Shale oil horizontal well support seam width evaluation method

Abstract

The invention belongs to the technical field of oil and gas field development, and particularly relates to a shale oil horizontal well supporting seam width evaluation method. The evaluation method comprises the following steps: acquiring stratum parameters, and filling the stratum parameters into a Sphir to determine a diagnostic analysis model; importing pressure data and flow data into the diagnostic analysis model to obtain a pressure section history, a flow section history and a pressure difference-pressure derivative double logarithmic scatter diagram; historical fitting is conducted on the pressure difference-pressure derivative double logarithmic scatter diagram, a pressure difference-pressure derivative double logarithmic curve is obtained, variable well storage pressure drop and total pressure drop are determined, and according to the main fracture half length, the fracture height and variable well shaft storage time, the needed fracture volume is calculated so that the fracture width can be calculated. According to the evaluation method, field actual measurement data can be effectively utilized, and the accuracy of the predicted seam width is high.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to a method for evaluating the width of a supporting fracture of a shale oil horizontal well. Background Art

[0002] Shale oil is a non-gaseous hydrocarbon that exists in the effective hydrocarbon-generating mudstone formation system in various forms such as free (including condensate), adsorbed and dissolved (soluble in natural gas, kerogen and residual water, etc.) and has exploration and development significance. my country is rich in shale oil resources. With the deepening of shale oil and gas enrichment theory and the advancement of exploration and development technology, shale oil has now become a hot spot for reserve growth in various oilfields. Therefore, it is more important to carry out a series of related theoretical studies around shale oil. Due to the different trajectories of horizontal wells and the complex formations encountered during drilling, the distribution of ground stress, fracture initiation, and fracture extension laws are very different from those of vertical wells. In addition, horizontal wells can connect natural fractures to each other in rock formations with natural fractures. Since the permeability of natural fractures is much greater than the permeability of rock matrix, the pressure loss of oil and gas flowing into the wellbore is reduced, forming an oil transmission line with very little resistance, making the oil reservoir have industrial exploitation value.

[0003] When the surface production changes, the change in bottom hole production lags behind the surface production change because the wellbore has a certain storage capacity and the fluid in the wellbore has a certain compressibility. This phenomenon of asynchronous changes in surface and underground production is called the wellbore reservoir effect (wellbore reservoir effect for short). For wells filled with unidirectional fluid and with rising or falling fluid levels in the wellbore, the wellbore reservoir coefficient is a constant. However, in many cases, the wellbore reservoir coefficient will change over time during the test, so it is a variable wellbore reservoir coefficient. The variable wellbore reservoir effect model in the well test interpretation software is as follows: Figure 1 shown.

[0004] Commonly used numerical models of fracture extension are divided into planar fracture model (PFM) and unconventional fracture extension model (UFM). Planar fracture model includes wire mesh model and equivalent fracture model, which can only simulate plane extension fractures, mainly simulating the extension of simple fractures by fracturing, so as to analyze and predict the scale of fractures formed by fracturing. Unconventional fracture extension model can simulate the fracture network of fracturing under real construction parameters according to reservoir stress field, rock mechanics model and natural fracture distribution.

[0005] According to these conventional fracturing simulation methods, the formation of complex fracture networks requires certain reservoir geological conditions (rock physics and stress field parameters, etc.), natural fracture distribution and appropriate construction pressure (controlled by displacement and other parameters). In other words, the formation of complex fracture networks in reservoirs is due to the interlacing of artificial fractures and natural fractures. The formation of complex fracture networks must be based on the existence of natural fractures and meet certain geological parameters and geostress parameter constraints, otherwise only simple double-wing fractures can be formed.

[0006] The complex fracture network formed by the interaction of artificially induced fractures and natural fractures cannot obtain relatively accurate results by using microseismic detection technology to reflect the specific morphology and fracture parameters of the fractures, and it is still very blind.

[0007] Fracture width plays an important role in fracture extension simulation and post-fracture capacity evaluation. However, the existing fracture width calculation methods mainly focus on establishing models based on assumptions under certain conditions in the pre-fracture simulation stage to simulate and calculate fracture parameters. However, there is a lack of calculation of fracture width in the post-fracture evaluation stage and a lack of effective use of field measured data. Therefore, the predicted fracture width is less accurate. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a method for evaluating the width of the supporting fracture of a shale oil horizontal well. The present invention provides a method for inverting fracture data using well test interpretation software and calculating the width of the supporting fracture of a shale oil horizontal well using the invented formula to make up for the shortcomings that the microseismic detection technology cannot reflect the specific morphology and specific parameters of the fracture and the existing fracture width calculation method cannot make full use of the field data. In addition, geological information is provided for the reservoir by studying the characteristics of shale oil fractures.

[0009] In order to achieve the above-mentioned purpose of the present invention, the specific technical solution adopted by the present invention is:

[0010] A method for evaluating the width of a shale oil horizontal well support seam comprises the following steps:

[0011] (1) Obtain formation parameters and enter them into Saphir to determine the diagnostic analysis model;

[0012] (2) Importing pressure data and flow data into the diagnostic analysis model to obtain the pressure segment history, flow segment history, and double logarithmic scatter plot of pressure difference-pressure derivative;

[0013] (3) Perform historical fitting on the pressure difference-pressure derivative scatter plot to obtain the pressure difference-pressure derivative double logarithmic curve to determine the variable well storage pressure drop ΔP and the total pressure drop ΔP 总 ;

[0014] (4) The propped crack volume is calculated according to the following formula:

[0015] Vf =C final (ΔP 总 -ΔP)

[0016] Among them, V f is the volume of the support joint, m 3 ; C final is the final well storage coefficient, m 3 / MPa;ΔP 总 is the total pressure drop, MPa;

[0017] (5) The width of the support crack is calculated according to the following formula:

[0018]

[0019] Among them, W f V is the width of the supporting crack, mm; f is the volume of the support joint, m 3 ;X f is the half length of the supporting crack, m; H f To support the crack height, m.

[0020] Preferably, the formation parameters in step (1) include well radius, effective reservoir thickness, rock compressibility, porosity and reservoir top depth.

[0021] Preferably, the diagnostic analysis model in step (1) includes a well model and a boundary model.

[0022] The pressure data and flow data imported in step (2) include: the flow history of the fracturing stage is generally obtained by dividing the fracturing time by the total liquid volume; the pressure after the pump is stopped is generally obtained by actual field data, and the flow history after the pump is stopped is 0, correspondingly generating a double logarithmic scatter plot of the pressure segment history and the flow segment history and the pressure difference-pressure derivative.

[0023] Preferably, the history fitting process in step (3) includes: fixing the well radius, effective reservoir thickness, rock compressibility, porosity and reservoir top depth of the reservoir model, and continuously changing the unknown parameter values ​​until the pressure difference-pressure derivative double logarithmic curve fits the theoretical curve; the unknown parameters include the variable wellbore storage coefficient C, the variable wellbore storage time Delta_t, the fracture half-length and the number of fractures.

[0024] Specifically, perform manual historical fitting on the scatter plot. In order to achieve fitting, it is necessary to clarify the size and direction of each parameter that needs to be adjusted. For example, if the wellbore reservoir coefficient is increased, the unit slope of the simulated pressure response will move to the right (or downward); if the wellbore reservoir coefficient is reduced, the unit slope will move to the left (or upward). Keep changing the parameters within the appropriate range until the fit is achieved.

[0025] Preferably, the change of the wellbore storage coefficient C includes linear change and exponential change.

[0026] Further preferably, the formula for the linear change is:

[0027] C1=C initial (1+a / C initial )

[0028] Among them, C initual is the initial wellbore storage coefficient, and a is a constant that characterizes the speed of change of the wellbore storage coefficient.

[0029] Further preferably, the formula for the index change is:

[0030]

[0031] Among them, C unitial is the initial wellbore storage coefficient, and a is a constant that characterizes the speed of change of the wellbore storage coefficient.

[0032] Preferably, in step (3), the variable well storage pressure drop ΔP and the total pressure drop ΔP 总 The determination method includes: finding the ordinate of the corresponding pressure difference-pressure derivative double logarithmic curve on the coordinate axis according to the variable well storage time Delta_t, and the value is the variable well storage pressure drop ΔP; the ordinate corresponding to the end of the curve is the total pressure drop ΔP 总 .

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Fully utilize the accuracy of on-site construction data, and utilize the feature of the variable wellbore storage coefficient in Saphir software to fit the original data (pressure history and flow history) through Saphir, select appropriate fracture characteristic parameter values ​​according to the fitting effect, and analyze the generated pressure difference-pressure derivative double logarithmic curve. According to the method in the present invention, the curve is analyzed, and the required fracture volume is calculated according to the main fracture half-length, fracture height, and variable wellbore storage time, thereby calculating the main fracture width.

[0035] (2) The method of using the invented formula to calculate the width of the supporting fracture of shale oil horizontal wells makes up for the shortcomings that the microseismic detection technology cannot reflect the specific shape and specific parameters of the fracture and the existing fracture width calculation method cannot fully utilize the field data. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the Saphir variable wellbore reservoir model diagram in Example 1;

[0037] Figure 2It is the pressure difference-pressure derivative double logarithmic curve and the linear change diagram of the derivative diagram in Example 1;

[0038] Figure 3 It is the pressure difference-pressure derivative double logarithmic curve and derivative graph exponential change graph in Example 1;

[0039] Figure 4 is the pressure difference-pressure derivative double logarithmic fitting curve diagram in Example 1;

[0040] Figure 5 is the Saphir pressure difference-pressure derivative double logarithmic scatter plot in Example 2;

[0041] Figure 6 It is the Saphir pressure difference-pressure derivative double logarithmic fitting curve graph in Example 2. DETAILED DESCRIPTION

[0042] Example 1

[0043] A method for evaluating the width of supporting fractures in shale oil horizontal wells:

[0044] (1) Obtain the formation parameters required for fitting and determine the diagnostic analysis model.

[0045] According to the on-site construction data, the formation parameters required for fitting are obtained, such as well radius (in m), effective reservoir thickness (in m), rock compression coefficient (in MPa). -1 ), porosity, reservoir top depth (in meters); enter the obtained parameters into Saphir. In this example, the well radius is set to 0.126m, the effective reservoir thickness is 25m, and the rock compression coefficient is 3E-6MPa -1 , porosity is 0.06, segment length is 90m, enter the diagnostic model selection interface, and select the diagnostic analysis model.

[0046] (2) Import pressure and flow data.

[0047] The flow history during the fracturing stage is obtained by dividing the fracturing time by the total liquid volume; the pressure after the pump is stopped is obtained from the actual field data, and the flow history after the pump is stopped is 0, correspondingly generating a double logarithmic scatter plot of the pressure segment history, the flow segment history and the pressure difference-pressure derivative.

[0048] (3) Modify some parameters to improve the double logarithmic curve.

[0049] Manual history fitting was performed on the scatter plot, with the well radius, effective reservoir thickness, rock compressibility, porosity and reservoir top depth of the reservoir model fixed, and the variable wellbore storage coefficient C continuously changed until the double logarithmic curve of pressure difference-pressure derivative fitted the theoretical curve.

[0050] The variation of variable wellbore storage coefficient C varies greatly, and roughly presents linear variation and exponential variation. The double logarithmic curve C shows a linear variation curve that deviates from the 45° straight line. The pressure curve coincides with the double logarithmic curve at the beginning, and then gradually moves away from the double logarithmic curve. The faster the C change deceleration rate, the higher the hump, and finally enters the 0.5 horizontal line. Figure 2 Figure A in the middle. The initial wellbore storage coefficient decreases, the hump decreases, the depression moves to the right, and finally enters the 0.5 horizontal line. Figure 2 Figure B. The derivative curve gradually deviates from the double logarithmic curve in the early stage and is located below the double logarithmic curve. As the rate of change of C decreases, the hump changes less and less obvious, and the degree of concavity decreases, eventually falling below the horizontal line of 0.5, as shown in Figure 2. Figure 3 Figure A in the middle. The smaller the initial wellbore storage coefficient, the lower depression moves to the right and enters the 0.5 horizontal line later. Figure 3 Middle Figure B.

[0051] The following is the formula for the linear change of the wellbore storage coefficient:

[0052] C1=C initial (1+a / C initial )

[0053] In the formula, C initial is the initial wellbore storage coefficient, and a is a constant that characterizes the speed of change of the wellbore storage coefficient.

[0054] The following is the formula for the exponential change of the wellbore storage coefficient:

[0055]

[0056] In the formula, C initial is the initial wellbore storage coefficient, and a is a constant that characterizes the speed of change of the wellbore storage coefficient.

[0057] (4) Determine the parameters required to calculate the seam width.

[0058] Read the corresponding data on the double logarithmic curve according to the fitting results. Find the ordinate of the corresponding pressure drop curve on the coordinate axis according to the variable well storage time Delta_t. This value is the variable well storage pressure drop ΔP, such as Figure 4 Point A in the middle. The ordinate corresponding to the end of the pressure drop curve is the total pressure drop ΔP 总 ,like Figure 4 Point B. Therefore, Delta_t is 80sec, ΔP is 2MPa, and ΔP 总 It is 6MPa.

[0059] (5) Calculate the volume of the supporting crack.

[0060] The propped crack volume is calculated according to the following formula:

[0061] V f=C final (ΔP 总 -ΔP)

[0062] Where V f is the volume of the support joint, m 3 ; C final is the final well storage coefficient, m 3 / MPa;ΔP 总 is the total pressure drop, MPa. Calculate the width of the support crack.

[0063] The final wellbore storage coefficient C final 10m 3 / MPa and the total pressure drop are substituted into the formula to obtain the propped crack volume of 40m 3 .

[0064] (6) Calculate the width of the support crack.

[0065] The width of the support crack is calculated according to the following formula:

[0066]

[0067] Where W f V is the width of the supporting crack, mm; f is the supporting crack volume, m 3 ;X f is the half length of the supporting crack, m; H f To support the crack height, m.

[0068] Substitute the propped crack volume obtained in step (5), the propped crack half-length obtained by fitting, and the set propped crack height into the formula to obtain the propped crack width. In this example, the propped crack half-length obtained by fitting is 100m, so the propped crack width is 8mm.

[0069] Example 2

[0070] This embodiment adopts the technical solution described in Example 1 and carries out practical application in the development of shale oil in the Fuxing area of ​​Sichuan Basin, as follows:

[0071] This embodiment adopts the "variable well reservoir + horizontal well + uniform medium + rectangular boundary" model and applies it to the second section of the Xingye 10-1HF well.

[0072] (1) Obtain the formation parameters required for fitting and determine the diagnostic analysis model.

[0073] According to the on-site construction data, the formation parameters required for fitting are obtained, such as well radius (in m), effective reservoir thickness (in m), rock compression coefficient (in MPa), etc. -1), porosity. Enter the obtained parameters into Saphir. In this example, the well radius is set to 0.126m, the effective reservoir thickness is 25m, and the rock compression coefficient is 3E-6MPa. -1 , porosity is 0.06 and section length is 66m.

[0074] (2) Import pressure and flow data.

[0075] Import the pressure history of the site in the main interface of Saphir and set the flow history. The fracturing time of this section is 12633 seconds, and the total liquid volume is -2281m 3 / sec, calculate the corresponding traffic history and generate a scatter plot such as Figure 5 shown.

[0076] (3) Modify some parameters to improve the double logarithmic curve.

[0077] Modify the double logarithmic curve generated by continuously adjusting the wellbore storage coefficient and wellbore storage time, fracture half-length, number of fractures, etc. In this example, the final wellbore storage coefficient is 0.25, the number of fractures is 190, the fracture half-length is 100m, and the conductivity is 120md.m. The obtained fitting image is as follows Figure 6 shown.

[0078] (4) Determine the parameters required to calculate the support joint width.

[0079] In this example, the pressure difference-pressure derivative double logarithmic curve is fitted, and the fitting process is consistent with Example 1. The partial parameter table after Saphir fitting is shown in Table 1, and the variable well storage time Delta_t obtained is 150 sec. Figure 6 As shown, when the horizontal axis is 150 seconds, the vertical axis of the curve is about 3MPa, which is the variable well storage pressure drop ΔP. The vertical axis corresponding to the end of the curve is about 6MPa, which is the total pressure drop ΔP 总 .

[0080] Table 1. Partial parameters after Saphir fitting

[0081]

[0082] (5) Calculate the volume of the support crack using the following formula:

[0083] V f =C final (ΔP 总 -ΔP)

[0084] Where V f is the volume of the support joint, m 3 ; C final is the final well storage coefficient, m 3 / MPa;ΔP 总is the total pressure drop, MPa.

[0085] The final well-reservoir coefficient C obtained by Saphir final 16m 3 / MPa. Substitute the ΔP obtained in step (4) into 总 and ΔP, the propped fracture volume is calculated to be 48m 3 .

[0086] (6) Calculate the width of the support crack using the following formula.

[0087]

[0088] Where W f V is the width of the supporting crack, mm; f is the supporting crack volume, m 3 ;X f is the half length of the supporting crack, m; H f To support the crack height, m.

[0089] Substituting the support crack volume obtained in step (5), the fitted support crack half-length and the set support crack height into the formula, the support crack width can be obtained as 9.6 mm.

[0090] The current cutting-edge fracture width calculation method can calculate the optimal fracture conductivity according to the fracture construction parameters, thereby calculating the optimal fracture length, and finally obtaining the optimal fracture width. The method of the present invention uses well test interpretation software to analyze the construction parameters, invert fracture parameters such as fracture length and conductivity, and thus calculate the supporting fracture volume and then obtain the supporting fracture width. This method can obtain more fracture parameters, and the combination of software and calculation formula has high accuracy.

[0091] The fracture length and conductivity can be obtained through fitting inversion, and the propped fracture volume is calculated first to obtain the propped fracture height. The propped fracture width is predicted based on the well test interpretation method. The construction parameters are analyzed using the well test interpretation software, and the fracture parameters including fracture length and conductivity are inverted.

[0092] The above detailed description is a specific description of one feasible embodiment of the present invention. The embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not deviate from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for evaluating the width of supporting fractures in shale oil horizontal wells, characterized in that: The following steps are involved: (1) Obtain formation parameters and enter them into Saphir to determine the diagnostic analysis model; (2) Importing pressure data and flow data into the diagnostic analysis model to obtain the pressure segment history, flow segment history, and double logarithmic scatter plot of pressure difference-pressure derivative; (3) Perform historical fitting on the double logarithmic scatter plot of pressure difference-pressure derivative to obtain the double logarithmic curve of pressure difference-pressure derivative and determine the variable well storage pressure drop ΔP and the total pressure drop ΔP 总 ; (4) The propped crack volume is calculated according to the following formula: V f =C final (ΔP 总 -ΔP) Among them, V f is the volume of the support joint, m 3 ; C final is the final well storage coefficient, m 3 / MPa;ΔP 总 is the total pressure drop, MPa; (5) The width of the support crack is calculated according to the following formula: Among them, W f V is the width of the supporting crack, mm; f is the volume of the support joint, m 3 ;X f is the half length of the supporting crack, m; H f To support the crack height, m.

2. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 1, characterized in that: The formation parameters in step (1) include well radius, effective reservoir thickness, rock compressibility, porosity and reservoir top depth.

3. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 1, characterized in that: The diagnostic analysis model in step (1) includes a well model and a boundary model.

4. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 1, characterized in that: The history fitting process in step (3) includes: fixing the well radius, effective reservoir thickness, rock compressibility, porosity and reservoir top depth of the reservoir model, and continuously changing the unknown parameter values ​​until the pressure difference-pressure derivative double logarithmic curve fits the theoretical curve; the unknown parameters include the variable wellbore storage coefficient C, the variable wellbore storage time Delta_t, the propped fracture half-length and the number of fractures.

5. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 4, characterized in that: The change of the wellbore storage coefficient C includes linear change and exponential change.

6. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 5, characterized in that: The formula for the linear change is: C1=C initial (1+a / C initial ) Among them, C initial is the initial wellbore storage coefficient, and a is a constant that characterizes the speed of change of the wellbore storage coefficient.

7. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 5, characterized in that: The formula for the exponential change is: Among them, C initial is the initial wellbore storage coefficient, and a is a constant that characterizes the speed of change of the wellbore storage coefficient.

8. The method for evaluating the width of supporting fractures of shale oil horizontal wells according to claim 1, characterized in that: The variable well storage pressure drop ΔP and the total pressure drop ΔP in step (3) 总 The determination method includes: according to the variable well storage time Delta_t, the ordinate of the corresponding pressure difference-pressure derivative double logarithmic curve on the coordinate axis is the variable well storage pressure drop ΔP; the ordinate value corresponding to the end of the pressure difference-pressure derivative double logarithmic curve is the total pressure drop ΔP 总 .

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