Fault-containing microfracture-large fracture coupling reservoir characterization method and system

Abstract

The invention provides a fault-containing microfracture-large fracture coupling reservoir characterization method and system, and the method comprises the following steps: carrying out the characterization of a microfracture of a target region, and obtaining a small-size grid; representing a large crack of the target area to obtain a medium-size grid; representing the fault of the target area to obtain a large-size grid; and coupling the small-size grid, the medium-size grid and the large-size grid to obtain a numerical model for representing the fault-containing micro-fracture-large-fracture coupled reservoir in the target area, so that the problem that the yield pressure of the complex development fractured low-porosity sandstone reservoir cannot be accurately simulated by the existing conventional fracture representation method is solved; and the production dynamic state is difficult to accurately predict.

Description

Technical Field

[0001] The invention belongs to the field of dynamic technology of oil and gas reservoir development, and in particular relates to a method and system for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults. Background Art

[0002] my country has large amounts of naturally fractured oil and gas reservoirs, which are widely distributed in major oil and gas basins such as the Sichuan Basin, Tarim Basin, Qaidam Basin and Ordos Basin. For example, the Gaoshiti-Moxi gas reservoir in the Sichuan Basin, the Dongping gas field in the Qaidam Basin and the main gas source for the West-East Gas Transmission Project - Kela 2 gas field, and the Keshen gas field in the Tarim Basin. The reservoirs of these gas fields all have more or less developed natural micro-fractures.

[0003] In recent years, unconventional oil and gas has gradually become an important force in increasing oil and gas reserves and production in my country. Unconventional oil and gas reservoirs have developed microcracks and faults. Microcracks are not only the storage space of oil and gas resources, but also the main oil and gas seepage channels. At the same time, some wells have been fracturing to form large cracks. These multi-scale cracks composed of microcracks and large cracks play a vital role in the development of the entire fractured oil and gas field.

[0004] Most fractured sandstone reservoirs have low matrix permeability, and microcracks and faults are well developed, resulting in complex seepage mechanisms. The complex fracture system formed by the coupling of microcracks, large fractures and faults is even more complex, making it difficult to accurately describe multi-scale fractures. At present, ultra-deep fractured tight sandstone gas reservoirs such as the Keshen gas field are relatively rare at home and abroad, and the research on well test characteristics is mainly focused on conventional fractured gas reservoirs. At present, the well test models of fractured reservoirs can be divided into two categories: continuous medium model and discrete fracture model. The continuous medium model is based on the continuous medium assumption, that is, it is assumed that there are two media, fractures and matrix, at any position in the reservoir. This type of model has two media, fractures and matrix. The actual reservoir microcracks show discrete and irregular characteristics. The fractures are different from the conventional continuous medium model in terms of length, opening and spacing, especially when the fractures are dispersed and the spacing is large. Therefore, continuous models such as dual medium models are not applicable. The discrete fracture model accurately describes the shape, orientation and conductivity of any fracture by explicitly processing the fractures. Therefore, this model has obvious advantages in processing fractured sandstone reservoirs.

[0005] At present, conventional fracture characterization methods are not sufficient to analyze the problems existing in complex fractured low-porosity sandstone reservoirs, resulting in the inability to accurately characterize the fractures of such reservoirs, the inability to accurately simulate the production pressure, and the difficulty in accurately predicting the production dynamics, which is disadvantageous to production, specifically manifested in:

[0006] (1) Microcracks are not only the storage space of oil and gas resources, but also the main oil and gas seepage channels. At the same time, some wells have been fracturing, forming large cracks. The multi-scale cracks composed of these microcracks and large cracks lead to complex seepage mechanisms;

[0007] (2) Micro-fractures, large fractures and faults form complex reservoirs. The traditional dual-porosity medium model is difficult to accurately characterize fractured reservoirs and is no longer applicable. Summary of the invention

[0008] The purpose of the present invention is to provide a method and system for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults, which solves the problems that the existing conventional fracture characterization methods cannot accurately simulate the production pressure of complex fractured low-porosity sandstone reservoirs and are difficult to accurately predict production dynamics.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] The present invention provides a method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults, comprising the following steps:

[0011] Characterize the microcracks in the target area and obtain a small-size grid;

[0012] Characterize the large cracks in the target area and obtain the medium-sized grid;

[0013] Characterize the faults in the target area and obtain a large-size grid;

[0014] The small-size grid, the medium-size grid and the large-size grid are coupled to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area.

[0015] Preferably, the microcracks in the target area are characterized to obtain a small-size grid, and the specific method is:

[0016] Determine the development density and strike distribution of microcracks in the target area, and use the Markov chain method to generate random crack distribution parameters that conform to the microcrack distribution characteristics;

[0017] The random crack distribution parameters are combined with the numerical discretization method to obtain a small-size grid for characterizing microcracks.

[0018] Preferably, large cracks in the target area are characterized to obtain a medium-sized grid, and the specific method is:

[0019] The conductivity of the half-length and orientation of large fractures is obtained based on actual mine data and fracturing data;

[0020] The conductivity of the half-length and azimuth of large fractures is combined with the deterministic fracture modeling method to establish a medium-sized grid to characterize large fractures.

[0021] Preferably, the faults in the target area are characterized to obtain a large-size grid, and the specific method is:

[0022] The fault orientation, size, and leakage capacity of the target area are obtained, and combined with the semi-permeability model, a large-size grid is established to characterize the fault.

[0023] Preferably, the small-size grid, the medium-size grid and the large-size grid are coupled to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area, and the specific method is:

[0024] The obtained small-size grid, medium-size grid and large-size grid are coupled with the two-point flux approximation method to establish a numerical model for characterizing the micro-fracture-large-fracture coupled reservoir containing faults.

[0025] Preferably, the microcracks are cracks with a length of 1 to 5 m; and the macrocracks are cracks with a length greater than 5 m.

[0026] A micro-fracture-macro-fracture coupled reservoir characterization system containing faults, comprising:

[0027] A microcrack characterization unit is used to characterize the microcracks in the target area and obtain a small-size grid;

[0028] Large crack characterization unit, used to characterize large cracks in the target area and obtain a medium-sized grid;

[0029] A fault characterization unit is used to characterize the faults in the target area and obtain a large-size grid;

[0030] The coupling unit is used to couple the small-size grid, the medium-size grid and the large-size grid to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area.

[0031] A computer-readable storage medium storing one or more programs, the one or more programs including instructions, which when executed by a computing device, cause the computing device to perform the method described.

[0032] A computing device comprises: one or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include steps for executing the method.

[0033] A chip, comprising: a memory having a computer program stored therein;

[0034] A processor is used to execute the computer program in the memory to implement the steps of the method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a method for characterizing a micro-fracture-large fracture coupled reservoir containing faults. First, characterization methods for micro-fractures, large fractures and faults are respectively established, a large fracture characterization method based on deterministic modeling and a fault characterization method based on a semi-permeable model are established, and then based on the numerical discretization of fractures, a Markov chain method is used to characterize the endpoints, length, azimuth, etc. of micro-fractures, and finally a method for characterizing a micro-fracture-large fracture coupled reservoir containing faults is formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of fault representation;

[0038] Figure 2 It is a schematic diagram of the large crack;

[0039] Figure 3 is a schematic diagram of microcracks;

[0040] Figure 4 It is a schematic diagram of a multi-scale fracture reservoir model with faults;

[0041] Figure 5 It is the development pattern of microfractures and faults in Keshen gas field;

[0042] Figure 6 is a schematic diagram of a computer device provided by an embodiment of the present invention;

[0043] Figure 7 A block diagram of a chip provided according to one embodiment of the present invention. DETAILED DESCRIPTION

[0044] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0045] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0046] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0047] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0048] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0049] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0050] Example 1

[0051] Fractured low-porosity sandstone reservoirs have relatively developed microcracks. Some wells form large cracks after acid fracturing or hydraulic fracturing. Large cracks easily form a complex fracture system with microcracks, and the reservoirs have developed faults. Therefore, accurately describing complex fractured reservoirs is the primary condition for subsequent research.

[0052] Therefore, the present embodiment provides a method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults, comprising the following steps:

[0053] Step 1: Fault characterization method based on semi-permeability model

[0054] According to the actual mine data corresponding to the target area, such as fault orientation and size, combined with the leakage capacity, a large-size grid that characterizes the fault is obtained according to the semi-permeable model, such as Figure 1 As shown, Q 2 =le·Q 1 , where Q2 is the flow out of the fault, Q 1 is the flow rate into the fault, and le is the leakage coefficient.

[0055] Step 2: Large crack characterization method based on deterministic modeling

[0056] According to the actual mine data and fracturing data corresponding to the target area, combined with the conductivity of the half-length and azimuth of the large fractures, a medium-sized grid for characterizing large fractures is established according to the deterministic fracture modeling method, such as Figure 2 shown.

[0057] Large cracks refer to cracks with a length greater than 5m.

[0058] Step 3: Microcrack Characterization

[0059] Based on the geological data of the target area, the density and strike distribution of microcracks in the target area are determined. Then, the random crack distribution parameters that meet the distribution characteristics of microcracks are generated by the Markov chain method. The obtained random crack distribution parameters are processed by the numerical discretization method to obtain a small-size grid to characterize the microcracks.

[0060] Microcracks refer to cracks with a length of 1 to 5 meters.

[0061] The Markov chain method is a statistical method used to obtain random samples from complex distributions. When the random samples are independent, the method that conforms to the law of large numbers can be used to obtain random numbers. However, the random samples are not independent of each other, so the Markov chain method is needed to obtain random numbers that conform to a certain probability distribution function. The steps to generate random numbers that conform to a probability distribution function using the Markov chain method are:

[0062] 1) Basic principles of Markov chain method

[0063] ①Construct Markov chain

[0064] The Markov chain assumes that the random variable X at the current moment t and the random variable X at the previous moment t-1 There is a functional relationship between them and only depends on X t-1 , which does not depend on the past random variables {X 0 ,X 1 ,...X t-2}. Define the one-step transition probability matrix P of the Markov chain:

[0065] P=P ij (X t+1 |X t ) (1)

[0066] Random variable X tThe k-step transition probability is:

[0067] P( k )=P k (2)

[0068] If the transfer probability matrix is ​​stable and no longer changes after multiple transfers, then a random sample that conforms to the corresponding stable probability distribution function is finally obtained, which is usually called a Markov chain stationary distribution.

[0069] ② Generate random numbers that obey the Markov chain stationary distribution

[0070] The method used to generate random numbers of a certain distribution is called sampling method. Combined with the Markov chain method, a stable distribution of random samples can be obtained. The following example introduces the direct sampling method of normal distribution. The probability density function of normal distribution is:

[0071]

[0072] Its distribution function:

[0073]

[0074] Get normal random numbers:

[0075]

[0076] Where x is a random number that follows a normal distribution; rand is a uniformly distributed random number in the interval [0,1].

[0077] Assume that the initial probability distribution is F 0 (x), the probability distribution after the first round of Markov chain transfer is F 1 (x), after n rounds, the Markov chain converges to obtain a stationary distribution F(x) that conforms to the normal distribution, and finally obtains a random number that conforms to the normal stationary distribution.

[0078] 2) Programming implementation of generating microcracks based on Markov chain method

[0079] Using the Markov chain method, a fracture geometry parameter model that conforms to the normal stationary distribution is randomly generated, including the initial fracture coordinates, fracture length and azimuth. A computer program based on the Markov chain method to achieve the normal stationary distribution was written in the MATLAB environment. The generated small-size grid is as follows Figure 3 shown.

[0080] Step 4: Generate a model to characterize a microfracture-macrofracture coupled reservoir with faults

[0081] The obtained small-size grid, medium-size grid and large-size grid are coupled with the two-point flux approximation method to establish a numerical model for characterizing the micro-fracture-large fracture coupled reservoir with faults, such as Figure 4 shown.

[0082] Example 2

[0083] This example is based on the actual project "Research on Well Test Interpretation and Productivity Evaluation Method of Fractured Low-Porosity Sandstone in Kuche" and is actually applied to the studied area. The matrix permeability of the fractured sandstone reservoir in Kuche is poor, micro-cracks are well developed, and the fracture distribution in some blocks is highly heterogeneous, and there are faults, which leads to complex seepage mechanism and difficulty in accurately describing the fractures (such as Figure 5 As shown in Figure 2, the existing well testing method based on homogeneous sandstone theory is difficult to reflect the true physical properties of the reservoir. The reservoir characterization method is the basis for establishing the well testing method. Therefore, establishing a fracture reservoir characterization method that couples large fractures, micro fractures and faults is the premise for establishing a well testing model.

[0084] This embodiment considers microfractures and uses numerical discretization to describe reservoir fractures; a multi-scale fracture reservoir characterization method of coupling large fractures, microfractures and faults is established based on a random fracture distribution method and a semi-permeability model, such as Figure 4 As shown, structured gridding technology is used to simulate the corresponding actual reservoir.

[0085] Example 3

[0086] This embodiment provides a micro-fracture-macro-fracture coupled reservoir characterization system containing faults, comprising:

[0087] A microcrack characterization unit is used to characterize the microcracks in the target area and obtain a small-size grid;

[0088] Large crack characterization unit, used to characterize large cracks in the target area and obtain a medium-sized grid;

[0089] A fault characterization unit is used to characterize the faults in the target area and obtain a large-size grid;

[0090] The coupling unit is used to couple the small-size grid, the medium-size grid and the large-size grid to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area.

[0091] Example 4

[0092] This embodiment provides a terminal device, which includes a processor and a memory, wherein the memory is used to store a computer program, wherein the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults.

[0093] Example 5

[0094] A schematic diagram of a computer device provided in this embodiment.

[0095] See also Figure 6 , the terminal device is a computer device. The computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When the computer program 63 is executed by the processor 61, the method for calculating the fluid composition in the reservoir transformation wellbore in the embodiment is implemented. To avoid repetition, it is not described one by one here. Alternatively, when the computer program 63 is executed by the processor 61, the functions of each model / unit in the system of embodiment 4 are implemented. To avoid repetition, it is not described one by one here.

[0096] The computer device 60 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will appreciate that Figure 6 This is only an example of the computer device 60 and does not constitute a limitation of the computer device 60. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0097] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0098] The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc., equipped on the computer device 60.

[0099] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.

[0100] Example 7

[0101] Figure 7 A block diagram of a chip provided in this embodiment.

[0102] See also Figure 7 , the terminal device is a chip, and the chip 600 of this embodiment includes a processor 622, which may be one or more, and a memory 632 for storing a computer program executable by the processor 622. The computer program stored in the memory 632 may include one or more modules, each corresponding to a set of instructions. In addition, the processor 622 may be configured to execute the computer program to perform the above-mentioned method for characterizing a microfracture-macrofracture coupled reservoir containing faults.

[0103] In addition, the chip 600 may further include a power supply component 626 and a communication component 650, wherein the power supply component 626 may be configured to perform power management of the chip 600, and the communication component 650 may be configured to implement communication, for example, wired or wireless communication, of the chip 600. In addition, the chip 600 may further include an input / output (I / O) interface 658. The chip 600 may operate based on an operating system stored in the memory 632.

[0104] Example 10

[0105] This embodiment also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and the extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory, or a non-volatile memory (Non-Volatile Memory), such as at least one disk memory.

[0106] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of a method for characterizing a microfracture-large fracture coupled reservoir containing faults in the above-mentioned embodiment; one or more instructions in the computer-readable storage medium are loaded and executed by a processor for a method for characterizing a microfracture-large fracture coupled reservoir containing faults described in Example 1.

[0107] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for characterizing a microfracture-macrofracture coupled reservoir containing faults, characterized in that: The following steps are involved: Characterize the microcracks in the target area and obtain a small-size grid; Characterize the large cracks in the target area and obtain the medium-sized grid; Characterize the faults in the target area and obtain a large-size grid; The small-size grid, the medium-size grid and the large-size grid are coupled to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area.

2. A method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults according to claim 1, characterized in that: Characterize the microcracks in the target area and obtain a small-size grid. The specific method is: Determine the development density and strike distribution of microcracks in the target area, and use the Markov chain method to generate random crack distribution parameters that conform to the microcrack distribution characteristics; The random crack distribution parameters are combined with the numerical discretization method to obtain a small-size grid for characterizing microcracks.

3. A method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults according to claim 1, characterized in that: Characterize the large cracks in the target area and obtain the medium-sized grid. The specific method is: The conductivity of the half-length and orientation of large fractures is obtained based on actual mine data and fracturing data; The conductivity of the half-length and azimuth of large fractures is combined with the deterministic fracture modeling method to establish a medium-sized grid to characterize large fractures.

4. A method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults according to claim 1, characterized in that: Characterize the faults in the target area and obtain a large-size grid. The specific method is: The fault orientation, size, and leakage capacity of the target area are obtained, and combined with the semi-permeability model, a large-size grid is established to characterize the fault.

5. The method for characterizing a micro-fracture-macro-fracture coupled reservoir containing faults according to claim 1, characterized in that: The small-size grid, the medium-size grid and the large-size grid are coupled to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area. The specific method is: The obtained small-size grid, medium-size grid and large-size grid are coupled with the two-point flux approximation method to establish a numerical model for characterizing the micro-fracture-large-fracture coupled reservoir containing faults.

6. A method for characterizing a microfracture-macrofracture coupled reservoir containing faults according to claim 1, characterized in that: The micro cracks are cracks with a length of 1 to 5 m; the large cracks are cracks with a length greater than 5 m.

7. A micro-fracture-macro-fracture coupled reservoir characterization system containing faults, characterized in that: include: A microcrack characterization unit is used to characterize the microcracks in the target area and obtain a small-size grid; Large crack characterization unit, used to characterize large cracks in the target area and obtain a medium-sized grid; A fault characterization unit is used to characterize the faults in the target area and obtain a large-size grid; The coupling unit is used to couple the small-size grid, the medium-size grid and the large-size grid to obtain a numerical model for characterizing the micro-fracture-macro-fracture coupled reservoir containing faults in the target area.

8. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions, which, when executed by a computing device, cause the computing device to perform the method of any one of claims 1 to 6.

9. A computing device, characterized in that include: One or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include steps for executing the method described in any one of claims 1 to 6.

10. A chip, characterized in that: a memory having a computer program stored thereon; A processor, configured to execute the computer program in the memory to implement the steps of the method according to any one of claims 1 to 6.

Images