A method for optimizing soak time after volume fracturing

Abstract

The application provides a volume fracturing post-pressure soaking time optimization method, which is based on well logging interpretation to obtain the temperature, saturated original water saturation, formation stress and pore pressure of a target layer; a target layer sample is selected to measure the core porosity and geometric size, and the core water saturation is equal to the formation water saturation under the formation temperature condition; the spontaneous imbibition curve is measured under the formation temperature and confining pressure condition, the spontaneous imbibition curve is plotted on the double logarithmic coordinate axis, the inflection point is found, and the inflection point time is recorded; the fitting equation is obtained by repeating the experiment; under the actual well condition, the average fracture spacing of micro-fracture and the actual formation saturation are estimated, the parameters are brought into the fitting equation, and the optimized soaking time interval can be obtained, so that the volume fracturing post-pressure soaking time is optimized. The method is simple, easy to operate, and good in reliability, can realize the estimation of the optimal soaking time on the site based on the indoor experiment, and achieves the purpose of soaking time optimization.

Description

Technical Field

[0001] This application relates to the field of oil extraction, and in particular to a method for optimizing the well shut-in time after volumetric fracturing. Background Technology

[0002] Atmospheric shale gas wells have low initial formation pressure coefficients. Some wells can achieve self-flowing after fracturing and energy enhancement, but a few wells still cannot. After a large amount of fracturing fluid enters the reservoir, under certain conditions, the fracturing fluid can block small pores, causing water-locking damage. Under other conditions, the fracturing fluid can replenish the pore pressure in the near-wellbore zone, achieving 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 research issues, especially in the micro-pore space. The occurrence and migration laws of fluids in micro- and nano-pore and micro-fracture systems are the focus and difficulty of research. Macroscopically, it needs to be matched with the well shut-in time, which has important engineering significance.

[0003] Existing volumetric fracturing followed by well shut-in techniques mainly rely on empirical methods, atmospheric pressure permeation, and wellhead pressure drop methods. Empirical methods have poor reliability and are limited in application in new blocks; atmospheric pressure permeation cannot accurately reflect the actual underground conditions and has a large deviation; and wellhead pressure drop methods cannot fully reflect the fluid absorption of the matrix. Summary of the Invention

[0004] This application provides a method for optimizing the well-keeping time after volumetric fracturing, aiming to solve the problem of inaccurate calculation of existing well-keeping time.

[0005] The technical solution of this application is:

[0006] A method for optimizing the post-fracturing well shut-in time in volumetric fracturing includes the following steps:

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

[0008] S2, Select the first core sample from the target layer;

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

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

[0011] S5, select the second core sample in the target layer, repeat the operations in steps S2 to S4, obtain 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 establish the fitting equations t1~(L, Sw) and t2~(L, Sw).

[0012] S6. Under actual well conditions, the average spacing of microfractures Lm and the actual formation saturation Swt are obtained. Substitute (Lm / 2, Swt) into the fitting equations 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 well stagnation time interval.

[0013] As one technical solution in this application, in step S1, the physical properties 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 one technical solution in this application, in step S2, a first core sample is selected in a direction parallel to the strata, and the diameter D, length L, and core porosity φ of the first core sample are measured.

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

[0016] As a technical solution in this 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. Under the condition of confining pressure P-Pp, the spontaneous permeation curve is measured, the spontaneous permeation 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 one technical solution in this application, the method for finding inflection points on the double logarithmic coordinate axis in step S4 includes the following steps:

[0018] Record the water absorption mass and time of the first core sample at a specified time interval △t, and use the water absorption mass and time of the core as the raw data;

[0019] Normalized data, converting the core water absorption mass M to the core water absorption mass per unit volume M0, the conversion formula is as follows: In the formula, M0 is the water absorption mass per unit volume of 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] Using time as the x-axis and the water absorption mass per unit volume of core as the y-axis, with a double logarithmic coordinate system, each data point was placed in the coordinate system, and the first and second inflection points of the first core sample were obtained through data fitting.

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

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

[0023] The beneficial effects of this application are:

[0024] This application provides a method for optimizing the post-fracturing shut-in time in volumetric fracturing. The method is simple, easy to operate, and highly reliable, enabling the estimation of the optimal shut-in time based on laboratory experiments, thus achieving the goal of optimizing the shut-in time. Furthermore, this application fully considers parameters such as underground confining pressure, initial water saturation, and core length, more accurately reflecting the actual underground conditions. It also considers fluid absorption under fractured conditions, effectively solving the problem of optimizing the reasonable shut-in time under volumetric fracturing conditions. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show...

[0026] Some embodiments of the application should not be considered as limiting the scope. For those skilled in the art, other related drawings can be obtained from these drawings without any inventive effort.

[0027] Figure 1 This is a schematic diagram of the method for optimizing the post-fracturing well shut-in time in volumetric fracturing, provided in an embodiment of this application.

[0028] Figure 2 This is a schematic diagram for determining the inflection point in an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can typically be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0031] Example:

[0032] Please refer to Figure 1 (Refer to) Figure 2 This application provides a method for optimizing the post-fracturing well shut-in time in volumetric fracturing, comprising the following steps:

[0033] S1, based on well logging interpretation, obtains the target layer's temperature T, initial water saturation Swi, formation stress P, and pore pressure Pp;

[0034] S2, Select the first core sample of the target layer, take samples parallel to the stratum, and measure the diameter D, length L and core porosity φ of the first core sample;

[0035] S3. Adjust the constant temperature chamber to the formation temperature T, dry the first core sample and measure its dry weight m1; place the dried first core sample and a beaker of water in a sealed device, place the sealed device in the constant temperature chamber, and measure the core weight m2 in real time, and 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 temperature T, the confining pressure is set to be the difference between formation pressure P and pore pressure Pp. The spontaneous permeation curve is measured under the condition of confining pressure (P-Pp). The spontaneous permeation curve is plotted on a double logarithmic coordinate axis, the inflection point is found, and the inflection point time t is recorded.

[0037] S5, Select the second core sample in the target layer. Select the second core sample in a direction parallel to the strata and measure the diameter D, length L and core porosity φ of the second core sample. Repeat the operation method in steps S2 to S4 to obtain the first inflection point time t1 and the second inflection point time t2 under different core length L and saturation Sw conditions of the second core sample. Establish the fitting equations t1~(L,Sw) and t2~(L,Sw).

[0038] S6. Under actual well conditions, estimate the average microfracture spacing Lm and the actual formation saturation Swt. 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 well-closing time interval, realizing the optimization of the well-closing time after volumetric fracturing.

[0039] Furthermore, in step S4, the method for finding inflection points on the logarithmic coordinate axes includes the following steps:

[0040] Record the water absorption mass and time of the core at specified time intervals Δt, and use the water absorption mass and time of the core as raw data;

[0041] Normalized data, converting water absorption mass M to water absorption mass M0 per unit volume of core, the conversion formula is as follows: In the formula, M0 is the water absorption mass per unit volume of 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] Using time as the x-axis and the mass of water absorbed per unit volume of core as the y-axis, and employing a double logarithmic coordinate system, the data points are placed in the coordinate system, and the first and second inflection points are obtained through data fitting.

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

[0044] In summary, this application provides a method for optimizing the post-fracturing shut-in time in volumetric fracturing. This method is simple, easy to operate, and highly reliable, enabling the estimation of the optimal shut-in time based on laboratory experiments, thus achieving the goal of shut-in time optimization. When applied to shale gas blocks, it demonstrates greater adaptability and practicality compared to conventional methods, effectively optimizing the shut-in time. Furthermore, this application fully considers parameters such as underground confining pressure, initial water saturation, and core length, more accurately reflecting the actual underground conditions. It also considers fluid absorption under fractured conditions, effectively solving the problem of optimizing the reasonable shut-in time under volumetric fracturing conditions.

[0045] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for optimizing the post-fracturing well shut-in time in volumetric fracturing, characterized in that, Includes the following steps: S1, obtain the physical properties of the target layer based on well logging interpretation; S2, Select the first core sample from the target layer; S3, calculate the water saturation of the first core sample, and proceed to the next step when the water saturation of the first core sample is equal to the original water saturation of the target layer; In step S3, the constant temperature chamber is adjusted to the formation temperature T, the first core sample is dried and the dry weight m1 is measured; the dried first core sample is placed in a sealed device together with a beaker of water, the sealed device is placed in the constant temperature chamber, and the weight m2 of the first core sample is measured in real time, and then the water saturation of the first core sample is calculated. S4, Measure the inflection point time t of the first core sample: Under temperature T, set the measuring confining pressure to the difference between formation pressure P and pore pressure Pp. Measure the spontaneous permeation curve under the condition of confining pressure P-Pp, plot the spontaneous permeation curve on a double logarithmic coordinate axis, find the inflection point, and record the inflection point time t of the first core sample. The method for finding inflection points on a log-log coordinate axis includes the following steps: Record the water absorption mass and time of the first core sample at a specified time interval △t, and use the water absorption mass and time of the core as the raw data; Normalized data, converting the core water absorption mass M to the core water absorption mass per unit volume M0, the conversion formula is as follows: In the formula, M0 is the water absorption mass per unit volume of 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. Using time as the x-axis and water absorption mass per unit volume of core as the y-axis, with a double logarithmic coordinate system, each data point was placed in the coordinate system, and the first and second inflection points of the first core sample were obtained by data fitting. S5, select the second core sample from the target layer, repeat the operations in steps S2 to S4, obtain 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 establish fitting equations for t1~(L, Sw) and t2~(L, Sw); in step S5, select the second core sample in a direction parallel to the strata, and measure the diameter D, length L and core porosity φ of the second core sample; S6. Under actual well conditions, the average spacing between microfractures Lm and the actual formation saturation Swt are obtained. Substitute (Lm / 2, Swt) into the fitting equations 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 well stagnation time interval.

2. The method for optimizing the well-keeping time after volumetric fracturing according to claim 1, characterized in that, In step S1, the physical properties 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-keeping time after volumetric fracturing according to claim 1, characterized in that, In step S2, the first core sample is selected in a direction parallel to the strata, and the diameter D, length L, and porosity φ of the first core sample are measured.

4. The method for optimizing the well-keeping time after volumetric fracturing according to claim 1, characterized in that, The time interval Δt is 1 second.

Images