Fracture-cavity group reservoir acid fracturing evaluation method and system based on acid fracturing pump stop pressure drop model

Abstract

The invention provides a fracture-cavity group reservoir acid fracturing evaluation method and system based on an acid fracturing pump stop pressure drop model, and the method comprises the steps: building a reservoir acid fracturing pump stop pressure drop model through analyzing the fluid parameters of a complex fracture small-cavity group system formed by acid fracturing, and carrying out the sensitivity analysis of the sensitive parameters affecting the pressure; reservoir parameters and fracture parameters are introduced, and dynamic bottom hole pressure data of a set scene after pump stopping under different sensitive parameters are simulated through the pump stopping pressure drop model; performing double logarithmic characteristic curve analysis, and fitting actual pressure change curves of different fluid flow scenes of the fracture-cavity group; and the pumping stop pressure drop model is utilized to invert data representing the fracture key parameters of the reservoir to be evaluated, the cave group scale and the fracture-cave communication degree, and then the acid fracturing effect is evaluated. By adopting the scheme, the problems of insufficient practicability and inaccurate analysis result in the prior art are solved, and the communication effect between the complex crack formed by acid fracturing and the fracture-cavity group is accurately identified.

Description

Technical Field

[0001] The invention relates to the technical field of acid fracturing for oil and gas field development, and in particular to a fracture-cavity reservoir acid fracturing evaluation method and system based on an acid fracturing pump stop pressure drop model. Background Art

[0002] The carbonate karst fracture-vuggy reservoirs have the characteristics of different reservoir space scales, large structural changes, and strong heterogeneity. With the continuous deepening of oilfield development, the large-scale fracture-vuggy reservoirs of carbonate karst fracture-vuggy type are increasingly utilized, and the development targets are gradually shifting from large-scale single fractures and caves to small-scale continuous fracture-vuggy aggregates. In addition, in field production practice, it was found that some wells have high cumulative production, indicating that although the individual small fractures and caves are small in size, they are numerous and interconnected through faults, cracks, and dissolution channels, forming interconnected small fracture-vuggy groups with a large overall scale and huge exploration and development potential. Therefore, it is particularly important to carry out research on the identification of small-scale fracture-vuggy groups to further deepen the development of such reservoirs.

[0003] However, there are many problems such as weak research foundation and less previous relevant data and research on small fracture-cavity reservoirs, which bring great challenges to the development of small fracture-cavity group carbonate reservoirs. There are some methods for identifying reservoirs and acid fracturing analysis in the existing technology, but the pressure drop model used in carbonate fracturing construction is relatively simple and simplified, without considering the characteristics of multiple clusters of complex fractures and viscosity-temperature changes of fracturing fluids, and unable to explain the parameters of primary and secondary fractures and the communication mode of fracture-cavity groups. There are problems of insufficient practicality and inaccurate analysis results.

[0004] The information disclosed in the background technology section of the present invention is only intended to deepen the understanding of the general background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0005] To solve the above problems, the present invention provides a fracture-cavity reservoir acid fracturing evaluation method based on an acid fracturing pump-off pressure drop model. In one embodiment, the method comprises:

[0006] The steps of constructing the medium model are as follows: Based on the terrain characteristics and the set geological model simplification principles, combined with the simulation of reservoir connectivity and distribution characteristics, a multi-scale fracture-cavity-matrix discrete medium model representing the fracture-cavity geological system is constructed;

[0007] Steps for establishing the pump-off pressure drop model: Based on different types of multi-scale fracture-cavern-matrix discrete medium models, the fluid parameters of the fracture-cavern geological system formed by acid fracturing are analyzed, and the pump-off pressure drop model for carbonate reservoir acid fracturing is established based on the combination of reservoir parameters and acid fracturing fracture parameters;

[0008] Sensitive parameter analysis steps: by conducting sensitivity analysis on the established carbonate reservoir acid fracturing pump-off pressure drop model, determine the sensitive parameters whose influence on pressure change meets the set conditions;

[0009] Dynamic simulation steps: introduce the reservoir parameters and acid fracturing fracture parameters of the current part of the reservoir, and use the established carbonate reservoir acid fracturing pump stop pressure drop model to simulate the dynamic bottom hole pressure data under different sensitive parameters after pump stop and the dynamic closure scenario of the fracture;

[0010] Pressure change fitting step: Perform double logarithmic characteristic curve analysis on the dynamic bottom hole pressure obtained by simulation, and fit the dynamic bottom hole pressure change curve to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity geological system;

[0011] Parameter inversion steps: Based on the fitted dynamic pressure data, the carbonate reservoir acid fracturing pump-off pressure drop model corresponding to the fluid flow scenario is used to invert the data representing the key parameters of the reservoir fractures to be evaluated, the scale of the cave group, and the degree of fracture-cave communication;

[0012] Steps for determining the evaluation results: Analyze the key parameters of the reservoir fractures, the size of the cave group and the degree of fracture-cavity communication to determine the acid fracturing effect evaluation results.

[0013] In a preferred embodiment, in the medium model construction step, the zone with densely developed fractures and pores is simplified into a karst reservoir, and the fracturing fracture system is simplified into a high-permeability connected zone. The high-permeability connected zone connects the randomly distributed small cave group reservoirs, and a multi-scale fracture-cave-matrix discrete medium model is established as a complex fracture-discrete small cave group system formed by acid fracturing.

[0014] Further, in one embodiment, the step of establishing a pump stopping and pressure reducing model includes:

[0015] The steps of cave group fluid characterization are as follows: Use the seepage relationship and Nevi-Stokes pipe flow theory to analyze the fluid parameters of different fluid flow scenarios in the fracture-cavity geological system formed by acid fracturing;

[0016] The computational model establishment step is to establish a carbonate reservoir acid fracturing pump stop pressure drop model for wellbore-complex fracture-cavern coupling based on the fluid parameters combined with reservoir parameters and acid fracturing fracture parameters.

[0017] Optionally, in one embodiment, in the cave group fluid characterization step, for different fluid flow scenarios of the fracture-cave group geological system, the fluid parameters analyzed using the seepage relationship and the Nevi-Stokes pipe flow theory include: the exchange mechanism and flow law of the fluid in the system between different media in small caves and multi-scale fractures.

[0018] Furthermore, in one embodiment, in the computational model establishment step, the reservoir parameters include: reservoir physical property parameters, horizontal well length and cave group distribution location; the acid fracturing fracture parameters include: fracturing fluid parameters, the number of primary fractures, the number of secondary fractures and primary / secondary fracture lengths.

[0019] Preferably, in one embodiment, in the computational model establishment step, the carbonate reservoir acid fracturing pump stop pressure drop model includes a plurality of computational equations, and the computational equations include a multi-object material conservation model of a fracture-cavity geological system, a karst cave flow pattern model, a fluid filtration mechanism model, and a crossflow mechanism model;

[0020] The multi-object material conservation model in the operation equation includes a fracture material conservation equation and a cave material conservation equation; the fracture material conservation equation includes a primary fracture material conservation equation and a secondary fracture material conservation equation.

[0021] Furthermore, in one embodiment, in the dynamic simulation step, the equations of the carbonate reservoir acid fracturing pump-off pressure drop model are discretized using the finite difference method and the semi-implicit method, the coefficient matrix of the equation group is obtained, the equations are solved and calculated using the LU decomposition method, and the horizontal well pressure at the required time is calculated based on the time step.

[0022] Optionally, in one embodiment, in the pressure change fitting step, a construction pressure drop characteristic chart under different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities is drawn based on the solved pressure data, and the flow state change is identified in combination with the change in the slope of the double logarithmic diagnostic curve. The dynamic bottom hole pressure change curve is fitted to determine the dynamic pressure data corresponding to different fluid flow scenarios of the overall fracture-cavity geological system.

[0023] In a preferred embodiment, the data characterizing the current key parameters of reservoir fractures, cave group size and fracture-cavity communication degree include: reservoir formation permeability, multi-cavity location, multi-cavity volume, cave storage constant, fracture half-length, and fracture volume parameters.

[0024] Based on the application aspects of the method described in any one or more of the above embodiments, the present invention also provides an acid fracturing evaluation system for fracture-cavity reservoirs based on an acid fracturing pump-off pressure drop model, which executes the method described in any one or more of the above embodiments.

[0025] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0026] The present invention provides a fracture-cavity group reservoir acid fracturing evaluation method and system based on an acid fracturing pump-off pressure drop model. The method establishes a reservoir acid fracturing pump-off pressure drop model by analyzing the fluid parameters of a complex fracture-cavity group system formed by acid fracturing; based on the multi-scale fracture-cavity characteristics of carbonate rock volume acid fracturing, the complex fracture-discrete small cave group system formed by acid fracturing is simplified into a discrete medium physical model, and the seepage relationship and Nevi-Stokes pipe flow theory are used to reliably characterize the fluid exchange mechanism and flow law between different media in small caves and multi-scale fractures;

[0027] After conducting sensitivity analysis on the sensitive parameters that affect pressure, reservoir parameters and fracture parameters are introduced, and the pump-off pressure drop model is used to simulate the dynamic bottom hole pressure data of the set scene after pump-off under different sensitive parameters; then a double logarithmic characteristic curve analysis is performed, and the dynamic pressure data of some reservoirs are used to fit the pressure change curves of different flow scenarios of the fracture-cavity group system, and the pump-off pressure drop model is optimized based on the fitting result data; then the optimized pump-off pressure drop model is used to invert the data that characterizes the key parameters of the reservoir fractures to be evaluated, the scale of the cave group, and the degree of fracture-cavity communication, and then the acid fracturing effect is evaluated. The present invention uses a double logarithmic well test interpretation method to analyze the influence of fracture parameters, cave group scale, and fracture-cavity communication degree on the pressure response characteristic curve, and forms a comprehensive interpretation method for the effect of pressure drop after pump-off in carbonate fracture-cavity group reservoirs, which provides a basis for effectively evaluating the communication effect of complex fractures and fracture-cavity groups formed by acid fracturing.

[0028] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 It is a flow chart of a fracture-cavity reservoir acid fracturing evaluation method based on an acid fracturing pump stop pressure drop model provided by an embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of a fracture-cavity-matrix discrete medium model of an acid fracturing evaluation method for fracture-cavity reservoirs based on an acid fracturing pump-off pressure drop model provided in an embodiment of the present invention;

[0032] Figure 3 It is a schematic diagram of a solution process of an acid fracturing pump-off pressure drop equation group of a fracture-cavity reservoir acid fracturing evaluation method based on an acid fracturing pump-off pressure drop model provided in an embodiment of the present invention;

[0033] Figure 4 It is a structural schematic diagram of a fracture-cavity reservoir acid fracturing evaluation system based on an acid fracturing pump stop pressure drop model provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will describe the implementation methods of the present invention in detail in conjunction with the accompanying drawings and embodiments, so that the implementers of the present invention can fully understand how the present invention applies technical means to solve technical problems and achieve the implementation process of technical effects and implement the present invention specifically according to the above implementation process. It should be noted that as long as there is no conflict, the various embodiments and various features of the embodiments in the present invention can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0035] Although the flowcharts describe the operations as sequential processes, many of the operations may be performed in parallel, concurrently, or simultaneously. The order of the operations may be rearranged. A process may be terminated when its operations are completed, but may also have additional steps not included in the accompanying drawings. A process may correspond to a method, function, procedure, subroutine, subprogram, etc.

[0036] Computer devices include user devices and network devices. Among them, user devices or clients include but are not limited to computers, smart phones, PDAs, etc.; network devices include but are not limited to a single network server, a server group consisting of multiple network servers, or a cloud composed of a large number of computers or network servers based on cloud computing. Computer devices can be operated alone to implement the present invention, or they can be connected to the network and implement the present invention through interactive operations with other computer devices in the network. The network where the computer device is located includes but is not limited to the Internet, wide area network, metropolitan area network, local area network, VPN network, etc.

[0037] The terms "first", "second", etc. may be used herein to describe various units, but these units should not be limited by these terms, and these terms are used only to distinguish one unit from another unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items. When a unit is referred to as being "connected" or "coupled" to another unit, it can be directly connected or coupled to the other unit, or there can be intermediate units.

[0038] The terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "one", "one" and "item" used herein are also intended to include plural numbers. It should also be understood that the terms "include" and / or "comprise" used herein specify the existence of stated features, integers, steps, operations, units and / or components, without excluding the existence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0039] With the continuous deepening of oilfield development, the large-scale fracture-cave reservoirs of carbonate karst fracture-cave type have been increasingly utilized, and the development targets have gradually shifted from large-scale single fractures and caves to small-scale continuous fracture-cave aggregates. Field production practice has found that some wells have high cumulative production, indicating that although the individual small fractures and caves are small in size, they are numerous and interconnected through faults, cracks and dissolution channels, forming interconnected small fracture-cave groups with a large overall scale and huge exploration and development potential. Therefore, it is particularly important to carry out research on the identification of small-scale fracture-cave groups and further deepen the development of such reservoirs.

[0040] However, there are many problems with small fracture-cavity reservoirs, such as weak research foundation and less previous relevant data and research, which bring great challenges to the development of small fracture-cavity carbonate reservoirs. For example, in the invention patent "Acid fracturing method and device for fracture-cavity carbonate reservoirs" (CN202011279489.2), temporary plugging particles are the effective ingredients of plugging and filtration loss reducers. Therefore, when pumped in, the temporary plugging particles can temporarily block the beads near the wellbore and the natural fractures along the way. After the acid fracturing construction is completed, the temporary plugging particles temporarily blocked in the beads near the wellbore and the natural fractures along the way can be dissolved when encountering oil, and the flow channels on both sides of the acid fracturing fractures are restored; the acid fracturing fractures can communicate with the fracture-cavity reservoirs far away from the wellbore, greatly increasing the efficiency of acid fracturing transformation, reducing operating costs, and improving the production increase and transformation effect of fracture-cavity carbonate rocks;

[0041] In the invention patent "A method for evaluating the effect of acid fracturing based on the theory of acid fracturing "transformation zone"" (CN202210537578.5), the present invention discloses a method for evaluating the effect of acid fracturing based on the theory of acid fracturing "transformation zone". Considering the improvement of the seepage pattern of the "transformation zone" near the acid-etched fracture by acid, the cumulative production is predicted on this basis, and the acid fracturing effect is evaluated, which can effectively improve the accuracy of the acid fracturing effect evaluation and help to achieve cost-saving and efficiency-enhancing development of carbonate reservoirs;

[0042] In the invention patent "A quantitative evaluation method for the acid fracturing effect of carbonate rocks" (CN202110756436.3), a quantitative evaluation method for the acid fracturing effect of carbonate rocks is disclosed. First, a rock plate acid etching simulation device is used to acid-etch the crack wall of the rock plate, and the groove depth of the acid at the entrance and exit of the rock plate is measured; then the quality of the rock plate before and after acid etching is measured, and finally the acid etching groove depth of the rock plate is comprehensively considered to obtain the acid etching groove morphology factor. Comparing the rock plate acid etching groove morphology factor with the crack wall morphology and the crack conductivity, it is shown that there is a good correspondence between the rock plate acid etching groove morphology factor and the crack wall morphology and the crack conductivity, which can be used as a quantitative evaluation method for the acid fracturing effect of carbonate rocks;

[0043] In the invention patent "A method for evaluating the acid fracturing effect of carbonate rocks" (CN201610143414.9), the acid fracturing effect is evaluated by the morphological characteristics of the core sample surface before and after acid etching, thereby providing data reference and theoretical basis for the subsequent acid selection, acid fracturing design and optimization, and the understanding of carbonate rock acidification production increase records;

[0044] The invention patent "A method for temporary plugging deep in fractures and turning to acid fracturing to find holes along the fractures" (CN202011127694.7) involves a method for temporary plugging deep in fractures and turning to acid fracturing to find holes along the fractures, including injecting a pre-fluid to press open the fractures in the direction of the maximum principal stress and extend them to a certain distance to form a main fracture; pumping a temporary plugging agent so that the temporary plugging agent reaches the front end of the main fracture for temporary plugging, thereby increasing the pressure in the fracture; injecting acid for acid fracturing at a displacement higher than the initiation pressure, so that the acid dissolves the main fracture and the natural fractures in contact with it, increases the conductivity of the natural fractures, and extends the natural fractures along the non-principal stress direction to form secondary fractures; continuing to inject acid at a displacement lower than the initiation pressure, so that the acid reacts in the three fractures, and the filtered acid flows and dissolves along the high permeability zone around the target cave, connects with the nearby target caves, and connects with the caves in the non-maximum principal stress direction in the far well area, thereby increasing the production of oil and gas wells.

[0045] In summary, the above-mentioned existing technologies in the current field have at least the following problems: During the pump-off pressure drop period, the characteristic slope segment generated by the pressure change on the analysis curve can be used to calculate the basic parameters such as the geometric shape of the fracture using the well test analysis theory. At present, the pressure drop model of carbonate rock fracturing construction is relatively simplified, and does not take into account the characteristics of multiple clusters of complex fractures and the viscosity-temperature changes of the fracturing fluid. It is impossible to explain the parameters of the primary and secondary fractures and the communication mode of the fracture-cavity group. It is necessary to further establish a model that combines the fracturing construction of carbonate rock fracture-cavity group reservoirs with the characteristics of pump-off pressure drop for simulation research. At the same time, after the volume acid fracturing of the carbonate rock small fracture-cavity group, it presents the characteristics of multi-scale fracture-cavity carbonate reservoirs, that is, there are multiple small cave groups connected by fracture networks, and multiple micro-fractures are interlaced. The difficulty in modeling the pressure drop of multi-scale multi-fracture-cavity systems lies in the characterization of the flow law in the multi-scale multi-fracture-cavity system, and the traditional models are based on the Darcy flow assumption of a continuous homogeneous seepage field, which cannot solve the nonlinear Darcy flow or pipe flow problems in complex multi-scale fracture-cavity carbonate oil and gas reservoirs.

[0046] The researchers of the present invention considered that acid fracturing is one of the key technical means for the construction of fracture-cavity carbonate reservoirs, and how to effectively evaluate the communication mode between the complex fractures formed by acid fracturing and the small fracture-cavity group is very important. During the acid fracturing construction process, the pump-off pressure value varies. For example, the pump-off pressure value will be different under different circumstances such as whether the artificial fractures are opened, whether the natural fracture-cavity system is communicated, and the scale of the fracture-cavity body communicated is different. Based on this, the researchers of the present invention considered that the pump-off pressure data can be analyzed to truly reflect the connectivity between the actual underground hydraulic fractures and the small fracture-cavity body. The extension range of the artificial fractures and the fracture-cavity communication status can be judged according to the pump-off pressure drop curve during the construction process, so as to achieve a quantitative evaluation of the acid fracturing effect. However, the traditional pump-off pressure drop interpretation methods for carbonate reservoirs at home and abroad are mainly aimed at large-scale fracture-cavity models, and cannot be well applied to small fracture-cavity group reservoirs.

[0047] In order to solve the above problems, the present invention provides a method and system for acid fracturing evaluation of fracture-cavity reservoirs based on an acid fracturing pump-off pressure drop model. By combining the multi-scale characteristics of volumetric acid fracturing of carbonate fracture-cavity reservoirs, an acid fracturing pump-off pressure drop model is established. Based on the acid fracturing pump-off pressure drop model, a well test interpretation method is used to invert key parameters such as fractures, cave group scale and fracture-cavity communication degree, and comprehensively evaluate the acid fracturing effect.

[0048] After fracturing, the matrix, fractures and caves together form a complex pore system of the reservoir, namely a complex fracture-cavity-matrix small cave system, where "matrix" refers to the basic material that constitutes the reservoir rock. The characteristics of the matrix have an important influence on the reservoir performance and fluid flow characteristics of the oil and gas reservoir.

[0049] The embodiment of the present invention uses the whole fracture-cavity geological system formed by the connection after fracturing as a unit for numerical calculation research. The fracture-cavity geological system is mainly composed of natural fractures and caves, which form a highly heterogeneous reservoir system. Fractures are usually rock fractures caused by geological stress, while caves are cavities formed by chemical dissolution.

[0050] Next, the detailed process of the method of the embodiment of the present invention is described in detail based on the accompanying drawings. The steps shown in the flowchart of the accompanying drawings can be executed in a computer system including a set of computer executable instructions. Although the logical order of each step is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0051] Embodiment 1:

[0052] Figure 1 The schematic diagram of the process of the fracture-cavity reservoir acid fracturing evaluation method based on the acid fracturing pump stop pressure drop model provided in the first embodiment of the present invention is shown, referring to Figure 1 It can be seen that the method includes the following steps.

[0053] The steps of constructing the medium model are as follows: Based on the terrain characteristics and the set geological model simplification principles, combined with the simulation of reservoir connectivity and distribution characteristics, a multi-scale fracture-cavity-matrix discrete medium model representing the fracture-cavity geological system is constructed;

[0054] Steps for establishing the pump-off pressure drop model: Based on different types of multi-scale fracture-cavern-matrix discrete medium models, the fluid parameters of the fracture-cavern geological system formed by acid fracturing are analyzed, and the pump-off pressure drop model for carbonate reservoir acid fracturing is established based on the combination of reservoir parameters and acid fracturing fracture parameters;

[0055] Sensitive parameter analysis steps: by conducting sensitivity analysis on the established carbonate reservoir acid fracturing pump-off pressure drop model, determine the sensitive parameters whose influence on pressure change meets the set conditions;

[0056] Dynamic simulation steps: introduce the reservoir parameters and acid fracturing fracture parameters of the current part of the reservoir, and use the established carbonate reservoir acid fracturing pump stop pressure drop model to simulate the dynamic bottom hole pressure data under different sensitive parameters after pump stop and the dynamic closure scenario of the fracture;

[0057] Pressure change fitting step: Perform double logarithmic characteristic curve analysis on the dynamic bottom hole pressure obtained by simulation, and fit the dynamic bottom hole pressure change curve to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity geological system;

[0058] Parameter inversion steps: Based on the fitted dynamic pressure data, the carbonate reservoir acid fracturing pump-off pressure drop model corresponding to the fluid flow scenario is used to invert the data representing the key parameters of the reservoir fractures to be evaluated, the scale of the cave group, and the degree of fracture-cave communication;

[0059] Steps for determining the evaluation results: Analyze the key parameters of the reservoir fractures, the size of the cave group and the degree of fracture-cavity communication to determine the acid fracturing effect evaluation results.

[0060] The discrete physical model decomposes the behavior of the reservoir and fluid into many small discrete parts based on the complex fracture-cavity-matrix small cave system, and simulates the behavior of each part and its interaction. Common discrete models include discrete element method (DEM), particle fluid dynamics (PFD), lattice Boltzmann method (LBM), etc.

[0061] The scheme in the above embodiment is adopted, considering that the pump-off pressure value will change with whether the artificial fracture is opened, whether the natural fracture-cavity system is connected, and the scale of the fracture-cavity body connected, which can most truly reflect the connection state between the actual underground hydraulic fractures and the small fracture-cavity body. Therefore, the extension range of the artificial fracture and the fracture-cavity communication status are judged according to the pump-off pressure drop curve during the construction process, and the quantitative evaluation of the acid fracturing effect is realized. By combining the multi-scale characteristics of volume acid fracturing of carbonate fracture-cavity reservoirs, an acid fracturing pump-off pressure drop model is established, and the key parameters such as the fracture, cave group scale and fracture-cavity communication degree are inverted by using the well test interpretation method, and the acid fracturing effect is comprehensively evaluated. It is not only applicable to large-scale fracture-cavity models, but also can be well applied to small fracture-cavity reservoirs, providing a basis for effectively evaluating the communication effect of complex fractures and fracture-cavity groups formed by acid fracturing.

[0062] In a preferred embodiment, in the pressure change fitting step, the simulated dynamic bottom hole pressure is subjected to a double logarithmic characteristic curve analysis, and after the dynamic bottom hole pressure change curve is fitted to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity group geological system, the model parameters of the carbonate reservoir acid fracturing pump-down pressure drop model are corrected based on the dynamic pressure data corresponding to the different fluid flow scenarios obtained by fitting; based on this, the corrected carbonate reservoir acid fracturing pump-down pressure drop model is used in the parameter inversion step to invert data representing the key parameters of the reservoir fractures to be evaluated, the scale of the cave group, and the degree of fracture-cavity communication.

[0063] The embodiment of the present invention analyzes the fluid parameters of the complex fracture-discrete small cave system formed by acid fracturing through the step of establishing a pump-off pressure drop model based on different types of acid fracturing reservoirs, and establishes a carbonate reservoir acid fracturing pump-off pressure drop model of wellbore-complex fracture-cavern body coupling based on the combination of reservoir parameters and acid fracturing fracture parameters.

[0064] In practical application, the multi-scale fracture-cavern-matrix discrete medium model representing the fracture-cavern geological system is first constructed through the medium model construction step according to the terrain characteristics and the set geological model simplification principle, combined with the simulation of reservoir connectivity and distribution characteristics.

[0065] In an optional embodiment, in the medium model construction step, the zone with densely developed fractures and pores is simplified into a karst reservoir, and the fracturing fracture system is simplified into a high-permeability connection zone, which connects the randomly distributed small cave group reservoirs to establish a multi-scale fracture-cavity-matrix discrete medium model, such as Figure 2 As shown; as a complex fracture-discrete small hole group system formed by acid fracturing. Among them, in the field of oil and gas geology, the fracture-vug network zone (Fracture-Vug Network Zone) usually refers to the area where fractures and caves (pores) are highly developed and interconnected in the reservoir. This type of geological feature is particularly common in carbonate reservoirs, and has important development value due to its complex pore structure and high permeability. High permeability connectivity zone (High Permeability Connectivity Zone) refers to a highly connected and extremely permeable geological area in the reservoir. These zones are usually due to the presence of fractures, pores or other high permeability channels, making the flow of oil and gas smoother and more efficient. In oil and gas geology, small vug group reservoirs (Small Vug Group Reservoir) refer to reservoirs composed of many small caves in the reservoir. This type of reservoir usually appears in carbonate reservoirs and has attracted much attention due to its unique pore structure and reservoir characteristics.

[0066] In a preferred embodiment, the step of establishing the pump-off pressure drop model includes the following operations.

[0067] Cave group fluid characterization steps: Use the seepage relationship and Nevi-Stokes pipe flow theory to analyze the fluid parameters of different fluid flow scenarios in the complex fracture-discrete small cave group geological system formed by acid fracturing;

[0068] The computational model establishment step is to establish a carbonate reservoir acid fracturing pump stop pressure drop model for wellbore-complex fracture-cavern coupling based on the fluid parameters combined with reservoir parameters and acid fracturing fracture parameters.

[0069] In the cave group fluid characterization step, for various fluid flow scenarios in the complex fracture-discrete small cave group fracture-cave group geological system, the fluid parameters analyzed using the seepage relationship and Nevi-Stokes pipe flow theory include: the exchange mechanism and flow law of the fluid in the system between different media in small caves and multi-scale fractures.

[0070] In the computational model establishment step, the reservoir parameters include: reservoir physical property parameters, horizontal well length and cave group distribution location; the acid fracturing fracture parameters include: fracturing fluid parameters, number of primary fractures, number of secondary fractures and primary / secondary fracture lengths.

[0071] In the step of establishing the computational model, the material conservation principle of the set fluid flow scenario between adjacent underground media and the dynamic closure scenario of the fracture is considered, and the multi-media material conservation equation of the wellbore-complex fracture-cave body coupling, the matrix material conservation equation and the filtration equation of the fracturing fluid in fractures and caves of different levels are established to comprehensively form a carbonate reservoir acid fracturing pump stop pressure drop model.

[0072] A complex fracture network is formed after volume acid fracturing of fracture-cavity carbonate reservoirs. During the pump stop stage, the injection volume of fracturing fluid is zero, and there is flow of fracturing fluid between two adjacent media underground (wellbore continuation of WF, cross-flow between primary and secondary fractures of Ff, filtration loss of primary fractures of Fm, filtration loss of secondary fractures of fm, and cross-flow of fractures and caves of Fv). The inflow and outflow of multiple media of F, f, m, and v offset each other, and the material conservation of the whole system is maintained.

[0073] In an optional embodiment, the carbonate reservoir acid fracturing pump-off pressure drop model includes multiple operational equations; the operational equations include a multi-object material conservation model of the fracture-cavity geological system, a cave flow pattern model, a fluid loss mechanism model and a crossflow mechanism model.

[0074] The multi-object material conservation model in the operation equation includes a fracture material conservation equation and a cave material conservation equation; the fracture material conservation equation includes a primary fracture material conservation equation and a secondary fracture material conservation equation.

[0075] The material conservation equation of the main fracture is established based on the porosity of the main fracture, the density of the fracturing fluid, the viscosity of the fracturing fluid, the fluid pressure in the main fracture, and the factors of the fracturing fluid saturation of the main fracture, the fracturing fluid loss of the main fracture, the crossflow between the main fracture and the secondary fracture, the longitudinal migration distance of the fluid, and the continuous flow between the wellbore and the fracture;

[0076] According to the porosity of the secondary fractures, the density of the fracturing fluid, the viscosity of the fracturing fluid, the fluid pressure in the secondary fractures, the secondary fracture fracturing fluid saturation, the fracturing fluid loss in the secondary fractures, the longitudinal migration distance of the fluid, and the cross-flow between the main fractures and the secondary fractures, the secondary fracture material conservation equation is established;

[0077] The cross-flow rate between the main fracture and the secondary fracture is determined according to the fracturing fluid density, the main fracture fluid pressure, the secondary fracture fluid pressure, the fracturing fluid viscosity and the change in the longitudinal migration distance of the fluid;

[0078] The flow rate from the wellbore to the main fracture is determined by introducing the matrix shape factor according to the reservoir thickness, fracturing fluid density, main fracture width, fluid pressure in the main fracture, fracturing fluid viscosity, fracturing fluid volume factor, reservoir radius, wellbore radius and skin factor.

[0079] The density of the fracturing fluid, the absolute permeability of the matrix, the viscosity of the fracturing fluid, the flow velocity, the saturation of the fracturing fluid in the cave, the fluid pressure in the cave are comprehensively considered, and the material conservation equation of the cave is established in combination with the crossflow rate between the main fracture and the cave and the crossflow rate between the secondary fracture and the cave.

[0080] The flow pattern of the cave space adopts the free flow of viscous fluid, and a cave flow pattern model that changes with time is established based on the viscosity of the fracturing fluid, the density of the fracturing fluid, the flow velocity, and the fluid pressure in the cave.

[0081] Furthermore, in one embodiment, the fluid loss mechanism model in the operational equation includes the loss equation of the fracturing fluid in the main fracture and the loss equation of the fracturing fluid in the secondary fracture; the crossflow mechanism model includes the crossflow equation between the main fracture and the cave and the crossflow equation between the secondary fracture and the cave.

[0082] In an optional embodiment, a fracture shape factor of the main fracture is introduced, and a filtration equation of the fracturing fluid in the main fracture is established based on the permeability of the fracturing fluid in the matrix, the density of the fracturing fluid, the fluid pressure in the main fracture, the fluid pressure in the matrix, the viscosity of the fracturing fluid and the change in the longitudinal migration distance of the fluid.

[0083] The fracture shape factor of the secondary fracture is introduced, and the filtration equation of the fracturing fluid in the secondary fracture is established according to the fracturing fluid density, the permeability of the fracturing fluid in the matrix, the fluid pressure in the matrix, the fluid pressure in the secondary fracture, the fracturing fluid viscosity and the longitudinal migration distance change of the fluid.

[0084] The cave shape factor of the main fracture is introduced, and the crossflow equation between the main fracture and the cave is established according to the fracturing fluid density, the permeability of the fracturing fluid in the cave, the fluid pressure in the main fracture, the fluid pressure in the cave, the fracturing fluid viscosity and the longitudinal migration distance of the fluid.

[0085] The cave shape factor of the secondary fracture is introduced, and the crossflow equation between the secondary fracture and the cave is established according to the fracturing fluid density, the permeability of the fracturing fluid in the cave, the fluid pressure in the secondary fracture, the fluid pressure in the cave, the fracturing fluid viscosity and the longitudinal migration distance of the fluid.

[0086] In a preferred embodiment, before the dynamic simulation step, a sensitivity analysis is performed on the established wellbore-complex fracture-cave coupled pressure drop model through a sensitive parameter analysis step to determine the sensitive parameters whose influence on the pressure change meets the set conditions; in actual application, the parameters that have a greater impact on the horizontal well pressure drop are found through sensitivity analysis, and the subsequent dynamic simulation steps are focused on these parameters, while providing a basis for selecting the target parameters of the inversion process. Fracturing parameters are important factors that affect the fracturing effect and fracture characteristics. Reasonable selection and optimization of these parameters help to improve the production capacity and economic benefits of oil and gas wells. In actual operation, it is necessary to comprehensively consider the geological conditions of the reservoir, the characteristics of the fracturing fluid and proppant, and the construction parameters to formulate the best fracturing plan.

[0087] By conducting a sensitivity analysis on the established wellbore-complex fracture-cavern coupled pressure drop model, the sensitive parameters whose influence on pressure change meets the set conditions are determined, and the corresponding available configuration parameters are set based on these sensitive parameters.

[0088] In an optional embodiment, the sensitive parameters may include different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeability parameters.

[0089] The dynamic simulation step is further performed to introduce the reservoir parameters and acid fracturing fracture parameters of the current reservoir, and the established carbonate reservoir acid fracturing pump stop pressure drop model is used to simulate the dynamic bottom hole pressure data under the set fluid flow scenario after pump stop under different sensitive parameters and the dynamic closure scenario of the fracture.

[0090] In practical applications, multi-scale flow medium and fluid parameters of reservoirs are acquired in advance and stored for later use;

[0091] Based on the multi-scale flow medium and fluid parameters of the reservoir, combined with the reservoir parameters and acid fracturing fracture parameters of the reservoir, the established carbonate reservoir acid fracturing pump stop pressure drop model is used to simulate the dynamic bottom hole pressure data under the fluid flow scenario and the dynamic closure scenario of the fracture after stopping the pump under different sensitive parameters, and determine the pressure drop change pattern of the fractured horizontal well under different reservoir parameters. The embodiment of the present invention establishes a wellbore-complex fracture-formation coupled fracturing construction pressure drop model; wherein the construction pressure drop refers to the pressure loss caused by fluid friction, formation rupture and other factors during the fracturing construction process. This parameter is crucial to the success of the fracturing construction because it affects the formation of the fracture, the transportation of the proppant and the injection effect of the fracturing fluid. The embodiment of the present invention simulates the physical processes involved in the scene during the reservoir pressure drop process through the fracturing construction pressure drop model: the extension and closure of the main fracture; the change in the flexibility of the fracture before and after closure; the development of secondary fractures; the flow of fluid in the fracture; the flow between the fracture and the wellbore; the filtration from the fracture to the formation; the fracture-cavern channeling

[0092] The set fluid flow scenarios include: the state of continued flow from the wellbore to the fracture, the state of crossflow between the primary and secondary fractures, the state of filtration from the primary and secondary fractures to the cave body, and the state of filtration from the primary and secondary fractures to the formation. Among them, continued flow refers to the phenomenon that the fracturing fluid continues to flow through the fracture system after the fracturing operation is completed. This continued flow phenomenon can help maintain the open state of the fracture and enhance the permeability of the rock, thereby increasing the production capacity of the oil field or reservoir. Interzonal flow refers to the phenomenon of fluid movement that may occur between different formations, reservoirs, fractures, pores and other spaces. This phenomenon may cause the fluid to flow from one space to another due to pressure differences or connectivity between formations. Filtration loss: refers to the phenomenon that drilling fluid or fracturing fluid penetrates from the drill pipe or fracture into the rock formation during drilling or fracturing operations.

[0093] This embodiment of the present invention establishes a wellbore-complex fracture-formation coupled acid fracturing pump-off pressure drop model, uses a finite difference discretization method to discretize the multi-scale medium seepage equations of fractures, matrix and caves, and solves them in combination with the Newton-Raphson iterative algorithm. Simulate the construction pressure drop characteristics under different perforation cluster numbers, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities. According to the pre-acquired reservoir multi-scale flow medium and fluid parameters, and the acid fracturing pump-off pressure drop model, the pressure drop pattern of the fractured horizontal well under different reservoir parameters is determined.

[0094] Furthermore, in an optional embodiment, in the dynamic simulation step, the equations of the carbonate reservoir acid fracturing pump-off pressure drop model are discretized using the finite difference method and the semi-implicit method, the coefficient matrix of the equation group is obtained, the equations are solved and calculated using the LU decomposition method, and the horizontal well pressure at the required time is calculated based on the time step.

[0095] Specifically, the finite difference method and the semi-implicit method are used to linearize the nonlinear equations. The Gauss-Seidel iteration method is used to iteratively solve the equations, and the calculated parameter values ​​of the time step are used as the initial values ​​of the next time step to continue the iterative calculation.

[0096] In practical applications, programming tools can be used to solve the matrix equations using the LU decomposition method, and the pump-off pressure drop of the fracturing horizontal well under different parameters at different times can be obtained according to the time step. For example, Matlab programming tools can be used to solve the problem. The solution process includes:

[0097] Input basic parameters in Matlab: reservoir properties and fracturing fluid parameters, number of primary fractures, number of secondary fractures, primary / secondary fracture length, horizontal well length, cave group distribution location, pump stop time; use finite difference method and semi-implicit method to discretize the fracture-matrix-cavity equation, find the coefficient matrix of the equation group, and use LU decomposition method to solve the equation; according to the time step, the horizontal well pressure drop at any time can be calculated; Figure 3 shown.

[0098] It should be noted that in other embodiments, other reservoir and fluid parameters can be selected for input according to the actual reservoir geological conditions, and other programming software can also be selected for programming and solving.

[0099] Further, a pressure change fitting step is performed, a double logarithmic characteristic curve analysis is performed on the simulated dynamic bottom hole pressure, the dynamic bottom hole pressure change curve is fitted to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity group geological system as a whole, and the model parameters of the carbonate reservoir acid fracturing pump-off pressure drop model are corrected based on the dynamic pressure data corresponding to the fracture-cavity group geological system obtained by fitting;

[0100] In this embodiment, the dynamic pressure data corresponding to different fluid flow scenarios controlled by the overall multi-scale medium of the fracture-cavity geological system are fitted based on the calculated dynamic pressure data of the local reservoir in the fracture-cavity geological system, without the need for large-scale repeated simulation operations; further, the model parameters of the carbonate reservoir acid fracturing pump-down pressure drop model are corrected based on the fitted dynamic pressure data of the fracture-cavity geological system to obtain a corrected and optimized pump-down pressure drop model, thereby improving the reliability and accuracy of the constructed pump-down pressure drop model and making the parameter information obtained by the subsequent inversion analysis more closely fit the real reservoir data.

[0101] Among them, according to the pressure data obtained by the solution, the construction pressure drop characteristic chart under different perforation cluster numbers, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities is drawn, and the flow state changes are identified by combining the changes in the slope of the double logarithmic diagnostic curve, and the dynamic bottom hole pressure change curve is fitted to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity geological system as a whole. The construction pressure drop characteristic chart (Pressure Drawdown Diagnostic Plot) is a tool for analyzing the condition of oil wells or gas wells. By displaying the production pressure drop of oil wells or gas wells in different time periods, it helps engineers and geologists evaluate the performance characteristics of oil or gas reservoirs and diagnose possible problems, such as crack blockage.

[0102] In an optional embodiment, firstly, according to the well test interpretation theory, the bottom hole pressure obtained by simulation is subjected to double logarithmic curve analysis to identify the division charts of various flow states under the dynamic control of the wellbore-fracture-cavern multi-scale medium.

[0103] In actual application, the construction pressure drop characteristic charts under different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities and different permeabilities are drawn according to the solved pressure data. That is, according to the programming calculation results, the construction pressure drop characteristic charts under different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities and different permeabilities are drawn, and the flow state changes are identified in combination with the changes in the slope of the double logarithmic diagnostic curve.

[0104] The embodiment of the present invention is based on the established pump-off pressure drop model and utilizes the double logarithmic well testing method of the pressure characteristic curve to invert the fracture parameters, the scale of the cave group and the degree of fracture-cavity communication to evaluate the acid fracturing effect.

[0105] Therefore, the parameter inversion step is then used to invert the data characterizing the key parameters of the current reservoir fractures, the size of the cave group, and the degree of fracture-cavity communication based on the pressure change curve using the carbonate reservoir acid fracturing pump-off pressure drop model; and the fracture parameters, the size of the cave group, and the degree of fracture-cavity communication are inverted using the double logarithmic well testing method of the pressure characteristic curve. Among them, it is preferred to select the data characterizing the key parameters of the current reservoir fractures, the size of the cave group, and the degree of fracture-cavity communication from the input parameters when constructing the carbonate reservoir acid fracturing pump-off pressure drop model according to the sensitive parameters whose influence degree meets the set conditions determined in the sensitive parameter analysis step.

[0106] In an optional embodiment, the data characterizing the key parameters of the current reservoir fractures, the size of the cave group and the degree of communication between the fractures and caves include the formation permeability, multi-cavern location, multi-cavern volume, cave storage constant, fracture half-length, and fracture volume parameters of the reservoir. That is, finally, by fitting the simulated pump stop pressure drop data and the actual pressure drop data, the formation permeability, multi-cavern location, multi-cavern volume, cave storage constant, fracture half-length, fracture volume and other parameters are inverted. Among them, the cave storage constant (Cave Storage Constant) refers to the quantitative index of the ability of the cave or pore space in the oil and gas reservoir to store oil and gas during the development and production of underground oil and gas reservoirs; the half-length of the fracture (Half-Length of Fracture) refers to the length of the semi-major axis of a fracture in the vertical direction.

[0107] Finally, the evaluation result determination step is performed: the key parameters of the reservoir fractures, the size of the cavity group and the degree of fracture-cavity communication are analyzed to determine the acid fracturing effect evaluation results, and the parameter interpretation results are derived.

[0108] The present invention establishes a pump-off pressure drop modeling method based on the multi-scale fracture-cavity characteristics and dynamic closure characteristics of carbonate rock volume acid fracturing, and forms an evaluation method for the volume acid fracturing effect of carbonate rock fracture-cavity reservoirs, which provides a basis for effectively evaluating the communication effect of complex fractures and fracture-cavity groups formed by acid fracturing.

[0109] For the above-mentioned method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the order of the actions described, because according to the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0110] It should be pointed out that in other embodiments of the present invention, the method can also obtain a new fracture-cavity reservoir acid fracturing evaluation method by combining one or several of the above embodiments to achieve accurate evaluation of the acid fracturing effect of the fracture-cavity reservoir.

[0111] It should be noted that, based on the method in any one or more of the above embodiments of the present invention, the present invention also provides a storage medium, on which is stored a program code that can implement the method as described in any one or more of the above embodiments, and when the code is executed by the operating system, it can implement the acid fracturing evaluation method for fracture-cavity reservoirs based on the acid fracturing pump-off pressure drop model as described above.

[0112] Embodiment 2:

[0113] The method is described in detail in the embodiments disclosed in the above invention. The method of the present invention can be implemented by various forms of devices or systems. Therefore, based on other aspects of the method described in any one or more embodiments, the present invention also provides a fracture-cavity reservoir acid fracturing evaluation system based on an acid fracturing pump-off pressure drop model. The system is used to execute the fracture-cavity reservoir acid fracturing evaluation method based on an acid fracturing pump-off pressure drop model described in any one or more embodiments. Specific embodiments are given below for detailed description.

[0114] Specifically, Figure 4 FIG. 4 is a schematic diagram showing a structural diagram of a fracture-cavity reservoir acid fracturing evaluation system based on an acid fracturing pump stop pressure drop model provided in an embodiment of the present invention. Figure 4 As shown, the system includes:

[0115] A medium model construction module is configured to construct a multi-scale fracture-cavity-matrix discrete medium model that characterizes the fracture-cavity geological system based on topographic features and set geological model simplification principles, combined with simulation of reservoir connectivity and distribution characteristics;

[0116] A pump-off pressure drop model establishment module is configured to analyze the fluid parameters of the fracture-cavity geological system formed by acid fracturing based on different types of multi-scale fracture-cavity-matrix discrete medium models, and establish a carbonate reservoir acid fracturing pump-off pressure drop model based on the combination of reservoir parameters and acid fracturing fracture parameters;

[0117] A sensitive parameter analysis module configured to perform sensitivity analysis on the established carbonate reservoir acid fracturing pump stop pressure drop model to determine sensitive parameters whose influence on pressure change meets set conditions;

[0118] A dynamic simulation module is configured to introduce reservoir parameters and acid fracturing fracture parameters of the current part of the reservoir, and use the established carbonate reservoir acid fracturing pump stop pressure drop model to simulate the dynamic bottom hole pressure data of the set fluid flow scenario after pump stop under different sensitive parameters and the dynamic closure scenario of the fracture;

[0119] A pressure change fitting module is configured to perform a double logarithmic characteristic curve analysis on the simulated dynamic bottom hole pressure, fit the dynamic bottom hole pressure change curve to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity geological system, and modify the model parameters of the carbonate reservoir acid fracturing pump-off pressure drop model based on the fitted dynamic pressure data corresponding to different fluid flow scenarios;

[0120] A parameter inversion module configured to use a modified carbonate reservoir acid fracturing pump-off pressure drop model to invert data representing key parameters of the reservoir fractures to be evaluated, the size of the cave group, and the degree of fracture-cavity communication;

[0121] The evaluation result determination module is configured to analyze the key parameters of the reservoir fractures, the size of the cave group and the degree of fracture-cavity communication to determine the acid fracturing effect evaluation results.

[0122] Optionally, in one embodiment, the medium model construction module is configured to simplify the zone with densely developed fractures and pores into a karst reservoir, simplify the fracturing fracture system into a high-permeability connected zone, the high-permeability connected zone connects the randomly distributed small cave group reservoirs, and establish a multi-scale fracture-cave-matrix discrete medium model as a complex fracture-discrete small cave group system formed by acid fracturing.

[0123] Furthermore, the pump stop pressure drop model building module is configured to perform the following operations:

[0124] The cave group fluid characterization unit is used to analyze the fluid parameters of different fluid flow scenarios in the fracture-cave geological system formed by acid fracturing using the seepage relationship and Nevi-Stokes pipe flow theory;

[0125] The computational model building unit is used to build a carbonate reservoir acid fracturing pump stop pressure drop model for wellbore-complex fracture-cavern coupling based on the fluid parameters combined with reservoir parameters and acid fracturing fracture parameters.

[0126] Preferably, in a specific embodiment, the cave group fluid characterization unit analyzes the fluid parameters of the fracture-cavity geological system by using the seepage relationship and the Nevi-Stokes pipe flow theory for different fluid flow scenarios of the fracture-cavity geological system, including: the exchange mechanism and flow law of the fluid in the system between different media in small caves and multi-scale fractures.

[0127] On the other hand, in an optional embodiment, the computational model establishment unit sets the reservoir parameters including: reservoir physical property parameters, horizontal well length and cave group distribution location; the acid fracturing fracture parameters include: fracturing fluid parameters, the number of primary fractures, the number of secondary fractures and primary / secondary fracture lengths.

[0128] Furthermore, in one embodiment, the computational model building unit is configured to consider the material conservation principle of the set fluid flow scenario between adjacent underground media and the dynamic closure scenario of the fracture, establish the material conservation equations of different levels of fractures coupled with the wellbore-complex fractures-cavern body, the matrix material conservation equations and the filtration equations of the fracturing fluid in different levels of fractures, and comprehensively form a carbonate reservoir acid fracturing pump stop pressure drop model.

[0129] Optionally, in one embodiment, the dynamic simulation module is configured to discretize the equations of the carbonate reservoir acid fracturing pump-off pressure drop model using a finite difference method and a semi-implicit method, obtain the coefficient matrix of the equation group, use the LU decomposition method to solve the equations, and calculate the horizontal well pressure at the required time based on the time step.

[0130] Furthermore, in one embodiment, the pressure change fitting module is configured to draw a construction pressure drop characteristic chart under different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities based on the solved pressure data, and identify flow state changes in combination with changes in the slope of the double logarithmic diagnostic curve.

[0131] In a preferred embodiment, the data characterizing the key parameters of the current reservoir fractures, the size of the cave group and the degree of fracture-cavity communication include: formation permeability of the reservoir, location of multiple caves, volume of multiple caves, cave storage constant, fracture half-length, and fracture volume parameters.

[0132] In the fracture-cavity reservoir acid fracturing evaluation system based on the acid fracturing pump-off pressure drop model provided by the embodiment of the present invention, each module or unit structure can be operated independently or in combination according to actual data management requirements and model calculation requirements to achieve corresponding technical effects.

[0133] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0134] The "one embodiment" mentioned in the specification means that a particular feature, structure or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrase "one embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0135] Although the embodiments disclosed in the present invention are as above, the above contents are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A fracture-cavity reservoir acid fracturing evaluation method based on an acid fracturing pump-off pressure drop model, characterized in that: The method comprises: The steps of constructing the medium model are as follows: Based on the terrain characteristics and the set geological model simplification principles, combined with the simulation of reservoir connectivity and distribution characteristics, a multi-scale fracture-cavity-matrix discrete medium model representing the fracture-cavity geological system is constructed; Steps for establishing the pump-off pressure drop model: Based on different types of multi-scale fracture-cavern-matrix discrete medium models, the fluid parameters of the fracture-cavern geological system formed by acid fracturing are analyzed, and the pump-off pressure drop model for carbonate reservoir acid fracturing is established based on the combination of reservoir parameters and acid fracturing fracture parameters; Sensitive parameter analysis steps: by conducting sensitivity analysis on the established carbonate reservoir acid fracturing pump-off pressure drop model, determine the sensitive parameters whose influence on pressure change meets the set conditions; Dynamic simulation steps: introduce the reservoir parameters and acid fracturing fracture parameters of the current part of the reservoir, and use the established carbonate reservoir acid fracturing pump stop pressure drop model to simulate the dynamic bottom hole pressure data under different sensitive parameters after pump stop and the dynamic closure scenario of the fracture; Pressure change fitting step: Perform double logarithmic characteristic curve analysis on the dynamic bottom hole pressure obtained by simulation, and fit the dynamic bottom hole pressure change curve to determine the dynamic pressure data corresponding to different fluid flow scenarios of the fracture-cavity geological system; Parameter inversion steps: Based on the fitted dynamic pressure data, the carbonate reservoir acid fracturing pump-off pressure drop model corresponding to the fluid flow scenario is used to invert the data representing the key parameters of the reservoir fractures to be evaluated, the scale of the cave group, and the degree of fracture-cave communication; Steps for determining the evaluation results: Analyze the key parameters of the reservoir fractures, the size of the cave group and the degree of fracture-cavity communication to determine the acid fracturing effect evaluation results.

2. The method according to claim 1, characterized in that In the medium model construction step, the zone with densely developed fractures and pores is simplified into a karst reservoir, and the fracturing fracture system is simplified into a high-permeability connected zone. The high-permeability connected zone connects the randomly distributed small cave group reservoirs, and a multi-scale fracture-cave-matrix discrete medium model is established as a complex fracture-discrete small cave group system formed by acid fracturing.

3. The method according to claim 1, characterized in that The steps for establishing the pump stop pressure drop model include: The steps of cave group fluid characterization are as follows: Use the seepage relationship and Nevi-Stokes pipe flow theory to analyze the fluid parameters of different fluid flow scenarios in the fracture-cavity geological system formed by acid fracturing; The computational model establishment step is to establish a carbonate reservoir acid fracturing pump stop pressure drop model for wellbore-complex fracture-cavern coupling based on the fluid parameters combined with reservoir parameters and acid fracturing fracture parameters.

4. The method according to claim 3, characterized in that In the cave group fluid characterization step, for different fluid flow scenarios of the fracture-cave group geological system, the fluid parameters analyzed using the seepage relationship and the Nevi-Stokes pipe flow theory include: the exchange mechanism and flow law of the fluid in the system between different media of small caves and multi-scale fractures; the fluid flow scenarios include: the continuous flow state from the wellbore to the fracture, the crossflow state between the primary and secondary fractures, the filtration state from the primary and secondary fractures to the cave body, and the filtration state from the primary and secondary fractures to the formation.

5. The method according to claim 3, characterized in that: In the computational model establishment step, the reservoir parameters include: reservoir physical property parameters, horizontal well length and cave group distribution location; the acid fracturing fracture parameters include: fracturing fluid parameters, number of primary fractures, number of secondary fractures and primary / secondary fracture lengths.

6. The method according to claim 3, characterized in that In the computational model establishment step, the carbonate reservoir acid fracturing pump stop pressure drop model includes a plurality of computational equations, and the computational equations include a multi-object material conservation model of a fracture-cavity geological system, a karst cave flow mode model, a fluid filtration mechanism model, and a crossflow mechanism model; The multi-object material conservation model in the operation equation includes a fracture material conservation equation and a cave material conservation equation; the fracture material conservation equation includes a primary fracture material conservation equation and a secondary fracture material conservation equation.

7. The method according to claim 1, characterized in that In the dynamic simulation step, the equations of the carbonate reservoir acid fracturing pump-off pressure drop model are discretized using the finite difference method and the semi-implicit method, the coefficient matrix of the equation group is obtained, the LU decomposition method is used to solve the equations, and the horizontal well pressure at the required time is calculated according to the time step.

8. The method according to claim 1, characterized in that In the pressure change fitting step, the construction pressure drop characteristic charts under different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities are drawn according to the solved pressure data. The flow state changes are identified by combining the changes in the slope of the double logarithmic diagnostic curve, and the dynamic bottom hole pressure change curve is fitted to determine the dynamic pressure data corresponding to different fluid flow scenarios of the overall fracture-cavity geological system.

9. The method according to claim 1, characterized in that: The data characterizing the key parameters of the current reservoir fractures, the size of the cave group and the degree of fracture-cavity communication include: the formation permeability of the reservoir, the location of multiple caves, the volume of multiple caves, the cave storage constant, the fracture half-length and the fracture volume parameters.

10. A fracture-cavity reservoir acid fracturing evaluation system based on an acid fracturing pump stop pressure drop model, characterized in that: The system executes the method according to any one of claims 1 to 9.

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