Quantitative selection method and device for unconventional natural gas dessert area in carbonate rock source

Abstract

The invention discloses a quantitative selection method and device for an unconventional natural gas dessert area in a carbonate rock source, and the method comprises the steps: building an evaluation key factor and factor system for the unconventional natural gas in the carbonate rock source based on the analysis of enrichment high-yield main control factors, and forming the quantitative selection method for the dessert area. Quantitative selection of the sweet spot area based on the geophysical technology is achieved, and exploration and development of unconventional natural gas in a carbonate rock source can be guided.

Description

Technical Field

[0001] This invention specifically relates to the field of natural gas exploration and development technology, and more specifically to a method and apparatus for quantitative selection of unconventional natural gas sweet spots within carbonate rock sources. Background Technology

[0002] my country has achieved fruitful results in the exploration and development of conventional natural gas in carbonate reservoirs, discovering and establishing a number of large natural gas fields in regions such as the Sichuan Basin, Tarim Basin, and Junggar Basin. However, among carbonate reservoirs, there is a type of reservoir with high clay content and rich organic matter, possessing significant self-generating capacity and certain adsorption properties. Natural gas is primarily derived from within the reservoir itself, clearly distinguishing it from conventional carbonate reservoirs. Similar to the self-generating and self-storing characteristics of shale gas reservoirs, this type is termed unconventional reservoirs within carbonate sources. Recently, the industry has discovered that this type of unconventional reservoir has significant exploration and development potential for unconventional natural gas within carbonate sources. The unconventional natural gas resources within the first section of the Maokou Formation in the Sichuan Basin alone exceed 2 trillion cubic meters, potentially becoming an important area for increasing reserves and production. Accurately and quickly identifying sweet spots for this type of unconventional natural gas has become an urgent need for the industry. Because the exploration and development of this type of unconventional natural gas is still in its early stages, and its reservoir characteristics differ from both conventional carbonate reservoirs and shale reservoirs, the selection of sweet spots faces the following challenges:

[0003] 1. Conventional methods for evaluating the selection of natural gas in carbonate rock sources and methods for evaluating the selection of natural gas in shale rock sources are not applicable to the selection of sweet spots for unconventional natural gas within carbonate rock sources;

[0004] 2. A key factor and factor system for evaluating unconventional natural gas in carbonate source rocks has not yet been established based on the analysis of the main controlling factors of enrichment and high yield;

[0005] 3. A quantitative selection model for unconventional natural gas sweet spots within carbonate source rocks has not yet been established to achieve quantitative selection of sweet spots;

[0006] 4. A quantitative selection method for unconventional natural gas sweet spots in carbonate rock sources based on geophysical technology has not yet been developed, which cannot meet the production needs of areas with low exploration levels. Summary of the Invention

[0007] Therefore, the present invention proposes a method and apparatus for quantitative selection of unconventional natural gas sweet spots in carbonate rock sources to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for quantitative selection of unconventional natural gas sweet spots within carbonate source rocks, comprising the following steps:

[0009] Step 1: Select a scaled area with a high degree of exploration, conduct geological evaluation and enrichment and high-yield pattern analysis of unconventional natural gas in carbonate source rocks, and identify the main controlling factors of enrichment and high yield;

[0010] Step 2: Based on the analysis of the main controlling factors of enrichment and high production in Step 1, establish the key factors and factor system for the evaluation of unconventional natural gas in carbonate source rocks;

[0011] Step 3: Based on the key factors and factor system for evaluating unconventional natural gas in carbonate sources in Step 2, establish a quantitative selection model for unconventional natural gas sweet spots in carbonate sources;

[0012] Step 4: Based on geophysical interpretation and prediction, obtain the key factors and characteristics of unconventional natural gas evaluation in the carbonate source area of ​​the evaluation area;

[0013] Step 5: Based on the key factors and characteristics of unconventional natural gas evaluation in the carbonate source area of ​​the evaluation area in Step 4, calculate the comprehensive evaluation index of the sweet spot area of ​​unconventional natural gas in the carbonate source area of ​​the evaluation area, and select the sweet spot area.

[0014] Furthermore, as a preferred option, in step 1, the comprehensive evaluation of the geological conditions for natural gas accumulation in unconventional carbonate reservoirs in the calibration area includes: sedimentary characteristic analysis, petrological characteristic analysis, geochemical characteristic analysis, reservoir characteristic analysis, structural characteristic analysis, preservation condition analysis, gas-bearing characteristic analysis, and analysis of accumulation evolution and matching relationship, so as to dissect in detail the characteristics of each accumulation element of unconventional natural gas in carbonate source rocks.

[0015] The reasons for high and low production in wells with different yields in the calibration zone were analyzed, the high-yield enrichment pattern of unconventional natural gas in carbonate source rocks was summarized, and the main factors controlling natural gas enrichment and high production were identified.

[0016] Furthermore, as a preferred option, in step 2, the key factors for evaluating unconventional natural gas within carbonate source rocks include: evaluation factors for self-generated hydrocarbons, evaluation factors for structural preservation conditions, and evaluation factors for fracture development characteristics.

[0017] Among them, the self-generating hydrocarbon characteristic evaluation factor is used to evaluate the hydrocarbon generation capacity of unconventional carbonate reservoirs, and it includes unconventional reservoir thickness and organic matter abundance evaluation factors.

[0018] The structural preservation condition evaluation factors are used to evaluate the unconventional natural gas preservation conditions in carbonate rocks, and include structural features, trap features, formation pressure coefficient, gas content, and distance from erosion boundary evaluation factors.

[0019] The evaluation factors for fracture development characteristics are used to evaluate the natural fracture development characteristics of unconventional carbonate reservoirs, and include evaluation factors for mesoscale fracture development characteristics and small-scale fracture development characteristics.

[0020] Furthermore, as a preferred option, in step 3, based on three types of evaluation factors—the hydrocarbon generation characteristics of unconventional carbonate reservoirs themselves, structural preservation conditions, and fracture development characteristics—and the controlling effect of nine evaluation factors on the enrichment and high production of unconventional natural gas within carbonate source rocks, a quantitative evaluation model for unconventional natural gas sweet spots within carbonate source rocks is established. The sweet spot level is then evaluated by calculating the comprehensive evaluation index EI, as shown in the matrix below:

[0021] EI = (abc)(EI) 自身生烃特征 EI 构造保存条件 EI 裂缝发育特征 );

[0022] In the formula:

[0023] EI is a comprehensive evaluation index with dimensionless units.

[0024] a, b, and c are weighting coefficients for the self-hydrogenation characteristics, structural preservation conditions, and fracture development characteristics, respectively, with dimensionless units, and a+b+c=1;

[0025] EI 自身生烃特征 This is a characteristic index of its own hydrocarbon generation, with dimensionless units.

[0026] EI 构造保存条件 To construct the preservation condition index, the unit is dimensionless;

[0027] EI 裂缝发育特征 This is a crack development characteristic index, with dimensionless units.

[0028] The evaluation matrix of the self-generated hydrocarbon characteristic index is as follows:

[0029] EI 自身生烃特征 =(a1 a2)(EI) 非常规储层厚度 EI 有机质丰度 );

[0030] In the formula:

[0031] EI 非常规储层厚度 This is the unconventional reservoir thickness index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0032] EI 有机质丰度 This is the organic matter abundance index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0033] a1 and a2 are the weighting coefficients for unconventional reservoir thickness and organic matter abundance, respectively, with dimensionless units, and a1+a2=1;

[0034] The formula for calculating the unconventional reservoir thickness index is as follows:

[0035]

[0036] In the formula:

[0037] H represents the unconventional reservoir thickness, in meters (m).

[0038] The formula for calculating the organic matter abundance index is as follows:

[0039]

[0040] In the formula:

[0041] TOC represents the organic matter abundance of unconventional reservoirs, expressed as a percentage.

[0042] The preservation condition index evaluation matrix is ​​constructed as follows:

[0043] EI 构造保存条件 =(b1 b2 b3 b4 b5)(EI) 构造特征 EI 圈闭特征 EI 地层压力系数 EI 含气性 EI 离剥蚀边界距离 );

[0044] In the formula:

[0045] b1, b2, b3, b4, and b5 are weighting coefficients for structural features, trap features, formation pressure coefficient, gas content, and distance from erosion boundary, respectively, with dimensionless units. b1+b2+b3+b4+b5=1;

[0046] EI 构造特征 To construct the characteristic index, the minimum value is 0, the maximum value is 1, and the unit is dimensionless;

[0047] EI 圈闭特征 This is the trap characteristic index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0048] EI 地层压力系数 This is the formation pressure coefficient index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0049] EI 含气性 This is the gas content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0050] EI 离剥蚀边界距离 This is the distance exponent from the erosion boundary, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0051] The formula for calculating the characteristic index is as follows:

[0052]

[0053] The formula for calculating the trap characteristic index is as follows:

[0054]

[0055] The formula for calculating the formation pressure coefficient index is as follows:

[0056]

[0057] In the formula:

[0058] PK is the formation pressure coefficient, with dimensionless units.

[0059] The formula for calculating the gas content index is as follows:

[0060]

[0061] In the formula:

[0062] MuRho is the product of shear modulus and density, in GPa*g / cm³. 3 ;

[0063] The formula for calculating the distance index from the erosion boundary is as follows:

[0064]

[0065] In the formula:

[0066] L represents the distance from the erosion boundary, in km;

[0067] The evaluation matrix of crack development characteristic index is as follows:

[0068] EI 裂缝发育特征指数 =(c1 c2)(EI 中尺度裂缝发育特征 EI 小尺度裂缝发育特征 );

[0069] In the formula:

[0070] c1 and c2 are the weighting coefficients for mesoscale and small-scale crack development characteristics, respectively, with dimensionless units; c1+c2=1;

[0071] EI 中尺度裂缝发育特征 This is a mesoscale crack development characteristic index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0072] EI 小尺度裂缝发育特征 This is a characteristic index of small-scale crack development, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0073] The formula for calculating the mesoscale crack development characteristic index is as follows:

[0074]

[0075] In the formula:

[0076] AFE is a fault coherence enhancement property, and its unit is dimensionless.

[0077] The formula for calculating the small-scale crack development characteristic index is as follows:

[0078]

[0079] In the formula:

[0080] Azimuth AVO represents the amplitude variation with offset distance in different azimuths, and the unit is dimensionless.

[0081] Furthermore, as a preferred option, in step 4, a detailed interpretation of the earthquake in the area to be evaluated is carried out, a structural map of the target layer is compiled, and evaluation factor characteristics such as structural features, trap features, and distance from the erosion boundary are obtained.

[0082] Using forward modeling, attribute extraction, and pre-stack and post-stack inversion techniques, attribute prediction of the area to be evaluated is carried out, and contour maps of target layer thickness, TOC, formation pressure coefficient, MuRho attribute distribution, AFE attribute distribution, and azimuth AVO attribute distribution are compiled to obtain the evaluation factor characteristics of unconventional reservoir thickness, organic matter abundance, formation pressure coefficient, gas content, mesoscale fractures, and small-scale fractures.

[0083] Furthermore, as a preferred embodiment, in step 5, based on the quantitative evaluation model of unconventional natural gas sweet spots within carbonate source areas obtained in step 3 and the key evaluation factors and characteristics of the area to be evaluated obtained in step 4, the comprehensive evaluation index EI of the area to be evaluated is calculated. Based on the EI value, the area to be evaluated is divided into three levels: Class I, Class II, and Class III.

[0084]

[0085] Among them, the unconventional natural gas exploration potential in carbonate rock sources is relatively large in Class I areas; the unconventional natural gas exploration potential in carbonate rock sources is moderate in Class II areas; and the unconventional natural gas exploration potential in carbonate rock sources is relatively poor in Class III areas.

[0086] The present invention also provides a device for quantitative selection of unconventional natural gas sweet spots in carbonate sources, which is used to perform the quantitative selection method for unconventional natural gas sweet spots in carbonate sources as described above. It includes: an input unit U1 for evaluation factors and evaluation coefficients of the area to be evaluated, an input unit U2 for weight coefficients of evaluation factors and evaluation coefficients of the area to be evaluated, a calculation unit U3 for self-generated hydrocarbon characteristic index, a calculation unit U4 for structural preservation condition index, a calculation unit U5 for fracture development characteristic index, a calculation unit U6 for comprehensive evaluation index, and a sweet spot grade determination and selection unit U7.

[0087] Among them, the evaluation factor and evaluation factor input unit U1 of the area to be evaluated is used to input the characteristics of the evaluation factors and evaluation factors of the area to be evaluated.

[0088] The evaluation factor and evaluation factor weight coefficient input unit U2 is used to input the weight coefficients of each evaluation factor and evaluation factor, including a, b, c, a1, a2, b1, b2, b3, b4, b5, c1, c2;

[0089] The self-generated hydrocarbon characteristic index calculation unit U3 is used to calculate the self-generated hydrocarbon characteristic index EI of the area to be evaluated. 自身生烃特征 ;

[0090] Construction preservation condition index calculation unit U4 is used to calculate the construction preservation condition index EI of the area to be evaluated. 构造保存条件 ;

[0091] The crack development characteristic index calculation unit U5 is used to calculate the crack development characteristic index EI of the area to be evaluated. 裂缝发育特征 ;

[0092] The comprehensive evaluation index calculation unit U6 is used to calculate the comprehensive evaluation index EI of the area to be evaluated.

[0093] The dessert area level determination and selection unit U7 is used to determine the dessert area level and select the dessert area.

[0094] Furthermore, as a preferred embodiment, it also includes a computer device, which includes a processor, a memory, a display, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the quantitative selection method for unconventional natural gas sweet spots in carbonate rock sources as described above.

[0095] The present invention employs the above technology and has the following beneficial effects compared with existing technologies:

[0096] 1. The present invention provides a method and apparatus for quantitative selection of unconventional natural gas sweet spots in carbonate source areas. Based on the analysis of the main controlling factors of enrichment and high production, it selects three categories of evaluation factors, namely, its own hydrocarbon generation characteristics, structural preservation conditions, and fracture development characteristics, and nine evaluation factors, namely, unconventional reservoir thickness, organic matter abundance, structural characteristics, trap characteristics, formation pressure coefficient, gas content, distance from erosion boundary, mesoscale fracture development characteristics, and small-scale fracture development characteristics. It establishes a key factor and factor system for the evaluation of unconventional natural gas in carbonate source areas, with highly targeted parameters.

[0097] 2. A quantitative selection model for unconventional natural gas sweet spots within carbonate rock sources was established, enabling quantitative selection of sweet spots.

[0098] 3. A quantitative selection method for unconventional natural gas sweet spots in carbonate rock sources based on geophysical technology has been developed, which can meet the production needs of areas with low exploration levels.

[0099] 4. It is of great significance for deepening the geological research on unconventional natural gas in carbonate source areas and accelerating the exploration and development process. Attached Figure Description

[0100] Figure 1 This is a schematic flowchart of the method of the present invention;

[0101] Figure 2 This invention provides a diagram of the quantitative selection and evaluation factors and factor system structure for unconventional natural gas sweet spots within carbonate source regions, as provided in this embodiment.

[0102] Figure 3 A schematic diagram of the functional modules of the quantitative selection device for unconventional natural gas sweet spot region in carbonate rock source provided in an embodiment of the present invention;

[0103] Figure 4 A schematic diagram of the structure of a computer device for quantitative selection of unconventional natural gas sweet spots within carbonate rock sources, provided in an embodiment of the present invention.

[0104] In the diagram: 10, memory; 20, computer program; 30, display; 40, processor. Detailed Implementation

[0105] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0106] Example: Please refer to the appendix. Figure 1-4 Taking the first section of the Maokou Formation (hereinafter referred to as Maokou First Section) of the Permian system in the A and B tectonic zones of the southeastern margin of the Sichuan Basin as an example, this invention provides a technical solution: a method for quantitative selection of unconventional natural gas sweet spots within carbonate source rocks, which includes the following steps:

[0107] Step 1: Select a scaled area with a high degree of exploration, conduct geological evaluation and enrichment and high-yield pattern analysis of unconventional natural gas in carbonate source rocks, and identify the main controlling factors of enrichment and high yield;

[0108] Specifically, the aforementioned high-exploration-level scale area refers to an area where multiple unconventional natural gas exploration or appraisal wells have been drilled within carbonate source rocks, geological evaluation data has been systematically obtained, industrial gas flow has been obtained, and the level of exploration and understanding is high.

[0109] Specifically, a comprehensive evaluation of the geological conditions for natural gas accumulation in unconventional carbonate reservoirs in the calibration area will be conducted, including analysis of sedimentary characteristics, petrological characteristics, geochemical characteristics, reservoir characteristics, structural characteristics, preservation conditions, gas-bearing characteristics, and accumulation evolution and matching relationships. The characteristics of each accumulation element of unconventional natural gas within the carbonate source rock will be dissected in detail.

[0110] Specifically, we will conduct an analysis of the reasons for high and low production in wells with different yields in the calibration zone, summarize the high-yield patterns of unconventional natural gas enrichment in carbonate source rocks, and identify the main factors controlling natural gas enrichment and high production.

[0111] The Maoyi section of the A structural zone in this invention is a set of unconventional carbonate reservoirs rich in organic matter and argillaceous material, exhibiting self-generating and self-storing characteristics, representing typical unconventional natural gas within a carbonate source. Currently, the area has achieved full 3D seismic coverage, with 9 completed exploration and appraisal wells drilled, testing daily gas production ranging from 35,000 to 225,000 cubic meters. A systematic collection of core, logging, analytical, fracturing, and testing data has been obtained, indicating a high level of exploration and geological understanding. Therefore, the A structural zone was selected as the calibration area. Through analysis of the reasons for high and low production in wells with different yields within the A structural zone, it was clarified that the high production of unconventional natural gas within the carbonate source in this area follows the pattern of "self-generating hydrocarbon characteristics controlling the gas source scale, structural and preservation conditions controlling natural gas preservation and reservoir formation, and fracture development characteristics controlling the degree of natural gas enrichment and single-well production." Self-generating hydrocarbon characteristics, structural and preservation conditions, and fracture development characteristics are the main factors controlling natural gas enrichment and high production.

[0112] Step 2: Based on the analysis of the main controlling factors of enrichment and high production in Step 1, establish the key factors and factor system for the evaluation of unconventional natural gas in carbonate source rocks;

[0113] Specifically, the key evaluation factors are the main controlling factors for the enrichment and high production of unconventional natural gas within carbonate source rocks. Since unconventional natural gas in carbonate rocks accumulates and forms reservoirs within the source, the hydrocarbon generation characteristics of the carbonate rocks themselves determine the scale of the gas source, which is a significant difference between them and conventional carbonate reservoirs. The structure and preservation conditions determine whether the naturally generated gas can be preserved and formed into reservoirs. Unconventional carbonate reservoirs are very dense, with natural fractures serving as the main storage space and seepage channels. The characteristics of fracture development determine the degree of natural gas enrichment and the production per well.

[0114] Therefore, the key evaluation factors include three categories: evaluation factors of self-generated hydrocarbon characteristics, evaluation factors of structural preservation conditions, and evaluation factors of fracture development characteristics.

[0115] Specifically, the self-generating hydrocarbon characteristics evaluation factors are used to evaluate the hydrocarbon generation capacity of unconventional carbonate reservoirs, and include two evaluation factors: unconventional reservoir thickness and organic matter abundance.

[0116] The thickness of unconventional reservoirs refers to the thickness of unconventional carbonate reservoirs, which can be obtained through drilling or by predicting seismic properties. The greater the thickness of unconventional reservoirs, the stronger their hydrocarbon generation capacity.

[0117] Organic matter abundance refers to the average organic matter abundance of unconventional carbonate reservoirs. It can be obtained through experimental analysis of drilling or interpretation of well logging, or through prediction of seismic attributes. The higher the organic matter abundance of unconventional reservoirs, the stronger their hydrocarbon generation capacity.

[0118] Specifically, the structural preservation condition evaluation factors are used to evaluate the unconventional natural gas preservation conditions in carbonate rocks, and include five evaluation factors: structural features, trap features, formation pressure coefficient, gas content, and distance from the erosion boundary.

[0119] Among them, the structural features are the structural features of unconventional carbonate reservoirs in the study area, which can be obtained through detailed seismic interpretation; for unconventional natural gas in carbonate rocks, complete anticline structures are more conducive to gas preservation and accumulation; synclines are second; monoclines are not conducive to gas preservation and accumulation because the target layer is exposed at the surface, and gas is easy to escape. The shallow part of the monocline is not conducive to gas preservation and accumulation, while the deep part has certain preservation conditions.

[0120] Traps are the characteristics of unconventional carbonate reservoirs and can be obtained through detailed seismic interpretation. Because unconventional natural gas in carbonate rocks possesses characteristics of both shale and conventional natural gas, the development of structural or lithological traps is more conducive to gas preservation and accumulation.

[0121] The formation pressure coefficient refers to the formation pressure coefficient of unconventional carbonate reservoirs. It can be obtained by combining drilling micro-injection pressure drop tests with seismic attribute prediction. The higher the formation pressure coefficient, the better the gas reservoir preservation conditions.

[0122] Gas content refers to the gas content of unconventional carbonate reservoirs. It can be represented by the gas content obtained through drilling experimental analysis or well logging interpretation, or by the MuRho attribute value obtained through seismic attribute prediction. Gas content is positively correlated with reservoir preservation conditions. The lower the MuRho attribute value, the better the reservoir preservation conditions and gas content.

[0123] The distance from the erosion boundary is the same as the distance from the erosion boundary of unconventional carbonate reservoirs. This distance can be obtained through detailed seismic interpretation, and the farther the distance from the erosion boundary, the better the gas reservoir preservation conditions.

[0124] Specifically, the fracture development characteristic evaluation factor is used to evaluate the natural fracture development characteristics of unconventional carbonate reservoirs, and it includes two evaluation factors: mesoscale fracture development characteristics and small-scale fracture development characteristics.

[0125] Among them, the mesoscale fracture development characteristics are the mesoscale fracture development characteristics of unconventional carbonate reservoirs, which can be represented by the AFE attribute value obtained by seismic attribute prediction; when the mesoscale fracture development is moderate (the AFE attribute value is moderate), it is more conducive to high production.

[0126] The development characteristics of small-scale fractures in unconventional carbonate reservoirs can be represented by the azimuth AVO attribute value obtained through seismic attribute prediction. The more developed the small-scale fractures (the larger the azimuth AVO attribute value), the more conducive it is to high production.

[0127] In this embodiment of the invention, unconventional natural gas in the Maomen section of the carbonate rock in the A structural zone was evaluated using three categories of factors: its own hydrocarbon generation characteristics, structural preservation conditions, and fracture development characteristics. Nine evaluation factors were also selected: unconventional reservoir thickness, organic matter abundance, structural characteristics, trap characteristics, formation pressure coefficient, gas content, distance from the erosion boundary, mesoscale fracture development characteristics, and small-scale fracture development characteristics. A key factor and factor system for evaluating unconventional natural gas within carbonate source rocks was established (see Table 1 and appendix). Figure 2 ).

[0128] Table 1A Key factors and characteristics of unconventional natural gas assessment within the Mao-1 carbonate source rock of the structural belt.

[0129]

[0130]

[0131] Step 3: Based on the key factors and factor system for evaluating unconventional natural gas in carbonate sources in Step 2, establish a quantitative selection model for unconventional natural gas sweet spots in carbonate sources;

[0132] Specifically, in step 3, based on three categories of evaluation factors—the hydrocarbon generation characteristics of unconventional carbonate reservoirs themselves, structural preservation conditions, and fracture development characteristics—and the controlling effect of nine evaluation factors on the enrichment and high production of unconventional natural gas within carbonate source rocks, a quantitative evaluation model for unconventional natural gas sweet spots within carbonate source rocks is established. The sweet spot level is then evaluated by calculating the comprehensive evaluation index EI, as shown in the matrix below:

[0133] EI = (abc)(EI) 自身生烃特征 EI 构造保存条件 EI 裂缝发育特征 );

[0134] In the formula:

[0135] EI is a comprehensive evaluation index with dimensionless units.

[0136] a, b, and c are weighting coefficients for the self-hydrogenation characteristics, structural preservation conditions, and fracture development characteristics, respectively, with dimensionless units, and a+b+c=1;

[0137] EI 自身生烃特征 This is a characteristic index of its own hydrocarbon generation, with dimensionless units.

[0138] EI 构造保存条件 To construct the preservation condition index, the unit is dimensionless;

[0139] EI 裂缝发育特征 This is a crack development characteristic index, with dimensionless units.

[0140] The evaluation matrix of the self-generated hydrocarbon characteristic index is as follows:

[0141] EI 自身生烃特征 =(a1 a2)(EI) 非常规储层厚度 EI 有机质丰度 );

[0142] In the formula:

[0143] EI 非常规储层厚度 This is the unconventional reservoir thickness index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0144] EI 有机质丰度 This is the organic matter abundance index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0145] a1 and a2 are the weighting coefficients for unconventional reservoir thickness and organic matter abundance, respectively, with dimensionless units, and a1+a2=1;

[0146] The formula for calculating the unconventional reservoir thickness index is as follows:

[0147]

[0148] In the formula:

[0149] H represents the unconventional reservoir thickness, in meters (m).

[0150] The formula for calculating the organic matter abundance index is as follows:

[0151]

[0152] In the formula:

[0153] TOC represents the organic matter abundance of unconventional reservoirs, expressed as a percentage.

[0154] The preservation condition index evaluation matrix is ​​constructed as follows:

[0155] EI 构造保存条件 =(b1 b2 b3 b4 b5)(EI) 构造特征 EI 圈闭特征 EI 地层压力系数 EI 含气性 EI离剥蚀边界距离 );

[0156] In the formula:

[0157] b1, b2, b3, b4, and b5 are weighting coefficients for structural features, trap features, formation pressure coefficient, gas content, and distance from erosion boundary, respectively, with dimensionless units. b1+b2+b3+b4+b5=1;

[0158] EI 构造特征 To construct the characteristic index, the minimum value is 0, the maximum value is 1, and the unit is dimensionless;

[0159] EI 圈闭特征 This is the trap characteristic index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0160] EI 地层压力系数 This is the formation pressure coefficient index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0161] EI 含气性 This is the gas content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0162] EI 离剥蚀边界距离 This is the distance exponent from the erosion boundary, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0163] The formula for calculating the characteristic index is as follows:

[0164]

[0165] The formula for calculating the trap characteristic index is as follows:

[0166]

[0167] The formula for calculating the formation pressure coefficient index is as follows:

[0168]

[0169] In the formula:

[0170] PK is the formation pressure coefficient, with dimensionless units;

[0171] The formula for calculating the gas content index is as follows:

[0172]

[0173] In the formula:

[0174] MuRho is the product of shear modulus and density, in GPa*g / cm³. 3 ;

[0175] The formula for calculating the distance index from the erosion boundary is as follows:

[0176]

[0177] In the formula:

[0178] L represents the distance from the erosion boundary, in km;

[0179] The evaluation matrix of crack development characteristic index is as follows:

[0180] EI 裂缝发育特征指数 =(c1 c2)(EI 中尺度裂缝发育特征 EI 小尺度裂缝发育特征 );

[0181] In the formula:

[0182] c1 and c2 are the weighting coefficients for mesoscale and small-scale crack development characteristics, respectively, with dimensionless units; c1+c2=1;

[0183] EI 中尺度裂缝发育特征 This is a mesoscale crack development characteristic index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0184] EI 小尺度裂缝发育特征 This is a characteristic index of small-scale crack development, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless.

[0185] The formula for calculating the mesoscale crack development characteristic index is as follows:

[0186]

[0187] In the formula:

[0188] AFE is a fault coherence enhancement property, and its unit is dimensionless.

[0189] The formula for calculating the small-scale crack development characteristic index is as follows:

[0190]

[0191] In the formula:

[0192] Azimuth AVO represents the amplitude variation with offset distance in different azimuths, and the unit is dimensionless.

[0193] Step 4: Based on geophysical interpretation and prediction, obtain the key factors and characteristics of unconventional natural gas evaluation in the carbonate source area of ​​the evaluation area;

[0194] Specifically, conduct detailed interpretation of earthquakes in the area to be evaluated, compile structural maps of the target layer, and obtain evaluation factor characteristics such as structural features, trap features, and distance from erosion boundaries;

[0195] Specifically, using techniques such as forward modeling, attribute extraction, and pre-stack and post-stack inversion, attribute prediction of the area to be evaluated is carried out, and contour maps of target layer thickness, TOC, formation pressure coefficient, MuRho attribute distribution, AFE attribute distribution, and azimuth AVO attribute distribution are compiled to obtain the characteristics of evaluation factors such as unconventional reservoir thickness, organic matter abundance, formation pressure coefficient, gas content, mesoscale fractures, and small-scale fractures.

[0196] The B structural zone of this invention contains unconventional carbonate reservoirs in the Maomen No. 1 formation, but its exploration and understanding are limited, making it the area to be evaluated in this invention. Based on the detailed 3D seismic interpretation of the B structural zone, a structural map of the Maomen No. 1 bottom surface was compiled, clarifying that the structural characteristics of this area are monocline, without traps, and the distance from the erosion boundary is 10 km (Table 2). Using forward modeling, attribute extraction, and pre-stack and post-stack inversion techniques, attribute predictions were conducted for the B structural zone. Contour maps of target layer thickness, TOC, formation pressure coefficient, MuRho attribute distribution, AFE attribute distribution, and azimuthal AVO attribute distribution were compiled, clarifying that the unconventional reservoir thickness in this area is 125 m, organic matter abundance is 1.0%, formation pressure coefficient is 1.0, and MuRho attribute is 75 GPa*g / cm³. 3 The AFE attribute value is 100, and the AVO attribute value is 23 (Table 2).

[0197] Table 2B: Key Factors and Characteristics for Unconventional Natural Gas Evaluation within the Mao-1 Carbonate Source Rock of the Structural Belt

[0198]

[0199]

[0200] Step 5: Based on the key factors and characteristics of unconventional natural gas evaluation in the carbonate source area of ​​the evaluation area in Step 4, calculate the comprehensive evaluation index of the sweet spot area of ​​unconventional natural gas in the carbonate source area of ​​the evaluation area, and select the sweet spot area.

[0201] Specifically, in step 5, based on the quantitative evaluation model of unconventional natural gas sweet spots within carbonate source areas obtained in step 3 and the key evaluation factors and characteristics of the area to be evaluated obtained in step 4, the comprehensive evaluation index EI of the area to be evaluated is calculated. Based on the EI value, the area to be evaluated is divided into three levels: Class I, Class II, and Class III.

[0202]

[0203] Among them, the unconventional natural gas exploration potential in carbonate rock sources is relatively large in Class I areas; the unconventional natural gas exploration potential in carbonate rock sources is moderate in Class II areas; and the unconventional natural gas exploration potential in carbonate rock sources is relatively poor in Class III areas.

[0204] Furthermore, the region with the highest EI value and an EI value ≥ 0.6 in the evaluation area was selected as the dessert area.

[0205] According to Embodiment A of the present invention, the geological characteristics and enrichment and high-yield patterns of unconventional natural gas in the carbonate source rock of the Daimao section are constructed. The weight coefficients of the evaluation factors in step 3 are as follows: a is 0.2, b is 0.4, and c is 0.4.

[0206] The weight coefficients of the evaluation factors are as follows: a1 = 0.5, a2 = 0.5, b1 = 0.2, b2 = 0.2, b3 = 0.3, b4 = 0.2, b5 = 0.1, c1 = 0.3, c2 = 0.7;

[0207] The comprehensive evaluation index (EI) of structural zone B in the evaluation area is calculated to be 0.72, which determines it to be a Class II area. The unconventional natural gas exploration potential within the carbonate source is moderate, and it is selected as a sweet spot area.

[0208] The present invention also provides a device for quantitative selection of unconventional natural gas sweet spots in carbonate sources, which is used to perform the quantitative selection method for unconventional natural gas sweet spots in carbonate sources as described above. It includes: an input unit U1 for evaluation factors and evaluation coefficients of the area to be evaluated, an input unit U2 for weight coefficients of evaluation factors and evaluation coefficients of the area to be evaluated, a calculation unit U3 for self-generated hydrocarbon characteristic index, a calculation unit U4 for structural preservation condition index, a calculation unit U5 for fracture development characteristic index, a calculation unit U6 for comprehensive evaluation index, and a sweet spot grade determination and selection unit U7.

[0209] Among them, the evaluation factor and evaluation factor input unit U1 of the area to be evaluated is used to input the characteristics of the evaluation factors and evaluation factors of the area to be evaluated.

[0210] The evaluation factor and evaluation factor weight coefficient input unit U2 is used to input the weight coefficients of each evaluation factor and evaluation factor, including a, b, c, a1, a2, b1, b2, b3, b4, b5, c1, c2;

[0211] The self-generated hydrocarbon characteristic index calculation unit U3 is used to calculate the self-generated hydrocarbon characteristic index EI of the area to be evaluated. 自身生烃特征 ;

[0212] Construction preservation condition index calculation unit U4 is used to calculate the construction preservation condition index EI of the area to be evaluated. 构造保存条件 ;

[0213] The crack development characteristic index calculation unit U5 is used to calculate the crack development characteristic index EI of the area to be evaluated. 裂缝发育特征 ;

[0214] The comprehensive evaluation index calculation unit U6 is used to calculate the comprehensive evaluation index EI of the area to be evaluated.

[0215] The dessert area level determination and selection unit U7 is used to determine the dessert area level and select the dessert area.

[0216] In this embodiment, a computer device is also included, which includes a processor 40, a memory 10, a display 30, and a computer program 20 for quantitative selection of unconventional natural gas sweet spots in carbonate sources, which is stored in the memory and can be run on the processor. When the processor executes the computer program, it implements the quantitative selection method for unconventional natural gas sweet spots in carbonate sources as described above.

[0217] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for quantitatively selecting unconventional natural gas sweet spots within carbonate source rocks, characterized in that, It includes the following steps: Step 1: Select a scaled area with a high degree of exploration, conduct geological evaluation and enrichment and high-yield pattern analysis of unconventional natural gas in carbonate source rocks, and identify the main controlling factors of enrichment and high yield; Step 2: Based on the analysis of the main controlling factors of enrichment and high production in Step 1, establish the key factors and factor system for the evaluation of unconventional natural gas in carbonate source rocks; Step 3: Based on the key factors and factor system for evaluating unconventional natural gas in carbonate sources in Step 2, establish a quantitative selection model for unconventional natural gas sweet spots in carbonate sources; Step 4: Based on geophysical interpretation and prediction, obtain the key factors and characteristics of unconventional natural gas evaluation in carbonate source areas of the evaluation area; Step 5: Based on the key factors and characteristics of unconventional natural gas evaluation in the carbonate source area of ​​the evaluation area in Step 4, calculate the comprehensive evaluation index of the sweet spot area of ​​unconventional natural gas in the carbonate source area of ​​the evaluation area, and select the sweet spot area.

2. The method for quantitative selection of unconventional natural gas sweet spots in carbonate source rocks according to claim 1, characterized in that: In step 1, the comprehensive evaluation of the geological conditions for natural gas accumulation in unconventional carbonate reservoirs in the calibration area includes: sedimentary characteristic analysis, petrological characteristic analysis, geochemical characteristic analysis, reservoir characteristic analysis, structural characteristic analysis, preservation condition analysis, gas-bearing characteristic analysis, and analysis of accumulation evolution and matching relationship, so as to dissect in detail the characteristics of each accumulation element of unconventional natural gas in carbonate source rocks. The reasons for high and low production in wells with different yields in the calibration zone were analyzed, the high-yield enrichment pattern of unconventional natural gas in carbonate source rocks was summarized, and the main factors controlling natural gas enrichment and high production were identified.

3. The method for quantitative selection of unconventional natural gas sweet spots in carbonate source rocks according to claim 1, characterized in that: In step 2, the key factors for evaluating unconventional natural gas in carbonate source rocks include: evaluation factors of self-generated hydrocarbon characteristics, evaluation factors of tectonic preservation conditions, and evaluation factors of fracture development characteristics. Among them, the self-generating hydrocarbon characteristic evaluation factor is used to evaluate the hydrocarbon generation capacity of unconventional carbonate reservoirs, and it includes unconventional reservoir thickness and organic matter abundance evaluation factors. The structural preservation condition evaluation factors are used to evaluate the unconventional natural gas preservation conditions in carbonate rocks, and they include structural features, trap features, formation pressure coefficient, gas content, and distance from the erosion boundary evaluation factors. The evaluation factors for fracture development characteristics are used to evaluate the natural fracture development characteristics of unconventional carbonate reservoirs, and include evaluation factors for mesoscale fracture development characteristics and small-scale fracture development characteristics.

4. The method for quantitative selection of unconventional natural gas sweet spots in carbonate source rocks according to claim 3, characterized in that: In step 3, based on three evaluation factors—the hydrocarbon generation characteristics of unconventional carbonate reservoirs themselves, structural preservation conditions, and fracture development characteristics—and the controlling effect of nine evaluation factors on the enrichment and high production of unconventional natural gas within carbonate source rocks, a quantitative evaluation model for the sweet spot region of unconventional natural gas within carbonate source rocks is established. The sweet spot region is then evaluated by calculating the comprehensive evaluation index EI, as shown in the matrix below: NO=(abc)(NO) 自身生烃特征 NO 构造保存条件 NO 裂缝发育特征 ); In the formula: EI is a comprehensive evaluation index with dimensionless units. a, b, and c are weighting coefficients for the self-hydrogenation characteristics, structural preservation conditions, and fracture development characteristics, respectively, with dimensionless units, and a+b+c=1; EI 自身生烃特征 This is a characteristic index of its own hydrocarbon generation, with dimensionless units. EI 构造保存条件 To construct the preservation condition index, the unit is dimensionless; EI 裂缝发育特征 This is a crack development characteristic index, with dimensionless units. The evaluation matrix of the self-generated hydrocarbon characteristic index is as follows: NO 自身生烃特征 =(a1 a2)(NO) 非常规储层厚度 NO 有机质丰度 ); In the formula: EI 非常规储层厚度 This is the unconventional reservoir thickness index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. EI 有机质丰度 This is the organic matter abundance index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. a1 and a2 are the weighting coefficients for unconventional reservoir thickness and organic matter abundance, respectively, with dimensionless units, and a1+a2=1; The formula for calculating the unconventional reservoir thickness index is as follows: In the formula: H represents the unconventional reservoir thickness, in meters (m). The formula for calculating the organic matter abundance index is as follows: In the formula: TOC represents the organic matter abundance of unconventional reservoirs, expressed as a percentage. The preservation condition index evaluation matrix is ​​constructed as follows: NO 构造保存条件 =(b1 b2 b3 b4 b5)(NO) 构造特征 NO 圈闭特征 NO 地层压力系数 NO 含气性 NO 离剥蚀边界距离 ); In the formula: b1, b2, b3, b4, and b5 are weighting coefficients for structural features, trap features, formation pressure coefficient, gas content, and distance from erosion boundary, respectively, with dimensionless units. b1+b2+b3+b4+b5=1; EI 构造特征 To construct the characteristic index, the minimum value is 0, the maximum value is 1, and the unit is dimensionless; EI 圈闭特征 This is the trap characteristic index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. EI 地层压力系数 This is the formation pressure coefficient index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. EI 含气性 This is the gas content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. EI 离剥蚀边界距离 This is the distance exponent from the erosion boundary, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. The formula for calculating the characteristic index is as follows: The formula for calculating the trap characteristic index is as follows: The formula for calculating the formation pressure coefficient index is as follows: In the formula: PK is the formation pressure coefficient, with dimensionless units. The formula for calculating the gas content index is as follows: In the formula: MuRho is the product of shear modulus and density, in GPa*g / cm³. 3 ; The formula for calculating the distance index from the erosion boundary is as follows: In the formula: L represents the distance from the erosion boundary, in km; The evaluation matrix of crack development characteristic index is as follows: NO 裂缝发育特征指数 =(c1 c2)(NO) 中尺度裂缝发育特征 NO 小尺度裂缝发育特征 ); In the formula: c1 and c2 are the weighting coefficients for mesoscale and small-scale crack development characteristics, respectively, with dimensionless units; c1+c2=1; EI 中尺度裂缝发育特征 This is a mesoscale crack development characteristic index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. EI 小尺度裂缝发育特征 This is a characteristic index of small-scale crack development, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. The formula for calculating the mesoscale crack development characteristic index is as follows: In the formula: AFE is a fault coherence enhancement property, and its unit is dimensionless. The formula for calculating the small-scale crack development characteristic index is as follows: In the formula: Azimuth AVO represents the amplitude variation with offset distance in different azimuths, and the unit is dimensionless.

5. The method for quantitative selection of unconventional natural gas sweet spots in carbonate source rocks according to claim 1, characterized in that: In step 4, a detailed interpretation of the earthquake in the area to be evaluated is carried out, a structural map of the target layer is compiled, and evaluation factor characteristics such as structural features, trap features, and distance from the erosion boundary are obtained. Using forward modeling, attribute extraction, and pre-stack and post-stack inversion techniques, attribute prediction of the area to be evaluated is carried out, and contour maps of target layer thickness, TOC, formation pressure coefficient, MuRho attribute distribution, AFE attribute distribution, and azimuth AVO attribute distribution are compiled to obtain the evaluation factor characteristics of unconventional reservoir thickness, organic matter abundance, formation pressure coefficient, gas content, mesoscale fractures, and small-scale fractures.

6. The method for quantitative selection of unconventional natural gas sweet spots in carbonate source rocks according to claim 1, characterized in that: In step 5, based on the quantitative evaluation model of unconventional natural gas sweet spots in carbonate source areas obtained in step 3 and the key evaluation factors and characteristics of the area to be evaluated obtained in step 4, the comprehensive evaluation index EI of the area to be evaluated is calculated. Based on the EI value, the area to be evaluated is divided into three levels: Class I, Class II, and Class III. Among them, the unconventional natural gas exploration potential in carbonate rock sources is relatively large in Class I areas; the unconventional natural gas exploration potential in carbonate rock sources is moderate in Class II areas; and the unconventional natural gas exploration potential in carbonate rock sources is relatively poor in Class III areas.

7. A quantitative selection device for unconventional natural gas sweet spots in carbonate source rocks, used to perform the method as described in any one of claims 1 to 6, characterized in that, It includes: U1, U2, U3, U4, U5, U6, U7, U8, U9, U1, U2, U3, U4, U5, U6, U7, U8, U9, U1, U2, U3, U4, U5, U6, U7, U8, U9, U1, U2, U9, U1, U2, U3, U4, U5, U6, U7, U8, U9, U1, U9, U1, U2, U9, U1, U2, U3, U4, U1, U9, U1, U2, U3, U4, U1, U1, U2, U3, U4, U1, U2, U3, U4, U1, U2, U3, U4, U1, U2, U3, U4, U4, U5, U6, U7, U1, U1, U2, U3, U4, U1, U2, U3, U4, U4, U5, U6, U7, U1, U1, U2, U3, U4, U4, U1, U2, U3, U4, U4, U4, U5, U6, U7 ...5, U6, U7, U1, U2, U3, U4, U4, U4, U5, U6, U7, U1, U2, U3, U4, U4, U Among them, the evaluation factor and evaluation factor input unit U1 of the area to be evaluated is used to input the characteristics of the evaluation factors and evaluation factors of the area to be evaluated. The evaluation factor and evaluation factor weight coefficient input unit U2 is used to input the weight coefficients of each evaluation factor and evaluation factor, including a, b, c, a1, a2, b1, b2, b3, b4, b5, c1, c2; The self-generated hydrocarbon characteristic index calculation unit U3 is used to calculate the self-generated hydrocarbon characteristic index EI of the area to be evaluated. 自身生烃特征 ; Construction preservation condition index calculation unit U4 is used to calculate the construction preservation condition index EI of the area to be evaluated. 构造保存条件 ; The crack development characteristic index calculation unit U5 is used to calculate the crack development characteristic index EI of the area to be evaluated. 裂缝发育特征 ; The comprehensive evaluation index calculation unit U6 is used to calculate the comprehensive evaluation index EI of the area to be evaluated. The dessert area level determination and selection unit U7 is used to determine the dessert area level and select the dessert area.

8. The quantitative selection device for unconventional natural gas sweet spots in carbonate rock sources according to claim 7, characterized in that: It also includes a computer device comprising a processor (40), a memory (10), a display (30), and a computer program (20) stored in the memory and executable on the processor, wherein the processor (40) executes the computer program (20) to implement the method for quantitative selection of unconventional natural gas sweet spots in carbonate rock sources according to any one of claims 1 to 4.

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