Evaluation method and exploration method for simulating formation process of disconnection-control karst reservoir

Abstract

The invention discloses an evaluation method and an exploration method for simulating the formation process of a fault-control karst reservoir, and the method comprises the steps: carrying out the seismic stratum slicing based on seismic data in a research region, and recognizing a vertical structure sequence in the research region, so as to determine the fracture activity period of the research region; carrying out geological analysis on fracture and fillers of the fault-control karst development area in the fracture activity period in the research area, recovering fracture and fluid activity events of the research area based on a geological analysis result, and further correcting a fracture activity evolution history and burial history model of the research area; and after establishing a fault control karst reservoir type and a curtain type evolution mode of the fault control karst reservoir type of the research area, carrying out a corrosion storage increase evaluation experiment under the constraint of geological conditions. According to the method, carbonate cement age, formation temperature of the carbonate cement and burial history recovery are combined, and an absolute age correction burial history is established in combination with an ancient ground temperature model; and the formation process of the fault-control karst reservoir in the research area is quantitatively recovered through a corrosion storage increase evaluation experiment under the constraint of geological conditions.

Description

Technical Field

[0001] The 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 related to national energy security. Carbonate rock is the main type of global oil and gas exploration. According to statistics, the total global resources are 877.7 billion tons of oil equivalent, of which carbonate rock is 632 billion tons, accounting for 72% (according to CNPC, 2011); the global oil and gas production is 6.95 billion tons, of which carbonate rock is 4.38 billion tons, accounting for 63% (2011 data, according to BP, 2012). Deep marine carbonate oil and gas reservoirs have become an important oil and gas exploration field in the world, especially in China, in recent years. The traditional marine carbonate oil and gas accumulation theory believes that there are four main types of carbonate reservoirs and oil and gas reservoirs: bioherms, grain beaches, dolomites, and karst weathering crusts. In recent years, exploration has gradually realized that fault zones are both oil and gas transmission channels and favorable spaces for accumulation. Taking a certain oil field as an example, under the influence of the Upper Ordovician cover, the development of karst fractures and caves has a good matching relationship with fault zones and structural deformation zones, and has obvious fault-controlled karst characteristics. The deep and large fault zones are the core of dissolution and expansion, making it a favorable zone for the development of karst fractures and caves in the Middle and Lower Ordovician in the cover area, thus creating a very special reservoir type in the Fuman area - fault-controlled karst reservoirs. Due to the obvious decline in carbonate reserves and production in the shallow and paleo-uplift areas, oil and gas exploration and development have expanded to deep and even ultra-deep oil and gas reservoirs, and the exploration status of fault-controlled karst reservoirs in low-lying structures has become increasingly prominent. However, the traditional carbonate reservoir and oil and gas accumulation theory can no longer meet the needs of deep marine carbonate oil and gas exploration and development in low-lying structures. In order to meet the key issues such as the genesis, main controlling factors and distribution laws of fault-controlled karst reservoirs, it is urgent to develop a method 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 an exploration method for simulating the formation process of fault-controlled karst reservoirs are provided in an embodiment 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 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;

[0006] Conduct geological analysis on the fractures and fillings in the fault-controlled karst development zone 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 in the study area, so as to establish the fault-controlled karst reservoir type and its episodic evolution model 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 was carried out under the constraints of geological conditions using carbonate 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 increase evaluation experiment under geological conditions is carried out, specifically including:

[0010] Obtain rock types, 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 prepared to simulate the customized 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] Based on the characteristic parameters of the reservoir diagenetic fluid, preparing an erosive fluid simulating the reservoir diagenetic fluid;

[0014] Under the constraints of the geological background parameters, using the carbonate rock plug sample and the corrosive fluid to carry out a dissolution and reserve enhancement simulation experiment, and collecting the reaction generated fluid 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 curtain 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, the porosity, the permeability, and the microscopic characteristic image obtained by CT scanning.

[0017] Optionally, when performing CT scans 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 and reserve enhancement simulation experiment specifically include:

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

[0023] Optionally, the simulated experimental fluid inlet pressure 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 value of the driving fluid is determined by the difference between the fluid pressure of the target layer where the karst action fluid comes from and the fluid pressure at the depth where the karst action 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] Among them, 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 solution provided by the embodiment of the present invention include at least:

[0029] The 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 second 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, to establish a burial history restoration technology with absolute age correction; the third aspect is to establish a technology that realizes quantitative restoration of the entire formation process of fault-controlled karst reservoirs in the study area based on the results of dissolution and reserve enhancement evaluation experiments under the constraints of geological conditions.

[0030] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the 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 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 The specific execution flow chart of step S13;

[0035] Figure 3 This is a cross-sectional diagram of the development of strike-slip fault styles 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 the 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] Fig. 9 This is a comparison chart of the porosity values ​​of the en echelon artificial carbonate rock samples before and after dissolution in the above example;

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

[0043] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the 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. On the contrary, 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 inventor 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, ignoring the insider 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 boundary of ultra-deep fault-controlled karst reservoirs" is based on the analysis of effective seismic attributes and the determination of effective attribute values, and then establishes a geological model of the boundary of typical ultra-deep fault-controlled karst reservoirs in the target area. Through forward simulation analysis, the effective attribute values ​​are adjusted to ensure the reliability of quantitative identification of karst reservoir boundaries. The inventor found that the patent is mainly aimed at the geophysical model of fault-controlled karst reservoirs and does not have the ability to quantitatively restore 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 early research on the characteristics of fault-controlled karst reservoirs, 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 viewpoints 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) Most of the research is on the characterization of fault-controlled karst reservoirs based on geophysical attribute analysis, while less research is involved in the formation process and main controlling factors of fault-controlled karst reservoirs. 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 records of synchronous strike-slip fault activities are mainly based on the unique strike-slip associated structures of each structural layer, and then 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 sub-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, which cannot achieve quantitative restoration of the formation process of fault-controlled karst reservoirs, especially the quantitative evaluation of the reservoir enhancement effect of different periods of faulting and karstification. In view of the above problems, the present invention is proposed to provide an evaluation method and an 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, performing seismic stratigraphic slicing based on seismic data in the study area, identifying the vertical structural sequence in the study area, and determining 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 in 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 correct the fault activity evolution history and burial history model in the study area, so as 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 carried out on the fractures and cementation 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 the constraints of geological conditions, so as 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 and reserve enhancement evaluation experiment under the constraints of geological conditions is carried out using carbonate plug samples with customized fracture occurrence, and 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 reservoir in the study area, determine the main controlling factors and distribution patterns of the development of the fault-controlled karst reservoir in the study area. This step clarifies the main controlling factors and distribution patterns of the development of the fault-controlled karst reservoir 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; on the second hand, combines the absolute age of carbonate cements and the formation temperature of carbonate cements with traditional burial history restoration, and combines with the paleogeothermal model of the study area to establish a burial history restoration technology with absolute age correction; the third aspect is to establish a technology that realizes quantitative restoration of the entire process of fault-controlled karst reservoir formation in the study area based on the results of dissolution and reserve enhancement evaluation experiments under the constraints of geological conditions.

[0058] In the above step S11, a complete vertical structural sequence structural style includes: flower-shaped structure, horsetail structure, en echelon structure and feather-shaped anticline belt. Through seismic profile and seismic stratigraphic slicing technology, the strata where the flower-shaped structure, horsetail structure, en echelon structure and feather-shaped anticline belt develop are sorted out from the profile and plane, and then the period of development of the four structural style faults is determined.

[0059] In specific implementation, the determination of the internal period of a single en echelon structural pattern is as follows: under the background of pure shear and tensile shear stress, the angle between the direction of the en echelon normal fault and the direction of the deep strike-slip fault is different; under the same tensile shear stress background, the direction of the regional principal compressive (or tensile) stress is different, and the direction of the en echelon normal fault will also be different. Therefore, the appearance of en echelon structure in a single structural layer indicates that strike-slip movement occurred at the same time; the appearance of en echelon structures with different attitudes in multiple structural layers indicates that there are multiple periods of strike-slip fault activity. The normal faults of the en echelon structure are generally syngenetic faults, and the normal fault growth index can be used to assist in determining the period and activity intensity.

[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 in flower-shaped structures, horsetail structures, and feather-shaped anticline belts. 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 correct the evolution history and burial history model of the fault activity 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 relationship between the surrounding rock and the fracture; the absolute age of carbonate cement 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 the fracture of the rock sample, they are all micro-analysis of cement 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 growth temperature of the secondary calcite cement in the fault zone. The calcite fluid source is comprehensively analyzed by surface scanning of U-Pb age, carbon isotope, oxygen isotope, strontium isotope and trace elements, and the secondary calcite growth model under the constraints of specific absolute age and fluid source is restored; the results of the determination of the period of small-scale episodic strike-slip faults are obtained, and the fault activity model of the study area is corrected, and the fault activity period model after absolute age correction is obtained by combining the secondary calcite growth model; the episodic activity of fluid in the study area is obtained, and the episodic activity of fluid under the constraints of absolute age of the study area is established by using the secondary calcite growth model, the analysis results of the source of secondary calcite fluid, asphalt and hydrothermal filling minerals; based on the source of fluids in the karstification of the fault, the fault-controlled karst reservoir types in the study area include hydrothermal dissolution type, organic acid dissolution type, atmospheric water dissolution type and mixed dissolution type;

[0065] The third step is to obtain the paleo-geothermal model and burial history model of the study area, and use the absolute age of each period of subcarbonate cementation and the formation temperature of each period of subcarbonate cementation, 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, the corrected burial history model, and the 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 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, sample thin sections I made from representative rock samples in the study area are used to clarify the periods of mutually intersecting carbonate cements in rock samples.

[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 representative rock samples of the study area is used. More preferably, the thickness of the sample thin slice II is about 100 μm.

[0070] In the above fault-controlled karst reservoir episodic evolution restoration method, the cluster isotope test is carried out using powder samples of carbonate cements of each period. For each representative rock sample obtained in the study area, two parallel samples corresponding to each representative rock sample are prepared from the sample slices I and II, and the residual part of the parallel samples is retained;

[0071] Observe the carbonate cements of sample thin section I to clarify the period of carbonate cements in the rock sample. In the corresponding sample thin section II, circle the carbonate cements of each period corresponding to the carbonate cements of each period in sample thin section I, and perform isotope dating, carbon isotope, oxygen isotope, strontium isotope, and trace element surface scanning analysis in turn to obtain the absolute age of carbonate cements of each period, and determine the source attribute of fluids in combination with the permeability of the root of the fault. In the corresponding parallel sample residue, obtain the powder samples of carbonate cements of each period corresponding to the carbonate cements of each period in sample thin section I, perform cluster isotope testing and inclusion analysis, and obtain the formation temperature of carbonate cements of each period. Obtain the paleogeothermal model and burial history model of the study area; use the absolute age of carbonate cements of each period and the formation temperature of carbonate cements of each period, combined with the paleogeothermal 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. Based on the corrected burial history model of the study area, the absolute age of each period of carbonate cement is used to determine the burial depth of each period of carbonate 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 by conventional technical means in the field, for example, according to the regional geological background, drilling and seismic data, the paleo-geothermal model and burial history model of the study area are established. In the above-mentioned method for restoring the episodic evolution of fault-controlled karst reservoirs, the absolute age of each period of calcite cement and the formation temperature of each period of calcite cement are used, combined with the paleo-geothermal model of the study area, to calibrate the burial history 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, obtaining the rock type, rock component parameters, reservoir fracture 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 prepared 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: Based on the characteristic parameters of the reservoir diagenetic fluid, prepare an erosive fluid simulating the reservoir diagenetic fluid. Step S24 may be performed after step S22, or before step S22, or simultaneously, and the embodiment of the present invention does not specifically limit this.

[0077] Step S25: Under the constraints of geological background parameters, a carbonate rock plug sample and an erosive fluid are used to carry out a dissolution and reserve enhancement simulation experiment, and the reaction generated fluid is collected in real time.

[0078] Before conducting the dissolution and reserve enhancement simulation experiment in this step, the inlet and outlet ends of the gas flow of the carbonate rock plug sample are marked, and the carbonate rock plug sample is placed in the core holder of the diagenesis simulation device based on the marked inlet and outlet ends of the carbonate rock plug sample 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, so as to determine the carbonate rock pore evolution characteristics, dissolution effect and dissolution mechanism of the carbonate reservoir corresponding to the target curtain in the study area in combination with the ion composition and content analysis results of the collected reaction liquid.

[0081] The embodiment of the present invention quantitatively restores the formation process of the fault-controlled karst reservoir in the study area according to the experimental results. Each episode of karstification restored by the fault-controlled karst model of the study area is used to determine the simulation experimental conditions of the corresponding karstification, and 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, the porosity, the permeability, and the microscopic characteristic image obtained by CT scanning.

[0083] In the above step S26, 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.

[0084] In an optional embodiment, the geological background parameter constraints on the dissolution and reserve enhancement simulation experiment in the above 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 a reactor confining pressure control system and a 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 stratum from which the karstification fluid comes 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 stratum from which the karstification fluid comes and the fluid pressure at the depth at which the karstification occurs, and this 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 the dissolution reserve increase evaluation experiment under the constraints of geological conditions is carried out accordingly, including the following conditions:

[0087] According to the type of corrosive fluid of the restored karstification, the fluid of the simulation experiment is prepared; according to the type of fluid of the restored karstification, the corresponding geological stress type that drives the migration of geological fluid is clarified, such as tectonic movement force, hydrodynamic force, geostatic pressure, thermodynamic force, etc.; according to the identified fault style, the fracture occurrence of the artificial carbonate rock core is determined, such as en echelon, Y-shaped, X-shaped, vertical fracture type, etc. The artificial carbonate rock core is the rock sample of the simulation experiment (carbonate rock plunger sample with customized fracture occurrence); according to the burial depth of the restored karstification, the formation temperature corresponding to the development and dissolution of the geological fluid is determined, which is the temperature condition of the simulation experiment; according to the burial depth of the restored karstification, combined with the geothermal gradient and the 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, and 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 karstification fluids 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 for solution, and mixed karst refers to karstification that undergoes two or more of the above karstifications and is simulated separately.

[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 simulated experimental area.

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

[0092] In this step, the selection of carbonate rock types mainly selects the rock types whose thin section identification and rock component analysis results are consistent with the target reservoir in the simulation experiment area, and the selection of diagenetic fluid types is mainly based on the fluid history of the simulation experiment area. The selection of experimental conditions in the process of carbonate rock burial dissolution must be closely combined with the geological background of the study area.

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

[0094] (4) Prepare corrosive fluids that are consistent with geological knowledge. For example, for organic acid karst, analytical grade 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. For the same plug sample used in the simulation experiment in this step, the one used for microscopic feature analysis should be the plug sample that is closest to the simulation experiment and meets 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) to carry out a continuous water-rock reaction until the designed reaction time is reached.

[0100] (8) The carbonate rock plug samples after the experiment were dried, weighed, subjected to physical property analysis, and subjected to experimental analysis such as CT scanning of the rock's internal pore structure; the reaction liquid was analyzed for ion composition and content.

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

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

[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 karst fluid source and the fluid pressure of the karst occurrence 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 plunger sample after the experiment to analyze the microscopic morphology characteristics of the plunger sample after the experiment; when the plunger sample is subjected to CT scanning in step (8), the analysis conditions in step (3) should be consistent, such as resolution and analysis position; when the plunger sample is subjected to CT scanning based on CT, the CT scanning image of step (8) should be compared to achieve in-situ comparison of the occurrence of internal fractures in the rock; wherein, the analysis of the reaction generated fluid in step (8) refers to Ca 2+ Mg 2+ Concentration analysis;

[0106] According to the embodiment of the present invention, the carbonate rock dissolution and dissolution effect are evaluated in step (8) mainly based on the dissolution amount, the 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 process of quantitative restoration of fault-controlled karst reservoir formation in a certain study area is carried out to provide technical means to clarify the main controlling factors and distribution laws of the development of fault-controlled karst reservoirs in the study area, which specifically includes the following steps:

[0108] In step S11, the set features of the key constructors are judged in phase, referring to Figure 3 As shown, the period of 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 pores and caves of different periods in the fault-controlled karst reservoir in the above study area show that the Upper Ordovician has undergone multiple stages of tectonic activity transformation, and a total of 7 stages of related calcite have been identified, involving various fluids such as atmospheric water, organic acid and formation water. Figure 4 As shown, each period 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 fault-controlled karst model restoration in the study area, refer to Figure 5 As shown in the figure, taking the Late Caledonian-Early Hercynian period as an example, the source of calcite fluid was comprehensively analyzed through the in situ U-Pb age of calcite cement in the fault zone, strontium isotopes and inclusions, and the secondary calcite growth model under the constraints of specific absolute age and fluid source was restored. It was recognized that the Late Caledonian-Early Hercynian was the main activity period of the northeast strike-slip fault. The carbon, strontium isotopes 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 organic acid activity controlled by the geothermal field and of deep origin 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 enhancement evaluation experiment. Figure 7 to Figure 10 The three-dimensional fracture diagram and porosity value comparison before and after dissolution shown in the figure can quantitatively restore the entire process of fault-controlled karst reservoir formation in the study area after analysis.

[0112] Based on the same inventive concept, an oil and gas exploration method is also provided in an embodiment of the present invention, which explores the 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 can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

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 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; Conduct geological analysis on the fractures and fillings in the fault-controlled karst development zone 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 in the study area, so as to establish the fault-controlled karst reservoir type and its episodic evolution model in the study area; For each episode of karstification in the fault-controlled karst model in the study area, a dissolution and reserve enhancement evaluation experiment was carried out under the constraints of geological conditions using carbonate 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.

2. The method according to claim 1, characterized in that Also includes: 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.

3. 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, including: Obtain rock types, rock component parameters, reservoir fracture 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 prepared to simulate the customized 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; Based on the characteristic parameters of the reservoir diagenetic fluid, preparing an erosive fluid simulating the reservoir diagenetic fluid; Under the constraints of the geological background parameters, using the carbonate rock plug sample and the corrosive fluid to carry out a dissolution and reserve enhancement simulation experiment, and collecting the reaction generated fluid 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 curtain in the study area were determined.

4. The method according to claim 3, 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 image obtained by CT scanning.

5. The method according to claim 3, 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.

6. The method according to claim 3, characterized in that Before conducting the dissolution and reserve enhancement simulation experiment, the inlet and outlet ends of the gas flow of the carbonate rock plug sample are marked, and the carbonate rock plug sample is placed in the core holder of the diagenesis simulation device based on the inlet and outlet ends marked on the carbonate rock plug sample to ensure that the flow direction of the corrosive fluid is consistent with the gas flow direction during physical property analysis.

7. The method according to claim 3, characterized in that 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; The types of geological stress include: tectonic force, hydrodynamic force, geostatic pressure and thermal force.

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

9. The method according to claim 8, characterized in that The fluid inlet pressure of the simulation experiment 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 value of the driving fluid is determined by the difference between the fluid pressure of the target layer where the karst action fluid comes from and the fluid pressure at the depth where the karst action occurs, and is used as the fluid inlet pressure of the simulation experiment.

10. A method for oil and gas exploration, 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; Wherein, 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 9.

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