Optimization method for acid fracturing crack matching of fractured carbonate rock

Abstract

The invention discloses a fractured carbonate rock acid fracturing crack matching optimization method, which comprises the following steps: establishing a crack model suitable for stress-sensitive fractured carbonate rocks according to basic data of a carbonate rock stratum; acid fracturing parameters are selected according to the fracture model and stratum conditions; and performing simulation calculation on the crack model and the acid fracturing parameters by adopting a numerical coupling simulation method, and optimizing crack matching. By considering the stress sensitivity and reasonable selection of fracture parameters, the optimization method provided by the invention can help to realize the optimal matching of the fracture and the stratum, which means that the fracture can be better connected with the stratum, so that the effective permeability is increased, and the oil gas flowing capacity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum engineering, and particularly relates to an optimization method for the matching of acid fracturing cracks in fractured carbonate rocks. Background Art

[0002] Acid fracturing (acidizing fracturing) of fractured carbonate rocks means that under a pressure higher than the reservoir fracture pressure or the closure pressure of natural fractures, acid fluid is squeezed into the reservoir to form hydraulic fractures in the reservoir. At the same time, the acid fluid chemically reacts with the rock on the fracture wall, unevenly etching the fracture wall to form grooved or unevenly etched fractures, so that the fractures do not completely close after the construction, and finally form acid-etched fractures with a certain geometric size and conductivity to achieve the stimulation of oil and gas wells. It is a commonly used technology for enhancing the productivity of oil and gas reservoirs, mainly used for deep fractured carbonate reservoirs with well-developed natural fractures and relatively poor matrix storage and permeability capabilities.

[0003] During the acid fracturing process, a large amount of acid fluid leaks along natural fractures, but at the same time, it will also dissolve the natural fracture wall, increasing the width of natural fractures and improving the flow capacity of natural fractures during production. However, after the flow capacity of natural fractures is improved, additional requirements will be imposed on the flow capacity of the main fractures. And during the acid fracturing process, the conductivity and length of fractures are mainly affected by the acid injection rate and the amount of acid injection. Therefore, how to match the fracture conductivity under different acid injection rates and amounts of acid injection with the reservoir flow capacity considering the dissolution of natural fractures is one of the core problems in enhancing the productivity of oil and gas reservoirs.

[0004] Currently, the commonly used fracture parameter matching method generally sets the conductivity and length of acid fracturing fractures directly, and then calculates the production within a certain period of time to select ideal fracture parameters. However, in fractured carbonate reservoirs, the leakage of natural fractures will greatly weaken the etching of acid fluid on hydraulic fractures, making this method unreliable; and the stress sensitivity effect of natural fractures, the azimuth angle of hydraulic fractures, and seepage characteristics, etc. will all have a significant impact on the flow capacity of fractures. Moreover, the conductivity of acid-etched fractures will change as the fluid pressure in the fractures rapidly decreases and the effective closure stress rapidly increases during the production process. Therefore, the existing methods for optimizing the fracture matching during acid fracturing are unreliable. Summary of the Invention

[0005] The purpose of the present invention is to provide an optimization method for the matching of acid fracturing cracks in fractured carbonate rocks to solve the above technical problems.

[0006] To achieve the above purpose, the present invention provides an optimization method for the matching of acid fracturing cracks in fractured carbonate rocks, including:

[0007] Based on the basic data of carbonate rock formations, a fracture model suitable for stress-sensitive fractured carbonate rocks is established;

[0008] According to the fracture model and formation conditions, acid fracturing parameters are selected;

[0009] A numerical coupling simulation method is used to simulate and calculate the fracture model and the acid fracturing parameters to optimize the fracture matching.

[0010] The technical effects and advantages of the present invention:

[0011] 1. By considering stress sensitivity and the reasonable selection of fracture parameters, the optimization method provided by the present invention can help achieve the best match between fractures and the formation, which means that the fractures can be better connected to the formation, thereby increasing the effective permeability and improving the ability of oil and gas flow;

[0012] 2. By increasing the connectivity between fractures and the reservoir, the optimization method provided by the present invention can improve the permeability of carbonate rock reservoirs, increase the flow channels of oil and gas, thereby increasing the oil and gas production, which helps to maximize the potential of the reservoir and improve the production efficiency;

[0013] 3. The optimized fracture matching can reduce potential non-productive fractures and fractures that do not match the formation, reduce the risk of ineffective fracturing, can reduce the waste of energy, materials and human resources during the mining process, and reduce the mining cost;

[0014] 4. By optimizing the fracture matching, the acid fracturing technology can more effectively improve the productivity of carbonate rock reservoirs, obtain more oil and gas resources with higher production efficiency, achieve a more sustainable mining process, and improve the production efficiency.

[0015] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will become apparent from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained by the structures pointed out in the specification and the drawings. Brief Description of the Drawings

[0016] Figure 1 is a flowchart of an optimization method for acid fracturing fracture matching of fractured carbonate rocks;

[0017] Figure 2 is a schematic diagram of fracture discretization of line source solution;

[0018] Figure 3 is a diagram of an electronic device. Detailed Embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all 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.

[0020] It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limited conditions under which the present invention can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration, rather than used to limit the scope within which the present invention can be implemented. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope within which the present invention can be implemented.

[0021] The present invention discloses an optimization method for the matching of acid fracturing fractures in fractured carbonate rocks. The following will be combined with Figure 1 to explain this method in detail.

[0022] 1. According to the basic data of the carbonate rock formation, establish a fracture model suitable for stress-sensitive fractured carbonate rocks.

[0023] Specifically, it includes: collecting the basic data of the carbonate rock formation by using one or more of on-site drilling, core analysis, and seismic exploration; according to the basic data, comprehensively considering the elastic modulus, Poisson's ratio, fracture spacing, and fracture width to establish a fracture model suitable for stress-sensitive fractured carbonate rocks.

[0024] Among them, the basic data includes: rock properties, stress state, and pore structure.

[0025] Among them, the fracture model includes: a steady-state matrix system seepage model, an unsteady-state matrix system seepage model, a natural fracture model, and a hydraulic fracture seepage model. The model equations are specifically as follows:

[0026] The steady-state matrix system seepage model is:

[0027]

[0028]

[0029] In the formula, V D is the acid concentration; tD t is time; λ is the diffusion coefficient; p is the injection pressure; sc p0 is the standard pressure, unit Pa; q sc q is the production; T is the temperature, unit K; K i K is the permeability, unit m 2 ; h is the oil reservoir depth, unit m; T SC T0 is the temperature under standard conditions, unit K; V L V is the oil reservoir volume; ψ is the pseudopressure, unit Pa; p is the oil reservoir pressure, unit Pa;

[0030] The unsteady-state matrix system seepage model is:

[0031]

[0032] In the formula, Cr is the acid concentration in Laplace space, r D r is the radial distance, ψs is the pseudopressure in Laplace space, s is the Laplace variable;

[0033] The natural fracture model is:

[0034]

[0035] In the formula, r is the radial distance; μ i μ is the oil viscosity; C gi C is the compressibility, unit Pa -1 ; ψ0 is the pseudopressure in the original state; α is the permeability modulus parameter, unit s / Pa; γ is the sensitivity coefficient, unit Pa -1 ; φ is the porosity, %, t is the time;

[0036] The hydraulic fracture seepage model is:

[0037]

[0038] In the formula, pf is the fracture tip pressure, unit Pa, pw is the horizontal wellbore pressure, unit Pa, qf is the fracture production, unit sm 3 / s, μ is the viscosity, K F Kh is the hydraulic fracture permeability, unit m 2 , ω F ω is the horizontal fracture width, unit m, r w rw is the horizontal wellbore radius, unit m, x fl , x fr x is the length of the two wings, unit m, m represents the mth fracture.

[0039] 2. Select acid fracturing parameters according to the fracture model and formation conditions.

[0040] Specifically: Based on the established fracture model and formation conditions, select acid fracturing parameters to minimize the mismatch between the fracture and the formation while ensuring effective acidification.

[0041] Among them, the acid fracturing parameters include: acid concentration, injection rate, and injection pressure.

[0042] 3. Use the numerical coupling simulation method to simulate and calculate the fracture model and the acid fracturing parameters to optimize the fracture matching.

[0043] That is, use the numerical coupling simulation method to simulate and calculate the selected fracture model and acid fracturing parameters, and find the best matching optimization scheme through the acid fracturing parameters. Specifically: The method of numerical coupling simulation is as follows: First, couple the natural fracture model with two matrix system seepage models (the steady-state matrix system seepage model and the unsteady-state matrix system seepage model) to obtain the solution of the oil storage point source, and then substitute the point source solution of the oil reservoir into the hydraulic fracture to solve and obtain the line source solution. See if the geometric size expression of the hydraulic fracture can be obtained, and find the best matching optimization scheme by changing the parameters in the expression.

[0044] Among them, by integration, the line source solution generated by any microelement (x w , y w ) (as shown in Figure 2 ) at any point (x, y) in the formation is:

[0045]

[0046] In the formula, is the pseudo-pressure after perturbation transformation in the Laplace space, is the flow rate, K0 is the correction coefficient, f is the coupling function, R D is the distance from the microelement center to the formation, x D is the abscissa, y D is the ordinate, x wD is the abscissa of the microelement center, Y wD is the ordinate of the microelement center;

[0047] The coupling and solution of the steady-state and unsteady-state matrices with natural fractures are:

[0048]

[0049]

[0050]

[0051] In the formula, is the zero-order pseudo-pressure, is the point source flow rate;

[0052] Coupling and solution of hydraulic fractures and natural fractures:

[0053]

[0054]

[0055]

[0056] In the formula, F is the corresponding pressure of the fracture, in Pa, L τef is the reference length, in m, C FD is the storage coefficient of the fracture; x fld is the length of the left wing of the fracture, x frD is the length of the right wing of the fracture, x wD is the integration variable for integration on the fracture micro-element.

[0057] This method further includes experimental verification and adjustment: According to the numerical simulation results, design an experimental scheme for verification, and according to the experimental results, adjust the model and the above acid fracturing parameters, and repeat steps 2-3 to optimize the matching of acid fracturing fractures.

[0058] The present invention also provides an optimization device for the matching of acid fracturing fractures in fractured carbonate rocks, including:

[0059] A building unit, configured to build a fracture model adapted to stress-sensitive fractured carbonate rocks according to the basic data of the carbonate rock formation;

[0060] A selection unit, configured to select acid fracturing parameters according to the fracture model and formation conditions;

[0061] An optimization unit, configured to perform simulation calculations on the fracture model and the acid fracturing parameters by using a numerical coupling simulation method to optimize the fracture matching.

[0062] Since the content protected by this device is similar to the content protected by the above method, no more introduction will be made here. For details, please refer to the discussion part of the above method.

[0063] The present invention also provides a device, such as Figure 3As shown. The electronic device includes: at least one processor, at least one communication interface, at least one memory, and at least one communication bus; optionally, the communication interface may be the interface of a communication module, such as the interface of a GSM module; the processor may be a processor CPU, or a specific integrated circuit ASIC (Application Specific Integrated Circuit), or one or more integrated circuits configured to implement the embodiments of the present invention. The memory may include high-speed RAM memory and may also include non-volatile memory, such as at least one disk memory. Among them, the memory stores a program, and the processor calls the program stored in the memory to execute the method provided in the above embodiments of the present application.

[0064] Corresponding to the above method of the present application, the present application also provides a computer storage medium. The computer storage medium stores a computer program, and the computer program is run by a processor to execute the method provided in the above embodiments of the present application.

[0065] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optimization method for the matching of acid fracturing cracks in fractured carbonate rocks, characterized in that, Including: Based on the basic data of the carbonate rock formation, establish a fracture model suitable for stress-sensitive fractured carbonate rocks; Select acid fracturing parameters according to the fracture model and formation conditions; Use the numerical coupling simulation method to simulate and calculate the fracture model and the acid fracturing parameters to optimize the fracture matching.

2. The method according to claim 1, wherein The basic data includes: rock property data, stress state data, pore structure data.

3. The method according to claim 1, wherein Based on the basic data of the carbonate rock formation, establish a fracture model suitable for stress-sensitive fractured carbonate rocks, including: Obtain the factors affecting stress sensitivity; Based on the basic data of the carbonate rock formation and the factors affecting stress sensitivity, establish a fracture model suitable for stress-sensitive fractured carbonate rocks; Among them, the factors affecting stress sensitivity include: elastic modulus, Poisson's ratio, fracture spacing and fracture width.

4. The method according to claim 1, wherein The fracture model includes: steady-state matrix system seepage model, unsteady-state matrix system seepage model, natural fracture model and hydraulic fracture seepage model.

5. The method according to claim 4, wherein The formula of the steady-state matrix system seepage model is: Where, V D is the concentration of acid solution; t D is the time; λ is the diffusion coefficient; is the injection pressure; p sc is the standard pressure; q sc is the production rate; T is the temperature; K i is the permeability; h is the oil reservoir depth; T SC is the temperature under standard conditions; V L is the oil reservoir volume; is the pseudopressure; is the oil reservoir pressure.

6. The method according to claim 4, wherein The formula of the unsteady-state matrix system seepage model is: In the formula, is the acid concentration in the Laplace space; r D is the radial distance; is the pseudopressure in the Laplace space; s is the Laplace variable; λ is the diffusion coefficient; σ is the coefficient.

7. The method according to claim 4, characterized in that, The formula of the natural fracture model is: Wherein, is the pseudo-pressure; r is the radial distance; μ i is the viscosity of the oil body; C gi is the compressibility; is the pseudo-pressure under the original state; α is the permeability modulus parameter; γ is the sensitivity coefficient; φ is the porosity; t is the time; K i is the permeability; T SC is the temperature under standard conditions; p SC is the standard pressure; V is the volume.

8. The method according to claim 4, characterized in that, The formula of the hydraulic fracture seepage model is: Wherein, pf is the pressure at the crack tip; pw is the horizontal wellbore pressure; qf is the crack production; μ is the viscosity; K F is the hydraulic fracture permeability; ω F is the horizontal crack width; r w is the horizontal wellbore radius; x fl , x fr is the length of both wings; m represents the m-th crack; h is the oil reservoir depth.

9. The method according to claim 1, wherein The acid fracturing parameters include: acid concentration, injection rate, injection pressure.

10. The method according to claim 4, wherein Use the numerical coupling simulation method to simulate and calculate the fracture model and the acid fracturing parameters to optimize the fracture matching, including: Couple the natural fracture model with the steady-state matrix system seepage model and the unsteady-state matrix system seepage model to obtain the oil storage point source solution; Substitute the point source solution into the hydraulic fracture seepage model to solve, obtain the line source solution, and superimpose to obtain the hydraulic fracture geometric size expression; Optimize the fracture matching by changing the parameters in the hydraulic fracture geometric size expression.

11. The method according to claim 10, wherein The equation of the line source solution is: In the formula, is the pseudo-pressure after perturbation transformation in the Laplace space; is the flow rate; K0 is the correction coefficient; f is the coupling function; R D is the distance from the center of the micro-element to the formation; x D is the abscissa; y D is the ordinate; x wD is the abscissa of the center of the micro-element; Y wD is the ordinate of the center of the micro-element.

12. The method according to claim 10, wherein The formula for coupling and solving the natural fracture model with the steady-state matrix system seepage model and the unsteady-state matrix system seepage model is: In the formula, is the zero-order pseudo-pressure, is the point source flow rate, s is the Laplace variable, K0 is the correction coefficient, f is the coupling function, ω is the elastic storage ratio, σ is the coefficient; r D is the radial distance.

13. The method according to claim 10, wherein The formula for coupling and solving the hydraulic fracture model with the natural fracture model is: where F is the corresponding pressure of the fracture; L τef is the reference length; C FD is the storage coefficient of the fracture; x flD is the length of the left wing of the fracture; x frD is the length of the right wing of the fracture; x wD is the integration variable for the integration on the fracture micro-element; h is the oil storage depth; r w is the horizontal wellbore radius.

14. The method according to claim 1, characterized in that, Also including: Verify the optimized fracture matching.

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