Method and system for evaluating fracturing effect of reservoir

Abstract

A method and system for evaluating the fracturing effect of a reservoir. In the method, fluid parameters of a complex fracture-vug group system formed by means of fracturing are analyzed, a fracturing pump-stopping pressure drop model that includes a plurality of operational equations is established for a fracture-vug group geological system, reservoir parameters and fracture parameters are introduced, the fracturing pump-stopping pressure drop model is used to simulate dynamic bottom hole pressure data of a set scene after pump stopping under different sensitive fracturing parameters, so as to obtain a bottom hole pressure distribution chart, a pressure change curve of a fracturing segment to be evaluated is fitted, a flow state is identified on the basis of the pressure change curve, and evaluation parameters are inverted by using an operational equation matching the flow state, thus evaluating a fracturing effect. By using the solution, the problems in respect of insufficient practicability and inaccurate analysis results in the prior art are overcome, and a communication effect between complex fractures and fracture-vug groups which are formed by means of fracturing is accurately identified.

Description

A reservoir fracturing effect evaluation method and system Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a reservoir fracturing effect evaluation method and system. Background Art

[0002] Carbonate karst fracture-vuggy reservoirs are characterized by large variations in reservoir space scale and structure, as well as strong heterogeneity. With the continued development of oil fields, large-scale fracture-vuggy reservoirs in carbonate karst fracture-vuggy reservoirs are being increasingly utilized, and the focus of development is gradually shifting from large-scale single fractures and vuggy bodies to small-scale continuous fracture-vuggy aggregates. Furthermore, field production practices have revealed high cumulative production rates in some wells, indicating that while small fractures and vuggy bodies are individually small, they are numerous and interconnected through faults, cracks, and karst caves, forming interconnected small fracture-vuggy groups. These groups, with their large overall scale, hold enormous exploration and development potential. Therefore, conducting research on the identification of small-scale fracture-vuggy groups is crucial to further developing these reservoirs.

[0003] However, the current research on small fracture-vuggy reservoirs faces numerous challenges, including a weak foundation and limited prior research data. These challenges pose significant challenges to the development of carbonate reservoirs with clusters of small fractures and vuggy structures. Existing methods exist for reservoir identification and fracturing analysis, but these applied pressure drop models for carbonate fracturing are relatively simplistic and fail to account for complex fracture clusters and the viscosity-temperature variations of fracturing fluids. These models are unable to account for primary and secondary fracture parameters and the communication patterns between fractures and vuggy structures, resulting in limited practicality and inaccurate analytical 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 an admission or any form of suggestion that the information constitutes the prior art known to those skilled in the art.

[0005] Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for evaluating reservoir fracturing effects. In one embodiment, the method comprises:

[0007] Constructing a discrete physical model of fractures, caves, and matrix for the historical fracturing section, and establishing a pump-down pressure drop model for the fracture-cavity geological system formed in the reservoir after fracturing based on the discrete physical model, wherein the pump-down pressure drop model includes multiple operational equations;

[0008] The fracturing pump-off pressure drop model is used to simulate the simulated construction pressure drop distribution characteristics of historical fracturing sections under different fracturing parameters;

[0009] Fitting a pump-off pressure change curve of the to-be-evaluated fracturing section based on the simulated construction pressure drop distribution characteristics, and identifying the flow state of the fracture-cavity geological system according to the pump-off pressure change curve;

[0010] An operational equation is selected from the fracturing pump-off pressure drop model in combination with the flow state to obtain evaluation parameters of the fracturing section to be evaluated, and an evaluation result is determined based on the evaluation parameters.

[0011] Preferably, in one embodiment, a fracture-cavity-matrix discrete physical model of the fracture-cavity geological system of the fractured section is constructed based on the terrain characteristics and the set geological model simplification principle, and combined with the reservoir characteristics.

[0012] Furthermore, in one embodiment, the geological model simplification principles include:

[0013] The zone with dense development of fractures and pores is simplified into karst reservoirs, and the fracture system is simplified into high-permeability connecting belts. High-permeability connecting belts are used to connect the randomly distributed small cave group reservoirs to form a complex fracture-cavity-matrix discrete medium small cave group system formed after fracturing.

[0014] Specifically, in an optional embodiment, the fluid parameters of different flow states of the fracture-cavity-matrix discrete physical model are analyzed in the fracture-cavity geological system formed by fracturing, and the reservoir parameters and fracturing crack parameters of the historical fracturing section are combined to establish a fracturing pump stop pressure drop model.

[0015] In one embodiment, the fracturing pump-off pressure drop model is established by considering the material conservation principle and seepage mechanism between underground media corresponding to different flow states; and

[0016] The flow state includes at least one of a continuous flow state from the wellbore to the fracture, a cross-flow state between the primary and secondary fractures, a filtration state from the primary and secondary fractures to the cave body, a filtration state from the primary and secondary fractures to the formation, and a dynamic closure state of the fracture.

[0017] Optionally, in one embodiment, 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.

[0018] In a preferred embodiment, the multi-object material conservation model in the computational 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.

[0019] Furthermore, in one embodiment, the material conservation equation for 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, and the fluid pressure in the main fracture, taking into account the fracturing fluid saturation of the main fracture, the fracturing fluid loss in the main fracture, the crossflow rate between the main fracture and the secondary fracture, the longitudinal migration distance of the fluid, and the continuous flow rate between the wellbore and the fracture.

[0020] The secondary fracture material conservation equation is established based on the porosity of the secondary fracture, the density of the fracturing fluid, the viscosity of the fracturing fluid, the fluid pressure in the secondary fracture, and the factors of the fracturing fluid saturation in the secondary fracture, the fracturing fluid loss in the secondary fracture, the longitudinal migration distance of the fluid, and the crosstalk flow between the primary fracture and the secondary fracture;

[0021] The crossflow rate between the primary fracture and the secondary fracture is determined by the density of the fracturing fluid, the pressure of the primary fracture fluid, the pressure of the secondary fracture fluid, the viscosity of the fracturing fluid, and the change in the longitudinal migration distance of the fluid.

[0022] The flow rate from the wellbore to the main fracture is determined by introducing the matrix shape factor based on the reservoir thickness, fracturing fluid density, main fracture width, fluid pressure in the main fracture, fracturing fluid viscosity, fracturing fluid volume coefficient, reservoir radius, wellbore radius, and skin factor.

[0023] In an optional embodiment, 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, and the fluid pressure in the cave are comprehensively considered, and the crossflow rate between the primary fracture and the cave and the crossflow rate between the secondary fracture and the cave are combined to establish the material conservation equation of the cave.

[0024] Preferably, in one embodiment, 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 fracturing fluid viscosity, fracturing fluid density, flow velocity, and fluid pressure in the cave.

[0025] 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.

[0026] 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;

[0027] The fracture shape factor of the secondary fracture is introduced, and the filtration equation of the fracturing fluid in the secondary fracture is established based on 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 of the fluid.

[0028] In one embodiment, the cave shape factor of the main fracture is introduced, and the crossflow equation between the main fracture and the cave is established based on 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 change in the longitudinal migration distance of the fluid;

[0029] 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.

[0030] Specifically, in one embodiment, based on the reservoir parameters and fracturing crack parameters of the historical fracturing sections, the operational equation corresponding to the flow state in the fracturing pump-off pressure drop model is used to simulate and calculate the dynamic bottom hole pressure after pump-off under different fracturing parameters in each historical fracturing section.

[0031] Preferably, in one embodiment, the method further comprises the following steps: after obtaining the simulated construction pressure drop distribution characteristics of the historical fracturing section through simulation calculation, determining a pressure drop characteristic plate division rule for different flow states of the historical fracturing section.

[0032] On the other hand, in one embodiment, the method further comprises:

[0033] By conducting a sensitivity analysis on the established fracturing pump-off pressure drop model, the fracturing parameters whose impact on the dynamic bottom hole pressure change meets the set conditions are determined and used to simulate the dynamic bottom hole pressure.

[0034] In an optional embodiment, the operational equations in the fracturing pump-off pressure drop model are discretized using a finite difference method and a semi-implicit method to solve and obtain the dynamic bottom hole pressure.

[0035] In actual operation, in one embodiment, a construction pressure drop characteristic map is drawn based on the dynamic bottom hole pressure as a simulated construction pressure drop distribution feature of the historical fracturing section.

[0036] In a specific embodiment, based on the pump-off pressure change curve, the flow state of the fracture-cavity geological system formed after the fracturing of the to-be-evaluated fracturing section is identified according to the pressure drop characteristic plate division rule.

[0037] Furthermore, in one embodiment, evaluation parameters in the geological system of the fracture-cavity group in the fracturing section to be evaluated are obtained by inversion, and the evaluation parameters include at least one of formation permeability, multi-cavity location, multi-cavity volume, cave storage constant, fracture half-length, and fracture volume.

[0038] Based on other aspects of the reservoir fracturing effect evaluation method described in any one or more of the above embodiments, the present invention also provides a storage medium storing program code that can implement the reservoir fracturing effect evaluation method described in any one or more of the above embodiments.

[0039] Based on the application of the reservoir fracturing effect evaluation method described in any one or more of the above embodiments, the present invention also provides a reservoir fracturing effect evaluation system, which executes the method described in any one or more of the above embodiments.

[0040] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0041] The present invention provides a reservoir fracturing effect evaluation method and system. The method constructs a discrete physical model of fractures, caves, and matrix for a historical fracturing section, and establishes a fracturing pump-off pressure drop model for the fracture-cavity group geological system formed in the reservoir after fracturing based on the discrete physical model. The reservoir fracturing pump-off pressure drop model is established by analyzing the fluid parameters of the complex fracture and small cave group system formed by fracturing. The method first presents multi-scale fracture and cave characteristics based on volume fracturing, simplifies the complex fracture-discrete small cave group system formed by fracturing into a discrete physical model, and uses the seepage relationship and Nevi-Stokes pipe flow theory to reliably characterize the exchange mechanism and flow law of fluids between different media in small caves and multi-scale fractures.

[0042] After determining the fracturing parameters to be used, the reservoir parameters and fracture parameters are introduced, and the fracturing pump-off pressure drop model is used to simulate the dynamic bottom hole pressure data after pump-off under different fracturing parameters; then the pressure drop distribution characteristics are analyzed, and the dynamic pressure data of some historical reservoirs are used to fit the pressure change curve of the fracture-cavity group system of the reservoir to be evaluated, the flow state is identified, and the operation equation corresponding to the flow state is used to obtain data characterizing the key parameters of the fractures of the reservoir to be evaluated, the scale of the cave group, and the degree of fracture-cavity communication, and then the fracturing effect is evaluated. The present invention combines the different flow stage states of the fracture-cavity group combined geological system with matching operation equations to realize well test interpretation, analyzes 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 fracturing.

[0043] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes 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

[0044] 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:

[0045] FIG1 is a schematic flow chart of a reservoir fracturing effect evaluation method provided by one embodiment of the present invention;

[0046] FIG2 is a schematic diagram of a discrete physical model of fractures, caves, and matrix in a reservoir fracturing effect evaluation method according to an embodiment of the present invention;

[0047] FIG3 is a schematic diagram of a flow chart of solving a group of pressure drop equations during pump-off during fracturing in a reservoir fracturing effect evaluation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will describe in detail the implementation methods of the present invention in conjunction with the accompanying drawings and embodiments, so that practitioners 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 can implement the present invention in accordance with the above implementation process. It should be noted that as long as no conflict exists, the various embodiments and various features of each embodiment in the present invention can be combined with each other, and the resulting technical solutions are all within the scope of protection of the present invention.

[0049] Although the flowcharts depict the operations as sequential processes, many of the operations can be performed in parallel, concurrently, or simultaneously. The order of the operations can be rearranged. A process can be terminated when its operations are completed, but can also have additional steps not included in the figures. A process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0050] Computer devices include user devices and network devices. User devices or clients include, but are not limited to, computers, smartphones, PDAs, and the like; network devices include, but are not limited to, a single network server, a server group consisting of multiple network servers, or a cloud computing-based cloud consisting of a large number of computers or network servers. Computer devices can operate independently to implement the present invention, or they can connect to a network and interact with other computer devices in the network to implement the present invention. Networks in which computer devices reside include, but are not limited to, the Internet, wide area networks, metropolitan area networks, local area networks, VPN networks, and the like.

[0051] The terms "first," "second," and the like may be used herein to describe various elements, but these elements should not be limited by these terms, and these terms are used merely to distinguish one element from another. The term "and / or" as used herein includes any and all combinations of one or more of the listed associated items. When an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present.

[0052] The terms used herein are intended only to describe specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "a", "an", "an item" used herein are also intended to include the plural. It should also be understood that the terms "comprise" and / or "include" used herein specify the presence of stated features, integers, steps, operations, units and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0053] With the continued development of oilfields, large-scale fracture-vuggy reservoirs in carbonate karst fracture-vuggy reservoirs are being increasingly utilized, and the focus of development is gradually shifting from large, single fractures to small, continuous fracture-vuggy aggregates. Field production practices have revealed high cumulative production rates in some wells, indicating that while small fractures and vuggy reservoirs are individually small, they are numerous and interconnected through faults, cracks, and karst caves, forming interconnected clusters of small fractures and vuggy reservoirs. These clusters are large in scale and possess enormous exploration and development potential. Therefore, research on the identification of small-scale fracture-vuggy clusters is crucial to further develop these reservoirs.

[0054] However, there are currently many problems with small fracture-cavity reservoirs, such as a weak research foundation and a lack of relevant previous data and research, which pose great challenges to the development of small fracture-cavity group carbonate reservoirs. For example, in the invention patent "Acid fracturing method and device for fracture-cavity carbonate reservoirs" (CN202011279489.2), temporary plugging particles are an effective component of leak-proof and filtration-loss reducers. Therefore, when pumped in, the temporary plugging particles can temporarily block the near-well beads and natural cracks along the way. After the acid fracturing construction is completed, the temporary plugging particles temporarily blocked in the near-well beads and natural cracks 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 away from the wellbore, greatly increasing the efficiency of the acid fracturing transformation, reducing operating costs, and improving the production-increasing transformation effect of fracture-cavity carbonate rocks;

[0055] In the patent document "A Method for Obtaining Fracture Length Using Fracturing Operation Data" (CN112084454A), a seepage model of the fracturing fluid in the formation is established based on the amount of fracturing fluid injected during fracturing operation. Based on this seepage model, a real-space bottomhole pressure solution is obtained. The wellhead pressure is then converted to bottomhole pressure based on the displacement and sand addition during fracturing operation, and the bottomhole pressure is processed. The real-space bottomhole pressure solution is then fitted with the processed bottomhole pressure data to obtain fracture length, permeability, and formation pressure parameters. The method solves the established fracturing fluid seepage model to obtain a pressure distribution solution, integrates it along the fracture direction, and obtains the real-space bottomhole pressure. The wellhead pressure is then converted to bottomhole pressure based on the displacement and sand addition during fracturing operation.

[0056] In the invention patent "A Method for Evaluating Acid Fracturing Effects Based on the Acid Fracturing 'Reformation Zone' Theory" (CN202210537578.5), the present invention discloses a method for evaluating acid fracturing effects based on the acid fracturing 'reformation zone' theory. This method considers the improvement in the seepage pattern of the "reformation zone" near the acid-etched fractures by acid, and on this basis predicts the cumulative production and conducts acid fracturing effect evaluation. This method can effectively improve the accuracy of acid fracturing effect evaluation and help achieve cost-effective development of carbonate reservoirs.

[0057] In summary, the existing technologies in this field present at least the following challenges: The characteristic slope of the pressure change on the analysis curve during pump-off pressure drop can be used to calculate basic parameters such as fracture geometry using well test analysis theory. Current carbonate rock fracturing pressure drop models are relatively simplistic and fail to account for characteristics such as multiple complex fracture clusters and the viscosity-temperature variations of the fracturing fluid. These models are unable to account for primary and secondary fracture parameters and the communication patterns between fracture-vuggy groups. Further simulation research is needed to establish a model that integrates the characteristics of fracturing and pump-off pressure drop in carbonate rock fracture-vuggy reservoirs. Furthermore, after volumetric fracturing, small fracture-vuggy groups in carbonate rock exhibit multi-scale fracture-vuggy carbonate reservoir characteristics, namely, the presence of multiple small vuggy groups connected by fracture networks and multiple microfractures interlaced. The difficulty in modeling pressure drop in multi-scale, multi-fracture-vuggy systems lies in characterizing the flow patterns within these systems. Conventional models, all based on the Darcy flow assumption of a continuous, homogeneous seepage field, cannot account for nonlinear Darcy flow or tubular flow in complex, multi-scale, fracture-vuggy carbonate reservoirs.

[0058] The researchers of the present invention took into account that fracturing is one of the key technical means for the construction of production in fracture-cavity carbonate reservoirs, and how to effectively evaluate the communication mode between the complex fractures formed by fracturing and the small fracture-cavity group is very important. During the 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 fracture is 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 analyzing the pump-off pressure data to truly reflect the connectivity status of the actual underground hydraulic fractures and the small fracture-cavity body. The extension range of the artificial fracture 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 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 reservoir systems.

[0059] To solve the above problems, the present invention provides a reservoir fracturing effect evaluation method and system. By combining the multi-scale characteristics of volume fracturing in carbonate fracture-cavity reservoirs, a fracturing pump-off pressure drop model containing multiple operation equations is established. Based on the fracturing pump-off pressure drop model, the principle of well test interpretation is used to invert key parameters such as cracks, cave group size, and fracture-cavity communication degree to comprehensively evaluate the fracturing effect.

[0060] Next, the detailed process of the method according to the embodiment of the present invention is described in detail based on the accompanying drawings. The steps shown in the flowcharts of the accompanying drawings can be executed in a computer system including, for example, a set of computer-executable instructions. Although the logical order of the steps is shown in the flowcharts, in some cases, the steps shown or described can be executed in a different order than here.

[0061] Example 1:

[0062] FIG1 shows a flow chart of a reservoir fracturing effect evaluation method provided in a first embodiment of the present invention. Referring to FIG1 , it can be seen that the method includes the following steps.

[0063] Model building step S110: constructing a discrete physical model of fractures, caves, and matrix of the historical fracturing section, and establishing a pump-down pressure drop model for the fracture-cavity geological system formed in the reservoir after fracturing based on the discrete physical model, wherein the pump-down pressure drop model includes multiple operational equations;

[0064] Simulation operation step S120: using the fracturing pump stop pressure drop model to simulate the simulated construction pressure drop distribution characteristics of the historical fracturing section under different fracturing parameters;

[0065] Fitting and identification step S130: fitting a pump-off pressure change curve of the to-be-evaluated fracturing section based on the simulated construction pressure drop distribution characteristics, and identifying the flow state of the fracture-cavity geological system according to the pump-off pressure change curve;

[0066] Parameter determination and evaluation step S140: selecting a calculation equation from the fracturing pump-off pressure drop model in combination with the flow state to obtain evaluation parameters of the fracturing section to be evaluated, and determining an evaluation result based on the evaluation parameters.

[0067] Adopting the scheme in the above embodiment, considering that the pump-off pressure value will correspond to different flow states depending on whether the artificial fracture is opened, whether it connects the natural fracture and cave system, and whether the scale of the connected fracture-cavity body changes, the corresponding pressure drop calculation model is adopted for different flow states to most realistically reflect the connectivity state of the actual underground hydraulic fractures and small fracture-cavity bodies. 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 to achieve quantitative evaluation of the fracturing effect. By combining the multi-scale characteristics of volume fracturing in carbonate fracture-cavity reservoirs, a fracturing pump-off pressure drop model is established. Using the well test interpretation method, key parameters such as fractures, cave group scale and fracture-cavity communication degree are inverted to comprehensively evaluate the fracturing effect. This model is not only applicable to large-scale fracture-cavity models, but also well applicable to small fracture-cavity reservoirs, providing a basis for effectively evaluating the communication effect of complex fractures and fracture-cavity groups formed by fracturing.

[0068] The embodiment of the present invention analyzes the differences in fluid parameters and seepage characteristics of the complex fracture-cavity discrete small hole group system formed by fracturing based on different types and stages of fractured reservoirs, and establishes a fracturing pump-off pressure drop model for the wellbore-complex fracture-cavity coupled reservoir based on the combination of reservoir parameters and fracturing fracture parameters. After fracturing, the matrix, together with the fractures and caves, constitutes a complex pore system of the reservoir, namely a complex fracture-cavity-matrix small hole group system, where "matrix" refers to the basic material that constitutes the reservoir rock. The characteristics of the matrix have a significant impact on the storage performance and fluid flow characteristics of oil and gas reservoirs.

[0069] The present invention uses a numerical calculation model based on a geological system of interconnected fractures and caves formed after hydraulic fracturing. This system is primarily composed of natural fractures and caves, which form a highly heterogeneous reservoir system. Fractures are typically rock fractures caused by geological stress, while caves are cavities formed by chemical dissolution.

[0070] In practical applications, a multi-scale fracture-cavity-matrix discrete physical model is constructed to characterize the fracture-cavity geological system by first simplifying the terrain characteristics and the established geological model, combined with simulations of reservoir connectivity and distribution characteristics. This discrete physical model decomposes the behavior of the reservoir and fluid into many small discrete components based on the complex fracture-cavity-matrix small-cavity system, and simulates the behavior of each component and their interactions separately. Common discrete models include the discrete element method (DEM), particle fluid dynamics (PFD), and the lattice Boltzmann method (LBM).

[0071] In an optional embodiment, in the model building step S110, a multi-scale fracture-cavity-matrix discrete physical model representing the fracture-cavity geological system is constructed based on the terrain characteristics and the set geological model simplification principle, combined with the reservoir characteristics of each geological type in the historical fracturing section. The reservoir characteristics include reservoir connectivity characteristics and reservoir distribution characteristics.

[0072] Furthermore, in a preferred embodiment, the geological model simplification principle includes:

[0073] Zones with dense fracture and vug development are simplified as karst reservoirs, and fracture systems are simplified as high-permeability connectivity zones. These connectivity zones are used to connect randomly distributed small vug reservoirs, forming a complex fracture-vug-matrix discrete medium system (Figure 2). In oil and gas geology, a fracture-vug network zone generally refers to an area within a reservoir where fractures and vugs (pores) are highly developed and interconnected. This geological feature is particularly common in carbonate reservoirs, where their complex pore structure and high permeability make them of great development value. A high-permeability connectivity zone refers to a highly connected and extremely permeable geological region within a reservoir. These zones, typically due to the presence of fractures, pores, or other highly permeable pathways, facilitate smoother and more efficient oil and gas flow. In oil and gas geology, a small vug group reservoir refers to a reservoir composed of numerous small vugs within a reservoir. This type of reservoir usually occurs in carbonate reservoirs and has attracted much attention due to its unique pore structure and storage characteristics.

[0074] In practical applications, the corresponding fracture-cavity-matrix discrete physical model is constructed according to the actual reservoir requirements. There are no special requirements for the reservoir type and it can be applied to reservoirs in different regions and types.

[0075] Furthermore, in the model establishment step S110, based on the constructed multi-scale fracture-cavity-matrix discrete (medium) physical model, the fluid parameters of different flow states of the fracture-cavity geological system formed by fracturing are analyzed, and the reservoir parameters and fracturing crack parameters of the historical fracturing section are combined to establish a fracturing pump stop pressure drop model.

[0076] In a preferred embodiment, the process of establishing the fracturing pump-off pressure drop model includes the following operations.

[0077] Cavity group fluid characterization steps: Use the seepage relationship and Nevi-Stokes pipe flow theory to analyze the fluid parameters of the fluid flow state at different stages (scenarios) of the complex fracture-discrete small cave group geological system formed by fracturing;

[0078] The computational model establishment step is to establish a fracturing pump-off pressure drop model for a wellbore-complex fracture-cavern coupled reservoir based on the fluid parameters combined with reservoir parameters and fracturing fracture parameters.

[0079] Among them, 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.

[0080] In the computational model establishment step, the reservoir parameters include: reservoir physical properties, horizontal well length, and cave group distribution; the fracturing parameters include: fracturing fluid parameters, number of primary fractures, number of secondary fractures, and primary / secondary fracture lengths.

[0081] During the computational model establishment step, the material conservation equations for the wellbore-complex fracture-cavern coupling, matrix material conservation equations, and fluid loss equations for the fracturing fluid within fractures and caves of varying levels are established, taking into account the different fluid flow states between adjacent underground media and the principle of material conservation in the dynamic closure scenario of fractures. This is used to comprehensively form a fracturing pump-off pressure drop model. The fracturing pump-off pressure drop model is established by taking into account the material conservation principles and seepage mechanisms between underground media corresponding to different flow states. The flow states include continuous flow from the wellbore to the fractures, crossflow between primary and secondary fractures, fluid loss from primary and secondary fractures to the caves, fluid loss from primary and secondary fractures to the formation, and at least one of the following: fluid loss from primary and secondary fractures to the formation and dynamic closure of the fractures.

[0082] Specifically, volume fracturing of fracture-cavity carbonate reservoirs forms a complex fracture network. During the pump-off phase, the fracturing fluid injection rate is zero, and fracturing fluid flows between adjacent underground media (wellbore flow in WF, crossflow between primary and secondary fractures in Ff, filtration loss in primary fractures in Fm, filtration loss in secondary fractures in fm, and crossflow between fractures and caves in Fv). The inflow and outflow of the multiple media (F, f, m, and v) offset each other, ensuring conservation of mass throughout the system.

[0083] The operational equations of the fracturing pump-off pressure drop model include a multi-object material conservation model of a fracture-cavity geological system, a cave flow pattern model, a fluid loss mechanism model, and a crossflow mechanism model.

[0084] In a preferred embodiment, the multi-object material conservation model in the computational 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. In oil and gas geology, a primary fracture refers to the main natural or artificial fracture system in a reservoir. These fractures usually play a key role in oil and gas storage and flow channels. Secondary fractures refer to smaller cracks or fissures formed in formation rocks, usually secondary branches or tributaries of the main structural fractures (main fractures). These secondary fractures may be associated with the main structural fracture system, but are smaller in scale and have a certain impact on the permeability and fluid migration of the formation.

[0085] Furthermore, in one embodiment, the material conservation equation for 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, and the fluid pressure in the main fracture, taking into account the fracturing fluid saturation of the main fracture, the fracturing fluid loss in the main fracture, the crossflow rate between the main fracture and the secondary fracture, the longitudinal migration distance of the fluid, and the continuous flow rate between the wellbore and the fracture.

[0086] The secondary fracture material conservation equation is established based on the porosity of the secondary fracture, the density of the fracturing fluid, the viscosity of the fracturing fluid, the fluid pressure in the secondary fracture, and the factors of the fracturing fluid saturation in the secondary fracture, the fracturing fluid loss in the secondary fracture, the longitudinal migration distance of the fluid, and the crosstalk flow between the primary fracture and the secondary fracture;

[0087] The crossflow rate between the primary fracture and the secondary fracture is determined by the density of the fracturing fluid, the pressure of the primary fracture fluid, the pressure of the secondary fracture fluid, the viscosity of the fracturing fluid, and the change in the longitudinal migration distance of the fluid.

[0088] The flow rate from the wellbore to the main fracture is determined by introducing the matrix shape factor based on the reservoir thickness, fracturing fluid density, main fracture width, fluid pressure in the main fracture, fracturing fluid viscosity, fracturing fluid volume coefficient, reservoir radius, wellbore radius, and skin factor.

[0089] In an optional embodiment, 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, and the fluid pressure in the cave are comprehensively considered, and the crossflow rate between the primary fracture and the cave and the crossflow rate between the secondary fracture and the cave are combined to establish the material conservation equation of the cave.

[0090] Preferably, in one embodiment, 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 fracturing fluid viscosity, fracturing fluid density, flow velocity, and fluid pressure in the cave.

[0091] 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.

[0092] 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;

[0093] The fracture shape factor of the secondary fracture is introduced, and the filtration equation of the fracturing fluid in the secondary fracture is established based on 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 of the fluid.

[0094] In one embodiment, the main fracture and cave shape factor is introduced, and the crossflow equation between the main fracture and cave is established based on 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;

[0095] The secondary fracture and cave shape factor is introduced, and the crossflow equation between secondary fractures and caves is established based on the fracturing fluid density, permeability of fracturing fluid in caves, fluid pressure in secondary fractures, fluid pressure in caves, fracturing fluid viscosity and longitudinal migration distance of the fluid.

[0096] Furthermore, in the simulation operation step S120, based on the reservoir parameters and fracturing crack parameters of the historical fracturing section, the operation equation corresponding to the flow state in the fracturing pump-off pressure drop model is used to simulate and calculate the dynamic bottom hole pressure after pump-off under different fracturing parameters in each historical fracturing section.

[0097] In a preferred embodiment, the method further includes, before simulating the dynamic bottom hole pressure, conducting a sensitivity analysis on the established wellbore-complex fracture-cavern coupled fracturing pump-down pressure drop model to determine the sensitive fracturing parameters whose influence on the pressure change meets the set conditions; in actual application, the sensitivity analysis is used to find out the parameters that have a greater impact on the horizontal well pressure drop, and the subsequent simulation steps are focused on these parameters. Fracturing parameters are important factors that affect the fracturing effect and fracture characteristics. Reasonable selection and optimization of these parameters can help 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.

[0098] By conducting a sensitivity analysis on the established wellbore-complex fracture-cavern coupled pressure drop model, the sensitive fracturing parameters whose impact on pressure changes meets the set conditions are determined as the fracturing parameters to be used, and the corresponding available configuration parameters are set based on these sensitive fracturing parameters.

[0099] In an optional embodiment, the sensitive fracturing parameters may include different numbers of perforation clusters, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeability parameters.

[0100] Further dynamic simulation operations are performed, the reservoir parameters and fracturing crack parameters of the current reservoir are introduced, and the established fracturing pump-off pressure drop model is used to simulate the dynamic bottom hole pressure data under the set fluid flow scenarios and fracture dynamic closure scenarios after pump-off under different (sensitive) fracturing parameters.

[0101] In practical applications, the reservoir multi-scale flow medium and fluid parameters are acquired in advance and stored for later use;

[0102] Based on the multi-scale flow medium and fluid parameters of the reservoir, combined with the reservoir parameters and fracture parameters, a fracturing pump-off pressure drop model is established to simulate dynamic bottomhole pressure data under different sensitive fracturing parameters, including fluid flow scenarios after pump-off and dynamic fracture closure scenarios, to determine the pressure drop variation pattern of fractured horizontal wells under different reservoir parameters. The present embodiment establishes a wellbore-complex fracture-formation coupled fracturing operation pressure drop model. The operation pressure drop refers to the pressure loss caused by fluid friction, formation fractures, and other factors during the fracturing operation. This parameter is crucial to the success of the fracturing operation because it affects fracture formation, proppant delivery, and fracturing fluid injection. The present embodiment uses the fracturing operation pressure drop model to simulate the physical processes involved in the reservoir pressure drop scenario, including: the extension and closure of the primary fracture; changes in fracture flexibility before and after closure; the development of secondary fractures; the flow of fluid within the fracture; the flow between the fracture and the wellbore; filtration from the fracture to the formation; and crossflow between fractures and cavities.

[0103] Therefore, the setting of the fluid flow scenario includes: the continuous flow state from the wellbore to the fracture, the crossflow state between the primary and secondary fractures, the filtration state of the primary and secondary fractures to the cave body, and the filtration state of the primary and secondary fractures to the formation. Among them, continuous flow refers to the phenomenon that the fracturing fluid continues to flow through the fracture system after the fracturing operation is completed. This continuous flow phenomenon can help maintain the open state of the fracture, enhance the permeability of the rock, and thus increase the production capacity of the oil field or oil reservoir. Crossflow (Interzonal Flow) refers to the fluid movement phenomenon that may occur between different formations, reservoirs, fractures, pores and other spaces. This phenomenon may be due to pressure differences or connectivity between formations, causing fluid to flow from one space to another. Filtration loss: (Fluid 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.

[0104] This embodiment of the present invention establishes a wellbore-complex fracture-formation coupled pump-off pressure drop model. Finite-difference discretization is used to discretize the multiscale flow equations for fractures, matrix, and caves, and the solution is achieved using a Newton-Raphson iterative algorithm. The pressure drop characteristics of fractures under different perforation cluster numbers, different operation fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities are simulated. The pressure drop patterns of fractured horizontal wells under different reservoir parameters are determined based on pre-acquired multiscale flow medium and fluid parameters of the reservoir and the pump-off pressure drop model.

[0105] Furthermore, in an optional embodiment, in the simulation operation step, the equations of the fracturing pump stop 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 according to the time step.

[0106] 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.

[0107] In practical applications, programming tools can be used to solve the matrix equation using the LU decomposition method. The pump-off pressure drop of the fractured horizontal well under different parameters at different times can be obtained according to the time step. For example, Matlab programming tools can be used for the solution. The solution process includes:

[0108] Basic parameters were input into Matlab: reservoir properties and fracturing fluid parameters, number of primary fractures, number of secondary fractures, primary / secondary fracture lengths, horizontal well length, cave group distribution, and pump down time. The fracture-matrix-cavity equations were discretized using the finite difference method and the semi-implicit method to obtain the coefficient matrix of the equations, and the LU decomposition method was used to solve the equations. Based on the time step, the horizontal well pressure drop at any time can be calculated, as shown in Figure 3.

[0109] It should be noted that in other embodiments, other reservoir and fluid parameters may be selected for input according to actual reservoir geological conditions, and other programming software may also be selected for programming and solving.

[0110] Based on the obtained pressure data, a pressure drawdown characteristic plot is then plotted for different perforation cluster numbers, different operation fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities to simulate the operation pressure drawdown distribution. The Pressure Drawdown Diagnostic Plot is a tool used to analyze the condition of oil or gas wells. By displaying the production pressure drawdown of an oil or gas well over different time periods, it helps engineers and geologists assess the performance characteristics of an oil or gas reservoir and diagnose potential problems, such as fracture blockage.

[0111] Preferably, in one embodiment, the method further comprises the following steps: after simulating and obtaining the simulated construction pressure drop distribution characteristics of the historical fracturing section, determining a pressure drop characteristic plate division rule for different flow states of the historical fracturing section.

[0112] The flow state changes were identified by combining the changes in the slope of the double-logarithmic diagnostic curve. The dynamic bottomhole pressure change curves of different flow states in the historical fracturing sections were analyzed to determine the shapes of the dynamic pressure distribution curves corresponding to different fluid flow scenarios of the fracture-cavity geological system as a whole. That is, the association rules between the simulated construction pressure drop distribution characteristics and the flow state were determined, which served as the rules for dividing the pressure drop characteristic map.

[0113] In actual application, according to the solved simulated construction pressure drop characteristic data, that is, according to the programming calculation results, the construction pressure drop characteristic plates under different perforation cluster numbers, different construction fluid volumes, different horizontal stresses, different fluid viscosities, and different permeabilities are drawn. Combined with the changes in the slope of the double logarithmic diagnostic curve, the associated flow state changes are identified to form the pressure drop characteristic plate division rules.

[0114] Furthermore, the fitting and identification step S130 is performed to fit the actual pump-off pressure variation curve of the to-be-evaluated fracturing section based on the simulated construction pressure drop distribution characteristics of the historical fracturing section.

[0115] Then, the parameter determination and evaluation step S140 is executed to identify the flow state of the fracture-cavity geological system according to the pump-off pressure change curve, and to identify the flow state of the fracture-cavity geological system formed after the fracturing of the to-be-evaluated fracturing section by using the pressure drop characteristic plate division rule.

[0116] Furthermore, in an optional embodiment, in the parameter determination and evaluation step, an evaluation parameter of the fracture-cavity geological system of the to-be-evaluated fracturing section is obtained by inversion, wherein the evaluation parameter includes at least one of formation permeability, location of multiple caves, volume of multiple caves, cave storage constant, fracture half-length, and fracture volume. The cave storage constant refers to a quantitative indicator of the ability of caves or pore spaces in an oil and gas reservoir to store oil and gas during the development and production of underground oil and gas reservoirs; and the half-length of a fracture refers to the semi-major axis length of a fracture in the vertical direction.

[0117] The embodiment of the present invention is based on the established fracturing pump-off pressure drop model, and uses the double logarithmic well testing method of the pressure characteristic curve to invert the evaluation parameters reflecting the fracture parameters, the scale of the cave group and the degree of fracture-cavity communication to evaluate the fracturing effect.

[0118] Therefore, based on the pressure change curve, the fracturing pump-off pressure drop model is used to invert data representing the current key parameters of reservoir fractures, the size of the cavity group, and the degree of fracture-cavity communication. Among them, the sensitive fracturing parameters whose influence meets the set conditions determined by the sensitive parameter analysis operation can be preferably selected from the input parameters used in constructing the fracturing pump-off pressure drop model to determine the data representing the current key parameters of reservoir fractures, the size of the cavity group, and the degree of fracture-cavity communication.

[0119] In an optional embodiment, data characterizing key reservoir fracture parameters, cave group size, and fracture-cavity connectivity include reservoir formation permeability, location of multiple caves, volume of multiple caves, cave storage constant, fracture half-length, and fracture volume. Specifically, by fitting simulated pump-off pressure drop data with actual pressure drop data, parameters such as formation permeability, location of multiple caves, volume of multiple caves, cave storage constant, fracture half-length, and fracture volume are inverted.

[0120] Finally, 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 fracturing effect evaluation results, and the parameter interpretation results are derived.

[0121] 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 fracturing, forming an evaluation method for the volume fracturing effect of carbonate rock fracture-cavity reservoirs, which provides a basis for effectively evaluating the communication effect of complex cracks and fracture-cavity groups formed by fracturing transformation.

[0122] For simplicity of description, the aforementioned method embodiments are described as a series of actions. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, as certain steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions and modules involved are not necessarily required for the present invention.

[0123] It should be noted that, in other embodiments of the present invention, the method can also obtain a new reservoir fracturing effect evaluation method by combining one or several of the above embodiments to achieve accurate evaluation of the reservoir fracturing effect of the combined system.

[0124] It should be noted that, based on the method in any one or more of the above-mentioned embodiments of the present invention, the present invention also provides a storage medium, which stores program code that can implement the method described in any one or more of the above-mentioned embodiments, and when the code is executed by the operating system, it can implement the reservoir fracturing effect evaluation method described above.

[0125] Example 2:

[0126] The methods disclosed in the embodiments of the present invention are described in detail. The methods of the present invention can be implemented using various devices or systems. Therefore, based on other aspects of the methods described in any one or more of the above embodiments, the present invention further provides a reservoir fracturing effect evaluation system for executing the reservoir fracturing effect evaluation methods described in any one or more of the above embodiments. Specific embodiments are provided below for detailed description.

[0127] Specifically, the reservoir fracturing effect evaluation system provided in the embodiment of the present invention includes:

[0128] a model building module configured to construct a discrete physical model of fractures, caves, and matrix for a historical fracturing stage, and to establish a pump-down pressure drop model for a fracture-cavity geological system formed in the reservoir after fracturing based on the discrete physical model, wherein the pump-down pressure drop model includes a plurality of operational equations;

[0129] A simulation operation module configured to use the fracturing pump stop pressure drop model to simulate the simulated construction pressure drop distribution characteristics of historical fracturing sections under different fracturing parameters;

[0130] a fitting and identification module configured to fit a pump-off pressure change curve of the to-be-evaluated fracturing section based on the simulated construction pressure drop distribution characteristics, and identify the flow state of the fracture-cavity geological system according to the pump-off pressure change curve;

[0131] The parameter determination and evaluation module is configured to select an operational equation from the fracturing pump-off pressure drop model in combination with the flow state to obtain evaluation parameters of the fracturing section to be evaluated, and determine an evaluation result based on the evaluation parameters.

[0132] Preferably, in one embodiment, the model building module is configured to construct a fracture-cavity-matrix discrete physical model of the fracture-cavity geological system based on topographic features and set geological model simplification principles, in combination with reservoir characteristics.

[0133] Furthermore, in one embodiment, the geological model simplification principles include:

[0134] The zone with dense development of fractures and pores is simplified into karst reservoirs, and the fracture system is simplified into high-permeability connecting belts. High-permeability connecting belts are used to connect the randomly distributed small cave group reservoirs to form a complex fracture-cavity-matrix discrete medium small cave group system formed after fracturing.

[0135] Specifically, in an optional embodiment, the model building module is configured to analyze the fluid parameters of different flow states of the fracture-cavity-matrix discrete physical model formed by fracturing, and to establish a fracturing pump-down pressure drop model in combination with the reservoir parameters and fracturing crack parameters of the historical fracturing section.

[0136] In one embodiment, the model building module is configured to perform the following operations:

[0137] The fracturing pump-off pressure drop model is established by considering the material conservation principle and seepage mechanism between underground media corresponding to different flow states; and

[0138] The flow state includes at least one of a continuous flow state from the wellbore to the fracture, a cross-flow state between the primary and secondary fractures, a filtration state from the primary and secondary fractures to the cave body, a filtration state from the primary and secondary fractures to the formation, and a dynamic closure state of the fracture.

[0139] Optionally, in one embodiment, 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.

[0140] In a preferred embodiment, the multi-object material conservation model in the computational 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.

[0141] Furthermore, in one embodiment, the material conservation equation for 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, and the fluid pressure in the main fracture, taking into account the fracturing fluid saturation of the main fracture, the fracturing fluid loss in the main fracture, the crossflow rate between the main fracture and the secondary fracture, the longitudinal migration distance of the fluid, and the continuous flow rate between the wellbore and the fracture.

[0142] The secondary fracture material conservation equation is established based on the porosity of the secondary fracture, the density of the fracturing fluid, the viscosity of the fracturing fluid, the fluid pressure in the secondary fracture, and the factors of the fracturing fluid saturation in the secondary fracture, the fracturing fluid loss in the secondary fracture, the longitudinal migration distance of the fluid, and the crosstalk flow between the primary fracture and the secondary fracture;

[0143] The crossflow rate between the primary fracture and the secondary fracture is determined by the density of the fracturing fluid, the pressure of the primary fracture fluid, the pressure of the secondary fracture fluid, the viscosity of the fracturing fluid, and the change in the longitudinal migration distance of the fluid.

[0144] The flow rate from the wellbore to the main fracture is determined by introducing the matrix shape factor based on the reservoir thickness, fracturing fluid density, main fracture width, fluid pressure in the main fracture, fracturing fluid viscosity, fracturing fluid volume coefficient, reservoir radius, wellbore radius, and skin factor.

[0145] In an optional embodiment, 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, and the fluid pressure in the cave are comprehensively considered, and the crossflow rate between the primary fracture and the cave and the crossflow rate between the secondary fracture and the cave are combined to establish the material conservation equation of the cave.

[0146] Preferably, in one embodiment, 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 fracturing fluid viscosity, fracturing fluid density, flow velocity, and fluid pressure in the cave.

[0147] 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.

[0148] 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;

[0149] The fracture shape factor of the secondary fracture is introduced, and the filtration equation of the fracturing fluid in the secondary fracture is established based on 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 of the fluid.

[0150] In one embodiment, the cave shape factor of the main fracture is introduced, and the crossflow equation between the main fracture and the cave is established based on 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 change in the longitudinal migration distance of the fluid;

[0151] 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.

[0152] Specifically, in one embodiment, the simulation operation module is configured to simulate and calculate the dynamic bottom hole pressure after pumping is stopped under different fracturing parameters in each historical fracturing section using the operation equation corresponding to the flow state in the fracturing pump-off pressure drop model based on the reservoir parameters and fracturing crack parameters of the historical fracturing section.

[0153] Preferably, in one embodiment, the system further comprises a division rule determination module, which is configured to determine the pressure drop characteristic plate division rules for different flow states of the historical fracturing section after simulating and obtaining the simulated construction pressure drop distribution characteristics of the historical fracturing section.

[0154] On the other hand, in one embodiment, the system further includes a fracturing parameter selection module, which is configured to perform the following operations:

[0155] By conducting a sensitivity analysis on the established fracturing pump-off pressure drop model, the fracturing parameters whose impact on the dynamic bottom hole pressure change meets the set conditions are determined and used to simulate the dynamic bottom hole pressure.

[0156] In an optional embodiment, the simulation operation module is configured to discretize the operation equations in the fracturing pump-off pressure drop model using a finite difference method and a semi-implicit method to obtain the dynamic bottom hole pressure.

[0157] In actual operation, in one embodiment, the simulation operation module draws an operation pressure drop characteristic chart based on the dynamic bottom hole pressure as a simulated operation pressure drop distribution characteristic of the historical fracturing section.

[0158] In a specific embodiment, the fitting and identification module is configured to identify the flow state of the fracture-cavity geological system formed after the fracturing of the to-be-evaluated fracturing section based on the pump-off pressure change curve and the pressure drop characteristic plate division rule.

[0159] Furthermore, in one embodiment, the parameter determination and evaluation module obtains evaluation parameters in the geological system of the fracture-cavity group of the fracturing section to be evaluated through inversion, and the evaluation parameters include at least one of formation permeability, multi-cavity location, multi-cavity volume, cave storage constant, fracture half-length, and fracture volume.

[0160] In the reservoir fracturing effect evaluation system 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 operation requirements to achieve corresponding technical effects.

[0161] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should extend to equivalent substitutions of these features understood by those skilled in the relevant art. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0162] The phrase "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.

[0163] Although the embodiments disclosed herein are as described above, the contents described herein are merely embodiments for facilitating understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art may make any modifications and variations in the form and details of the embodiments without departing from the spirit and scope of the present invention. However, the scope of patent protection of the present invention shall remain subject to the scope defined by the appended claims.

Claims

1. A reservoir fracturing effect evaluation method, characterized in that: The method comprises the following steps: Constructing a discrete physical model of fractures, caves and matrix of the historical fracturing section, and establishing a fracturing pump-off pressure drop model for the fracture-cavity geological system formed after the reservoir is fracturing based on the discrete physical model, wherein the fracturing pump-off pressure drop model includes a plurality of operation equations; The fracturing pump stop pressure drop model is used to simulate the simulated construction pressure drop distribution characteristics of the historical fracturing section under different fracturing parameters; Fitting a pump-off pressure change curve of the to-be-evaluated fracturing section based on the simulated construction pressure drop distribution characteristics, and identifying the flow state of the fracture-cavity group geological system according to the pump-off pressure change curve; An operational equation is selected from the fracturing pump stop pressure drop model in combination with the flow state to obtain evaluation parameters of the fracturing section to be evaluated, and an evaluation result is determined based on the evaluation parameters.

2. The reservoir fracturing effect evaluation method according to claim 1, characterized in that: According to the terrain characteristics and the set geological model simplification principles, combined with the reservoir characteristics, a fracture-cavity-matrix discrete physical model of the fracture-cavity geological system of the fracturing section is constructed.

3. The reservoir fracturing effect evaluation method according to claim 2, characterized in that: The geological model simplification principles include: The zone with densely developed fractures and pores is simplified into karst reservoirs, and the fracturing fracture system is simplified into a high-permeability connecting zone. The high-permeability connecting zone is used to connect the randomly distributed small cave group reservoirs to form a complex fracture-cavity-matrix discrete medium small cave group system after fracturing.

4. The reservoir fracturing effect evaluation method according to claim 1, characterized in that: Based on the fracture-cavern-matrix discrete physical model, the fluid parameters of different flow states of the fracture-cavern geological system formed by fracturing are analyzed, and the fracturing pump-down pressure drop model is established in combination with the reservoir parameters and fracturing fracture parameters of the historical fracturing section.

5. The reservoir fracturing effect evaluation method according to claim 4, characterized in that: The fracturing pump stop pressure drop model is established by considering the material conservation principle and seepage mechanism between underground media corresponding to different flow states; and The flow state includes the continuous flow state from the wellbore to the fracture, the cross-flow state between the primary and secondary fractures, the The filtration state of the cave body, and at least one of the filtration state of the primary and secondary fractures into the formation and the dynamic closure state of the fractures.

6. The reservoir fracturing effect evaluation method according to claim 1, characterized in that: The operation 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.

7. The reservoir fracturing effect evaluation method according to claim 1 or 6, characterized in that: 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.

8. The reservoir fracturing effect evaluation method according to claim 7, characterized in that: 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; 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; 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; 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.

9. The reservoir fracturing effect evaluation method according to claim 7, characterized in that: 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.

10. The reservoir fracturing effect evaluation method according to claim 7, characterized in that: 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.

11. The reservoir fracturing effect evaluation method according to claim 1 or 6, characterized in that: The fluid loss mechanism model in the operation 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.

12. The reservoir fracturing effect evaluation method according to claim 11, characterized in that: Introducing the fracture shape factor of the main fracture, establishing a filtration equation of the fracturing fluid in the main fracture according to 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; 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.

13. The reservoir fracturing effect evaluation method according to claim 11, characterized in that: 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 density of the fracturing fluid, the permeability of the fracturing fluid in the cave, the fluid pressure in the main fracture, the fluid pressure in the cave, the viscosity of the fracturing fluid and the longitudinal migration distance of the fluid; 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.

14. The reservoir fracturing effect evaluation method according to claim 1, characterized in that: Based on the reservoir parameters and fracturing crack parameters of the historical fracturing sections, the operational equation corresponding to the flow state in the fracturing pump-off pressure drop model is used to simulate and calculate the dynamic bottom hole pressure after pump-off under different fracturing parameters in each historical fracturing section.

15. The reservoir fracturing effect evaluation method according to claim 1, characterized in that: The method further comprises the following steps: after obtaining the simulated construction pressure drop distribution characteristics of the historical fracturing section by simulation calculation, determining the pressure drop characteristic plate division rules for different flow states of the historical fracturing section.

16. The reservoir fracturing effect evaluation method according to claim 1, characterized in that: The method further comprises: By conducting a sensitivity analysis on the established fracturing pump-off pressure drop model, the fracturing parameters whose influence on the dynamic bottom hole pressure change meets the set conditions are determined and used to simulate the dynamic bottom hole pressure.

17. The reservoir fracturing effect evaluation method according to claim 14, characterized in that: The operational equations in the fracturing pump-off pressure drop model are discretized using the finite difference method and the semi-implicit method to solve and obtain the dynamic bottom hole pressure.

18. The reservoir fracturing effect evaluation method according to claim 14 or 17, characterized in that: A construction pressure drop characteristic chart is drawn based on the dynamic bottom hole pressure as a simulated construction pressure drop distribution characteristic of the historical fracturing section.

19. The reservoir fracturing effect evaluation method according to claim 15, characterized in that: Based on the pump-off pressure change curve, the flow state of the fracture-cavity geological system formed after the fracturing of the to-be-evaluated fracturing section is identified according to the pressure drop characteristic plate division rule.

20. The reservoir fracturing effect evaluation method according to any one of claims 1 to 19, characterized in that: The evaluation parameters in the geological system of the fracture-cavity group of the to-be-evaluated fracturing section are obtained by inversion, and the evaluation parameters include at least one of the formation permeability, the location of multiple caves, the volume of multiple caves, the cave storage constant, the fracture half-length, and the fracture volume.

21. A storage medium, characterized in that: The storage medium stores program codes that can implement the reservoir fracturing effect evaluation method as described in any one of claims 1 to 20.

22. A reservoir fracturing effect evaluation system, characterized in that: The system executes the method according to any one of claims 1 to 20.

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