Unconventional oil and gas reservoir multi-stratification interference pressing crack height control design method

Abstract

The invention relates to an unconventional oil and gas reservoir multi-stratification interference pressing crack height control design method, and belongs to the technical field of hydraulic fracturing in oil and gas reservoir yield increasing transformation. The invention discloses an unconventional oil and gas reservoir multi-stratification interference pressing fracture height control design method which comprises the steps that geological parameters of a target horizontal well are obtained, and fracturing fluid displacement is preliminarily designed according to a productivity target; the hydraulic fracturing process of the target horizontal well is calculated, and the fracture height is evaluated; the fracture height is compared with the expected control height, if the fracture height is larger than the expected control height, the fracturing fluid displacement or the hydraulic fracturing total time is reduced, and evaluation is conducted again till the evaluated fracture height is smaller than the expected control height; and performing hydraulic fracturing construction on the target horizontal well based on the updated fracturing fluid displacement or the hydraulic fracturing total time. According to the method, the influence of interlayer filtration loss and bedding tensile strength on crack propagation is comprehensively considered, the height size of the crack is effectively evaluated, and the method is used for optimizing the overall hydraulic fracturing effect.

Description

Technical Field

[0001] The present invention relates to a high-control design method for hydraulic fracture height under the interference of multiple bedding planes in unconventional oil and gas reservoirs, belonging to the technical field of hydraulic fracturing technology in the stimulation and transformation of oil and gas reservoirs. Background Art

[0002] As a key measure to improve the production of unconventional low-permeability oil and gas reservoirs, the hydraulic fracturing technology plays an important role in enhancing the oil and gas recovery rate. A large number of nearly horizontal bedding planes are developed in the reservoirs of unconventional oil and gas reservoirs such as shale gas reservoirs. These structural weak planes interfere with the vertical extension of hydraulic fractures and affect the final fracture height. Fracture height control is crucial for improving the fracturing stimulation effect: when multiple oil and gas layers are vertically distributed, it is necessary to appropriately increase the fracture height to connect multiple small layers to activate the production potential of multiple-layer reservoirs; while when the thickness of the oil and gas reservoir is low or there is bottom water, too large a fracture height will greatly damage the stimulation effect, so it is necessary to strictly control the fracture height.

[0003] At present, the control of fracture height mainly relies on parameter trial and error and optimization based on previous engineering experience, or fracture height prediction and parameter optimization based on conventional reservoir hydraulic fracturing simulation technology, and the prediction and control effect of fracture height is unstable. In this regard, there is an urgent need to construct a new technology for reasonable prediction and effective control of fracture height to help improve the hydraulic fracturing effect of unconventional oil and gas reservoirs. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-control design method for hydraulic fracture height under the interference of multiple bedding planes in unconventional oil and gas reservoirs in view of the problems existing in the prior art.

[0005] The technical solution provided by the present invention to solve the above technical problems is: a high-control design method for hydraulic fracture height under the interference of multiple bedding planes in unconventional oil and gas reservoirs, comprising the following steps: Step S10: Obtain the geological parameters of the target horizontal well, select the fracturing fluid according to the production target of the target horizontal well, and preliminarily set the construction parameters; Step S20: Calculate the hydraulic fracturing process of the target horizontal well based on the hydraulic fracturing model considering multiple bedding plane interferences, and evaluate the fracture height; Step S30: Compare the fracture height with the expected control height. If the fracture height is greater than the expected control height, reduce the fracturing fluid displacement or the total hydraulic fracturing time, and repeat steps S20 - S30 until the evaluated maximum fracture height is less than the expected control height, then proceed to the next step; Step S40: Perform hydraulic fracturing on the target horizontal well based on the updated construction parameters.

[0006] A further technical solution is that the geological parameters in step S10 include the Young's modulus of the reservoir rock E and the Poisson's ratio of the reservoir rockν , reservoir fracture toughness K IC-1 , minimum horizontal principal stress σ h , vertical stress σ v , bedding tensile strength T o , bedding fracture toughness K IC-2 , bedding thickness w r , bedding permeability k r , bedding density C k , equivalent filtrate loss coefficient C L .

[0007] A further technical solution is that the construction parameters in step S10 include the number of perforation clusters N , fracturing fluid viscosity μ , fracturing fluid density ρ f , fracturing fluid displacement q 0 and the total time of hydraulic fracturing T a .

[0008] A further technical solution is that the fluid pressure in the fracture obtained by calculating based on the hydraulic fracturing model considering multi-bedding interference in step S20 p f , fracture width w , fracture length l , fracture height h .

[0009] A further technical solution is that the calculation process in step S20 specifically includes: Step S21, calculate the fluid pressure in the hydraulic fracture according to the geological parameters, the current time and the set construction parameters; Step S22, calculate the width of the hydraulic fracture; Step S23, calculate the length of the hydraulic fracture; Step S24, calculate the stress intensity factor and the maximum principal stress at the upper and lower tips of the hydraulic fracture; Step S25, judge whether the fracture tip encounters bedding at the current moment according to the bedding density; When the fracture tip does not encounter bedding, compare the stress intensity factor at the fracture tip with the reservoir fracture toughness. If the expansion critical condition is reached, update the fracture height; if the expansion critical condition is not reached, the fracture height remains unchanged; When the crack tip encounters bedding, compare the stress intensity factor at the crack tip with the bedding fracture toughness. At the same time, compare the maximum principal stress at the crack tip with the bedding tensile strength. If the cross-bedding critical condition is reached, update the crack height. If the cross-bedding critical condition is not reached, the crack height remains unchanged. Step S26: If bedding is encountered, calculate the currently accumulated bedding filtration volume, and calculate and update the equivalent filtration coefficient based on the accumulated bedding filtration volume. Step S27: Based on the total hydraulic fracturing time T a and the cumulative fracturing time t to determine whether the fracturing construction is completed. If t < T a , it means that the fracturing construction has not ended. Update the cumulative fracturing time t to t +Δ t , and then repeat the calculation of S21~S27. If t ≥ T a , it means that the fracturing construction is completed, and the calculation ends and the final crack height is obtained.

[0010] A further technical solution is that the expansion critical condition in step S25 is: the crack stress intensity factor is greater than or equal to the reservoir fracture toughness.

[0011] A further technical solution is that the cross-bedding critical condition in step S25 is: the crack stress intensity factor is greater than or equal to the bedding fracture toughness, and at the same time the maximum principal stress at the crack tip is greater than or equal to the bedding tensile strength.

[0012] A further technical solution is that in step S25, the crack stress intensity factor is selected as the stress intensity factor at the upper tip or the lower tip of the crack according to the position of the crack tip in contact with the bedding.

[0013] The beneficial effects of the present invention: Based on the hydraulic fracturing simulation model considering multi-bedding interference, the stress intensity factor and the maximum principal stress at the tip of the hydraulic fracture during the fracturing process are calculated. The influence of interlayer filtration and bedding tensile strength on crack propagation is comprehensively considered, and the crack height size is effectively evaluated to optimize the overall effect of hydraulic fracturing. Description of the Drawings

[0014] Figure 1 is a calculation flow block diagram based on the hydraulic fracturing simulation model considering multi-bedding interference; Figure 2 is a three-dimensional drawing of the simulation calculation results of the multi-cluster crack size after the hydraulic fracturing is completed. Detailed Embodiments

[0015] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] As Figure 1 shown, a high-control design method for hydraulic fracturing under multi-layer bedding interference in unconventional oil and gas reservoirs provided by the present invention includes the following steps: Step S10: Obtain the geological parameters of the target horizontal well, select the fracturing fluid according to the production target of the target horizontal well, and preliminarily set the construction parameters; Among them, the geological parameters include the Young's modulus of the reservoir rock E , the Poisson's ratio of the reservoir rock ν , the reservoir thickness H , the fracture toughness of the reservoir K IC-1 , the minimum horizontal principal stress σ h , the vertical stress σ v , the tensile strength of the bedding T o , the fracture toughness of the bedding K IC-2 , the bedding thickness w r , the bedding permeability k r , the interlayer friction coefficient λ , the bedding density C k , the equivalent filtration loss coefficient C L .

[0017] The construction parameters include the number of perforation clusters N , the viscosity of the fracturing fluid μ , the density of the fracturing fluid ρ f , the displacement of the fracturing fluid q 0 and the total time of hydraulic fracturing T a .

[0018] Step S20: Simulate the hydraulic fracturing process of the target horizontal well based on the hydraulic fracturing model considering multi-layer bedding interference, and evaluate the fracture height: Initialize and set the cumulative fracturing time t = 0 s, the fracture encounter coefficient α = 0, the cumulative bedding filtration loss volume V leak = 0 m3 / s, number of encountered bedding planes M = 0. Then perform the following steps.

[0019] Step S21: Calculate the fluid pressure inside the hydraulic fracture based on geological parameters, cumulative fracturing time, and set construction parameters: (1) In the formula: p f is the fluid pressure inside the fracture, MPa; E’ is the plane strain modulus, MPa; q is the displacement of fracturing fluid per cluster, m 3 / s; μ is the viscosity of the fracturing fluid, Pa·s; C L is the equivalent filtration coefficient, m / s 0.5 ; h is the fracture height, m; t is the cumulative fracturing time, s.

[0020] Among them, the plane strain modulus is calculated according to formula (2): (2) In the formula: E is the Young's modulus, MPa; ν is the Poisson's ratio, dimensionless.

[0021] Among them, the displacement of fracturing fluid per cluster q is calculated according to formula (3): (3) In the formula: q 0 is the displacement of the fracturing fluid, m 3 / s; N is the number of perforation clusters, dimensionless.

[0022] Step S22: Calculate the width of the hydraulic fracture: (4) In the formula: w is the fracture width, m; q is the displacement of fracturing fluid per cluster, m 3 / s; E’ is the plane strain modulus, MPa; μ is the viscosity of the fracturing fluid, Pa·s; C L is the equivalent filtration coefficient, m / s 0.5 ; h is the fracture height, m; t is the cumulative fracturing time, s.

[0023] Step S23: Calculate the hydraulic fracture length: (5) In the formula: l is the fracture length, m; q is the displacement of the fracturing fluid per cluster, m 3 / s; C L is the equivalent filtration coefficient, m / s 0.5 ; h is the fracture height, m; t is the cumulative fracturing time, s.

[0024] Step S24: Calculate the stress intensity factors and the maximum principal stresses at the upper and lower tips of the hydraulic fracture: (6) In the formula: K Iu 、 K Il are the stress intensity factors at the upper and lower tips of the fracture respectively, MPa·m 1 / 2 ; h is the fracture height, m; p f is the fluid pressure in the fracture, MPa; σ h,n is the minimum horizontal principal stress at the upper tip of the fracture, MPa; σ h , i is the i layer of formation horizontal minimum stress, MPa; σ h , i+1 is the i +1 layer of formation horizontal minimum stress, MPa; ρ f is the fracturing fluid density, kg / m 3 ; h cp is the perforation height, m; h i is the distance from the lower tip of the fracture to the top of the i layer of formation, m; g is the acceleration of gravity.

[0025] For the upper fracture tip, let K I = K Iu ; For the lower fracture tip, let K I = KIl ; Then there is: (7) In the formula: σ zz and σ yy are the normal stresses in the vertical and horizontal directions at the tip of the hydraulic fracture, respectively, in MPa; τ zy is the shear stress in the tip region of the hydraulic fracture, in MPa; σ v and σ h are the vertical stress and the minimum horizontal principal stress at the tip of the hydraulic fracture, respectively, in MPa; r , θ are the coordinates in the polar coordinate system with the tip of the hydraulic fracture as the origin; K I are the stress intensity factors at the upper and lower tips of the fracture.

[0026] Then the maximum principal stress can be calculated by the following formula: (8) In the formula: σ zz and σ yy are the normal stresses in the vertical and horizontal directions at the tip of the hydraulic fracture, respectively, in MPa; τ zy is the shear stress in the tip region of the hydraulic fracture, in MPa; σ v and σ h are the vertical stress and the minimum horizontal principal stress at the tip of the hydraulic fracture, respectively, in MPa; σ 1 is the maximum principal stress, in MPa.

[0027] Step S25: Calculate the fracture encounter coefficient at the current moment according to the bedding density, and judge whether the fracture encounters the bedding at the current moment: (9) In the formula: α n is the fracture encounter coefficient at the current moment, dimensionless; α n-1 is the fracture encounter coefficient at the previous moment, dimensionless; Δ h is the fracture height growth step, in m; C k is the bedding density, 1 / m.

[0028] If the fracture encounter coefficient at the current moment < 1, it is judged that the fracture tip does not encounter the bedding. The stress intensity factors at the upper and lower tips of the fractureK I Compare with the reservoir fracture toughness K IC-1 If K I is greater than or equal to K IC-1 , then update the fracture height h n = h n-1 +Δ h If K I is less than K IC-1 , then the fracture height h remains unchanged.

[0029] If the fracture encounter coefficient at the current moment ≥ 1, then it is judged that the fracture tip encounters bedding. Compare the stress intensity factors at the upper and lower tips of the fracture K I with the bedding fracture toughness K IC-2 At the same time, compare the maximum principal stress at the fracture tip σ 1 with the bedding tensile strength T o ; If the fracture stress intensity factor K I is greater than or equal to the bedding fracture toughness K IC-2 , and the maximum principal stress at the fracture tip σ 1 is greater than or equal to the bedding tensile strength T o , then update the fracture height h n = h n-1 +Δ h ; Otherwise, the fracture height h remains unchanged. After that, set the fracture encounter coefficient α =0 again, and the number of beddings encountered at the current time M n = M n-1 +1.

[0030] Where h n is the fracture height at the current moment, h n-1 is the fracture height at the previous moment; M n is the number of beddings encountered at the current time; M n-1 is the number of beddings encountered at the previous moment; Step S26: If the crack tip encounters bedding, calculate the cumulative bedding filtration volume, and calculate and update the equivalent filtration coefficient based on the cumulative bedding filtration volume: (10) In the formula: V leak is the cumulative bedding filtration volume, m 3 ; M is the total number of encountered beddings, dimensionless; m is the number of the encountered bedding, dimensionless; k r is the bedding permeability, m 2 ; t 、 t 0 are the cumulative fracturing time and the bedding filtration time respectively, s; w r is the bedding thickness, m; l is the crack length, m.

[0031] (11) In the formula: C L is the equivalent filtration coefficient, m / s 0.5 ; V leak is the cumulative bedding filtration volume, m 3 ; t is the cumulative fracturing time, s; h is the crack height, m; l is the crack length, m.

[0032] Step S27: Based on the relationship between the total hydraulic fracturing time T a and the cumulative fracturing time t to determine whether the fracturing construction is completed.

[0033] If t < T a , it means that the fracturing construction has not ended, and update the cumulative fracturing time to t +Δ t , where Δ t is the time step, and then repeat steps S21 - S27; If t ≥ T a , it means that the fracturing construction is completed, calculate and obtain the final crack height h .

[0034] Step S30: Compare the crack height h with the expected control height h cCompare. If the fracture height is greater than the expected control height, reduce the fracturing fluid displacement by 5% or the total fracturing time by 10%, and repeat steps S20 - S30 until the evaluated fracture height is less than the expected control height.

[0035] Step S40: Conduct hydraulic fracturing on the target horizontal well based on the updated construction parameters.

[0036] Embodiment For the unconventional low - permeability horizontal well W2, use the method for controlling fracture height under multi - bedding interference in unconventional oil and gas reservoirs described in the present invention to conduct hydraulic fracturing. The engineering and geological data of well W2 are collected as shown in Table 1.

[0037] Table 1 Engineering and geological data of the first fracturing stage of the unconventional low - permeability horizontal well W2

[0038] Initialize and set the cumulative fracturing time as t = 0s, the fracture encounter coefficient α = 0, the cumulative bedding filtration volume V leak = 0m 3 / s, the number of encountered bedding M = 0. Set the simulation calculation time step as Δ t = 2s, Δ h = 0.1m, the expected control height h c = 30m.

[0039] Calculate according to steps S20 - S30. The final simulation results are shown in Figure 2 . The final fracture height h = 19.6m, lower than the expected control height h c . Therefore, the design of parameters such as the fracturing displacement and the total hydraulic fracturing time in Table 1 can effectively control the fracture height. Finally, complete the hydraulic fracturing construction operation of the target horizontal well according to the design parameters in Table 1.

[0040] As described above, it is not any form of limitation to the present invention. Although the present invention has been disclosed through the above - mentioned embodiments, it is not intended to limit the present invention. Any person skilled in the relevant art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to the above - disclosed technical content to form equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above - mentioned embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. An underpressure fracture high-control design method for unconventional oil and gas reservoirs under multi-layer bedding interference, characterized in that, It includes the following steps: Step S10: Obtain the geological parameters of the target horizontal well, select the fracturing fluid according to the productivity target of the target horizontal well, and preliminarily set the construction parameters; Step S20: Calculate the hydraulic fracturing process of the target horizontal well based on the hydraulic fracturing model considering multi-layer bedding interference, and evaluate the fracture height; Step S30: Compare the fracture height with the expected controlled height. If the fracture height is greater than the expected controlled height, reduce the fracturing fluid displacement or the total hydraulic fracturing time, and repeat steps S20 - S30 until the evaluated fracture height is less than the expected controlled height, then proceed to the next step; Step S40: Conduct hydraulic fracturing on the target horizontal well based on the updated construction parameters.

2. The high-control design method for hydraulic fracture in unconventional oil and gas reservoirs under multi-layer bedding interference according to claim 1, characterized in that The geological parameters include the Young's modulus of the reservoir rock E , the Poisson's ratio of the reservoir rock ν , the fracture toughness of the reservoir K IC-1 , the minimum horizontal principal stress σ h , the vertical stress σ v , the tensile strength of bedding T o , the fracture toughness of bedding K IC-2 , the bedding thickness w r , the bedding permeability k r , the bedding density C k , the equivalent filtration coefficient C L .

3. A high-control design method for hydraulic fracture in unconventional oil and gas reservoirs under multi-layer bedding interference according to claim 1, characterized in that, The construction parameters include the number of perforation clusters N , the perforation height h cp , the viscosity of the fracturing fluid μ , the density of the fracturing fluid ρ f , the displacement of the fracturing fluid q 0 and the total time of hydraulic fracturing T a .

4. A high-control design method for hydraulic fracture in unconventional oil and gas reservoirs under multi-layer interference, as claimed in claim 1, wherein The in - fracture fluid pressure calculated based on the hydraulic fracturing model considering multi - layer interference in step S20 p f , fracture width w , fracture length l , fracture height h .

5. A high-control design method for hydraulic fracture under the interference of multiple bedding planes in unconventional oil and gas reservoirs according to claim 1, characterized in that The simulation calculation process in step S20 specifically includes: Step S21: Calculate the fluid pressure inside the hydraulic fracture according to the geological parameters, the cumulative fracturing time, and the set construction parameters; Step S22: Calculate the width of the hydraulic fracture; Step S23: Calculate the length of the hydraulic fracture; Step S24: Calculate the stress intensity factors at the upper and lower tips of the hydraulic fracture and the stress in the tip region of the hydraulic fracture; Step S25: Calculate the fracture encounter coefficient according to the bedding density, and judge whether the fracture encounters bedding at the current moment; When the fracture tip does not encounter bedding, compare the fracture tip stress intensity factor with the reservoir fracture toughness. If the expansion critical condition is reached, update the fracture height; if the expansion critical condition is not reached, the fracture height remains unchanged; When the fracture tip encounters bedding, compare the fracture tip stress intensity factor with the bedding fracture toughness, and at the same time, compare the maximum principal stress at the fracture tip with the bedding tensile strength; if the cross - layer critical condition is reached, update the fracture height; if the cross - layer critical condition is not reached, the fracture height remains unchanged; Step S26: If bedding is encountered, calculate the currently accumulated bedding filtration volume, and calculate and update the equivalent filtration coefficient according to the accumulated bedding filtration volume; Step S27, based on the total hydraulic fracturing time T a and the cumulative fracturing time t to determine whether the fracturing construction is completed: If t < T a , it indicates that the fracturing operation has not ended, and update the cumulative fracturing time t as t +Δ t , and then repeat the calculation of S21~S27; If t ≥ T a , it indicates that the fracturing operation is completed, the calculation is completed, and the final fracture height is obtained.

6. A high-control design method for hydraulic fracture in unconventional oil and gas reservoirs under multi-layer bedding interference according to claim 5, characterized in that, The expansion critical condition in step S25 is: the fracture stress intensity factor is greater than or equal to the reservoir fracture toughness.

7. A high-control design method for hydraulic fracture in unconventional oil and gas reservoirs under multi-layer interference, according to claim 5, characterized in that The cross - layer critical condition in step S25 is: the fracture stress intensity factor is greater than or equal to the bedding fracture toughness, and at the same time, the maximum principal stress at the fracture tip is greater than or equal to the bedding tensile strength.

8. A high-control design method for hydraulic fracture in unconventional oil and gas reservoirs under multi-layer bedding interference according to claim 5, characterized in that In step S25, the fracture stress intensity factor selected according to the position of the fracture tip in contact with the bedding is the stress intensity factor of the upper tip of the fracture or the stress intensity factor of the lower tip of the fracture.

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