Volume fracturing after-fracturing soaking time optimization method

Abstract

The invention provides a volume fracturing after-pressing soaking time optimization method. The method comprises the steps that the temperature, saturation original water saturation, stratum stress and pore pressure of a target layer are obtained on the basis of well logging interpretation; selecting a target layer sample, measuring the core porosity and geometric dimension, and enabling the core water saturation to be equal to the formation water saturation under the formation temperature condition; the method comprises the following steps: measuring a spontaneous imbibition curve under the conditions of formation temperature and confining pressure, drawing the spontaneous imbibition curve on a double logarithmic coordinate axis, searching an inflection point, and recording inflection point time; repeating the experiment to obtain a fitting equation; under the actual well condition, the average gap distance of the microcracks and the actual stratum saturation are estimated, parameters are substituted into the fitting equation, the optimized soaking time interval can be obtained, and optimization of the soaking time after volume fracturing is achieved. The method is simple, easy to operate, good in reliability and capable of achieving the purpose of estimating the on-site optimal soaking time based on indoor experiments and optimizing the soaking time.

Description

Technical Field

[0001] The present application relates to the field of oil production, and in particular to a method for optimizing the well shut-in time after volume fracturing. Background Art

[0002] The original formation pressure coefficient of normal pressure shale gas wells is low. Some gas wells can achieve self-flow after fracturing and energy enhancement, but there are still a few gas wells that cannot self-flow after fracturing. After a large amount of fracturing fluid enters the reservoir, under some conditions, the fracturing fluid can block small pores and cause water lock damage. Under some conditions, the fracturing fluid can replenish the pore pressure in the near-well area and achieve an energy enhancement effect. The interaction mechanism between fracturing fluid and reservoir is unclear. The interaction between fracturing fluid and reservoir is one of the key issues in research, especially in microscopic pore space, micro-nano pores, and micro-fracture systems. The occurrence and migration laws of fluids are the focus and difficulty of research. On a macro level, it needs to match the well soaking time, which has important engineering significance.

[0003] The existing technical methods for shut-in after volume fracturing mainly rely on empirical methods, normal pressure imbibition, wellhead pressure drop method, etc. The empirical methods have poor basis and are limited in their application in new blocks; the normal pressure imbibition method cannot truly reflect the actual situation underground and has a large deviation; the wellhead pressure drop method cannot fully reflect the liquid absorption of the matrix. Summary of the invention

[0004] The present application provides a method for optimizing the shut-in time after volume fracturing, aiming to solve the problem of inaccurate calculation of the existing shut-in time.

[0005] The technical solution of this application is:

[0006] A method for optimizing the well shut-in time after volume fracturing, comprising the following steps:

[0007] S1, obtain the physical property parameters of the target layer based on well logging interpretation;

[0008] S2, select the first core sample in the target layer;

[0009] S3, calculating the water saturation of the first core sample, and when the water saturation of the first core sample is equal to the original water saturation of the target layer, proceeding to the next step;

[0010] S4, measuring the inflection time t of the first core sample;

[0011] S5, selecting a second core sample in the target layer, repeating the operations from step S2 to step S4, obtaining the first inflection point time t1 and the second inflection point time t2 of the second core sample under the conditions of core length L and saturation Sw, and establishing fitting equations of t1~(L, Sw) and t2~(L, Sw);

[0012] S6, under actual well conditions, obtain the average microfracture spacing Lm and the actual formation saturation Swt, and substitute (Lm / 2, Swt) into the fitting equations of t1~(L, Sw) and t2~(L, Sw) in step S5 to obtain the first inflection point time tm1 and the second inflection point time tm2, respectively. Then tm1~tm2 is the optimized soaking time interval.

[0013] As a technical solution in the present application, in step S1, the physical property parameters of the target layer include the temperature T of the target layer, the original water saturation Swi of the target layer, the formation stress P and the pore pressure Pp.

[0014] As a technical solution in the present application, in step S2, a first core sample is selected in a direction parallel to the formation, and the diameter D, length L and core porosity φ of the first core sample are measured.

[0015] As a technical solution in the present application, in step S3, the thermostat is adjusted to the formation temperature T, the first core sample is dried to measure the dry weight m1; the dried first core sample is placed in a sealing device together with a beaker of water, the sealing device is placed in a thermostat, and the weight m2 of the first core sample is measured in real time, and the water saturation of the first core sample is calculated.

[0016] As a technical solution in the present application, in step S4, under the temperature T environment, the measured confining pressure is set to the difference between the formation pressure P and the pore pressure Pp, and the spontaneous imbibition curve is measured under the condition of confining pressure P-Pp. The spontaneous imbibition curve is plotted on a double logarithmic coordinate axis, the inflection point is found, and the inflection point time t of the first core sample is recorded.

[0017] As a technical solution in the present application, in step S4, the method for finding an inflection point on a double logarithmic coordinate axis includes the following steps:

[0018] The water absorption mass and time of the first core sample are recorded at every specified time interval △t, and the water absorption mass and time of the core are used as the original data;

[0019] Normalize the data and convert the core water absorption mass M into the core water absorption mass per unit volume M0. The conversion relationship is: Where M0 is the water absorption mass per unit volume of the core, M is the water absorption mass of the first core sample, D is the diameter of the first core sample, and L is the length of the first core sample;

[0020] With time as the horizontal coordinate and the water absorption mass per unit volume of the core as the vertical coordinate, the coordinate system is a double logarithmic coordinate. Each data point is placed in the coordinate system, and the first inflection point and the second inflection point of the first core sample are obtained by data fitting.

[0021] As a technical solution in the present application, the time interval Δt is 1 second.

[0022] As a technical solution in the present application, in step S5, a second core sample is selected in a direction parallel to the formation, and the diameter D, length L and core porosity φ of the second core sample are measured.

[0023] Beneficial effects of this application:

[0024] The present application provides a method for optimizing the soaking time after volume fracturing. The method is simple, easy to operate, and reliable. It can estimate the optimal soaking time on site based on indoor experiments to achieve the purpose of soaking time optimization. At the same time, the present application fully considers parameters such as underground confining pressure, initial water saturation, and core length, and can more truly reflect the actual situation underground. It also considers the liquid absorption under the condition of the existence of fractures, and effectively solves the problem of optimizing the reasonable soaking time under volume fracturing conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show the following technical solutions of the present application.

[0026] Certain embodiments of the application should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A schematic diagram of a process flow of a method for optimizing the well shut-in time after volume fracturing provided in an embodiment of the present application;

[0028] Figure 2 A schematic diagram of finding an inflection point provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0031] Example:

[0032] Please refer to Figure 1 , with reference Figure 2 In an embodiment of the present application, a method for optimizing the well shut-in time after volume fracturing is provided, comprising the following steps:

[0033] S1, based on well logging interpretation, obtain the temperature T, original water saturation Swi, formation stress P and pore pressure Pp of the target layer;

[0034] S2, select the first core sample of the target layer, sample it in parallel to the formation direction, and measure the diameter D, length L and core porosity φ of the first core sample;

[0035] S3, adjust the thermostat to the formation temperature T, dry the first core sample and measure the dry weight m1; place the dried first core sample together with a beaker of water in a sealed device, place the sealed device in the thermostat, and measure the core weight m2 in real time to calculate the water saturation of the first core sample When the water saturation Sw1 of the first core sample is equal to the original water saturation Swi of the target layer, proceed to the next step;

[0036] S4, under the temperature T environment, set the measured confining pressure to be the difference between the formation pressure P and the pore pressure Pp, measure the spontaneous imbibition curve under the condition of confining pressure (P-Pp), plot the spontaneous imbibition curve on a double logarithmic coordinate axis, find the inflection point, and record the inflection point time t;

[0037] S5, select a second core sample in the target layer, select the second core sample in a direction parallel to the formation, and measure the diameter D, length L and core porosity φ of the second core sample, repeat the operation method in step S2 to step S4, respectively obtain the first inflection point time t1 and the second inflection point time t2 of the second core sample under different core lengths L and saturation Sw conditions, and establish t1~(L,Sw) and t2~(L,Sw) fitting equations;

[0038] S6, under actual well conditions, estimate the average microfracture spacing Lm and the actual formation saturation Swt, and substitute (Lm / 2, Swt) into the fitting equation in step S5 to obtain the first inflection point time tm1 and the second inflection point time tm2 respectively. Then tm1~tm2 is the optimized shut-in time interval, thereby optimizing the shut-in time after volume fracturing.

[0039] Further, in step S4, the method for finding the inflection point on the double logarithmic coordinate axis includes the following steps:

[0040] The core water absorption mass and time are recorded at every specified time interval △t, and the core water absorption mass and time are used as the original data;

[0041] Normalize the data and convert the water absorption mass M into the water absorption mass per unit volume of the core M0. The conversion formula is: Where M0 is the water absorption mass per unit volume of the core, M is the water absorption mass of the first core sample, D is the diameter of the first core sample, and L is the length of the first core sample;

[0042] With time as the horizontal coordinate, the water absorption mass per unit volume of the core as the vertical coordinate, and the coordinate system as a double logarithmic coordinate, the data points are placed in the coordinate system, and the first inflection point and the second inflection point are obtained by data fitting.

[0043] It should be noted that the time interval Δt can be selected as 1 second.

[0044] In summary, the present application provides a method for optimizing the well shut-in time after volume fracturing. The method is simple, easy to operate, and reliable. It can estimate the optimal well shut-in time on site based on indoor experiments to achieve the purpose of well shut-in time optimization. It is applied to shale gas blocks. Compared with conventional methods, it has stronger adaptability and practicality and can achieve the purpose of well shut-in time optimization. At the same time, the present application fully considers parameters such as underground confining pressure, initial water saturation, and core length, and can more truly reflect the actual underground conditions. It also considers the liquid absorption under the condition of cracks, and effectively solves the problem of optimizing the reasonable well shut-in time under volume fracturing conditions.

[0045] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for optimizing the well shut-in time after volume fracturing, characterized in that: The following steps are involved: S1, obtain the physical property parameters of the target layer based on well logging interpretation; S2, select the first core sample in the target layer; S3, calculating the water saturation of the first core sample, and when the water saturation of the first core sample is equal to the original water saturation of the target layer, proceeding to the next step; S4, measuring the inflection time t of the first core sample; S5, selecting a second core sample in the target layer, repeating the operations from step S2 to step S4, obtaining the first inflection point time t1 and the second inflection point time t2 of the second core sample under the conditions of core length L and saturation Sw, and establishing fitting equations of t1~(L, Sw) and t2~(L, Sw); S6, under actual well conditions, obtain the average microfracture spacing Lm and the actual formation saturation Swt, and substitute (Lm / 2, Swt) into the fitting equations of t1~(L, Sw) and t2~(L, Sw) in step S5 to obtain the first inflection point time tm1 and the second inflection point time tm2, respectively. Then tm1~tm2 is the optimized soaking time interval.

2. The method for optimizing the well shut-in time after volume fracturing according to claim 1, characterized in that: In step S1 , the physical property parameters of the target layer include the temperature T of the target layer, the original water saturation Swi of the target layer, the formation stress P, and the pore pressure Pp.

3. The method for optimizing the well shut-in time after volume fracturing according to claim 1, characterized in that: In step S2, a first core sample is selected in a direction parallel to the formation, and the diameter D, length L and core porosity φ of the first core sample are measured.

4. The method for optimizing the well shut-in time after volume fracturing according to claim 1, characterized in that: In step S3, the thermostat is adjusted to the formation temperature T, the first core sample is dried to measure the dry weight m1; the dried first core sample is placed in a sealing device together with a beaker of water, the sealing device is placed in the thermostat, and the weight m2 of the first core sample is measured in real time, and the water saturation of the first core sample is calculated.

5. The method for optimizing the well shut-in time after volume fracturing according to claim 1, characterized in that: In step S4, under the temperature T environment, the measured confining pressure is set to be the difference between the formation pressure P and the pore pressure Pp, and the spontaneous imbibition curve is measured under the condition of confining pressure P-Pp. The spontaneous imbibition curve is plotted on a double logarithmic coordinate axis, the inflection point is found, and the inflection point time t of the first core sample is recorded.

6. The method for optimizing the well shut-in time after volume fracturing according to claim 5, characterized in that: In step S4, the method for finding the inflection point on the double logarithmic coordinate axis includes the following steps: The water absorption mass and time of the first core sample are recorded at every specified time interval △t, and the water absorption mass and time of the core are used as the original data; Normalize the data and convert the core water absorption mass M into the core water absorption mass per unit volume M0. The conversion relationship is: Where M0 is the water absorption mass per unit volume of the core, M is the water absorption mass of the first core sample, D is the diameter of the first core sample, and L is the length of the first core sample; With time as the horizontal coordinate and the water absorption mass per unit volume of the core as the vertical coordinate, the coordinate system is a double logarithmic coordinate. Each data point is placed in the coordinate system, and the first inflection point and the second inflection point of the first core sample are obtained by data fitting.

7. The method for optimizing the well shut-in time after volume fracturing according to claim 6, characterized in that: The time interval △t is 1 second.

8. The method for optimizing the well shut-in time after volume fracturing according to claim 1, characterized in that: In step S5, a second core sample is selected in a direction parallel to the formation, and the diameter D, length L and core porosity φ of the second core sample are measured.

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