Method for predicting fracture length of multi-stage fractured horizontal well in shale gas reservoir based on elastic productivity

Abstract

The present application relates to the technical field of oilfield development, in particular to a method for predicting the fracture length of a multi-stage fractured horizontal well in a shale gas reservoir based on elastic productivity. The method comprises the following steps: Step 1, calculating the elastic productivity of a shale gas well; Step 2, drawing a curve of the elastic productivity versus the volume of fracturing fluid and the volume of fracturing fluid to obtain a fracturing transformation coefficient; Step 3, establishing a single-well numerical simulation model of a calibration well, fitting the production performance of the calibration well, and determining the fracture length of the calibration well as the calibrated fracture length; Step 4, establishing a correlation between the fracturing transformation volume and the fracture length, the width of the fracturing zone, and the height of the fracture; and Step 5, calculating the fracture length of any shale gas well under the same geological conditions. The present application quickly determines the fracture length of a multi-stage fractured horizontal well in a shale gas reservoir by means of shale gas well elastic productivity analysis and single-well numerical simulation analysis, thereby solving the technical problems of the prior art and having important significance for dynamic analysis and numerical simulation of shale gas reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, specifically to a method for predicting fracture length in horizontal wells with multi-stage fracturing in shale gas reservoirs based on elastic yield. Background Technology

[0002] Horizontal well multi-stage fracturing technology has been widely applied to shale gas reservoirs and has become an important means of effectively developing shale gas reservoirs. The effectiveness of hydraulic fracturing directly determines the production capacity of a shale gas reservoir. During the hydraulic fracturing process, various factors such as heterogeneous rock mechanical parameters, geostress conditions, natural fractures, and the fracturing pumping process influence the fracture distribution, resulting in significant uncertainty. Generally, the scale of hydraulic fracturing fractures can be identified using microseismic monitoring data; however, only a minority of wells undergo microseismic monitoring. For wells without microseismic monitoring, predicting the fracture distribution remains a challenge in shale gas reservoir production capacity analysis and performance forecasting.

[0003] Numerical simulation of shale gas reservoirs can fit the production dynamics of shale gas wells, analyze and evaluate the volume of fracturing stimulation, and obtain the fracturing fracture distribution parameters. However, due to the presence of multiple media in shale gas reservoir models, including matrix, natural fractures, and multiple hydraulic fractures, the geological model has a large grid size, resulting in a large computational load for shale gas reservoir numerical simulation. Detailed historical fitting is time-consuming, making it difficult to predict the fracturing fracture distribution parameters of shale gas wells. Summary of the Invention

[0004] The main objective of this invention is to provide a method for predicting fracture length in multi-stage fracturing horizontal wells of shale gas reservoirs based on elastic yield. This method rapidly determines the fracture length in multi-stage fracturing horizontal wells of shale gas reservoirs through two means: elastic yield analysis of shale gas wells and single-well numerical simulation analysis. It solves the aforementioned technical problems and is of great significance for carrying out dynamic analysis and numerical simulation of shale gas reservoirs.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] This invention provides a method for predicting fracture length in multi-stage fracturing horizontal wells of shale gas reservoirs based on elastic yield. The method includes the following steps:

[0007] Step 1: Calculate the elastic yield of the shale gas well;

[0008] Step 2: Plot the relationship curves between elastic yield and fracturing fluid volume to obtain the fracturing stimulation coefficient;

[0009] Step 3: Establish a numerical simulation model of the calibration well, fit the production dynamics of the calibration well, and determine the fracture length of the calibration well as the calibration fracture length.

[0010] Step 4: Establish the correlation between fracturing volume and fracturing fracture length, fracturing width, and fracturing fracture height;

[0011] Step 5: Calculate the fracture length of any shale gas well with the same geological conditions.

[0012] The above objectives can also be achieved through the following technical solutions:

[0013] In step 1, a relatively stable production period is selected for multi-stage fractured horizontal wells in shale gas reservoirs. Based on the ratio of cumulative gas production to pressure drop within the corresponding period, the elastic production rate of the shale gas well is calculated. The calculation formula is as follows:

[0014]

[0015] In the formula, T i Let be the elastic production rate of the i-th shale gas well, i = 1, ..., k, ..., n, 10 4 m 3 / MPa; q i,t2 ,q i,t1 The cumulative gas production of the i-th shale gas well at times t2 and t1 are respectively, i = 1, ..., k, ..., n, 10 4 m 3 ;p i,t2 ,p i,t1 Let t2 and t1 be the casing pressures at the wellhead of the i-th shale gas well, respectively, i = 1, ..., k, ..., n, in MPa.

[0016] In step 2, the fracturing stimulation coefficients, α and β, of shale gas wells with the same geological characteristics are obtained according to the regression formula; the regression formula satisfies the following linear relationship:

[0017] T i =αV i +β (2)

[0018] In the formula, T i Let be the elastic production rate of the i-th shale gas well, i = 1, ..., k, ..., n, 10 4 m 3 / MPa;V i Let m be the volume of fracturing fluid in the i-th shale gas well, i = 1, ..., k, ..., n, m 3 .

[0019] In step 3, any shale gas well with the same geological characteristics is selected as the calibration well. A single-well dual-medium numerical simulation model is established, and the fracture parameters of the segmented fracturing operation are finely adjusted to fit the production dynamics of the calibration well. The fracturing fracture length of the calibration well is obtained and denoted as the calibration fracture length L. k .

[0020] In step 4, the fracture network formed by fracturing is approximated as an ellipsoid, thus determining the correlation between the fracturing volume of shale gas wells and the fracturing fluid volume, fracture length, fracture width, and fracture height as follows:

[0021]

[0022] In the formula, V k L represents the volume of fracturing fluid in a shale gas well. k M represents the length of the fracturing fracture in a shale gas well. k N represents the sweep width of the fracturing fracture zone along the well trajectory of a shale gas well. k φ is the height of the fracturing fracture in a shale gas well. k denoted as the average porosity of the shale gas well; where the subscript k represents a parameter related to the calibration well.

[0023] In step 5, since shale gas wells with the same geological characteristics have the same fracturing stimulation coefficient, and given the known elastic yield, fracturing bandwidth, fracture height, and calibration fracture length of the calibrated well, the formula for calculating the fracturing fracture length is as follows:

[0024]

[0025] In the formula, L i Let M be the length of the fracturing fracture in the i-th shale gas well, i = 1, ..., k, ..., n, m; i Let N be the sweep width of the fracturing fracture zone along the well trajectory of the i-th shale gas well (from the fracturing operation report), i = 1, ..., k, ..., n, m; i Let φ be the fracture height (approximately the fracture layer thickness) of the i-th shale gas well, i = 1,…k,…n, m; i Let be the average porosity of the i-th shale gas well (from a geological research report), i = 1, ..., k, ..., n, dimensionless; where the subscript k is a parameter related to the calibrated well.

[0026] Compared with the prior art, the present invention has the following technical advantages:

[0027] This invention utilizes numerical simulations of shale gas calibration wells with typical geological characteristics to fit the production dynamics of these wells, thereby obtaining the calibrated fracture lengths. By leveraging the correlation between elastic yield and fracture distribution parameters in shale gas wells with similar geological characteristics, the fracture lengths of calibrated wells are used to calibrate the fracture lengths of shale gas wells with the same geological characteristics. This allows for the rapid determination of fracture lengths in multi-stage fractured horizontal wells within shale gas reservoirs without the need for large-scale numerical simulations, providing a research foundation for dynamic analysis and production capacity evaluation of shale gas reservoirs. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 This is a flowchart of a method for predicting fracture length in a horizontal well with multi-stage fracturing in shale gas reservoirs based on elastic yield, as described in an embodiment of the present invention.

[0030] Figure 2 This is a graph showing the relationship between the elastic yield of a shale gas well and the volume of fracturing fluid in one embodiment of the present invention.

[0031] Figure 3 The numerical simulation model of the calibration well is an embodiment of the present invention: A is the numerical simulation model of the calibration well in the main area, and B is the numerical simulation model of the calibration well in the fault zone.

[0032] Figure 4 This is a schematic diagram illustrating the fracture length, fracture zone width, and fracture height of a shale gas well according to an embodiment of the present invention. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0036] In step 101, a relatively stable production period for shale gas wells is selected, and the elastic production rate T of the shale gas well is calculated based on the ratio of cumulative gas production to pressure drop within the corresponding period. i Its calculation formula is

[0037]

[0038] In the formula, T i Let be the elastic production rate of the i-th shale gas well, i = 1, ..., k, ..., n, 10 4 m 3 / MPa; qi,t2 ,q i,t1 The cumulative gas production of the i-th shale gas well at times t2 and t1 are respectively, i = 1, ..., k, ..., n, 10 4 m 3 ;p i，t2 p i，t1 Let t2 and t1 be the casing pressures at the wellhead of the i-th shale gas well, respectively, i = 1, ..., k, ..., n, MPa.

[0039] Shale gas well production data and calculation results are shown in Table 1. The process proceeds to step 102.

[0040] Table 1

[0041]

[0042] In step 102, the relationship curve between the elastic yield and fracturing fluid volume of shale gas wells is plotted. Shale gas wells with similar geological characteristics show similar fracturing effects in each segment, and their elastic yield-fracturing fluid volume relationship curves are nearly linear. The fracturing coefficients for two shale gas wells with different geological characteristics are obtained using regression formulas, denoted as α1, β1 and α2, β2, respectively. In this example, wells under α1 and β1 conditions are located in the main development area of ​​the shale gas reservoir, where foliation fractures are well-developed. With these fractures connected, the fracturing network of fractures exhibits good connectivity. In this example, wells under α2 and β2 conditions are located in the periphery of the shale gas reservoir, where large-scale natural fractures are developed. With these larger-scale natural fractures connected, the fracturing fractures have good ductility, but poor inter-fracture communication, resulting in a less effective fracturing effect. The regression curves are shown below. Figure 2 The regression formula satisfies the following form:

[0043] T i =αV i +β (2)

[0044] In the formula, T i Let be the elastic yield of the i-th shale gas well, i = 1, ..., k, ..., n, 10 4 m 3 / MPa;V i Let m be the volume of fracturing fluid in the i-th shale gas well, i = 1, ..., k, ..., n, m 3 .

[0045] The process proceeds to step 103.

[0046] In step 103, one well from each of the two types of shale gas wells with different geological characteristics is selected as a calibration well. A single-well dual-medium numerical simulation model is established for each well. The fracture parameters from the staged fracturing operation are used as the initial fracture reference values. The fracturing fracture length is then fine-tuned to fit the production dynamics of the calibration well, and the calibration fracture length L of the calibration well is obtained. kThe calibration seam length of the main area calibration well is 260m, and the calibration seam length of the fault zone calibration well is 350m.

[0047] In step 104, the fracture network formed by fracturing is approximated as an ellipsoid, thus determining the correlation between the fracturing volume of the shale gas well and the fracturing fluid volume, fracture length, fracture width, and fracture height as follows:

[0048]

[0049] In the formula, V k L represents the volume of fracturing fluid in a shale gas well. k M represents the length of the fracturing fracture in a shale gas well. k N represents the sweep width of the fracturing fracture zone along the well trajectory of a shale gas well. k φ is the height of the fracturing fracture in a shale gas well. k denoted as the average porosity of the shale gas well; where the subscript k represents a parameter related to the calibration well.

[0050] Among them, the fracture half-fracture length, fracture bandwidth, and fracture height are as follows: Figure 4 As shown, the fracturing bandwidth data comes from the fracturing operation report, and the fracturing fracture height is approximately equal to the fracturing formation thickness, with relatively fixed parameters. The process proceeds to step 105.

[0051] In step 105, since shale gas wells with the same geological characteristics have the same fracturing stimulation coefficient, and given the elastic yield, fracturing sweep bandwidth, fracture height, and calibrated fracture length of the calibrated well, the fracture length of any shale gas well with the same geological characteristics can be obtained by simultaneously solving formulas (2) and (3). The calculation formula is as follows:

[0052]

[0053] In the formula, L i Let M be the length of the fracturing fracture in the i-th shale gas well, i = 1, ..., k, ..., n, m; i Let N be the sweep width of the fracturing fracture zone along the well trajectory of the i-th shale gas well (from the fracturing operation report), i = 1, ..., k, ..., n, m; i Let φ be the fracture height (approximately the fracture layer thickness) of the i-th shale gas well, i = 1,…k,…n, m; i Let be the average porosity of the i-th shale gas well (from a geological research report), i = 1, ..., k, ..., n, dimensionless; where the subscript k is a parameter related to the calibrated well.

[0054] The calculated fracture lengths for all shale gas wells are shown in Table 2. The process is now complete.

[0055] Table 2

[0056]

[0057] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for predicting fracture length in multi-stage fracturing horizontal wells of shale gas reservoirs based on elastic yield, characterized in that, The method includes the following steps: Step 1: Calculate the elastic yield of the shale gas well; Step 2: Plot the relationship curves between elastic yield and fracturing fluid volume to obtain the fracturing stimulation coefficient; Step 3: Establish a numerical simulation model of the calibration well, fit the production dynamics of the calibration well, and determine the fracture length of the calibration well as the calibration fracture length. Step 4: Establish the correlation between fracturing volume and fracturing fracture length, fracturing width, and fracturing fracture height; Step 5: Calculate the fracture length for any shale gas well with identical geological conditions. This includes: Since shale gas wells with the same geological characteristics have the same fracturing stimulation coefficient, and given the elastic yield, fracturing bandwidth, fracture height, and calibration fracture length of the calibrated well, the formula for calculating the fracture length is as follows: (4) in, Let be the length of the fracturing fracture in the i-th shale gas well. ,m; Let be the sweep width of the fracturing fracture zone along the well trajectory of the i-th shale gas well. ,m; Let be the fracture height of the i-th shale gas well. ,m; Let be the average porosity of the i-th shale gas well. , dimensionless; where the subscript k is a parameter related to the calibration well; These are the fracturing stimulation coefficients for shale gas wells with the same geological characteristics; Let be the elastic production rate of the i-th shale gas well. 10 4 m 3 / MPa; Let be the elastic production rate of the k-th shale gas well.

2. The method according to claim 1, characterized in that, In step 1, a relatively stable production period is selected for multi-stage fractured horizontal wells in shale gas reservoirs. Based on the ratio of cumulative gas production to pressure drop within the corresponding period, the elastic production rate of the shale gas well is calculated. The calculation formula is as follows: (1) In the formula, Let be the elastic production rate of the i-th shale gas well. 10 4 m 3 / MPa; The cumulative gas production of the i-th shale gas well at times t2 and t1 are respectively. 10 4 m 3 ; The wellhead casing pressures of the i-th shale gas well at times t2 and t1 are respectively. , MPa.

3. The method according to claim 1, characterized in that, In step 2, the fracturing stimulation coefficients for shale gas wells with the same geological characteristics are obtained according to the regression formula, which are respectively The regression formula satisfies the following linear relationship: (2) In the formula, Let be the elastic production rate of the i-th shale gas well. 10 4 m 3 / MPa; Let be the fracturing fluid volume of the i-th shale gas well. m 3 .

4. The method according to claim 1, characterized in that, In step 3, any shale gas well with the same geological characteristics is selected as the calibration well. A single-well dual-medium numerical simulation model is established, and the fracture parameters of the segmented fracturing operation are finely adjusted to fit the production dynamics of the calibration well. The fracturing fracture length of the calibration well is obtained and recorded as the calibration fracture length. .

5. The method according to claim 1, characterized in that, In step 4, the fracture network formed by fracturing is approximated as an ellipsoid, thus determining the correlation between the fracturing volume of shale gas wells and the length, width, and height of the fracturing fractures as follows: (3) In the formula, Volume for fracturing and stimulation of shale gas wells; This refers to the length of the fracturing fracture in a shale gas well. The sweep width of the fracturing fracture zone along the well trajectory of a shale gas well; This refers to the height of the fracturing fracture in a shale gas well. denoted as the average porosity of the shale gas well; where the subscript k represents a parameter related to the calibration well.

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