the water hammer effect in the pressure curve, and make the analysis more accurate and efficient, the patent of the present invention provides a method for processing the shale gas fracturing pump stop curve based on digital filtering. All local maximum points and local minimum points in the pump stop curve are obtained, and the upper and lower envelopes of the water hammer effect part are calculated by using the cubic spline interpolation method. At the same time, the upper and lower envelopes are averaged. When the eigenmode function conditions are met, the decomposed variables are output, and the decomposed variables are subtracted from the original curve and iterated repeatedly to finally obtain the residual variables. At the same time, in view of the problem of endpoint effect in the interpolation method during the calculation process, data extension is performed to ensure the reliability of the processing results. The water hammer effect of the pump stop curve is eliminated through multiple iterations of the algorithm, which greatly improves the analyzability of the pump stop pressure curve, and also provides a new method for water hammer effect filtering.

[0068] Example 2

[0069] like Figures 1 to 7 As shown, as a further optimization of Example 1, based on Example 1, this embodiment also includes the following technical features:

[0070] This embodiment is a process of eliminating the water hammer effect of pump stop by utilizing the method of the present invention.

[0071] This embodiment is the 12th stage of fracturing construction of a certain well X. The total duration of fracturing construction is 15'39'11, and there are 40 construction stages in total. Pump stopping is the last process. It is judged by the moment when the displacement is 0 that the pump stopping time point is 15'12'49, from which the 70s pressure data P(t) with obvious pump stopping effect is selected (such as Figure 3 ):

[0072] (1) Obtain Figure 1 All extreme points of P(t). Since the left endpoint difference of P(t) is P'(1)=0.57,P'(70)=0.01 (approximately 0). Using the existing data points, extend the left endpoint data to the extreme point.

[0073] (2) Extend the left endpoint data. When the pump is stopped for the 12th stage of fracturing and extended forward for 16 seconds, P'(-16) = -0.01 (approximately 0), which is approximately the extreme point.

[0074] (3) Obtain all extreme points after extension. Recorded as S(83.9, 79.0, 83.1, 80.5, 82.12, 80.67, 81.4, 80.75, 80.9, 80.64) (e.g. Figure 4 ).

[0075] (4) Through cubic spline interpolation, the upper envelope of H(t) corresponding to the maximum point and the lower envelope of L(t) corresponding to the minimum point are obtained respectively, and the mean envelope of the upper and lower envelopes is m(t) (e.g. Figure 5 ).

[0076] (5) Calculate the Δx(t) curve. According to the P(t) and m(t) curves, the Δx(t) curve (e.g. Figure 6 ).

[0077] (6) Determine whether the difference between the number of extreme points and zero-crossing points of the Δx(t) curve is 0 or 1. The number of zero-crossing points is 10, and the number of extreme points is 10, which meets the conditions. Since the standard deviation is not calculated when Δx(t) is calculated for the first time.

[0078] (7) Determine whether the calculated m(t) curve is a monotonic curve. By calculating that m'(t) ≠ 0, it is a monotonic function, and m(t) is the r(t) curve (e.g. Figure 7 ).

[0079] Depend on Figure 7 It can be clearly seen that the pump-off pressure curve recalculated by the method of the present invention basically eliminates the influence of the water hammer effect after pump-off. Compared with before processing, the data is smooth and conforms to the seepage characteristics. The method of processing the pump-off pressure curve after fracturing by digital filtering method in the present invention can effectively make up for the difficulties that cannot be solved at present, provide more accurate and comprehensive pressure data for post-fracturing evaluation, and ensure the accuracy of analysis.

[0080] As described above, the present invention can be preferably implemented.

[0081] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

[0082] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for processing a shale gas fracturing pump stop curve, characterized in that: Based on the original pump-off pressure curve, the envelope of the part with water hammer effect is calculated, and then the original pressure data is processed into several decomposition variables and a residual variable based on the envelope. The residual variable is regarded as the pressure curve after eliminating the water hammer effect.

2. A method for processing a shale gas fracturing pump stop curve according to claim 1, characterized in that: The following steps are involved: S1, extreme point position calculation: determine the positions of all local extreme points of the original pressure data P(t); S2, envelope calculation: calculate the envelope of the pump stop pressure curve; S3, decomposition variable calculation: using the original pressure data P(t) and envelope to calculate the decomposition variable; S4, residual variable calculation: Calculate the residual variable using the decomposed variables; S5, pressure curve calculation: output the real pressure curve after removing the water hammer effect.

3. A method for processing a shale gas fracturing pump stop curve according to claim 2, characterized in that: Step S1 includes the following steps: S11, collecting and arranging gas well construction parameters according to the existing implementation status of the target block; S12, extracting the construction data of different fracturing stages of the gas well from the fracturing construction bulletin, extracting the original data of the second point of the single stage construction, and recording the original pressure data as P(t); S13, determine the positions of all extreme points of the original pressure data P(t), recorded as S(i); wherein i represents the extreme point number, i≥1 and i is an integer, and S(i) represents the i-th extreme point.

4. A method for processing a shale gas fracturing pump stop curve according to claim 3, characterized in that: In step S2, all extreme points S(i) in P(t) are fitted to obtain the upper envelope H(t) and the lower envelope L(t), and the average values ​​of the upper envelope and the lower envelope are calculated to obtain the mean envelope m(t) of the curve; wherein, m(t) = (H(t) - L(t)) / 2.

5. A method for processing a shale gas fracturing pump stop curve according to claim 4, characterized in that: In step S3, the difference between P(t) and the mean envelope m(t) is calculated, and the difference is recorded as the decomposition variable Δx(t); wherein Δx(t)=P(t)-m(t).

6. A method for processing a shale gas fracturing pump stop curve according to claim 5, characterized in that: Step S4 includes the following steps: S41, calculate the number of extreme values ​​and zero crossings of Δx(t) in the decomposed variable. When condition 1 is met, the decomposed variable is considered valid and is recorded as C i (t); if condition 1 is not satisfied, let it be P(t), and continue iterating until condition 1 is satisfied and then stop iterating; where condition 1 means: the number of extreme values ​​= the number of zero crossings, or the difference between the number of extreme values ​​and the number of zero crossings is within a set threshold; S42, calculate the decomposition variable C twice in a row i The standard deviation of (t) d , if condition 2 is satisfied, the local mean between the upper envelope and the lower envelope is considered to be zero; if condition 2 is not satisfied, let P(t) be, and continue to iterate until condition 2 is satisfied; where condition 2 refers to: S d <Set threshold.

7. A method for processing a shale gas fracturing pump stop curve according to claim 6, characterized in that: In step S5, when condition 1 in step S41 and condition 2 in step S42 are met, the decomposed variable C is output. i (t), and record Δx(t) at this time as r(t); if r(t) is a monotonic function, then output all C i (t) and r(t), end the iteration; otherwise, let r(t) = P(t), and then repeat steps S13 to S42.

8. A method for processing a shale gas fracturing pump stop curve according to claim 7, characterized in that: In step S5, Where T represents the total time of the original pressure data, C i-1 (t) represents the decomposition variable obtained in the last calculation, C i (t) represents the decomposed variable obtained by the current calculation.

9. A method for processing a shale gas fracturing pump stop curve according to any one of claims 3 to 8, characterized in that: In step S13, if the left endpoint and / or the right endpoint of P(t) is not an extreme point, the known pressure data is used to extend the data of the endpoint where P(t) is not an extreme point. The specific method is: extend the real data at the endpoint, and when the extension is greater than the first maximum value or smaller than the first minimum value closest to the endpoint, the extended data is used as the extreme point.

10. A system for processing shale gas fracturing pump stop curve, characterized in that: A method for processing a shale gas fracturing pump stop curve according to any one of claims 1 to 9, comprising the following modules connected in sequence: Extreme point position calculation module: used to determine the positions of all local extreme points of the original pressure data P(t); Envelope calculation module: used to calculate the envelope of the pump stop pressure curve; Decomposition variable calculation module: used to calculate the decomposition variable using the original pressure data P(t) and envelope; Residual variable calculation module: used to calculate residual variables using decomposed variables; Pressure curve calculation module: used to output the real pressure curve after removing the water hammer effect.

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