Exogenous supply type shale gas exploration favorable area prediction method

Abstract

The invention relates to the field of shale gas, and discloses an exogenous supply type shale gas exploration favorable area prediction method, which comprises the following steps of mining shale gas reservoir forming conditions; reservoir forming parameters and numerical values required by shale gas reservoir forming conditions are obtained through structural route investigation, sedimentary facies profile investigation, sample analysis and testing and sedimentary facies scientific research topic typical profile analysis; delineating an exogenous gas conduction path; establishing a gas source-channel-reservoir-preservation four-in-one reservoir forming model; a shale gas dessert area is predicted through a reservoir forming model, a shale gas favorable sedimentary facies belt, favorable structure preservation conditions, karst area low signal-to-noise ratio earthquake refined analysis and a reservoir dynamic change model; and according to the shale gas sweet spot area, further delineating a shale gas exploration favorable target area and a target area. The dynamic change of the reservoir is considered, and the prediction error is small.

Description

Technical Field

[0001] The present invention relates to the technical field of shale gas, and in particular to a method for predicting favorable exploration areas of exogenous recharge type shale gas. Background Art

[0002] Shale gas is an unconventional natural gas resource, mainly stored in dark mudstones with low porosity and extremely low permeability. Shale gas is the natural gas produced from fine-grained sedimentary rocks such as organic-rich mudstones. Compared with conventional gas reservoirs, shale gas has the characteristics of a delicate sealing mechanism, diverse caprock lithologies, and a relatively short hydrocarbon migration distance. Since organic-rich mudstones are often extremely low-permeability tight formations, existing shale gas development often requires artificial hydraulic fracturing for extraction. However, with the rapid development of the shale gas industry, the fracturing cost of shale gas development is high, environmental pollution is serious, earthquakes may be induced, and shale gas resources deeper than 4000 m cannot be fully developed and utilized. This series of technical bottlenecks are becoming increasingly prominent. Although existing processes attempt to reduce the fracturing cost by increasing the fracturing fluid flowback rate and increase the buried depth of exploitable shale gas resources by enhancing the fracturing capacity to alleviate the industry's technical bottlenecks, they still cannot fully break through the existing technical bottlenecks of the shale gas industry.

[0003] Based on the summary of the shale gas enrichment laws of typical domestic shale gas reservoirs and a large amount of profile and core data, according to the differences in the control of shale gas enrichment by the slip layer, shale gas can be divided into: in-situ enrichment type shale gas and exogenous recharge type shale gas. "Exogenous recharge type shale gas" means that there is not only the natural gas remaining after hydrocarbon expulsion in the organic-rich mudstone, but also the natural gas supplied laterally by the peripheral mudstone through faults or vertically by the micro-leakage of the underlying gas reservoir. Although there are hydrocarbon expulsion and natural gas dissipation, the supply rate of natural gas is greater than the dissipation rate, forming dynamic enrichment. The enrichment of shale gas therein is mainly controlled by fluid potential. Exogenous recharge type shale gas may have natural productivity due to the conduction of overpressure by high-permeability oil and gas conduction layers. Because this type of shale gas has not received high attention in the industry. Exogenous recharge type shale gas may have natural productivity due to the conduction of overpressure by high-permeability oil and gas conduction layers, and the enrichment law of exogenous recharge type shale gas can not only explain many theoretical problems found in the current shale gas exploration and development process, but also in-depth research on it will contribute to the research on the shale gas enrichment law and the dynamic hydrocarbon accumulation mechanism in complex tectonic areas in China. However, at present, existing methods for predicting favorable exploration areas of exogenous recharge type shale gas mostly require time-consuming exploration and do not consider the dynamic changes of reservoirs, and it is easy to have large errors in prediction. Summary of the Invention

[0004] The present invention provides a method for predicting favorable exploration areas of exogenous recharge type shale gas, aiming to solve the problems that it mostly requires time-consuming exploration, does not consider the dynamic changes of reservoirs, and is easy to have large errors in prediction.

[0005] A method for predicting favorable areas for exogenous-supplied shale gas exploration, comprising the following steps:

[0006] Excavating shale gas accumulation conditions, obtaining the accumulation parameters and values required for shale gas accumulation conditions through structural route surveys, sedimentary facies profile surveys, sample analysis and testing, and analysis of typical profiles of sedimentary facies research projects; delineating the transport paths of exogenous gas; establishing a four-in-one accumulation model of gas source-channel-reservoir-preservation;

[0007] Predicting shale gas sweet spots through the accumulation model, favorable sedimentary facies belts for shale gas, favorable structural preservation conditions, fine-resolution of low-signal-to-noise ratio seismic data in karst areas, and combining with the reservoir dynamic change model;

[0008] Further delineating favorable target areas and target zones for shale gas exploration based on the shale gas sweet spots.

[0009] Specifically, the structural route survey is specifically a 1:50,000 route geological survey of 550 km.

[0010] Specifically, the sedimentary facies profile survey is specifically a 1:500 geological profile measurement of 5 km and a 1:10,000 structural profile survey of 120 km.

[0011] Specifically, the analysis of typical profiles of sedimentary facies research projects is to clarify the shale gas accumulation process from hydrocarbon generation to hydrocarbon expulsion and then to accumulation based on the sedimentary facies profiles.

[0012] Specifically, three-dimensional seismic + electromagnetic method exploration is used to delineate the transport paths of exogenous gas, and horizontal well drilling + tracer testing are combined to verify the gas source replenishment efficiency, and finally a four-in-one accumulation model of gas source-channel-reservoir-preservation is established.

[0013] Specifically, the accumulation parameters and values are specifically: the sedimentary facies are the main sedimentary facies types of deep-water continental shelf or lower slope, and platform basin; effective thickness: the continuous thickness of the shale layer is greater than or equal to 20 m; organic matter abundance: TOC ≥ 1.5%; organic matter maturity: 1.3% - 4.0%; the organic matter type is: type I, II.

[0014] Specifically, the establishment of the reservoir dynamic change model includes the following steps:

[0015] S1. Identifying the fault system connecting the deep gas source based on three-dimensional seismic data, and combining with the permeability data of the detachment layer to construct a three-dimensional channel network for the transport of gas source to the shale reservoir;

[0016] S2. Obtaining the pressure evolution curves of the gas source layer and the shale reservoir through formation pressure testing, and establishing a gas migration kinetics equation driven by the pressure difference;

[0017] S3. Dynamically updating the pore distribution parameters by combining core SEM images and logging data;

[0018] S4. Introduce a four-parameter stochastic growth model to simulate the change in pore radius distribution under different effective stresses, and establish an exponential decay equation for the change in permeability with development pressure;

[0019] S5. Integrate viscous flow, diffusion flow, and slip flow to establish a diffusion coefficient model considering the temperature-pressure coupling;

[0020] S6. Establish the Langmuir equation based on isothermal adsorption experiments, and simulate the desorption rate of adsorbed gas by combining with reservoir pressure dynamic data;

[0021] S7. Evaluate the change trend of caprock integrity with development time through formation water chemical indicators and pressure sealing coefficients;

[0022] S8. Combine regional tectonic stress field simulation to establish a correlation equation between fault activation probability and gas escape rate;

[0023] S9. Numerically simulate and verify all the models and equations established in steps S1 - S9 by combining with actual historical exploration data of exogenous recharge type shale gas to obtain a reservoir dynamic change model; the reservoir dynamic change model inputs data after fine analysis of the hydrocarbon accumulation model, favorable sedimentary facies belts of shale gas, favorable tectonic preservation conditions, and low signal-to-noise ratio seismic data in karst areas, and outputs predicted data of reservoir dynamic changes.

[0024] Specifically, further delineate favorable target areas and target zones for shale gas exploration, and specifically set and select favorable target areas and target zones for shale gas exploration by meeting the following conditions:

[0025] Lithologic combination: a combination of calcareous mudstone, silt-bearing carbonaceous mudstone, carbonaceous mudstone, and a small amount of marl; burial depth less than or equal to 4500 m; excluding igneous rocks and contact zones baked by surrounding rocks, and outcropping areas of metamorphic rocks; porosity not less than 2.0%; gas content in the area or adjacent area ≥ 0.5 m 3 / t; distance from the regional major fault greater than or equal to 2 km; formation attitude relatively gentle 0° - 30°; thickness of impermeable rock layers at the top and bottom not less than 10 m; continuous area of a single distribution area not less than 50 km 2 .

[0026] Specifically, the specific method for predicting shale gas sweet spots is: delineate the conduction path through 3D seismic and electromagnetic exploration, and divide the matching shale gas sweet spots by combining the overlay analysis of TOC, porosity, brittleness index, and fracture density.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: By exploring the shale gas accumulation conditions, an accumulation model is obtained. Through the accumulation model, favorable sedimentary facies belts of shale gas, favorable structural preservation conditions, refined analysis of low signal-to-noise ratio seismic data in karst areas, and combined with the reservoir dynamic change model, the sweet spots of shale gas are predicted. Based on the sweet spots of shale gas, the favorable exploration target areas and target zones of shale gas are further delineated. By using the accumulation model and the reservoir dynamic change model to predict the sweet spots of shale gas, and then further delineating the favorable exploration target areas and target zones of shale gas from the sweet spots of shale gas, the dynamic changes of the reservoir are fully considered, and the prediction error is relatively small. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments.

[0029] Figure 1 It is a flowchart of the method for calculating the shale gas resource volume in the complex structural area of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0032] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Such as Figure 1As shown in the figure, a method for predicting favorable areas for exogenous-supplied shale gas exploration includes the following steps:

[0034] Excavating shale gas accumulation conditions, obtaining the accumulation parameters and values required for shale gas accumulation conditions through structural route surveys, sedimentary facies profile surveys, sample analysis and testing, and analysis of typical profiles of sedimentary facies research projects; delineating the transport paths of exogenous gas; establishing a four-in-one accumulation model of gas source-channel-reservoir-preservation. The structural route survey is specifically a 1:50,000 route geological survey of 550 km. The sedimentary facies profile survey is specifically a 1:500 geological profile measurement of 5 km and a 1:10,000 structural profile survey of 120 km. The analysis of typical profiles of sedimentary facies research projects clarifies the shale gas accumulation process from hydrocarbon generation to hydrocarbon expulsion and then to accumulation based on the sedimentary facies profile. The transport paths of exogenous gas are delineated by using 3D seismic + electromagnetic method exploration, and the gas source supply efficiency is verified by combining horizontal well drilling + tracer testing. Finally, a four-in-one accumulation model of gas source-channel-reservoir-preservation is established.

[0035] The accumulation parameters and values are specifically as follows: The sedimentary facies are the main sedimentary facies types of deep-water continental shelf or lower slope, and platform basin; Effective thickness: The continuous thickness of the shale layer is greater than or equal to 20 m; Organic matter abundance: TOC ≥ 1.5%; Organic matter maturity: 1.3% - 4.0%; Organic matter type: Type I and II.

[0036] Predicting the sweet spots of shale gas through the accumulation model, favorable sedimentary facies belts of shale gas, favorable structural preservation conditions, refined analysis of low signal-to-noise ratio seismic data in karst areas, combined with the reservoir dynamic change model;

[0037] The establishment of the reservoir dynamic change model includes the following steps:

[0038] S1. Identifying the fault system connecting the deep gas source based on 3D seismic data, and constructing a 3D channel network for the transport of gas source to the shale reservoir in combination with the permeability data of the detachment layer;

[0039] S2. Obtaining the pressure evolution curves of the gas source layer and the shale reservoir through formation pressure testing, and establishing a gas migration kinetics equation driven by the pressure difference;

[0040] S3. Dynamically updating the pore distribution parameters by combining core SEM images and logging data;

[0041] S4. Introducing a four-parameter stochastic growth model to simulate the change of pore radius distribution under different effective stresses, and establishing an exponential decay equation of permeability with the change of development pressure;

[0042] S5. Integrating viscous flow, diffusion flow and slip flow, and establishing a diffusion coefficient model considering the temperature-pressure coupling;

[0043] S6. Establish the Langmuir equation based on the isothermal adsorption experiment, and simulate the desorption rate of adsorbed gas by combining with the dynamic reservoir pressure data;

[0044] S7. Evaluate the change trend of caprock integrity with development time through formation water chemical indexes and pressure sealing coefficients;

[0045] S8. Combine the regional tectonic stress field simulation to establish the correlation equation between the fault activation probability and the gas escape rate;

[0046] S9. Numerically simulate and verify all the models and equations established in the entire steps S1 - S9 by combining with the actual historical exploration data of exogenous recharge - type shale gas to obtain the reservoir dynamic change model; the reservoir dynamic change model inputs the accumulation model, favorable sedimentary facies belts of shale gas, favorable tectonic preservation conditions, and data after refined analysis of low - signal - to - noise ratio seismic in karst areas, and outputs the predicted data of reservoir dynamic changes. The specific method for predicting the sweet spots of shale gas is as follows: delineate the migration paths through 3D seismic and electromagnetic exploration, and divide the matching sweet spots of shale gas by combining the overlay analysis of TOC, porosity, brittleness index, and fracture density.

[0047] Further delineate the favorable target areas and target zones for shale gas exploration based on the sweet spots of shale gas. To delineate the favorable target areas and target zones for shale gas exploration, specifically set the selection conditions by adapting to the following:

[0048] Lithological combination: the combination of calcareous mudstone, silt - bearing carbonaceous mudstone, carbonaceous mudstone, and a small amount of marl; burial depth less than or equal to 4500 m; excluding igneous rocks and contact zones baked with surrounding rocks, and outcropping areas of metamorphic rocks; porosity not less than 2.0%; gas content in the area or adjacent areas ≥ 0.5 m 3 / t; distance from the regional major fault greater than or equal to 2 km; formation attitude relatively gentle, 0° - 30°; thickness of impermeable rock layers at the top and bottom plates not less than 10 m; continuous area of a single distribution area not less than 50 km 2 .

[0049] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for predicting favorable areas for exogenous shale gas exploration, characterized in that: The following steps are involved: Exploration of shale gas reservoir conditions: obtaining the reservoir parameters and values ​​required for shale gas reservoir conditions through structural route investigation, sedimentary phase profile investigation, sample analysis and testing, and sedimentary phase scientific research topic typical profile analysis; delineating the exogenous gas transmission path; establishing a four-in-one reservoir model of gas source-channel-reservoir-preservation; The shale gas sweet spot is predicted through reservoir formation model, favorable shale gas sedimentary facies, favorable structural preservation conditions, and refined analysis of low signal-to-noise ratio seismic in karst areas combined with reservoir dynamic change model; Based on the shale gas sweet spots, favorable target areas and target areas for shale gas exploration are further identified.

2. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized in that: The structural route survey specifically involves a 1:50,000 route address survey covering 550 km.

3. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized in that: The sedimentary phase profile survey specifically includes a 1:500 geological profile measuring 5 km and a 1:10000 structural profile survey of 120 km.

4. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized in that: Typical profile analysis of sedimentary facies research topics is to clarify the shale gas accumulation process from hydrocarbon generation to hydrocarbon expulsion and then to accumulation based on sedimentary facies profiles.

5. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized in that: The three-dimensional seismic + electromagnetic exploration method is used to delineate the external gas transmission path, and the gas supply efficiency is verified by combining horizontal well drilling + tracer testing, and finally a four-in-one gas source-channel-reservoir-preservation accumulation model is established.

6. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized in that: The reservoir formation parameters and values ​​are as follows: the sedimentary facies is the main sedimentary facies type deep-water continental shelf or lower slope, basin; effective thickness: the continuous thickness of the shale layer is greater than or equal to 20m; organic matter abundance: TOC ≥ 1.5%; organic matter maturity: 1.3% to 4.0%; organic matter types: Type I and Type II.

7. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized in that: The establishment of the reservoir dynamic change model comprises the following steps: S1. Based on 3D seismic data, we identify the fault system that connects deep gas sources and, combined with the permeability data of the detachment layer, construct a 3D channel network for gas source transmission to the shale reservoir; S2. Obtain the pressure evolution curves of the gas source layer and the shale reservoir through formation pressure testing, and establish the kinetic equation of gas migration driven by pressure difference; S3. Dynamically update pore distribution parameters by combining core SEM images and logging data; S4. Introduce a four-parameter random growth model to simulate the change in pore radius distribution under different effective stresses and establish an exponential attenuation equation for the change in permeability with development pressure; S5. Integrate viscous flow, diffusion flow and slip flow to establish a diffusion coefficient model considering temperature-pressure linkage; S6. Establish the Langmuir equation based on isothermal adsorption experiments and simulate the desorption rate of adsorbed gas by combining reservoir pressure dynamic data; S7. Evaluate the changing trend of caprock integrity over development time through formation water chemical indicators and pressure sealing coefficient; S8. Combined with the regional tectonic stress field simulation, establish the correlation equation between fault activation probability and gas escape rate; S9. All models and equations established in the entire steps S1-S9 are combined with actual historical exogenous replenishment shale gas exploration data for numerical simulation and model verification to obtain a reservoir dynamic change model; the reservoir dynamic change model inputs the accumulation model, shale gas favorable sedimentary phase belts, favorable structural preservation conditions, and data after refined analysis of low signal-to-noise ratio seismic in karst areas, and outputs data for reservoir dynamic change prediction.

8. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1 is characterized by: Further define favorable target areas and target areas for shale gas exploration, specifically by setting and selecting favorable target areas and target areas for shale gas exploration according to the following conditions: Lithology combination: combination of calcareous mudstone, silt-carbonaceous mudstone, carbonaceous mudstone, and a small amount of marlstone; burial depth is less than or equal to 4500m; igneous rock and the contact area with surrounding rock baking, metamorphic rock outcrop area are excluded; porosity is not less than 2.0%; gas content in the area or adjacent area is ≥0.5m 3 / t; the distance from the regional major fault is greater than or equal to 2km; the formation dip is relatively gentle 0°~30°; the thickness of the top and bottom impermeable rock layers is not less than 10m; the continuous area of ​​a single distribution area is not less than 50km 2 .

9. The method for predicting favorable areas for shale gas exploration of exogenous supply type according to claim 1, characterized in that: The specific method for predicting shale gas sweet spots is: delineating the transport path through three-dimensional seismic and electromagnetic exploration, combining the superposition analysis of TOC, porosity, brittleness index and fracture density, and dividing the matching shale gas sweet spots.

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