An evaluation method and exploration method for simulating the formation process of fault-controlled karst reservoirs

Abstract

The present invention discloses an evaluation method and exploration method for simulating the formation process of fault-controlled karst reservoirs, comprising: performing seismic stratigraphic slicing based on seismic data within a study area, identifying vertical structural sequences within the study area, and determining fault activity periods in the study area; conducting geological analysis of the fractures and fillings in the fault-controlled karst development zones during the fault activity periods within the study area, restoring the fault and fluid activity events in the study area based on the geological analysis results, and then revising the evolutionary history and burial history model of the fault activity in the study area. This method establishes the type of fault-controlled karst reservoir in the study area and its episodic evolution model, and then conducts a dissolution-reserve evaluation experiment under geological constraints. This method combines the age of carbonate cements, the formation temperature of carbonate cements, and the restoration of burial history, and combines this with a paleo-geothermal model to establish an absolute age-corrected burial history; and then, through a dissolution-reserve evaluation experiment under geological constraints, quantitatively restores the formation process of the fault-controlled karst reservoir in the study area.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum and natural gas geological exploration, and in particular to an evaluation method and an exploration method for simulating the formation process of a fault-controlled karst reservoir. Background Art

[0002] The exploration of resources such as oil and natural gas is crucial to national energy security. Carbonate rocks are the primary type of oil and gas exploration globally. According to statistics, global resources total 877.7 billion tons of oil equivalent, of which carbonate rocks account for 632 billion tons, or 72% (according to CNPC, 2011). Global oil and gas production is 6.95 billion tons, of which carbonate rocks account for 4.38 billion tons, or 63% (according to BP, 2012, data from 2011). Deep marine carbonate oil and gas reservoirs have become a key area of ​​exploration globally, particularly in China, in recent years. Traditional theories of marine carbonate oil and gas accumulation posit four main types of carbonate reservoirs and reservoirs: bioherms, grain banks, dolomites, and karst weathering crusts. In recent years, exploration has increasingly recognized that fault zones serve as both oil and gas transport pathways and favorable reservoir formation areas. Taking a certain oilfield as an example, under the influence of the Upper Ordovician overburden, the development of karst fractures and caves closely matches fault zones and tectonic deformation zones, exhibiting distinct fault-controlled karst characteristics. Dissolution and expansion centered on deep, large fault zones have made these zones favorable for the development of Middle-Lower Ordovician karst fractures and caves within the overburden, creating a unique reservoir type in the Fuman area: fault-controlled karst reservoirs. Due to the significant decline in carbonate reserves and production in shallow and paleohigh areas, oil and gas exploration and development have expanded to deep and even ultra-deep reservoirs. The exploration potential of fault-controlled karst reservoirs in structural lowlands has become increasingly prominent. However, conventional theories of carbonate reservoirs and oil and gas accumulation are no longer sufficient for the exploration and development of deep marine carbonate reservoirs in structural lowlands. To address key questions regarding the genesis, primary controlling factors, and distribution patterns of fault-controlled karst reservoirs, there is an urgent need to develop methods for quantitatively restoring the formation process of fault-controlled karst reservoirs. Summary of the Invention

[0003] In order to clarify the main controlling factors and distribution patterns of the development of fault-controlled karst reservoirs in the study area, and thereby enrich technical routes and increase selection space, an evaluation method and exploration method for simulating the formation process of fault-controlled karst reservoirs are provided in the embodiments of the present invention.

[0004] In a first aspect, an embodiment of the present invention provides an evaluation method for simulating the formation process of a fault-controlled karst reservoir, which may include:

[0005] Performing seismic stratigraphic slicing based on seismic data within a study area to identify a vertical structural sequence within the study area, thereby determining a fault activity phase within the study area based on the vertical structural sequence;

[0006] Conducting geological analysis on the fractures and fillings in the fault-controlled karst development zones during each fault activity period within the study area, restoring the fault and fluid activity events in the study area based on the geological analysis results, and then revising the fault activity evolution history and burial history model in the study area to establish the fault-controlled karst reservoir types and their episodic evolution patterns in the study area;

[0007] For each episode of karstification in the fault-controlled karst model in the study area, a dissolution and reserve enhancement evaluation experiment under geological conditions was carried out using carbonate rock plug samples with customized fracture occurrence, so as to quantitatively restore the formation process of the fault-controlled karst reservoir in the study area based on the experimental results.

[0008] Optionally, the method may further include: determining the main controlling factors and distribution patterns of the development of the fault-controlled karst reservoirs in the study area based on the formation process and reservoir type of the fault-controlled karst reservoirs in the study area.

[0009] Optionally, for each episode of karstification in the fault-controlled karst model in the study area, a dissolution reserve enhancement evaluation experiment under geological conditions may be conducted, specifically including:

[0010] Obtaining the rock type, rock component parameters, reservoir diagenetic fluid characteristic parameters and geological background parameters of the carbonate reservoir corresponding to the target episode in the study area;

[0011] Based on the rock type, rock component parameters and reservoir fracture occurrence, a carbonate rock plug sample is produced to simulate the fracture occurrence of the carbonate reservoir in the study area;

[0012] Weighing and CT scanning the carbonate rock plug sample before the experiment to determine the initial weight of the carbonate rock plug sample and the initial internal pore structure of the rock;

[0013] preparing an erosive fluid simulating the reservoir diagenetic fluid based on characteristic parameters of the reservoir diagenetic fluid;

[0014] Under the constraints of the geological background parameters, a dissolution and reserve enhancement simulation experiment is carried out using the carbonate rock plug sample and the corrosive fluid, and the reaction generated fluid is collected in real time;

[0015] The samples after the dissolution and reserve enhancement simulation experiment were dried, weighed, and CT scanned, and compared with the initial weight and the initial internal porosity structure of the rock. Combined with the ion composition and content analysis results of the collected reaction liquid, the carbonate rock pore evolution characteristics, dissolution effect and dissolution mechanism of the carbonate reservoir corresponding to the target episode in the study area were determined.

[0016] Optionally, the dissolution effect and dissolution mechanism are obtained by qualitative and quantitative analysis based on the dissolution weight, the total concentration of calcium ions and magnesium ions in the reaction solution, porosity, permeability, and microscopic characteristic images obtained by CT scanning.

[0017] Optionally, when performing CT scanning before and after the experiment on the carbonate rock plug sample, an in-situ comparison is performed on the internal fracture occurrence of the carbonate rock plug sample to obtain the pore evolution characteristics of the carbonate rock.

[0018] Optionally, before conducting the dissolution and reserve enhancement simulation experiment, the gas flow inlet and outlet ends of the carbonate rock plug sample are marked, and based on the marked inlet and outlet ends of the carbonate rock plug sample, the carbonate rock plug sample is placed in the core holder of the diagenesis simulation device to ensure that the flow direction of the corrosive fluid is consistent with the gas flow direction during physical property analysis.

[0019] Optionally, the geological background parameter constraints include: the type of geological stress driving the migration of geological fluids, the temperature and pressure in the core holder;

[0020] The types of geological stress include: tectonic force, hydrodynamic force, geostatic pressure and thermal force.

[0021] Optionally, the geological background parameter constraints for the dissolution-reserve enhancement simulation experiment include:

[0022] The fluid inlet pressure of the simulated experimental fluid is set by a fluid pressure pump and kept constant; the confining pressure and axial pressure are applied to the carbonate rock plunger sample by the reactor confining pressure control system and the reactor axial hydraulic control system.

[0023] Optionally, the fluid inlet pressure of the simulation experiment is determined by the following method:

[0024] Based on the burial depth of the restored karstification, combined with the geothermal gradient and formation pressure gradient, determine the fluid pressure of the target layer of the karstification fluid source and the fluid pressure at the depth of karstification;

[0025] The pressure of the driving fluid is determined by the difference between the fluid pressure of the target layer where the karstification fluid originates and the fluid pressure at the depth where the karstification occurs, and is used as the fluid inlet pressure of the simulation experiment.

[0026] In a second aspect, an embodiment of the present invention provides an oil and gas exploration method, which explores oil and gas in a study area based on the formation process of fault-controlled karst reservoirs in the study area;

[0027] The formation process of the fault-controlled karst reservoir in the study area is determined based on the evaluation method for simulating the formation process of the fault-controlled karst reservoir described in the first aspect.

[0028] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0029] An embodiment of the present invention provides an evaluation method and an exploration method for simulating the formation process of fault-controlled karst reservoirs. On the one hand, the method combines carbonate cement dating with high-resolution seismic interpretation to establish a fault activity period restoration technology with absolute age correction; on the other hand, the absolute age of carbonate cements and the formation temperature of carbonate cements are combined with traditional burial history restoration, and combined with the paleo-geothermal model of the study area, a burial history restoration technology with absolute age correction is established; and on the third hand, a technology is established based on the results of dissolution reserve enhancement evaluation experiments under geological conditions to achieve quantitative restoration of the entire formation process of fault-controlled karst reservoirs in the study area.

[0030] 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 purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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:

[0033] Figure 1 This is a flow chart of an evaluation method for simulating the formation process of a fault-controlled karst reservoir provided in an embodiment of the present invention;

[0034] Figure 2 Flowchart for the specific execution of step S13;

[0035] Figure 3 This is a cross-sectional diagram of the development of strike-slip fault patterns in different periods in a certain study area in the example of the present invention;

[0036] Figure 4 Construct a diagram of burial evolution and fluid activity patterns for the above examples;

[0037] Figure 5 This is a cross-section of the Late Caledonian-Early Hercynian fault style in the above example;

[0038] Figure 6 This is an artificial carbonate rock sample with en echelon fractures in the above example;

[0039] Figure 7This is a three-dimensional image of the internal fractures of the en echelon artificial carbonate rock sample before dissolution in the above example;

[0040] Figure 8 This is a three-dimensional diagram of the internal cracks of the en echelon artificial carbonate rock sample after dissolution in the above example;

[0041] Figure 9 This is a comparison chart of the porosity values ​​of the en echelon artificial carbonate rock sample before and after dissolution in the above example;

[0042] Figure 10 This is a comparison chart of the permeability values ​​of the en echelon artificial carbonate rock sample before and after dissolution in the above example; DETAILED DESCRIPTION

[0043] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0044] Invention patent CN202011025429.8 "A method, device, electronic device and storage medium for simulating fault-controlled karst processes" includes: obtaining the initial state of the formation, including the fracture network and matrix model formed by strike-slip faults; dividing the matrix model into structured three-dimensional grids; using cellular automata to simulate the fault-controlled karst process of the formation under the action of atmospheric precipitation according to preset evolution rules, so that when the acid concentration of the surrounding three-dimensional grids is greater than the acid concentration of the current three-dimensional grid, the acid concentration of the current three-dimensional grid is increased, and the acid concentration of the surrounding three-dimensional grids is decreased. The inventors found that the patent has three shortcomings: first, it uses numerical simulation instead of physical simulation that is closer to actual conditions, and the simulation structure is random; second, it lacks geological condition constraints based on comprehensive geological research on faults and fluid activity events; third, it only considers the karst effect of atmospheric precipitation, and ignores the internal karst effects such as hydrothermal fluids and organic acids connected by deep and large faults.

[0045] Invention patent CN202011398817.0 "Small-scale fault-controlled karst reservoir seismic prediction method and device" provides a small-scale fault-controlled karst reservoir seismic prediction method and device. The inventor found that this method mainly uses geophysics to identify the internal structural characteristics of small-scale fault-controlled karst reservoirs, and it does not have the ability to quantitatively restore the formation process of fault-controlled karst reservoirs.

[0046] Invention patent CN202011132720.5, "A method and device for quantitatively identifying the boundaries of ultra-deep fault-controlled karst reservoirs," analyzes effective seismic attributes and determines their effective attribute values. This method then establishes a geological model of the boundaries of typical ultra-deep fault-controlled karst reservoirs in the target area. Through forward modeling and analysis, the effective attribute values ​​are adjusted to ensure the reliability of quantitative identification of karst reservoir boundaries. The inventors discovered that this patent, which primarily focuses on geophysical models of fault-controlled karst reservoirs, lacks the ability to quantitatively recover the formation process of fault-controlled karst reservoirs.

[0047] In the paper "Characteristics and Formation Mechanism of Fault-Controlled Karst Reservoirs in the Ordovician Carbonate Karst Slope of the Tahe Oilfield", the authors conducted research on the characteristics of fault-controlled karst reservoirs early on, analyzed the controlling effect of faults on the development of karst reservoirs, and explored the formation mechanism and evolution characteristics of fault-controlled karst reservoirs. However, the inventors found that the content of the article was mainly based on the views put forward by traditional theories, and did not involve specific methods and techniques for quantitatively restoring the formation process of fault-controlled karst reservoirs.

[0048] At present, the technical status of this field has at least the following problems: (1) The characterization of fault-controlled karst reservoirs is mainly carried out based on geophysical attribute analysis, while the research on the formation process and main controlling factors of fault-controlled karst reservoirs is rarely involved. In particular, facing the problem of differential distribution of fault-controlled karst reservoirs, the traditional geological understanding of carbonate reservoirs can no longer provide a reasonable explanation and prediction guidance; (2) Faults within superimposed basins generally have multi-stage activity characteristics. At present, the geological record of synchronous strike-slip fault activity is mainly based on the unique strike-slip associated structures of each structural layer, and the episodic activity process of strike-slip faults is restored from the current underground geological structure to determine the fault activity period. However, due to the lack of accurate age basis, the speculation of fault activity sequence and the duration of synchronous activity is often artificial and multi-analyzed; (3) The contribution of karstification in fault-controlled karst reservoirs is mainly inferred based on petrological characteristics. There is a lack of physical simulation of karstification guided by the type of fault-controlled karst reservoir and its episodic evolution model. It is impossible to quantitatively restore the formation process of fault-controlled karst reservoirs, especially to quantitatively evaluate the reserve-increasing effect of faulting and karstification at different stages. In view of the above problems, the present invention is proposed to provide an evaluation method and exploration method for simulating the formation process of fault-controlled karst reservoirs, which overcomes the above problems or at least partially solves the above problems.

[0049] The embodiment of the present invention provides an evaluation method for simulating the formation process of fault-controlled karst reservoirs, referring to Figure 1 As shown, the method may include the following steps:

[0050] Step S11: perform seismic stratigraphic slicing based on seismic data in the study area to identify the vertical structural sequence in the study area, so as to determine the fault activity period in the study area based on the vertical structural sequence.

[0051] In this step, by analyzing the three-dimensional seismic model and / or logging interpretation data of the study area, the characterization analysis of the fault-controlled karst reservoirs is carried out layer by layer, the development area of ​​the fault-controlled karst reservoirs in the study area is clarified, the characterization model of the geometric morphology of different types of reservoirs is established, and the fault activity period of the study area is preliminarily determined.

[0052] Step S12: Conduct geological analysis on the fractures and fillings in the fault-controlled karst development zones of each fault activity period in the study area, so as to restore the fault and fluid activity events in the study area based on the geological analysis results, and then revise the fault activity evolution history and burial history model of the study area to establish the fault-controlled karst reservoir type and its episodic evolution pattern in the study area.

[0053] In this step, a comprehensive study of structural geology, petrology, geochemistry and chronology is conducted on the fractures and cements in the fault-controlled karst development area, the fault and fluid activity events in the study area are restored period by period, the evolution history and burial history model of the fault activity in the study area are revised, and the fault-controlled karst reservoir type and its episodic evolution model in the study area are established.

[0054] Step S13: For each episode of karstification in the fault-controlled karst model in the study area, a dissolution and reserve enhancement evaluation experiment is carried out under geological conditions to quantitatively restore the formation process of the fault-controlled karst reservoir in the study area based on the experimental results.

[0055] In this step, for each episode of karstification in the fault-controlled karst model, a dissolution-reserve enhancement evaluation experiment under geological conditions is carried out using carbonate rock plug samples with customized fracture occurrence. The formation process of the fault-controlled karst reservoir in the study area is quantitatively restored based on the experimental results.

[0056] Step S14: Based on the formation process and reservoir type of the fault-controlled karst reservoirs in the study area, determine the main controlling factors and distribution patterns of the development of the fault-controlled karst reservoirs in the study area. This step clarifies the main controlling factors and distribution patterns of the development of the fault-controlled karst reservoirs in the study area based on the reservoir type.

[0057] The above-mentioned evaluation method for simulating the formation process of fault-controlled karst reservoirs provided in the embodiments of the present invention, on the one hand, combines the dating of carbonate cements with high-resolution seismic interpretation to establish a fault activity period restoration technology with absolute age correction; secondly, combines the absolute age of carbonate cements and the formation temperature of carbonate cements with traditional burial history restoration, and combines with the paleo-geothermal model of the study area to establish a burial history restoration technology with absolute age correction; thirdly, it establishes a technology for quantitatively restoring the entire process of fault-controlled karst reservoir formation in the study area based on the results of dissolution reserve enhancement evaluation experiments under geological conditions.

[0058] In step S11, a complete vertical structural sequence includes the following structural patterns: flower-shaped structure, horsetail structure, en echelon structure, and feather-shaped anticline belt. Using seismic profiles and seismic stratigraphic slicing techniques, the layers where the flower-shaped structure, horsetail structure, en echelon structure, and feather-shaped anticline belt develop are identified in both sections and planes, thereby determining the development periods of the four structural patterns.

[0059] In practice, the determination of the phase within a single en echelon structural pattern is as follows: under pure shear and tensile shear stress settings, the angle between the strike of en echelon normal faults and the strike of deep strike-slip faults varies; under the same tensile shear stress setting, the strike of en echelon normal faults will also differ depending on the direction of the regional principal compressive (or tensile) stress. Therefore, the presence of en echelon structures in a single structural layer indicates simultaneous strike-slip movement; the presence of en echelon structures with varying strikes across multiple structural layers indicates multi-phase strike-slip fault activity. Normal faults in en echelon structures are generally syngenetic, and the normal fault growth index can be used to assist in determining the phase and intensity of activity.

[0060] The process of determining the internal periods of other structural styles is as follows: within the identified large structural period, similar faults with different directions and attitudes are also found within the flower-shaped structure, horsetail structure, and feather-shaped anticline belt. Based on the cutting relationship between the faults, it is determined that different periods of structural movement developed within the same structural style (large structural background).

[0061] In the above step S12, a comprehensive petrological, geochemical and chronological study is conducted on the fractures and fillings in the fault-controlled karst development area to restore the fault and fluid activity events in the study area, and then revise the fault activity evolution history and burial history model in the study area to establish the fault-controlled karst reservoir type and its episodic evolution model in the study area, as follows:

[0062] The first step is to obtain representative rock samples from the fault-controlled karst development area in the study area. The characteristics of the representative rock samples may include: the development of cracks in the rock samples, the cracks are filled with cement and asphalt, and the surrounding rock, cracks, and cement are interconnected in the rock samples.

[0063] The second step is to obtain petrological, geochemical and chronological analysis of carbonate cements in rock sample fractures, including microstructure, formation period, absolute age, formation temperature and formation fluid properties;

[0064] In this step, the microstructure of carbonate cement is obtained by scanning electron microscopy analysis; the formation period is determined by the diagenetic sequence established by the mutual intersection of surrounding rocks and fractures; the absolute age of carbonate cements of each period is determined by calcite U-Pb isotope; the formation temperature is tested by carbonate cement cluster isotope and fluid inclusion test; the properties of the formation fluid are determined by carbon isotope, oxygen isotope, strontium isotope, trace element surface analysis, and compared with the same test results of surrounding rock minerals; according to the calcite U-Pb isotope, cluster isotope, carbon isotope, oxygen isotope, strontium isotope and trace element surface analysis of carbonate cement in rock sample fractures, they are all micro-analyses of cements of the same period; the secondary calcite growth model of the fault zone in the study area is obtained, and the original calcite cement of the fault zone is used to determine the formation temperature. The calcite fluid source was comprehensively analyzed by surface scanning using U-Pb age, carbon isotopes, oxygen isotopes, strontium isotopes, and trace elements, and the secondary calcite growth model under the constraints of specific absolute age and fluid source was restored. The results of the determination of small-scale episodic strike-slip faulting periods were obtained to calibrate the fault activity model of the study area. Combined with the secondary calcite growth model, the fault activity period model after absolute age correction was obtained for the study area. The episodic activity of fluids in the study area was obtained, and the secondary calcite growth model, the analysis results of the secondary calcite fluid source, asphalt, and hydrothermal filling minerals were used to establish the episodic activity of fluids under the constraints of absolute age in the study area. Based on the fluid source of the fault karstification, the fault-controlled karst reservoir types in the study area include hydrothermal dissolution, organic acid dissolution, atmospheric water dissolution, and mixed dissolution.

[0065] The third step is to obtain the paleo-geothermal model and burial history model of the study area. The absolute age of each period of subcarbonate cements and the formation temperature of each period of subcarbonate cements are used, combined with the paleo-geothermal model of the study area, to calibrate the burial history model of the study area and obtain the corrected burial history model of the study area.

[0066] The fourth step is to determine the burial depth of each period of subcarbonate cementation based on the corrected burial history model of the study area and the absolute age of each period of subcarbonate cementation.

[0067] The fifth step is to establish the fault-controlled karst reservoir type and its episodic evolution pattern in the study area based on the fault activity period model after absolute age correction, fluid episodic activity under absolute age constraints, corrected burial history model, and paleo-geothermal model.

[0068] In the above-mentioned method for restoring the episodic evolution of fault-controlled karst reservoirs, rock samples with the characteristics of carbonate cements filled in fractures and the existence of mutual intersection of carbonate cements in rock samples are easy to establish a complete and reliable diagenetic sequence and are suitable for dating and temperature measurement; the cementation characteristics and mutual intersection relationship of carbonate cements in representative rock samples in the study area are clear. In the above-mentioned method for restoring the episodic evolution of fault-controlled karst reservoirs, when clarifying the periods of mutually intersection of carbonate cements in rock samples, sample thin sections I made from representative rock samples in the study area are used.

[0069] In the above-mentioned fault-controlled karst reservoir episodic evolution restoration method, when performing isotope dating, carbon isotope, oxygen isotope, strontium isotope, and trace element surface scanning, a sample thin slice II made from a representative rock sample of the study area is used. More preferably, the thickness of the sample thin slice II is about 100 μm.

[0070] In the above-mentioned method for restoring the episodic evolution of fault-controlled karst reservoirs, cluster isotope testing was performed using powder samples of subcarbonate cements from each phase. For each representative rock sample obtained in the study area, two parallel samples corresponding to each representative rock sample were prepared from thin slices I and II of the rock sample, and the residual portion of the parallel samples was retained;

[0071] Carbonate cements were observed in Sample Section I to identify the stages of carbonate cements within the rock sample. In the corresponding Sample Section II, carbonate cements corresponding to each stage in Sample Section I were identified and subsequently subjected to isotope dating, carbon isotope analysis, oxygen isotope analysis, strontium isotope analysis, and trace element surface scanning analysis to determine the absolute ages of each stage of carbonate cements. Combined with the fracture root connectivity, the fluid source attributes were determined. Powder samples of carbonate cements corresponding to each stage in Sample Section I were obtained from the remaining portion of the corresponding parallel sample. Cluster isotope analysis and inclusion analysis were performed to determine the formation temperature of each stage of carbonate cements. A paleo-geothermal model and burial history model were obtained for the study area. The absolute ages and formation temperatures of each stage of carbonate cements, combined with the paleo-geothermal model, were used to calibrate the burial history model, resulting in a calibrated burial history model. Based on the calibrated burial history model of the study area, the burial depth of each subcarbonate cement is determined using the absolute age of each subcarbonate cement. In the above-mentioned method for restoring the episodic evolution of fault-controlled karst reservoirs, the burial history model of the study area can be obtained using conventional techniques in the field. For example, a paleo-geothermal model and burial history model of the study area are established based on the regional geological background, drilling, and seismic data. In the above-mentioned method for restoring the episodic evolution of fault-controlled karst reservoirs, the burial history model of the study area is calibrated using the absolute age and formation temperature of each sub-stage calcite cement, combined with the paleo-geothermal model of the study area.

[0072] In a specific embodiment, referring to Figure 2 As shown, the above step S13 may specifically include:

[0073] Step S21: Obtain the rock type, rock component parameters, reservoir fault occurrence, reservoir diagenetic fluid characteristic parameters and geological background parameters of the carbonate reservoir corresponding to the target episode in the study area.

[0074] Step S22: Based on the rock type, rock component parameters and reservoir fracture occurrence, a carbonate rock plug sample is produced to simulate the customized fracture occurrence of the carbonate reservoir in the study area.

[0075] Step S23: weighing and CT scanning the carbonate rock plug sample before the experiment to determine the initial weight of the carbonate rock plug sample and the initial internal pore structure of the rock.

[0076] Step S24: Prepare an erosive fluid simulating the reservoir diagenetic fluid based on the reservoir diagenetic fluid characteristic parameters. Step S24 can be performed after step S22, before step S22, or simultaneously, and this embodiment of the present invention does not specifically limit this.

[0077] Step S25: Under the constraints of geological background parameters, a dissolution and reserve enhancement simulation experiment is carried out using carbonate rock plug samples and corrosive fluids, and the reaction generated fluid is collected in real time.

[0078] Before conducting the dissolution and reserve enhancement simulation experiment in this step, the gas flow inlet and outlet ends of the carbonate rock plug sample are marked. Based on the marked inlet and outlet ends of the carbonate rock plug sample, the carbonate rock plug sample is placed in the core holder of the diagenesis simulation device to ensure that the flow direction of the corrosive fluid is consistent with the gas flow direction during physical property analysis.

[0079] The above geological background parameter constraints include: the type of geological stress that drives the migration of geological fluids, the temperature and pressure in the core holder; the geological stress type may include: tectonic movement force, hydrodynamic force, geostatic pressure and thermal force.

[0080] Step S26: Dry, weigh, and CT scan the samples after the dissolution and reserve enhancement simulation experiment, and compare them with the initial weight and the initial internal porosity structure of the rock. Combined with the ion composition and content analysis results of the collected reaction liquid, the carbonate rock pore evolution characteristics, dissolution effect, and dissolution mechanism of the carbonate reservoir corresponding to the target episode in the study area are determined.

[0081] The embodiment of the present invention quantitatively restores the formation process of the fault-controlled karst reservoir in the study area based on experimental results. Each episode of karstification restored by the fault-controlled karst model in the study area is used to determine the simulation experimental conditions of the corresponding karstification. Based on this, a dissolution and reserve increase evaluation experiment under the constraints of geological conditions is carried out. By superimposing the dissolution and reserve increase evaluation experimental results of each episode of karstification, the entire process of the formation of the fault-controlled karst reservoir in the study area is finally quantitatively restored.

[0082] The dissolution effect and dissolution mechanism in the above step S26 are obtained by qualitative and quantitative analysis based on the dissolution weight, the total concentration of calcium ions and magnesium ions in the reaction solution, porosity, permeability, and microscopic characteristic images obtained by CT scanning.

[0083] In the above step S26, when performing CT scanning before and after the experiment on the carbonate rock plug sample, in-situ comparison is performed on the internal fracture occurrence of the carbonate rock plug sample to obtain the pore evolution characteristics of the carbonate rock.

[0084] In an optional embodiment, the geological background parameter constraints on the dissolution and reserve enhancement simulation experiment in the above-mentioned step S25 specifically include: setting the simulation experiment fluid inlet pressure through a fluid pressure pump and keeping the experimental fluid inlet pressure constant; applying confining pressure and axial pressure to the carbonate rock plunger sample through the reactor confining pressure control system and the reactor axial hydraulic control system.

[0085] In this embodiment, the inlet pressure of the simulated experimental fluid is determined by the following method: based on the burial depth of the restored karstification, combined with the geothermal gradient and the formation pressure gradient, the fluid pressure of the target layer from which the karstification fluid originates and the fluid pressure at the depth at which the karstification occurs are determined; the pressure value of the driving fluid is determined by the difference between the fluid pressure of the target layer from which the karstification fluid originates and the fluid pressure at the depth at which the karstification occurs, and is used as the inlet pressure of the simulated experimental fluid.

[0086] In the embodiment of the present invention, for each episode of karstification restored by the fault-controlled karstification model in the study area, the simulation experimental conditions corresponding to the karstification are determined, and accordingly, the dissolution reserve enhancement evaluation experiment under the constraints of geological conditions is carried out, including the following conditions:

[0087] The fluid for the simulation experiment is prepared based on the type of corrosive fluid in the restored karstification. The corresponding geological stress type driving the migration of geological fluid is determined based on the type of fluid in the restored karstification, such as tectonic movement force, hydrodynamic force, geostatic pressure, thermodynamic force, etc. The fracture occurrence of the artificial carbonate rock core is determined based on the identified fracture pattern, such as en echelon, Y-shaped, X-shaped, vertical fracture type, etc. The artificial carbonate rock core is the rock sample for the simulation experiment (carbonate rock plug sample with customized fracture occurrence). Based on the burial depth of the restored karstification, the formation temperature corresponding to the development and dissolution of geological fluid is determined, which is the temperature condition of the simulation experiment. Based on the burial depth of the restored karstification, combined with the geothermal gradient and formation pressure gradient, the fluid pressure of the target layer of the karstification fluid source and the fluid pressure at the depth of karstification are converted. The difference between the two fluid pressures is the pressure value of the driving fluid, which is the fluid pressure condition of the simulation experiment.

[0088] The fluids prepared for the karstification are: acetic acid solution for organic acid karst, high pCO2 saturated solution for hydrothermal karst, low pCO2 saturated solution for atmospheric water karst, deionized water or formation water as the solution. Mixed karst refers to the process of experiencing two or more of the above karstifications and performing separate simulations.

[0089] In order to achieve the purpose of simulating each episode of karstification and reserve enhancement evaluation experiment, the embodiment of the present invention may specifically include the following steps:

[0090] (1) Detect the rock type and rock component parameters, reservoir fault occurrence, reservoir diagenetic fluid characteristic parameters, and geological background parameters of the carbonate reservoir in the simulation experimental area.

[0091] (2) Based on the test results of step (1), a carbonate rock sample for simulation is selected, and the sample components and contents are obtained through XRD analysis.

[0092] In this step, the carbonate rock type selected primarily focuses on those whose thin section identification and rock composition analysis results are consistent with the target reservoir in the simulation experiment area. The diagenetic fluid type is primarily selected based on the fluid history of the simulation experiment area. The experimental conditions selected during carbonate rock burial dissolution must be closely integrated with the geological context of the study area.

[0093] (3) The sample selected in step (2) was crushed into particles with a particle size of 100-200 mesh, and the binder was deionized water. The carbonate rock plug sample with the desired fracture occurrence (customized fracture occurrence) was prepared by 3D printing method, and the sample was cut into 3 cm long and directly 2.54 cm long.

[0094] (4) Prepare corrosive fluids that are consistent with geological knowledge. For example, for organic acid karst, analytically pure acetic acid reagent is added to deionized water or formation water; for hydrothermal karst, high-purity CO2 at a certain pressure is added to deionized water or formation water.

[0095] (5) The carbonate rock plug sample prepared in step (3) is subjected to pre-experimental analysis such as weighing, physical property analysis, and CT scanning based analysis of the internal pore structure of the rock. The same plug sample used in the simulation experiment in this step should be the plug sample closest to the simulation experiment for microscopic feature analysis, and at the same time meet the sample preparation requirements for microscopic features. Before conducting physical property analysis, the inlet and outlet ends of the gas flow should be marked on the plug sample; the physical property analysis includes porosity and permeability. During CT scanning, the inlet and outlet ends of the plug sample should be scanned separately, and the scanning conditions, such as resolution, should be recorded.

[0096] (6) Place the sample in the core holder of the diagenetic simulation device.

[0097] In this step, the plunger sample should be placed in the core holder of the diagenesis simulation device according to the inlet and outlet ends marked on the plunger sample to ensure that the flow direction of the diagenetic fluid is consistent with the gas flow direction during physical property analysis.

[0098] (7) Conduct a simulation experiment on dissolution and reserve enhancement evaluation under geological conditions, and collect the reaction liquid at the solution outlet.

[0099] The specific method of the simulation experiment in this step is to continuously inject the diagenetic fluid into the diagenetic device through a liquid pump. After the fluid solution is discharged from the device, the temperature and pressure of the core holder are set according to the geological background detected in step (1), and a continuous water-rock reaction is carried out until the designed reaction time is reached.

[0100] (8) After the experiment, the carbonate rock plug samples were dried, weighed, and subjected to physical property analysis, as well as experimental analysis of the rock internal pore structure based on CT scanning; the ion composition and content of the reaction liquid were analyzed.

[0101] (9) According to the fault-controlled karst model, by repeating steps (4)-(8), each episode of karstification simulation experiment is carried out successively on the same sample.

[0102] (10) Comprehensively evaluate the pore evolution characteristics, dissolution effect and dissolution mechanism of carbonate rocks based on the analysis results.

[0103] In the present invention, the core holder temperature and pressure are usually set to be consistent with the geological background (formation temperature and pressure) detected in step (1).

[0104] According to the method of the present invention, the fluid passes through the interior of the plunger sample at a constant pressure;

[0105] The constant pressure is converted into the fluid pressure of the target layer of the karstification fluid source and the fluid pressure of the karstification depth according to the burial depth of the restored karstification, combined with the geothermal gradient and the formation pressure gradient. The difference between the two fluid pressures is the pressure value of the driving fluid, which is the constant pressure condition of the simulation experiment; the simulation experiment fluid inlet pressure is set by a fluid pressure pump, and the experimental fluid inlet pressure is kept constant; the sample is applied with confining pressure and axial pressure by the reactor confining pressure control system and the reactor axial hydraulic control system, and the confining pressure and axial pressure are always 2.5MPa greater than the fluid inlet pressure; step (8) is to sequentially dry, weigh, analyze physical properties, and perform CT scanning on the post-experimental plunger sample to analyze the microscopic morphology characteristics of the post-experimental plunger sample; when the plunger sample is CT scanned in step (8), the analysis conditions in step (3) should be consistent, such as resolution and analysis position; when the plunger sample is CT scanned based on CT, the CT scan image of step (8) should be compared to achieve in-situ comparison of the occurrence of cracks in the rock; wherein, step (8) is to analyze the reaction generated liquid. 2+ Mg 2+ concentration analysis;

[0106] According to the embodiment of the present invention, the evaluation of carbonate rock dissolution and dissolution effect in step (8) is mainly based on the dissolution amount, Ca content in the solution, 2+ Mg 2+ The total amount of concentration, porosity, permeability, and microscopic characteristic images are used for qualitative and quantitative analysis and discussion.

[0107] In a specific example, the quantitative restoration process of fault-controlled karst reservoir formation in a certain study area was carried out to provide technical means to clarify the main controlling factors and distribution patterns of the development of fault-controlled karst reservoirs in the study area. The specific steps include:

[0108] In step S11, the key constructor's set features are judged in phase, referring to Figure 3 As shown, the period of the fault can be determined by identifying the pattern. The locations where the flower-shaped structure, horsetail structure, en echelon structure and feather-shaped anticline belt are broken correspond to the first and second acts of the middle Caledonian period, the late Caledonian period and the middle and late Hercynian period.

[0109] In step S12, U-Pb dating and carbon-oxygen cluster isotope analysis of calcite filling different periods of pores and caves in the fault-controlled karst reservoir in the above study area show that the Upper Ordovician has experienced multiple periods of tectonic activity transformation. A total of 7 periods of related calcite were identified, involving various fluids such as atmospheric water, organic acid and formation water. Figure 4 As shown in the figure, each phase of fluid activity may cause dissolution and filling during the temperature and pressure changes, causing reservoir transformation.

[0110] In step S13, for each episode of karstification in the restoration of fault-controlled karstification mode in the study area, refer to Figure 5 As shown in the figure, taking the Late Caledonian to Early Hercynian period as an example, the source of calcite fluid was comprehensively analyzed through in situ U-Pb age, strontium isotope and inclusions of calcite cement in the fault zone, and the secondary calcite growth model under the constraints of specific absolute age and fluid source was restored. It was found that the Late Caledonian to Early Hercynian period was the main activity period of the northeast strike-slip fault. The carbon, strontium isotope and CO2-CH4 inclusions of calcite veins showed that the fluid originated from deep. The buried dissolution fluid under high temperature conditions was acidic. The activity of organic acid from deep source, controlled by the geothermal field, had the characteristics of upward fluid transformation of "lower dissolution-upper filling".

[0111] Reference Figure 6 The artificial carbonate rock plug sample shown in step S13 was subjected to the dissolution and reserve evaluation test. Figures 7 to 10 The three-dimensional images of the fractures before and after dissolution and the comparison of porosity values ​​are shown. After analysis, the entire process of the formation of fault-controlled karst reservoirs in the study area can be quantitatively restored.

[0112] Based on the same inventive concept, an embodiment of the present invention also provides an oil and gas exploration method, which explores oil and gas in the study area based on the formation process of the fault-controlled karst reservoir in the study area; wherein the formation process of the fault-controlled karst reservoir in the study area is determined based on the above-mentioned evaluation method for simulating the formation process of the fault-controlled karst reservoir.

[0113] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. An evaluation method for simulating the formation process of fault-controlled karst reservoirs, characterized in that: include: Performing seismic stratigraphic slicing based on seismic data within a study area to identify a vertical structural sequence within the study area, thereby determining a fault activity phase within the study area based on the vertical structural sequence; Conducting geological analysis on the fractures and fillings in the fault-controlled karst development zones during each fault activity period within the study area, restoring the fault and fluid activity events in the study area based on the geological analysis results, and then revising the fault activity evolution history and burial history model in the study area to establish the fault-controlled karst reservoir types and their episodic evolution patterns in the study area; For each episode of karstification in the fault-controlled karst model in the study area, a dissolution-reserve evaluation experiment under geological constraints was conducted using carbonate rock plug samples with customized fracture occurrence, so as to quantitatively restore the formation process of the fault-controlled karst reservoir in the study area based on the experimental results; Based on the formation process and reservoir types of the fault-controlled karst reservoirs in the study area, the main controlling factors and distribution patterns of the development of the fault-controlled karst reservoirs in the study area are determined.

2. The method according to claim 1, characterized in that For each episode of karstification in the fault-controlled karst model in the study area, a dissolution reserve increase evaluation experiment was carried out under the constraints of geological conditions, specifically including: Obtain rock types, rock component parameters, reservoir fault occurrence, reservoir diagenetic fluid characteristic parameters and geological background parameters of the carbonate reservoir corresponding to the target episode in the study area; Based on the rock type, rock component parameters and reservoir fracture occurrence, a carbonate rock plug sample is produced to simulate the fracture occurrence of the carbonate reservoir in the study area; Weighing and CT scanning the carbonate rock plug sample before the experiment to determine the initial weight of the carbonate rock plug sample and the initial internal pore structure of the rock; preparing an erosive fluid simulating the reservoir diagenetic fluid based on characteristic parameters of the reservoir diagenetic fluid; Under the constraints of the geological background parameters, a dissolution and reserve enhancement simulation experiment is carried out using the carbonate rock plug sample and the corrosive fluid, and the reaction generated fluid is collected in real time; The samples after the dissolution and reserve enhancement simulation experiment were dried, weighed, and CT scanned, and compared with the initial weight and the initial internal porosity structure of the rock. Combined with the ion composition and content analysis results of the collected reaction liquid, the carbonate rock pore evolution characteristics, dissolution effect and dissolution mechanism of the carbonate reservoir corresponding to the target episode in the study area were determined.

3. The method according to claim 2, characterized in that The dissolution effect and dissolution mechanism are obtained by qualitative and quantitative analysis based on the dissolution weight, the total concentration of calcium ions and magnesium ions in the reaction solution, the porosity, the permeability, and the microscopic characteristic images obtained by CT scanning.

4. The method according to claim 2, characterized in that When the carbonate rock plug sample is subjected to CT scanning before and after the experiment, an in-situ comparison is performed on the internal fracture occurrence of the carbonate rock plug sample to obtain the pore evolution characteristics of the carbonate rock.

5. The method according to claim 2, characterized in that Before conducting the dissolution and reserve enhancement simulation experiment, the gas flow inlet and outlet ends of the carbonate rock plug sample are marked, and based on the marked inlet and outlet ends of the carbonate rock plug sample, the carbonate rock plug sample is placed in the core holder of the diagenesis simulation device to ensure that the flow direction of the corrosive fluid is consistent with the gas flow direction during physical property analysis.

6. The method according to claim 2, characterized in that The geological background parameter constraints include: the type of geological stress that drives the migration of geological fluids, the temperature and pressure in the core holder; The types of geological stress include: tectonic force, hydrodynamic force, geostatic pressure and thermal force.

7. The method according to claim 6, characterized in that The geological background parameter constraints for the dissolution-reserve enhancement simulation experiment specifically include: The fluid inlet pressure of the simulated experimental fluid is set by a fluid pressure pump and kept constant; the confining pressure and axial pressure are applied to the carbonate rock plunger sample by the reactor confining pressure control system and the reactor axial hydraulic control system.

8. The method according to claim 7, characterized in that The inlet pressure of the simulation experiment fluid is determined by the following method: Based on the burial depth of the restored karstification, combined with the geothermal gradient and formation pressure gradient, determine the fluid pressure of the target layer of the karstification fluid source and the fluid pressure at the depth of karstification; The pressure of the driving fluid is determined by the difference between the fluid pressure of the target layer where the karstification fluid originates and the fluid pressure at the depth where the karstification occurs, and is used as the fluid inlet pressure of the simulation experiment.

9. An oil and gas exploration method, characterized in that: Exploring oil and gas in the study area based on the formation process of fault-controlled karst reservoirs in the study area; The formation process of the fault-controlled karst reservoir in the study area is determined based on the evaluation method for simulating the formation process of the fault-controlled karst reservoir according to any one of claims 1 to 8.

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