Shale oil horizontal well support fracture width evaluation method

Abstract

The present application belongs to the technical field of oil and gas field development, and particularly relates to a shale oil horizontal well support fracture width evaluation method. The evaluation method comprises the following steps: obtaining formation parameters, filling into Saphir 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 differential pressure-pressure derivative double logarithmic scatter plot; performing history matching on the differential pressure-pressure derivative double logarithmic scatter plot to obtain a differential pressure-pressure derivative double logarithmic curve, determine a variable wellbore storage pressure drop and a total pressure drop, and calculate a required fracture volume according to a main fracture half length, a fracture height and a variable wellbore storage time to calculate a fracture width. The evaluation method can effectively utilize field measured data, and the predicted fracture width has high accuracy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas field development, and particularly relates to a shale oil horizontal well support fracture width evaluation method. BACKGROUND

[0002] Shale oil is a non-gaseous hydrocarbon that is in a free (containing condensate), adsorbed and dissolved (soluble in natural gas, casein and residual water) state and has exploration and development significance in the effective hydrocarbon generation shale formation series. China is rich in shale oil resources. With the deepening of shale oil and gas enrichment theory and the progress of exploration and development technology, shale oil has become a hot area for reserve growth in each oilfield area, so it is more important to carry out a series of related theoretical researches around shale oil. Due to different horizontal well trajectories and complex drilled formations, the ground stress distribution, fracture initiation and fracture extension law are very different from those of vertical wells. In the rock formation with natural fractures, the natural fractures can be connected by the horizontal well, and since the permeability of the natural fractures is much greater than that of the rock matrix, the pressure loss of the oil and gas flowing into the wellbore is reduced, forming a low-resistance oil transportation line to make the reservoir have industrial exploitation value.

[0003] When the surface production changes, due to the certain storage capacity of the wellbore and the certain compressibility of the fluid in the wellbore, the change of the bottom hole production lags behind the change of the surface production, and this phenomenon that the surface and underground production changes are not synchronized is called wellbore storage effect (abbreviated as well storage effect). For the wellbore filled with one-way fluid and the liquid level rising or falling, the wellbore storage coefficient is a constant. However, in many cases, the wellbore storage coefficient will change with time during the test, so it is a variable wellbore storage coefficient. The variable wellbore storage effect model in the well test interpretation software is shown in Figure 1

[0004] The commonly used fracture extension numerical model is divided into a planar fracture model (PFM) and an unconventional fracture extension model (UFM). The planar fracture model includes a wire mesh model and an equivalent fracture model, which can only simulate planar extension fractures, mainly simulates the extension of a simple fracture in fracturing to analyze and predict the size of the fracture formed by fracturing. The unconventional fracture extension model can simulate the fracturing fracture network according to the reservoir stress field, rock mechanics model and natural fracture distribution under true operation parameters.

[0005] ​According to these conventional fracturing simulation methods, the formation of a complex fracture network requires certain reservoir geological conditions (rock physics and stress field parameters, etc.), natural fracture distribution and suitable operation pressure (controlled by parameters such as discharge rate). That is, the formation of a complex fracture network in the reservoir by fracturing is caused by the intersection of artificial fractures and natural fractures, and the formation of a complex fracture network must be based on the existence of natural fractures and meet certain geological parameter and geostress parameter constraints, otherwise only a simple double-wing fracture can be formed.

[0006] The complex fracture network formed by the interaction of artificially induced fractures and natural fractures cannot be accurately reflected by the microseismic detection technology, and the specific form and parameters of the fractures cannot be obtained accurately, and there is still great blindness.

[0007] Fracture width plays an important role in fracture extension simulation and post-fracturing production capacity evaluation, but the existing fracture width calculation methods mainly focus on simulating and calculating fracture parameters based on certain conditions and assumptions in the pre-fracturing simulation stage, and lack of post-fracturing evaluation stage fracture width calculation and effective use of field measured data, so the accuracy of the predicted fracture width is low. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a shale oil horizontal well support fracture width evaluation method. The present application provides a method for calculating the support fracture width of a shale oil horizontal well by using a well test interpretation software to invert fracture data and using the formula of the present application, to make up for the shortcomings that the microseismic detection technology cannot reflect the specific form and parameters of the fractures and the existing fracture width calculation methods cannot fully utilize the field data. Moreover, the study of shale oil fracture characteristics provides geological information for the reservoir.

[0009] In order to achieve the above-mentioned purpose of the present application, the specific technical scheme adopted by the present application is as follows:

[0010] A shale oil horizontal well support fracture width evaluation method, comprising the following steps:

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

[0012] (2) Import pressure data and flow rate data into the diagnostic analysis model to obtain a pressure section history, a flow rate section history and a differential pressure-pressure derivative double logarithmic scatter plot;

[0013] (3) Perform history matching on the differential pressure-pressure derivative scatter plot to obtain a differential pressure-pressure derivative double logarithmic curve, and determine a variable well reservoir pressure drop ΔP and a total pressure drop ΔP 总 ;

[0014] (4) Calculate the support fracture volume according to the following formula:

[0015] Vf = C final (ΔP 总 - ΔP)

[0016] wherein V f is the proppant fracture volume, m 3 ; C final is the final well storage coefficient, m 3 / MPa; ΔP 总 is the total pressure drop, MPa;

[0017] (5) The proppant fracture width is obtained according to the following formula:

[0018]

[0019] wherein W f is the proppant fracture width, mm; V f is the proppant fracture volume, m 3 ; X f is the proppant fracture half-length, m; H f is the proppant fracture height, m.

[0020] Preferably, the formation parameters in step (1) include well radius, reservoir effective 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 imported pressure data and flow data in step (2) include: the flow history of the fracturing stage is generally obtained by dividing the total liquid volume by the fracturing time; the pressure after stopping the pump is generally obtained from the actual field data, and the flow history after stopping the pump is 0, corresponding to the generation of pressure segment history and flow segment history and differential pressure-pressure derivative double logarithmic scatter plot.

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

[0024] Specifically, the scatter plot is manually history matched, and in order to achieve the fitting, the size and direction of each parameter need to be adjusted. For example, increasing the wellbore storage coefficient, the unit slope straight line of the simulated pressure response moves to the right (or down); reducing the wellbore storage coefficient, the unit slope straight line moves to the left (or up). The parameters are constantly changed within a suitable range until the fitting is completed.

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

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

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

[0028] wherein C initual is the initial wellbore storage coefficient, and a is a constant representing the speed of the change of the wellbore storage coefficient.

[0029] Further preferably, the formula of the exponential change is:

[0030]

[0031] wherein C unitial is the initial wellbore storage coefficient, and a is a constant representing the speed of the change of the wellbore storage coefficient.

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

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

[0034] (1) The present application makes full use of the higher accuracy of the field construction data, and uses the characteristics of the Saphir software that the wellbore storage coefficient can be changed, and through the fitting of the Saphir to the original data (pressure history and flow history), the appropriate fracture characteristic parameter values are selected according to the fitting effect, and the differential pressure-pressure derivative double logarithmic curve is analyzed and generated. According to the method in the present application, the curve is analyzed, and the required fracture volume is calculated according to the main fracture half-length, the fracture height and the variable wellbore storage time, so as to calculate the main fracture width.

[0035] (2) The method for calculating the support fracture width of the shale oil horizontal well by using the formula of the present application makes up for the shortcomings that the microseismic detection technology cannot reflect the specific form and specific parameters of the fracture, and the existing fracture width calculation method cannot make full use of the field data. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is the Saphir variable wellbore storage model graph in Example 1;

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

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

[0039] Figure 4 is the fitting curve graph of the differential pressure-pressure derivative double logarithmic curve in Example 1;

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

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

[0042] Example 1

[0043] A shale oil horizontal well support fracture width evaluation method:

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

[0045] According to the field construction data, etc. Obtain the formation parameters required for fitting, well radius (unit: m), reservoir effective thickness (unit: m), rock compressibility (unit: MPa -1 ), porosity, reservoir top depth (unit: m); Fill the obtained parameters into Saphir. In this example, the well radius is set to 0.126 m, the reservoir effective thickness is 25 m, the rock compressibility is 3E-6 MPa -1 , the porosity is 0.06, the segment length is 90 m, enter the diagnostic model selection interface, and select the diagnostic analysis model.

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

[0047] The flow history of the fracturing stage is obtained by dividing the total liquid volume by the fracturing time; the pressure after stopping the pump is obtained from the actual field data, and the flow history after stopping the pump is 0, corresponding to the generated pressure segment history and flow segment history and differential pressure-pressure derivative double logarithmic scatter plot.

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

[0049] Manually fit the scatter plot, fix the well radius, reservoir effective thickness, rock compressibility, porosity and reservoir top depth of the reservoir model, and constantly change the wellbore storage coefficient C until the differential pressure-pressure derivative double logarithmic curve is fitted with the theoretical curve.

[0050] The change of the variable wellbore storage coefficient C varies greatly, and generally presents linear change and exponential change. The linear change of the double logarithmic curve C deviates from the 45° straight line, the pressure curve coincides with the double logarithmic curve at the beginning, and then gradually deviates from the double logarithmic curve, the faster the change rate of C, the higher the hump, and finally enters the 0.5 horizontal line. As shown in Figure 2 FIG. A in the middle. The initial wellbore storage coefficient decreases, the hump decreases, the concave portion moves to the right, and finally enters the 0.5 horizontal line, as shown in Figure 2 FIG. B in the middle. The derivative curve gradually deviates from the double logarithmic curve at the early stage, and is located below the double logarithmic curve. With the decrease of the change rate of C, the hump changes less and less obvious, and the concave degree decreases, and finally below the 0.5 horizontal line, as shown in Figure 3 FIG. A in the middle. The smaller the initial wellbore storage coefficient, the later the concave portion moves to the right and enters the 0.5 horizontal line, as shown in Figure 3 FIG. B in the middle.

[0051] The following is the formula for 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 representing the change rate of the wellbore storage coefficient.

[0054] The following is the formula for 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 representing the change rate of the wellbore storage coefficient.

[0057] (4) Determine the parameters required for calculating the fracture width.

[0058] According to the fitting results, read the corresponding data on the double logarithmic curve. According to the variable well storage time Delta_t, find the corresponding ordinate of the pressure drop curve on the coordinate axis, and the value is the variable well pressure drop ΔP, as shown in 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 , as shown in Figure 4 point B in the middle. Therefore, Delta_t is 80 seconds, ΔP is 2 MPa, and ΔP 总 is 6 MPa.

[0059] (5) Calculate the volume of propped fractures.

[0060] The volume of propped fractures 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, in MPa. Calculate the width of the support crack.

[0063] The final wellbore storage coefficient C obtained by fitting 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 fitted propped crack half-length, and the set propped crack height into the formula to obtain the propped crack width. In this example, the fitted propped crack half-length 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 ​​the 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 (unit: m), reservoir effective thickness (unit: m), rock compression coefficient (unit: MPa), etc. -1), porosity. Fill the parameters into Saphir. In this example, the well radius is set as 0.126 m, the reservoir effective thickness is 25 m, the rock compressibility is 3E-6 MPa -1 , the porosity is 0.06, and the segment length is 66 m.

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

[0075] Import the pressure history of the field in the main interface of Saphir, and set the flow rate history. The fracturing of this segment is 12633 seconds, the total liquid volume is -2281 m 3 / sec, the corresponding flow rate history is calculated, and the scatter plot is generated as shown in Figure 5 .

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

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

[0078] (4) Determine the parameters required for calculating the propped fracture width.

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

[0080] Table 1 Partial parameter table after Saphir fitting

[0081]

[0082] (5) Calculate the propped fracture volume. The following formula is used for calculation:

[0083] V f = C final (ΔP 总 -ΔP)

[0084] In the formula, V f is the propped fracture volume, m 3 ; C final is the final well storage coefficient, m 3 / MPa; ΔP 总Total pressure drop, MPa.

[0085] Final well storage coefficient C obtained from Saphir final 16 m 3 / MPa. ΔP obtained in step (4) is brought in 总 And ΔP, the support fracture volume is calculated to be 48 m 3 .

[0086] (6) Calculate the support fracture width. According to the following formula.

[0087]

[0088] In the formula, W f Support fracture width, mm; V f Support fracture volume, m 3 ; X f Support fracture half-length, m; H f Support fracture height, m.

[0089] The support fracture volume obtained in step (5) and the support fracture half-length and the set support fracture height obtained by fitting are brought into the formula to obtain the support fracture width of 9.6 mm.

[0090] The current leading fracture width calculation method can calculate the optimal fracture conductivity according to the fracture construction parameters, calculate the optimal fracture length, and finally obtain the optimal fracture width. The method of the application inverses the fracture parameters such as fracture length and conductivity by analyzing the construction parameters by using the well test interpretation software, thereby calculating the support fracture volume and further obtaining the support fracture width. The method can obtain more fracture parameters, and the accuracy is high by combining the software with the calculation formula.

[0091] The fracture length and conductivity can be obtained by inversion, and the support fracture height is further obtained by calculating the support fracture volume, and the support fracture width is predicted based on the well test interpretation method, and the fracture parameters including the fracture length and conductivity are inversely obtained by analyzing the construction parameters by using the well test interpretation software.

[0092] The above detailed description is a specific description of one of the feasible embodiments of the application, and this embodiment is not used to limit the patent scope of the application. Any equivalent implementation or change without departing from the application shall be included in the scope of the technical solutions of the application.

Claims

1. A method for evaluating the width of a horizontal well support fracture in shale oil, characterized in that, The method comprises the following steps: (1) obtaining formation parameters and filling them into Saphir to determine a diagnostic analysis model; (2) importing pressure data and flow data into the diagnostic analysis model to obtain a pressure section history, a flow section history and a differential pressure-pressure derivative double logarithmic scatter diagram; (3) The differential pressure-pressure derivative double logarithmic scatter diagram is historically fitted to obtain a differential pressure-pressure derivative double logarithmic curve, and a variable well reservoir pressure drop ΔP and a total pressure drop ΔP 总 ; (4) obtaining a support fracture volume according to the following formula: V f = C final (ΔP 总 -ΔP) where V f is the support fracture volume, m 3 ; C final is the final well storage coefficient, m 3 / MPa; ΔP 总 is the total pressure drop, MPa; (5) obtaining a support fracture width according to the following formula: where W f is the support fracture width, mm; V f is the support fracture volume, m 3 ; X f is the support fracture half-length, m; and H f is the support fracture height, m.

2. The method of claim 1, wherein, The formation parameters in step (1) include a well radius, a reservoir effective thickness, a rock compressibility, a porosity and a reservoir top depth.

3. The method of claim 1, wherein the method further comprises, The diagnostic analysis model in step (1) includes a well model and a boundary model.

4. The method of claim 1, wherein the method further comprises, The process of the history matching in step (3) includes fixing the well radius, the reservoir effective thickness, the rock compressibility, the porosity and the reservoir top depth of the reservoir model, constantly changing unknown parameter values until the differential pressure-pressure derivative double logarithmic curve and the theoretical curve are fitted, and the unknown parameters include a variable wellbore storage coefficient C, a variable wellbore storage time Delta_t, a support fracture half-length and a fracture number.

5. The method of claim 4, wherein, The change of the wellbore storage coefficient C includes linear change and exponential change.

6. The method of claim 5, wherein, The formula of the linear change is: C1 = C initial (1 + a / C initial ) where C initial is the initial wellbore storage coefficient, and a is a constant that characterizes how quickly the wellbore storage coefficient changes.

7. The method of claim 5, wherein, The formula of the exponential change is: where C initial is the initial wellbore storage coefficient, and a is a constant that characterizes how quickly the wellbore storage coefficient changes.

8. The method of claim 1, wherein the method further comprises, The determination method of the variable well storage pressure drop ΔP and the total pressure drop ΔP in step (3) includes: finding the vertical coordinate of the pressure difference-pressure derivative double logarithmic curve corresponding to the variable well storage time Delta_t on the coordinate axis as the variable well storage pressure drop ΔP; and the vertical coordinate value corresponding to the end of the pressure difference-pressure derivative double logarithmic curve as the total pressure drop ΔP 总 . 总 ​

Images