Quantitative selection method and device for shallow shale gas favorable area of complex structure area

Abstract

The invention discloses a quantitative selection method and device for a shallow shale gas favorable area in a complex structure area, and the method comprises the following steps: carrying out the geological evaluation of shallow shale gas in a target area, and obtaining the evaluation key parameters of the shallow shale gas; establishing a shallow shale gas favorable area quantitative evaluation model based on four favorable area evaluation key parameters including shallow shale gas resource conditions, adsorption capacity, free gas preservation and compressibility; and calculating a target area comprehensive index and determining a target area grade. According to the characteristic that the shallow shale gas in the complex structure area is mainly adsorbed gas, the shallow shale gas favorable area quantitative selection method with adsorption capacity evaluation and free gas preservation evaluation as the core is established, the favorable area grade can be evaluated rapidly and accurately, and therefore the exploration risk is reduced, and the exploration well success rate and the exploration effect are improved.

Description

Technical Field

[0001] The present invention specifically relates to the technical field of shale gas exploration and development, and particularly to a method and device for quantitatively selecting favorable areas of shallow shale gas in complex structural areas. Background Art

[0002] As is well known, shale gas mainly exists in dark mud shale in two forms: free state and adsorbed state. Free shale gas, also known as free gas, has relatively strong fluidity and is sensitive to preservation conditions. It is easy to escape when the preservation conditions are damaged. Adsorbed shale gas, also known as adsorbed gas, is adsorbed on the particle surface, has poor fluidity, is not sensitive to preservation conditions, and is not easy to escape when the preservation conditions are damaged.

[0003] Shallow shale gas refers to shale gas with a shale burial depth of 0 - 2000m. The shallow shale gas resources in China are nearly 26 trillion cubic meters, with huge resource potential and being an important strategic resource. At present, industrial breakthroughs have only been achieved in a few areas in the southern part of the Sichuan Basin in China's shallow shale gas, and the complex structural areas widely distributed in southern China are still in the exploration stage. Compared with the mid - deep to deep shale gas with commercial production at a burial depth of 2000 - 6000m, the maximum paleo - burial depth of shallow shale gas is roughly the same, but the later tectonic uplift and denudation are stronger, and the uplift and denudation amplitude is 500 - 5000m larger than that of mid - deep to deep shale gas. Due to strong tectonic action, large denudation amplitude of overlying strata, strong tectonic deformation, high - steep strata, and developed faults, the preservation conditions of shale gas are generally poor. Especially in the shallow shale gas in complex structural areas, the target shale layer has been widely exposed on the surface, forming a large number of obvious pressure - relief areas. The free part of shale gas is extremely easy to migrate and escape along the bedding plane towards the exposed area under the drive of concentration difference and pressure difference, and the formation pressure coefficient drops to below 0.8 - 1.1, becoming an atmospheric - low - pressure system, and the proportion of free gas drops to below 30%. Due to the fact that shale is rich in organic matter, clay minerals and other substances with a large specific surface area, and the formation temperature of shallow shale gas is low, shallow shale has a large adsorption capacity. The adsorbed gas has less demanding requirements for preservation conditions than free gas. Therefore, the adsorbed part of shallow shale gas in complex structural areas can be preserved to a large extent, and the proportion of adsorbed gas reaches more than 65 - 85%. Generally speaking, due to the poor preservation conditions of shale gas in complex structural areas, the occurrence state is mainly adsorbed gas, and the adsorbed gas is the main object of exploitation. When selecting favorable areas for exploration and development, there are significant differences in the evaluation focus compared with mid - deep to deep shale gas, and it is urgent to highlight evaluations such as adsorption capacity to scientifically guide the selection of favorable areas for shallow shale gas.

[0004] At present, certain research has been carried out on the optimization selection of favorable areas for shale gas at home and abroad, but there are the following problems:

[0005] First, previous studies mainly established an evaluation method for favorable areas of medium-deep to deep shale gas. For medium-deep to deep shale gas, the shale burial depth is large and the preservation conditions are relatively good. The occurrence state of shale gas is mainly free gas. However, for shallow shale gas in complex structural areas, the burial depth is relatively shallow, mainly adsorbed gas supplemented by free gas. Therefore, the evaluation method for favorable areas of medium-deep to deep shale gas is not applicable to the selection of favorable areas for shallow shale gas in complex structural areas.

[0006] Second, a quantitative selection method for favorable areas of shallow shale gas with the evaluation of adsorption capacity and preservation of free gas as the core has not been formed. In fact, adsorption capacity is the key factor controlling the enrichment of shallow shale gas. It is urgent to select key parameters with strong pertinence and quantifiable representation according to the geological characteristics, occurrence characteristics, and enrichment and high-yield laws of shallow shale gas in complex structural areas, and establish a key parameter index system and a quantitative evaluation model for shallow shale gas evaluation, so as to realize the quantitative hierarchical evaluation of favorable areas of shallow shale gas in complex structural areas. Summary of the Invention

[0007] Therefore, the present invention proposes a quantitative selection method and device for favorable areas of shallow shale gas in complex structural areas to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions: A quantitative selection method for favorable areas of shallow shale gas in complex structural areas, which includes the following steps:

[0009] Step 1: Conduct a geological evaluation of shallow shale gas in the target area to obtain key parameters for evaluating shallow shale gas.

[0010] Step 2: Based on the four key parameters for evaluating favorable areas, namely, shallow shale gas resource conditions, adsorption capacity, preservation of free gas, and compressibility, establish a quantitative evaluation model for favorable areas of shallow shale gas.

[0011] Step 3: Calculate the comprehensive index of the target area, determine the level of the target area, and select favorable areas.

[0012] Further, as a preference, in the above Step 1, when conducting a geological evaluation of shallow shale gas in the target area to obtain key parameters for the geological characteristics of shallow shale gas and controlling the enrichment and high yield of shallow shale gas, it includes resource condition evaluation parameters, adsorption capacity evaluation parameters, free gas preservation evaluation parameters, and compressibility evaluation parameters. Among them,

[0013] The resource condition evaluation parameters are used to evaluate the material basis for the formation of shale gas, including 2 sub-parameters such as the thickness with TOC greater than 1% and the thickness with TOC greater than 2%.

[0014] The adsorption capacity evaluation parameters are used to evaluate the adsorption capacity of shale in the target area, including 5 sub-parameters such as TOC, formation temperature, formation pressure, quartz content, and clay content.

[0015] Evaluation parameters for free gas preservation, which are used to evaluate the preservation conditions of free gas in the target area, including 4 sub-parameters such as the effective normal stress of the bedding plane, roof conditions, floor conditions, and the time when the last hydrocarbon generation stopped.

[0016] Compressibility evaluation parameters, which are used to evaluate the shale fracturing and transformation in the target area, including 3 sub-parameters such as brittle mineral content, brittleness index, and two-way stress difference coefficient.

[0017] Furthermore, as an optimization, in step 2, by using the control effects of the four key evaluation parameters of shallow shale gas resource conditions, adsorption capacity, free gas preservation, and compressibility on the enrichment and high production of shallow shale gas, a quantitative evaluation model for favorable areas of shallow shale gas is established. By calculating the comprehensive index CI of favorable areas of shallow shale gas, the favorable area grade is evaluated. The matrix is as follows:

[0018] CI = (a b c d)(CI 资源条件 CI 吸附能力 CI 游离气保存 CI 可压性 )

[0019] In the formula:

[0020] CI is the comprehensive index of favorable areas, with the unit being dimensionless;

[0021] a, b, c, and d are the weight coefficients of resource conditions, adsorption capacity, free gas preservation, and compressibility respectively, with the unit being dimensionless, and a + b + c + d = 1;

[0022] CI 资源条件 is the resource condition index, with the unit being dimensionless;

[0023] CI 吸附能力 is the adsorption capacity index, with the unit being dimensionless;

[0024] CI 游离气保存 is the free gas preservation index, with the unit being dimensionless;

[0025] CI 可压性 is the compressibility index, with the unit being dimensionless;

[0026] Among them, the evaluation matrix of the resource condition index is as follows:

[0027]

[0028] In the formula:

[0029] CI H1 is the thickness index with TOC greater than 1%, the minimum value is 0, the maximum value is 1, and the unit is dimensionless;

[0030] CI H2It is the thickness index with TOC greater than 2%, with a minimum value of 0, a maximum value of 1, and the unit is dimensionless;

[0031] a1 and a2 are the weight coefficients of the thickness with TOC greater than 1% and the thickness with TOC greater than 2% respectively, with the unit being dimensionless, and a1 + a2 = 1;

[0032] The calculation formula for the thickness index with TOC greater than 1% is as follows:

[0033]

[0034] In the formula:

[0035] H1 is the thickness with TOC greater than 1%, with the unit being m;

[0036] The calculation formula for the thickness index with TOC greater than 2% is as follows:

[0037]

[0038] In the formula:

[0039] H2 is the thickness with TOC greater than 2%, with the unit being m;

[0040] The evaluation matrix of the adsorption capacity index is as follows:

[0041] CI 吸附能力 =(b1 b2 b3 b4 b5)(CI TOC CI 地层温度 CI 地层压力 CI 石英含量 CI 黏土含量 )

[0042] In the formula:

[0043] b1, b2, b3, b4, and b5 are the weight coefficients of TOC, formation temperature, formation pressure, quartz content, and clay content respectively, with the unit being dimensionless, and b1 + b2 + b3 + b4 + b5 = 1;

[0044] CI TOC is the TOC index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless;

[0045] CI 地层温度 is the formation temperature index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless; CI 地层压力 is the formation pressure index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless; CI 石英含量 is the quartz content index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless; CI 黏土含量 is the clay content index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless. The calculation formula for the TOC index is as follows:

[0046]

[0047] In the formula:

[0048] TOC, in %;

[0049] The calculation formula for the formation temperature index is as follows:

[0050]

[0051] In the formula:

[0052] Formation temperature, in °C;

[0053] The calculation formula for the formation pressure index is as follows:

[0054]

[0055] In the formula:

[0056] Formation pressure, in MPa;

[0057] The calculation formula for the quartz content index is as follows:

[0058]

[0059] In the formula:

[0060] Quartz content, in %;

[0061] The calculation formula for the clay content index is as follows:

[0062]

[0063] In the formula:

[0064] Clay content, in %;

[0065] The evaluation matrix for the free gas preservation index is as follows:

[0066]

[0067] In the formula:

[0068] c1, c2, c3, and c4 are the weight coefficients of the roof condition, floor condition, effective normal stress on the bedding plane, and the time when the last hydrocarbon generation stopped, respectively, with the unit of dimensionless; when the structural type is a complete anticline or a complete syncline, c1 + c2 = 1; when the structural type is a monocline, c1 + c2 + c3 + c4 = 1;

[0069] CI 顶板 Is the roof condition index, with the minimum value of 0 and the maximum value of 1, and the unit of dimensionless;

[0070] CI 底板is the floor condition index, with a minimum value of 0, a maximum value of 1, and the unit is dimensionless;

[0071] CI P正应力 is the effective normal stress index of the bedding plane, with a minimum value of 0, a maximum value of 1, and the unit is dimensionless;

[0072] CI 末次生烃停止时间 is the last hydrocarbon generation stop time index, with a minimum value of 0, a maximum value of 1, and the unit is dimensionless;

[0073] The calculation formula for the roof condition index is as follows:

[0074]

[0075] In the formula:

[0076] H 顶板 is the roof thickness, with the unit of m;

[0077] The calculation formula for the floor condition index is as follows:

[0078]

[0079] In the formula:

[0080] H 底板 is the floor thickness, with the unit of m;

[0081] The calculation formula for the effective normal stress index of the bedding plane is as follows:

[0082]

[0083] The calculation formula for the last hydrocarbon generation stop time index is as follows:

[0084]

[0085] In the formula:

[0086] FT is the last hydrocarbon generation stop time, with the unit of Ma;

[0087] The compressibility index evaluation matrix is as follows:

[0088] CI 可压性 =(d1 d2 d3)(CI 脆性矿物含量 CI 脆性指数 CI 两向应力差异系数 )

[0089] In the formula:

[0090] d1, d2, and d3 are the weight coefficients of the brittle mineral content, brittle index, and two-way stress difference coefficient respectively, with the unit being dimensionless; d1 + d2 + d3 = 1;

[0091] CI 脆性矿物含量is the brittle mineral content index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless;

[0092] CI 脆性指数 is the brittleness index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless;

[0093] CI Kh is the two-way stress difference coefficient index, with a minimum value of 0, a maximum value of 1, and the unit being dimensionless;

[0094] The calculation formula for the brittle mineral content index is as follows:

[0095]

[0096] In the formula:

[0097] BMC is the brittle mineral content, with the unit of %;

[0098] Furthermore, the calculation formula for the brittleness index is as follows:

[0099]

[0100] Furthermore, the calculation formula for the two-way stress difference coefficient index is as follows:

[0101]

[0102] Furthermore, as an optimization, in step 3, according to the key evaluation parameters of the target area and the quantitative evaluation model of the favorable area for shallow shale gas in step 2, calculate the comprehensive index CI of the favorable area for shallow shale gas in the target area. According to the CI value, divide the target area into three levels: Class I area, Class II area, and Class III area, that is:

[0103]

[0104] Among them, the exploration potential of the shallow shale gas in the Class I area is the largest; the exploration potential of the shallow shale gas in the Class II area is medium; the exploration potential of the shallow shale gas in the Class III area is relatively poor.

[0105] The quantitative selection device for the favorable area of shallow shale gas in the complex structural area, which is used to execute any one of the quantitative selection methods for the favorable area of shallow shale gas in the complex structural area, includes:

[0106] The key parameter input module M1 of the target area, the weight coefficient input module M2 of the key parameters of the target area, the resource condition index calculation module M3, the adsorption capacity index calculation module M4, the free gas preservation index calculation module M5, the engineering condition index calculation module M6, the comprehensive index calculation module M7 of the favorable area for shallow shale gas, and the favorable area level determination module M8, where,

[0107] The target area key parameter input module M1 is used to input the key parameters for evaluating the favorable area in the target area;

[0108] The target area key parameter weight coefficient input module M2 is used to input the weight coefficients of each parameter, including a, b, c, d, a1, a2, b1, b2, b3, b4, b5, c1, c2, c3, c4, d1, d2, d3;

[0109] The resource condition index calculation module M3 is used to calculate the resource condition index CI of the target area 资源条件 ;

[0110] The adsorption capacity index calculation module M4 is used to calculate the adsorption capacity index CI of the target area 吸附能力 ;

[0111] The free gas preservation index calculation module M5 is used to calculate the free gas preservation index CI of the target area 游离气保存 ;

[0112] The engineering condition index calculation module M6 is used to calculate the engineering condition index CI of the target area 工程条件 ;

[0113] The favorable area comprehensive index calculation module M7 is used to calculate the favorable area comprehensive index CI of the target area;

[0114] The favorable area level determination module M8 is used to determine the favorable area level.

[0115] Furthermore, as a preference, it further includes a computer device, which consists of a processor, a memory, a computer program stored on the memory and executable on the processor, and a display. Among them, the processor can implement the quantitative selection method for the favorable area of shallow shale gas in complex structural areas described in any one of claims 1 to 4 when executing the computer program.

[0116] The present invention adopts the above technologies and has the following beneficial effects compared with the existing technologies:

[0117] 1. The quantitative selection method and device for the favorable area of shallow shale gas in complex structural areas provided by the present invention, in view of the geological characteristics, occurrence characteristics and enrichment and high-yield laws of shallow shale gas, select 14 sub-parameters that can be quantitatively characterized and affect the enrichment and high yield of shallow shale gas from four aspects of resource conditions, adsorption capacity, free gas preservation and compressibility, and establish an evaluation key parameter index system for shallow shale gas, with comprehensive parameters and strong pertinence.

[0118] 2. Fourteen sub-parameter quantification index calculation formulas were formed, a quantitative evaluation model for favorable areas of shallow shale gas with adsorption capacity evaluation and free gas preservation evaluation as the core was established, quantitative hierarchical evaluation of favorable areas of shallow shale gas in complex structural areas was realized, and it effectively guided the exploration of shallow shale gas in the out-of-basin complex structural areas in the southeastern Sichuan Basin.

[0119] 3. The present invention has important application value and promotion prospects in the exploration of shallow shale gas in complex structural areas, especially in the exploration of normal-pressure - low-pressure shallow shale gas areas with poor preservation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] Figure 1 is a schematic flow chart of the present invention;

[0121] Figure 2 is a structural diagram of the key parameter system for evaluating shallow shale gas in complex structural areas provided by an embodiment of the present invention;

[0122] Figure 3 is a schematic diagram of the functional modules of the device for quantitatively selecting favorable areas of shallow shale gas in complex structural areas provided by an embodiment of the present invention;

[0123] Figure 4 is a structural diagram of the computer device for quantitatively selecting favorable areas of shallow shale gas in complex structural areas provided by an embodiment of the present invention.

[0124] In the figure: 10, memory; 20, program for quantitatively selecting favorable areas of shallow shale gas in complex structural areas; 30, display; 40, processor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0125] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0126] Embodiment: Please refer to the attached Figures 1-4 , taking the LCP structure in the out-of-basin complex structural area in the southeastern Sichuan Basin as an example, the present invention provides a technical solution: a method for quantitatively selecting favorable areas of shallow shale gas in complex structural areas, including the following steps:

[0127] Step 1: Conduct geological evaluation of shallow shale gas in the target area to obtain key parameters for evaluating shallow shale gas;

[0128] Specifically, based on experimental analysis of shale in the target area and adjacent areas, as well as data from logging, mud logging, and seismic surveys, geological evaluation of shallow shale gas in the target area is carried out from aspects such as sedimentary characteristics, reservoir characteristics, organic geochemical characteristics, structural characteristics, preservation conditions, gas-bearing properties, and compressibility, to obtain the key parameters for shallow shale gas evaluation.

[0129] Specifically, the key evaluation parameters are those targeting the geological characteristics of shallow shale gas and the key parameters controlling the enrichment and high production of shallow shale gas, including: resource condition evaluation parameters, adsorption capacity evaluation parameters, free gas preservation evaluation parameters, and compressibility evaluation parameters (please refer to the appendix Figure 2 ).

[0130] Specifically, the resource condition evaluation parameters are used to evaluate the material basis for the formation of shale gas, including two sub-parameters: the thickness with TOC greater than 1% and the thickness with TOC greater than 2%. Further, the thickness with TOC greater than 1% is used to comprehensively evaluate the resource conditions of the shale section, and the thickness with TOC greater than 2% is used to evaluate the resource conditions of the organic-rich shale section. The larger these two values are, the better the resource conditions.

[0131] Specifically, the adsorption capacity evaluation parameters are used to evaluate the adsorption capacity of shale in the target area. Since the occurrence state of shallow shale gas is mainly adsorbed gas, it is particularly important to evaluate the adsorption capacity of shale. According to the analysis of factors affecting shale adsorption capacity, the adsorption capacity evaluation parameters include five sub-parameters: TOC, formation temperature, formation pressure, quartz content, and clay content.

[0132] Further, TOC is the average organic matter abundance of the core target layer, which can be obtained through core experimental analysis or based on logging interpretation; a large number of nanoscale pores are developed in organic matter, with a very rich specific surface area, which can provide a large number of adsorption sites for gas adsorption. The larger the TOC, the stronger the shale adsorption capacity.

[0133] Further, the formation temperature is the formation temperature under the actual underground conditions of the core target layer, which can be obtained through well testing or by using the geothermal gradient; the higher the formation temperature, the stronger the molecular activity, and the weaker the shale adsorption capacity.

[0134] Further, the formation pressure is the formation pressure under the actual underground conditions of the core target layer, which can be obtained through well testing or by using empirical formulas; the greater the formation pressure, the more conducive it is for gas to be tightly adsorbed on the particle surface, and the stronger the shale adsorption capacity.

[0135] Further, the quartz content is the average quartz content of the core target layer, which can be obtained through core experimental analysis or based on logging interpretation; quartz particles, especially biogenic quartz particles, have a certain adsorption capacity. The larger the quartz content, the stronger the shale adsorption capacity.

[0136] Furthermore, the clay content is the average clay content of the core target layer, which can be obtained through core experiment analysis or based on well logging interpretation. Clay minerals have a large specific surface area and strong adsorption capacity. The larger the clay content, the stronger the adsorption capacity of the shale.

[0137] Specifically, the free gas preservation evaluation parameters are used to evaluate the preservation conditions of free gas in the target area. Although shallow shale gas is mainly adsorbed gas, the role and contribution of free gas still need to be emphasized. Under the condition of the same adsorbed gas volume, the higher the free gas content, the more conducive to the enrichment and high production of shallow shale gas. The free gas preservation evaluation parameters are divided into two categories according to the different structural types of the target area: when the structural type is a complete anticline or a complete syncline, shale gas mainly escapes upward and downward in a diffusive manner, and the free gas preservation evaluation parameters include two sub-parameters such as the roof condition and the floor condition; when the structural type is a monocline, shale gas is more likely to escape laterally to the shale outcrop area, and the free gas preservation evaluation parameters include four sub-parameters such as the roof condition, the floor condition, the effective normal stress of the bedding plane, and the time when the last hydrocarbon generation stopped.

[0138] Furthermore, the complete anticline mentioned above refers to an anticline structure where the shale target layer does not outcrop on the surface.

[0139] Furthermore, the complete syncline mentioned above refers to a syncline structure where the shale target layer does not outcrop on the surface.

[0140] Furthermore, the monocline mentioned above refers to a slope structure where the shale target layer outcrops on the surface in the up-dip direction.

[0141] Furthermore, the roof condition is the direct overlying caprock of the shale in the core target layer. The denser and thicker the direct overlying caprock is, the better its sealing performance and the better the preservation condition of free gas.

[0142] Furthermore, the floor condition is the direct underlying floor of the shale in the core target layer. The denser and thicker the direct underlying floor is, the better its sealing performance and the better the preservation condition of free gas.

[0143] Furthermore, the effective normal stress of the bedding plane is the effective normal stress of the bedding plane of the shale in the core target layer. The greater the effective normal stress of the bedding plane is, the stronger the pressure on the bedding plane, the easier it is to close, the smaller the shale permeability, and the better the preservation condition of free gas. The calculation formula for the effective normal stress of the bedding plane is as follows:

[0144] P 正应力 =ρgh*cos(θ)

[0145] In the formula:

[0146] P 正应力 is the effective normal stress of the bedding plane, with the unit of MPa;

[0147] ρ is the density of the overlying formation of the shale, with the unit of g / cm 3 ;

[0148] g is the acceleration due to gravity, with the unit of m / s 2 ;

[0149] θ is the formation dip angle, with the unit of °;

[0150] h is the burial depth of shale, with the unit of m.

[0151] Furthermore, the time when the last hydrocarbon generation stopped is the time from the last hydrocarbon generation of shale to the present, which can be obtained through burial history - thermal history analysis or through apatite fission track experiment analysis. The longer the time when the last hydrocarbon generation stopped, the larger the scale of shale gas dissipation, the longer the time lacking the replenishment of new gas, and the worse the preservation conditions of free gas.

[0152] Specifically, the compressibility evaluation parameters are used to evaluate the fracturing and transformation of shale in the target area. Compared with medium - deep to deep shale, shallow - layer shale has a shallower burial depth, smaller in - situ stress, enhanced brittleness, and reduced difficulty in fracturing and transformation. However, compressibility is still an important factor affecting whether shallow - layer shale can be fully transformed to obtain commercial gas flow. The compressibility evaluation parameters include three sub - parameters: brittle mineral content, brittleness index, and two - way stress difference coefficient.

[0153] Furthermore, the brittle mineral content is the sum of the quartz content, feldspar content, and carbonate mineral content in the core target layer shale, which can be obtained through whole - rock X - ray diffraction experiment analysis of core samples or based on well - logging interpretation. The higher the brittle mineral content, the better the compressibility.

[0154] Furthermore, the brittleness index is the rock - mechanical brittleness index of the core target layer shale. The higher the brittleness index, the better the compressibility. The calculation formula of the brittleness index is as follows:

[0155]

[0156] In the formula:

[0157] BI is the brittleness index, with the unit of %;

[0158] E is the Young's modulus of the sample, with the unit of GPa;

[0159] E min is the minimum Young's modulus of the sample, with the unit of GPa;

[0160] E max is the maximum Young's modulus of the sample, with the unit of GPa;

[0161] μ is the Poisson's ratio of the sample, with the unit of dimensionless;

[0162] μ min is the minimum Poisson's ratio of the sample, with the unit of dimensionless;

[0163] μmax is the maximum Poisson's ratio of the sample, dimensionless;

[0164] Furthermore, the two-way stress difference coefficient is the horizontal stress difference coefficient of the shale in the core target layer. The smaller the two-way stress difference coefficient, the more conducive it is to the formation of a complex fracture network during fracturing. The calculation formula for the two-way stress difference coefficient is as follows:

[0165] K h =(σ hmax -σ hmin ) / σ hmin

[0166] In the formula:

[0167] K h is the two-way stress difference coefficient of the target layer, dimensionless;

[0168] σ hmax is the maximum horizontal principal stress of the target layer, in MPa;

[0169] σ hmin is the minimum horizontal principal stress of the target layer, in MPa.

[0170] In the LCP structure of the embodiment of the present invention, the shale target layer is the first member of the Wufeng Formation of the Upper Ordovician - Longmaxi Formation of the Lower Silurian. The core target layer is located in the first to fifth small layers at the bottom of the formation, formed in a deep-water continental shelf - semi-deep-water continental shelf sedimentary environment. The thickness with TOC greater than 1% is 85.8 m, and the thickness with TOC greater than 2% is 37.5 m, having good resource conditions for shale gas formation. The TOC of the core target layer of this structure is 3.82%, the formation temperature is 38.7 °C, the formation pressure is 9.8 MPa, the quartz content is 53.1%, and the clay content is 25.2%, having a large adsorption capacity; the adsorbed gas content interpreted by well logging of the shale gas wells drilled in this area reaches 2.78 m 3 / t, accounting for 80.3% of the total gas content, verifying that the shale in this area has a strong adsorption capacity. The LCP structure is a residual anticline structure in an extra-basin complex structural area. It is an anticline as a whole, but the shale target layers on the east and west sides are exposed on the surface over a large area, with strong tectonic actions. Affected by the orogenic movement, the last hydrocarbon generation stopped at 94 Ma, indicating a long and intense shale gas dissipation time in the later stage, and the preservation conditions of free gas have been severely damaged, with a large amount of loss occurring towards the outcropping area; the roof of the core target layer is thick, dense mud shale in the middle and upper parts of the first member of the Longmaxi Formation - the third member of the Longmaxi Formation, with good sealing properties, having a thickness of 186.5 m; the floor of the core target layer is dense limestone and marlstone of the Linxiang Formation - the Baota Formation, with good sealing properties, having a thickness of 40 m. The brittle mineral content of the core target layer is 71.5%, and the rock mechanics brittleness index is 59.2%, having good brittle characteristics, which is conducive to fracture initiation, but the two-way stress difference coefficient reaches 0.56, and it is not easy to form a complex fracture network. The key parameters of the LCP structure are shown in Table 1:

[0171] Table 1 Key Parameters for Evaluating Shallow Shale Gas in LCP Structures

[0172]

[0173] Step 2: Based on the four key parameters for evaluating favorable areas of shallow shale gas resources, adsorption capacity, free gas preservation, and compressibility, establish a quantitative evaluation model for favorable areas of shallow shale gas;

[0174] Using the control effects of the four key parameters for evaluating favorable areas of shallow shale gas resources, adsorption capacity, free gas preservation, and compressibility on the enrichment and high production of shallow shale gas, establish a quantitative evaluation model for favorable areas of shallow shale gas. By calculating the comprehensive index CI of favorable areas of shallow shale gas, evaluate the grade of favorable areas. The matrix is as follows:

[0175] CI = (a b c d)(CI 资源条件 CI 吸附能力 CI 游离气保存 CI 可压性 )

[0176] In the formula:

[0177] CI is the comprehensive index of the favorable area, with the unit being dimensionless;

[0178] a, b, c, and d are the weight coefficients of resource conditions, adsorption capacity, free gas preservation, and compressibility respectively, with the unit being dimensionless, and a + b + c + d = 1;

[0179] CI 资源条件 is the resource condition index, with the unit being dimensionless;

[0180] CI 吸附能力 is the adsorption capacity index, with the unit being dimensionless;

[0181] CI 游离气保存 is the free gas preservation index, with the unit being dimensionless;

[0182] CI 可压性 is the compressibility index, with the unit being dimensionless;

[0183] Specifically, the evaluation matrix of the resource condition index is as follows:

[0184]

[0185] In the formula:

[0186] CI H1 is the thickness index with TOC greater than 1%, with the minimum value being 0 and the maximum value being 1, and the unit being dimensionless;

[0187] CI H2The thickness index with TOC greater than 2% has a minimum value of 0 and a maximum value of 1, and the unit is dimensionless;

[0188] a1 and a2 are the weight coefficients of the thickness with TOC greater than 1% and the thickness with TOC greater than 2% respectively, the unit is dimensionless, and a1 + a2 = 1.

[0189] Furthermore, the calculation formula for the thickness index with TOC greater than 1% is as follows:

[0190]

[0191] In the formula:

[0192] H1 is the thickness with TOC greater than 1%, and the unit is m.

[0193] Furthermore, the calculation formula for the thickness index with TOC greater than 2% is as follows:

[0194]

[0195] In the formula:

[0196] H2 is the thickness with TOC greater than 2%, and the unit is m.

[0197] Specifically, the evaluation matrix of the adsorption capacity index is as follows:

[0198] CI 吸附能力 =(b1 b2 b3 b4 b5)(CI TOC CI 地层温度 CI 地层压力 CI 石英含量 CI 黏土含量 )

[0199] In the formula:

[0200] b1, b2, b3, b4, and b5 are the weight coefficients of TOC, formation temperature, formation pressure, quartz content, and clay content respectively, the unit is dimensionless, and b1 + b2 + b3 + b4 + b5 = 1;

[0201] CI TOC is the TOC index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless;

[0202] CI 地层温度 is the formation temperature index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless;

[0203] CI 地层压力 is the formation pressure index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless;

[0204] CI 石英含量 is the quartz content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless;

[0205] CI 黏土含量 is the clay content index, with a minimum value of 0, a maximum value of 1, and the unit is dimensionless.

[0206] Furthermore, the calculation formula for the TOC index is as follows:

[0207]

[0208] In the formula:

[0209] TOC, unit %.

[0210] Furthermore, the calculation formula for the formation temperature index is as follows:

[0211]

[0212] In the formula:

[0213] Formation temperature, unit °C.

[0214] Furthermore, the calculation formula for the formation pressure index is as follows:

[0215]

[0216] In the formula:

[0217] Formation pressure, unit MPa.

[0218] Furthermore, the calculation formula for the quartz content index is as follows:

[0219]

[0220] In the formula:

[0221] Quartz content, unit %.

[0222] Furthermore, the calculation formula for the clay content index is as follows:

[0223]

[0224] In the formula:

[0225] Clay content, unit %.

[0226] Specifically, the evaluation matrix for the free gas preservation index is as follows:

[0227]

[0228] In the formula:

[0229] c1, c2, c3, and c4 are the weight coefficients of the roof condition, floor condition, effective normal stress of the bedding plane, and the last hydrocarbon generation stop time, respectively, with no unit; when the structural type is a complete anticline or a complete syncline, c1 + c2 = 1; when the structural type is a monocline, c1 + c2 + c3 + c4 = 1;

[0230] CI 顶板 is the roof condition index, with a minimum value of 0, a maximum value of 1, and no unit;

[0231] CI 底板 is the floor condition index, with a minimum value of 0, a maximum value of 1, and no unit;

[0232] CI P正应力 is the effective normal stress index of the bedding plane, with a minimum value of 0, a maximum value of 1, and no unit;

[0233] CI 末次生烃停止时间 is the last hydrocarbon generation stop time index, with a minimum value of 0, a maximum value of 1, and no unit.

[0234] Furthermore, the calculation formula for the roof condition index is as follows:

[0235]

[0236] In the formula:

[0237] H 顶板 is the roof thickness, with the unit of m.

[0238] Furthermore, the calculation formula for the floor condition index is as follows:

[0239]

[0240] In the formula:

[0241] H 底板 is the floor thickness, with the unit of m.

[0242] Furthermore, the calculation formula for the effective normal stress index of the bedding plane is as follows:

[0243]

[0244] Furthermore, the calculation formula for the last hydrocarbon generation stop time index is as follows:

[0245]

[0246] In the formula:

[0247] FT is the last hydrocarbon generation stop time, with the unit of Ma.

[0248] Specifically, the compressibility index evaluation matrix is as follows:

[0249] CI 可压性 =(d1 d2 d3)(CI 脆性矿物含量 CI 脆性指数 CI 两向应力差异系数 )

[0250] In the formula:

[0251] d1, d2, and d3 are the weight coefficients of the brittle mineral content, brittleness index, and two-way stress difference coefficient, respectively, with the unit of dimensionless; d1 + d2 + d3 = 1;

[0252] CI 脆性矿物含量 is the brittle mineral content index, with the minimum value of 0 and the maximum value of 1, and the unit of dimensionless;

[0253] CI 脆性指数 is the brittleness index, with the minimum value of 0 and the maximum value of 1, and the unit of dimensionless;

[0254] CI Kh is the two-way stress difference coefficient index, with the minimum value of 0 and the maximum value of 1, and the unit of dimensionless;

[0255] Furthermore, the calculation formula for the brittle mineral content index is as follows:

[0256]

[0257] In the formula:

[0258] BMC is the brittle mineral content, with the unit of %.

[0259] Furthermore, the calculation formula for the brittleness index is as follows:

[0260]

[0261] Furthermore, the calculation formula for the two-way stress difference coefficient index is as follows:

[0262]

[0263] Step 3: Calculate the comprehensive index of the target area, determine the target area level, and select the favorable area

[0264] According to the key evaluation parameters of the target area and the quantitative evaluation model of the favorable area for shallow shale gas in Step 2, calculate the comprehensive index CI of the favorable area for shallow shale gas in the target area. According to the CI value, divide the target area into three levels: Class I area, Class II area, and Class III area, that is:

[0265]

[0266] Furthermore, the exploration potential of shallow shale gas in Class I areas is relatively large; that in Class II areas is medium; and that in Class III areas is relatively poor.

[0267] Furthermore, when there are multiple target areas, the area with the largest CI value and CI value ≥ 0.6 in the target areas is selected as the favorable area.

[0268] According to the geological characteristics and enrichment and high-yield laws of shallow shale gas in the embodiments of the present invention, the weight coefficients of the key evaluation parameters in step 2 are as follows: a is 0.3, b is 0.4, c is 0.2, and d is 0.1. The weight coefficients of the sub-parameters are as follows: a1 is 0.3, a2 is 0.7, b1 is 0.3, b2 is 0.2, b3 is 0.23, b4 is 0.12, b5 is 0.15, c1 is 0.2, c2 is 0.1, c3 is 0.4, c4 is 0.3, d1 is 0.4, d2 is 0.3, and d3 is 0.3. The comprehensive index CI of the favorable area of the LCP structure is calculated to be 0.82, which is determined as a Class I area. The exploration potential of shallow shale gas is relatively large, and it is selected as the favorable area for shallow shale gas. At present, 2 shale gas wells have been implemented in this area. The shale burial depth is 950 - 1100 m, the proportion of adsorbed gas content reaches 80%, and the proportion of free gas is only 20%. The daily gas production during the test is 41,000 - 45,000 m³, achieving a breakthrough in the exploration of shallow shale gas and proving that the LCP structure is a favorable area for the exploration and development of shallow shale gas.

[0269] The present invention also provides a device for quantitatively selecting favorable areas of shallow shale gas in complex structural areas, which is used to execute any method for quantitatively selecting favorable areas of shallow shale gas in complex structural areas, and includes:

[0270] A key parameter input module M1 for target areas, a weight coefficient input module M2 for key parameters of target areas, a resource condition index calculation module M3, an adsorption capacity index calculation module M4, a free gas preservation index calculation module M5, an engineering condition index calculation module M6, a comprehensive index calculation module M7 for favorable areas of shallow shale gas, and a favorable area level determination module M8, where

[0271] The key parameter input module M1 for target areas is used to input the key parameters for evaluating favorable areas of target areas;

[0272] The weight coefficient input module M2 for key parameters of target areas is used to input the weight coefficients of each parameter, including a, b, c, d, a1, a2, b1, b2, b3, b4, b5, c1, c2, c3, c4, d1, d2, d3;

[0273] The resource condition index calculation module M3 is used to calculate the resource condition index CI of the target area 资源条件 ;

[0274] The adsorption capacity index calculation module M4 is used to calculate the adsorption capacity index CI of the target area吸附能力 ;

[0275] The free gas preservation index calculation module M5 is used to calculate the free gas preservation index CI of the target area 游离气保存 ;

[0276] The engineering condition index calculation module M6 is used to calculate the engineering condition index CI of the target area 工程条件 ;

[0277] The favorable area comprehensive index calculation module M7 is used to calculate the favorable area comprehensive index CI of the target area;

[0278] The favorable area level determination module M8 is used to determine the favorable area level.

[0279] In this embodiment, a computer device is further included. The computer device is composed of a processor 40, a memory 10, a computer program stored on the memory 10 and executable on the processor 40, and a display 30. Among them, when the processor 40 can execute the computer program, it can implement any quantitative selection method for favorable areas of shallow shale gas in complex structural areas;

[0280] Among them, the computer program is set as a quantitative selection program 20 for favorable areas of shallow shale gas in complex structural areas that can run on the processor.

[0281] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A quantitative selection method for shallow shale gas favorable areas in complex structural areas, characterized by: It includes the following steps: Step 1: Conduct geological evaluation of shallow shale gas in the target area and obtain key parameters for shallow shale gas evaluation; Step 2: Based on the four key evaluation parameters of shallow shale gas resource conditions, adsorption capacity, free gas preservation, and compressibility, a quantitative evaluation model for shallow shale gas favorable areas is established; Step 3: Calculate the comprehensive index of the target area, determine the level of the target area, and select the favorable area.

2. The method for quantitatively selecting favorable areas for shallow shale gas in complex structural areas according to claim 1 is characterized by: In the step 1, a shallow shale gas geological evaluation is carried out in the target area to obtain key parameters for the geological characteristics of shallow shale gas and the control of shallow shale gas enrichment and high production, including resource condition evaluation parameters, adsorption capacity evaluation parameters, free gas preservation evaluation parameters, and compressibility evaluation parameters, wherein: Resource condition evaluation parameters are used to evaluate the material basis for shale gas formation, including two sub-parameters: thickness with TOC greater than 1% and thickness with TOC greater than 2%. Adsorption capacity evaluation parameters are used to evaluate the adsorption capacity of shale in the target area, including five sub-parameters: TOC, formation temperature, formation pressure, quartz content, clay content, etc. Free gas preservation evaluation parameters are used to evaluate the free gas preservation conditions in the target area, including four sub-parameters: effective normal stress of foliation surface, roof conditions, floor conditions, and the last hydrocarbon generation cessation time. The compressibility evaluation parameters are used to evaluate the fracturing properties of shale in the target area, including three sub-parameters: brittle mineral content, brittleness index, and two-way stress difference coefficient.

3. The method for quantitatively selecting favorable areas for shallow shale gas in complex structural areas according to claim 1 is characterized by: In step 2, the four key parameters of shallow shale gas resource conditions, adsorption capacity, free gas preservation, and compressibility are used to evaluate the control effect on the enrichment and high yield of shallow shale gas, and a quantitative evaluation model for shallow shale gas favorable areas is established. The comprehensive index CI of shallow shale gas favorable areas is calculated to evaluate the level of favorable areas. The matrix is ​​as follows: CI=(abcd)(CI 资源条件 CI 吸附能力 CI 游离气保存 CI 可压性 ) Where: CI is the comprehensive index of favorable areas, and the units are dimensionless; a, b, c, and d are the weight coefficients of resource conditions, adsorption capacity, free gas preservation, and compressibility, respectively, and the units are dimensionless, a+b+c+d=1; CI 资源条件 is the resource condition index, unit is dimensionless; CI 吸附能力 is the adsorption capacity index, unit is dimensionless; CI 游离气保存 is the free gas preservation index, unit is dimensionless; CI 可压性 is the compressibility index, unit is dimensionless; Among them, the resource condition index evaluation matrix is ​​as follows: Where: CI H1 It is the thickness index of TOC greater than 1%, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI H2 It is the thickness index of TOC greater than 2%, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; a1 and a2 are weight coefficients of the thickness with TOC greater than 1% and the thickness with TOC greater than 2%, respectively, and the units are dimensionless, a1+a2=1; The calculation formula for the thickness index of TOC greater than 1% is as follows: Where: H1 is the thickness where TOC is greater than 1%, in m; The calculation formula for the thickness index of TOC greater than 2% is as follows: Where: H2 is the thickness where TOC is greater than 2%, in m; The adsorption capacity index evaluation matrix is ​​as follows: IN 吸附能力 =(b1 b2 b3 b4 b5)(CI TOC IN 地层温度 IN 地层压力 IN 石英含量 IN 黏土含量 ) Where: b1, b2, b3, b4, and b5 are weight coefficients of TOC, formation temperature, formation pressure, quartz content, and clay content, respectively, and the units are dimensionless, b1+b2+b3+b4+b5=1; CI TOC is the TOC index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 地层温度 is the formation temperature index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 地层压力 is the formation pressure index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 石英含量 is the quartz content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 黏土含量 It is the clay content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless. The TOC index calculation formula is as follows: Where: TOC, unit %; The calculation formula of formation temperature index is as follows: Where: Formation temperature, unit: °C; The calculation formula of formation pressure index is as follows: Where: Formation pressure, unit: MPa; The calculation formula of quartz content index is as follows: Where: Quartz content, unit: %; The clay content index calculation formula is as follows: Where: Clay content, unit %; The free gas preservation index evaluation matrix is ​​as follows: Where: c1, c2, c3, c4 are weight coefficients of roof conditions, floor conditions, effective normal stress of foliation surface, and stop time of last hydrocarbon generation, respectively, and the units are dimensionless; when the structural type is a complete anticline or a complete syncline, c1+c2=1; when the structural type is a monocline, c1+c2+c3+c4=1; CI 顶板 is the roof condition index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 底板 is the base condition index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI P正应力 is the effective normal stress index of the lamina, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 末次生烃停止时间 is the last hydrocarbon generation stop time index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; The roof condition index calculation formula is as follows: Where: H 顶板 is the top plate thickness, in m; The floor condition index calculation formula is as follows: Where: H 底板 is the bottom plate thickness, in m; The calculation formula of effective normal stress index of lamina is as follows: The calculation formula of the last hydrocarbon generation stop time index is as follows: Where: FT is the last hydrocarbon generation stop time, unit is Ma; The compressibility index evaluation matrix is ​​as follows: IN 可压性 (d1 d2 d3)(CI 脆性矿物含量 IN 脆性指数 IN 两向应力差异系数 ) Where: d1, d2, d3 are the weight coefficients of brittle mineral content, brittleness index, and biaxial stress difference coefficient, respectively, and the units are dimensionless; d1+d2+d3=1; CI 脆性矿物含量 is the brittle mineral content index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI 脆性指数 is the brittleness index, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; CI Kh is the index of the difference coefficient of biaxial stress, with a minimum value of 0 and a maximum value of 1, and the unit is dimensionless; The calculation formula of brittle mineral content index is as follows: Where: BMC is the brittle mineral content, in %; Furthermore, the calculation formula of the brittleness index is as follows: Furthermore, the calculation formula of the two-way stress difference coefficient index is as follows:

4. The method for quantitatively selecting favorable shallow shale gas areas in complex structural areas according to claim 1, characterized in that: In step 3, according to the key evaluation parameters of the target area and the quantitative evaluation model of the shallow shale gas favorable area in step 2, the comprehensive index CI of the shallow shale gas favorable area in the target area is calculated, and according to the CI value, the target area is divided into three levels: Class I area, Class II area, and Class III area, that is: Among them, the shallow shale gas exploration potential of Class I areas is the greatest; the shallow shale gas exploration potential of Class II areas is medium; and the shallow shale gas exploration potential of Class III areas is relatively poor.

5. A quantitative selection device for shallow shale gas favorable areas in complex structural areas, which is used to perform the method as claimed in any one of claims 1 to 4, characterized in that: It includes: Target area key parameter input module M1, target area key parameter weight coefficient input module M2, resource condition index calculation module M3, adsorption capacity index calculation module M4, free gas preservation index calculation module M5, engineering condition index calculation module M6, shallow shale gas favorable area comprehensive index calculation module M7, favorable area grade determination module M8, among which, The target area key parameter input module M1 is used to input the key parameters for evaluating the favorable area of ​​the target area; The target area key parameter weight coefficient input module M2 is used to input the weight coefficient of each parameter, including a, b, c, d, a1, a2, b1, b2, b3, b4, b5, c1, c2, c3, c4, d1, d2, d3; Resource condition index calculation module M3, used to calculate the resource condition index CI of the target area 资源条件 ; Adsorption capacity index calculation module M4, used to calculate the adsorption capacity index CI of the target area 吸附能力 ; Free gas preservation index calculation module M5, used to calculate the free gas preservation index CI of the target area 游离气保存 ; Engineering condition index calculation module M6, used to calculate the target area engineering condition index CI 工程条件 ; The favorable area comprehensive index calculation module M7 is used to calculate the favorable area comprehensive index CI of the target area; The favorable area level determination module M8 is used to determine the favorable area level.

6. The device for quantitatively selecting favorable shallow shale gas areas in complex structural areas according to claim 5 is characterized in that: It also includes a computer device, which is composed of a processor (40), a memory (10), a computer program stored in the memory (10) and executable on the processor (40), and a display (30), wherein the processor (40) is capable of implementing the method for quantitatively selecting favorable areas for shallow shale gas in complex structural areas as described in any one of claims 1 to 4 when executing the computer program.

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