Shale hydrocarbon discharge efficiency calculation method and electronic device

Abstract

This invention provides a method and electronic device for calculating shale hydrocarbon expulsion efficiency, relating to the field of shale gas resource evaluation technology. The method includes: constructing a digital core model based on a target rock sample; solving a pre-determined set of microscopic control equations based on the digital prototype model to simulate the hydrocarbon expulsion process; obtaining the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs based on the solution results; wherein the pre-determined set of microscopic control equations includes a shale gas-induced fracturing hydrocarbon expulsion criterion; the shale gas-induced fracturing hydrocarbon expulsion criterion is used to characterize the initial hydrocarbon expulsion initiation conditions of shale and is controlled by the effective principal stress of the shale to which the target rock sample belongs. This invention uses the effective principal stress of the shale to which the target rock sample belongs as the control basis to simulate the micromechanical fracturing of the rock caused by gas generation. After obtaining the shale hydrocarbon expulsion efficiency based on the method provided by this invention, shale gas resource evaluation is then conducted accordingly, making the process and results more scientific and accurate.

Description

Technical Field

[0001] This invention relates to the field of shale gas resource evaluation technology, and in particular to a method for calculating shale hydrocarbon expulsion efficiency and an electronic device. Background Technology

[0002] The initial hydrocarbon expulsion of shale refers to the phenomenon where, after the organic matter in shale reaches the hydrocarbon generation threshold through thermal evolution, hydrocarbons generated within it break free from the constraints of the organic matter particles or the micropores of the rock. They migrate from their source sites, such as within the organic matter or between clay minerals, into the shale's internal pore system, such as nanopores, micropores, or early microfractures, thus completing the initial "generation-expulsion" process. This process is a crucial pre-requisite for shale gas accumulation, and the "self-generating and self-storing" nature of shale gas reservoirs makes initial hydrocarbon expulsion efficiency a core parameter for resource evaluation. Initial hydrocarbon expulsion efficiency refers to the proportion of natural gas generated from kerogen that can be expelled from the tight source rock matrix; it directly controls the amount of gas retained in the reservoir and the final amount of usable resources.

[0003] In existing basin simulation software, the initial hydrocarbon expulsion process is usually handled using an empirical "threshold" model. These models generally assume that the hydrocarbon expulsion process will only begin when the pore fluid pressure exceeds a certain critical proportion of the overlying formation pressure, or when the hydrocarbon saturation reaches a certain critical value.

[0004] However, the fundamental flaw of this empirical method lies in its lack of a solid physical foundation. It simplistically equates hydrocarbon expulsion to a seepage problem driven by fluid overpressure, ignoring the basic fact that shale matrix has extremely low permeability. In such a dense medium, large-scale fluid seepage is unlikely to occur. Geological and rock physics studies indicate that the initial hydrocarbon expulsion of shale gas is more likely a rock mechanical failure process: gas generation from kerogen leads to a sharp increase in local pore pressure. When the resulting tensile stress exceeds the microscopic tensile strength of the rock, it induces the formation and propagation of microcracks, thereby creating high-conductivity channels through which gas is rapidly expelled. Traditional empirical thresholds cannot describe this core physical mechanism of "gas generation-pressurization-fracture-hydrocarbon expulsion," resulting in a high degree of subjectivity and uncertainty in the selection of hydrocarbon expulsion threshold values. This has become a technical bottleneck that urgently needs to be overcome in the current field of shale gas resource evaluation. Summary of the Invention

[0005] This invention provides a method and electronic device for calculating shale hydrocarbon expulsion efficiency to address the problem that current shale gas resource evaluation results are too subjective and inaccurate.

[0006] In a first aspect, embodiments of the present invention provide a method for calculating shale hydrocarbon expulsion efficiency, including:

[0007] Construct a digital core model based on the target rock sample;

[0008] Based on the digital core model, the predetermined set of microscopic control equations are solved to simulate the hydrocarbon expulsion process;

[0009] Based on the solution results, the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs is obtained;

[0010] Among them, the pre-determined set of micro-control equations includes the shale gas-induced fracturing hydrocarbon expulsion criterion; the shale gas-induced fracturing hydrocarbon expulsion criterion is used to characterize the initial hydrocarbon expulsion initiation conditions of shale, which is controlled by the effective principal stress of the shale to which the target rock sample belongs.

[0011] In one possible implementation, the shale gas-induced fracturing hydrocarbon expulsion criterion is determined based on the minimum principal stress of the shale, pore fluid pressure, and microscopic tensile strength.

[0012] The shale gas-induced fracturing and hydrocarbon expulsion criterion describes that when gas generation from kerogen causes an increase in pore fluid pressure, making the minimum effective principal stress of the shale change to tensile stress, and the magnitude of the tensile stress exceeds the microscopic tensile strength, tensile fracturing occurs in the shale, initiating hydrocarbon expulsion.

[0013] In one possible implementation, the mathematical expression for the shale gas-induced fracturing and hydrocarbon expulsion criterion is:

[0014]

[0015] In the formula, It is tensile stress; The minimum effective principal stress; The Biot coefficient; Pore ​​fluid pressure; This refers to the microscopic tensile strength.

[0016] In one possible implementation, the predetermined set of microscopic governing equations also includes a gas mass conservation equation; the gas mass conservation equation is determined based on the gas generation rate of kerogen.

[0017] In one possible implementation, the gas mass conservation equation is expressed as:

[0018]

[0019] In the formula, Porosity; The density of the gas; Indicates gradient operation; Darcy velocity; Anger rate.

[0020] In one possible implementation, the predetermined set of microscopic governing equations also includes solid mechanical equilibrium equations;

[0021] The equilibrium equations for solid mechanics are:

[0022]

[0023] In the formula, Indicates effective stress; This indicates the change in void pressure;

[0024] The equilibrium equations in solid mechanics are used to describe the equilibrium relationship of the effective stress σ′ in shale under varying pore pressure P.

[0025] In one possible implementation, the predetermined set of microscopic control equations also includes a damage function;

[0026] The damage function is used to describe the degree of fracturing in the shale.

[0027] In one possible implementation, the predetermined set of microscopic control equations also includes a damage function;

[0028] The damage function is used to describe the degree of fracturing that begins after the shale gas-induced fracturing and hydrocarbon expulsion criterion is met.

[0029] The damage function is expressed as:

[0030]

[0031] In the formula, This represents the permeability of the shale matrix before fractures are formed. This is a damage mechanics variable, with a value between 0 and 1, used to describe the degree of fracture. This represents the permeability of shale when fractures form.

[0032] In one possible implementation, after obtaining the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs based on the solution results, the method further includes:

[0033] Regression analysis was performed on the shale hydrocarbon expulsion efficiency under different simulation data to obtain the micro-fractured hydrocarbon expulsion efficiency function.

[0034] Among them, the micro-crack-induced hydrocarbon expulsion efficiency function is used for basin simulation to evaluate shale gas resources within the target basin.

[0035] In one possible implementation, the method further includes:

[0036] Based on the shale gas-induced fracturing and hydrocarbon expulsion criterion, hydraulic fracturing prediction is carried out in various regions of the target basin.

[0037] Regions that meet the criteria for hydrocarbon expulsion caused by gas-induced fracturing in shale are considered regions prone to gas-induced fracturing.

[0038] In a second aspect, embodiments of the present invention provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation thereof.

[0039] Unlike traditional simulation methods that use pore fluid pressure or hydrocarbon saturation as the initiation condition for hydrocarbon expulsion, this invention uses the effective principal stress of the shale to which the target rock sample belongs as the control basis to simulate the micromechanical fracture of the rock caused by gas generation. Based on this, the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs is solved and calculated. After obtaining the shale hydrocarbon expulsion efficiency based on the method provided by this invention, shale gas resource evaluation is carried out accordingly. The process and results are more scientific and accurate. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the implementation of the shale hydrocarbon expulsion efficiency calculation method provided in this embodiment of the invention.

[0041] Figure 2 This is a flowchart illustrating the implementation of the basin simulation application provided in this embodiment of the invention. Detailed Implementation

[0042] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0043] The study of primary hydrocarbon expulsion from shale has developed into a multidisciplinary technical system, comprehensively utilizing geological experiments, numerical simulations, and geochemical analyses. Its research methods mainly include the following five aspects:

[0044] 1. Hydrocarbon generation potential difference method

[0045] This method is based on Rock-Eval pyrolysis, and its essence lies in the principle of hydrocarbon mass balance during the thermal evolution of organic matter. Specifically, the total amount of hydrocarbons generated by organic matter in shale under thermal action, i.e., the original hydrocarbon generation potential, can be divided into two parts during geological evolution: the amount of hydrocarbons expelled from the shale, i.e., the expelled hydrocarbons, and the amount of hydrocarbons still retained in the shale, i.e., the residual hydrocarbon generation potential. This satisfies the mass conservation relationship: Original hydrocarbon generation potential = Expelled hydrocarbons + Residual hydrocarbon generation potential.

[0046] The key to implementing the method lies in obtaining two core parameters: one is the residual hydrocarbon generation potential (S). Pr This parameter is the sum of the measured free hydrocarbon content (S1, unit: mg / g rock) and the pyrolysis hydrocarbon content (S2, unit: mg / g rock) of the target shale sample, measured directly using a Rock-Eval pyrolysis instrument.

[0047] S Pr =S1+S2.

[0048] Second, the original hydrocarbon generation potential (S P0 Since the target sample has usually already undergone hydrocarbon expulsion, it needs to be restored through geological analogy or thermal evolution model.

[0049] The geological analogy method selects samples with extremely low maturity (vitrinite reflectance Ro < 0.5%, no hydrocarbon expulsion initiated) from the same shale strata, and uses their measured S1+S2 values ​​as S. P0 .

[0050] The thermal evolution model is based on the thermal evolution kinetics model of kerogen. It infers the hydrocarbon generation potential of the immature stage of the target sample from its maturity (Ro), that is:

[0051] S P0 =S 10 +S 20 ;

[0052] Among them, S 10 The original free hydrocarbon content, S 20 The values ​​represent the original pyrolysis hydrocarbon content, all in mg / g rock.

[0053] Based on the above formula derivation, the formula for calculating hydrocarbon expulsion efficiency (η) is as follows:

[0054] η=(S P0 S Pr ) / S P0 ×100%

[0055] Among them, S P0 -S Pr This refers to the amount of hydrocarbons emitted.

[0056] This formula quantifies the proportion of hydrocarbons expelled from shale to the total hydrocarbons generated. Based on the mature Rock-Eval pyrolysis technology, this method offers convenient parameter acquisition, is suitable for large-scale batch analysis, and is commonly used for preliminary assessment of regional hydrocarbon expulsion potential during shale exploration. It is particularly suitable for study areas with maturity data and immature analog samples.

[0057] 2. Material balance method (organic carbon balance branch)

[0058] This method is based on the organic carbon balance method, and is implemented based on the principle of mass conservation of carbon elements during the hydrocarbon generation process of organic matter. Specifically:

[0059] Total Organic Carbon (TOC) in shale is the material basis for hydrocarbon generation. The thermal evolution of organic matter to form hydrocarbons is essentially a process of carbon transformation into hydrocarbon carbon. Therefore, the original total organic carbon = residual total organic carbon + total organic carbon transformed into hydrocarbons.

[0060] The implementation of this method includes three core steps:

[0061] (1) Determining the original total organic carbon content (TOC0): The current organic carbon content (TOCr, unit: %) of the target shale can be directly determined by an elemental analyzer, but it is necessary to restore its original value (TOC0) before hydrocarbon generation. Restoration methods include: immature sample analogy method (selecting the measured TOC of the same layer of shale with Ro<0.5% as TOC0); diagenetic compaction correction method: considering the organic carbon concentration effect caused by the compaction of clay minerals during the shale burial process, the original organic carbon content before compaction is inferred by back-calculating the compaction curve.

[0062] (2) Calculate the total hydrocarbon generation (Q) 生 Based on the conversion efficiency of organic carbon to hydrocarbons, a carbon conversion coefficient k is introduced (usually taken as 0.083, based on the fact that each gram of hydrocarbons in the kerogen hydrocarbon generation process contains approximately 0.083 grams of organic carbon). The total hydrocarbon generation is then:

[0063] Q 生 =k×TOC0 TOCr

[0064] Wherein, TOCO-TOCr represents the organic carbon content converted into hydrocarbons, expressed as a percentage (Q). 生 The unit is mg / g rock.

[0065] (3) Calculate hydrocarbon emission efficiency: Further calculation of residual hydrocarbon quantity (Q) is required. 残 (Unit: mg / g rock), can be determined by the S1+S2 content of Rock-Eval pyrolysis or the "A" content of chloroform bitumen (determined by Soxhlet extraction). Based on the formula: Total hydrocarbon generation = Hydrocarbon emissions + Residual hydrocarbons, the hydrocarbon emissions Q... 排 =Q 生 -Q 残 Therefore, the hydrocarbon removal efficiency is:

[0066] η=Q 排 / Q 生 ×100%=Q 生 (Q) 残 / Q 生 ) × 100%

[0067] The core advantage of this method is that it is not limited by maturity. Even for highly mature shale (Ro>2.0%), whose hydrocarbon generation potential parameters are distorted due to excessive organic matter decomposition, the method can still quantitatively assess hydrocarbon generation and hydrocarbon expulsion efficiency through changes in organic carbon. It is suitable for macroscopic studies of shale hydrocarbon expulsion efficiency at the regional scale, and is especially suitable for highly mature shale areas that lack hydrocarbon generation potential data.

[0068] 3. Material Balance Method

[0069] This method is based on pore volume balance, and its principle is based on the pore fluid transport patterns during the compaction process of shale burial. Specifically:

[0070] During burial, shale is subjected to pressure from the overlying strata. The compaction of the rock skeleton leads to a reduction in pore volume. Free and dissolved hydrocarbons stored in the pores are squeezed out due to the compression of the pore space, forming a hydrocarbon expulsion process. The hydrocarbon expulsion amount satisfies the following equation: difference in pore volume before and after compaction × mass density of hydrocarbons in the pores.

[0071] The implementation of this method requires obtaining four types of key physical parameters:

[0072] (1) Shale volume (V) 岩 ): Calculated based on the thickness and distribution area of ​​shale in the study area; the unit is usually cm. 3 or m 3 .

[0073] (2) Porosity evolution parameters: including original porosity ( 0 (unit: %) and current residual porosity ( r ,unit:%). 0 can be inferred from actual measurements of shallowly buried immature shale samples (such as helium porosimeter) or from compaction curves based on sedimentary facies. r It can be obtained through high-pressure mercury intrusion experiments, nano-CT imaging, or well logging interpretation (such as neutron-density intersection method).

[0074] (3) Hydrocarbon density (ρ) 烃 The density of liquid hydrocarbons is typically determined based on the hydrocarbon phase state in shale; it is usually 0.85-0.95 g / cm³. 3 The density of gaseous hydrocarbons is typically 0.0007-0.001 g / cm³. 3 It can be obtained through laboratory experiments or based on theoretical calculations of hydrocarbon components.

[0075] (4) Pore hydrocarbon saturation (S) 烃 ): refers to the proportion of hydrocarbon volume in the pore space to the total pore volume (unit: %), which can be obtained through core centrifugation experiments (after determining the saturation of bound water by displacement method and then back-calculating) or well logging interpretation (such as resistivity-neutron porosity cross-section).

[0076] Based on the above parameters, hydrocarbon emissions (Q) 排 The formula for calculating ) is:

[0077] Q 排 =V 岩 ×( 0 r )×ρ 烃 ×S烃 。

[0078] The total hydrocarbon generation amount (Q 生 ) is obtained in the same way as the organic carbon balance method. Therefore, the hydrocarbon expulsion efficiency is:

[0079] η = Q 排 / Q generation × 100%

[0080] This method directly depicts the physical process of hydrocarbon expulsion, i.e., compaction - pore compression - fluid discharge, avoiding subjective errors in hydrocarbon generation potential or organic carbon restoration. The results are closer to geological reality and are applicable to shales with well-developed pores and mainly free-state hydrocarbon expulsion, such as delta facies and shallow lake facies shales, especially suitable for research scenarios that require quantification of the contribution of compaction to hydrocarbon expulsion.

[0081] 4. Geochemical parameter ratio method

[0082] This method is based on the fractionation effect of hydrocarbon components during hydrocarbon expulsion: when hydrocarbons migrate from the interior of the shale to the outside, hydrocarbons with different molecular structures fractionate due to differences in migration ability - light hydrocarbons, such as saturated hydrocarbons, have small molecular masses and weak polarities and are more likely to break through the capillary resistance of the rock pore throats and be discharged; heavy hydrocarbons such as aromatics and non-hydrocarbons have large molecular masses and strong polarities and are more likely to be adsorbed by organic matter or clay minerals and retained, resulting in a decrease in the proportion of light hydrocarbons and an increase in the proportion of heavy hydrocarbons in the residual hydrocarbons of the shale.

[0083] Currently, the most widely used is the chloroform bitumen "A" component ratio method, and the technical route is as follows:

[0084] (1) Parameter selection: Select the saturated hydrocarbon / aromatic hydrocarbon ratio (S / A) as the core index, and this ratio can be obtained through the component separation experiment of chloroform bitumen "A". That is, chloroform bitumen "A" is separated into four components: saturated hydrocarbons, aromatic hydrocarbons, non-hydrocarbons, and asphaltenes by column chromatography, and the ratio is calculated after measuring the masses of saturated hydrocarbons and aromatic hydrocarbons.

[0085] (2) Determine the original ratio and the residual ratio: The original ratio (S / A)0 is obtained through actual measurement of non-hydrocarbon-expelled shale samples (Ro < 0.5%); the residual ratio (S / A) r is obtained through actual measurement of the target shale samples.

[0086] (3) Calculate the hydrocarbon expulsion efficiency: Based on the logic that the higher the hydrocarbon expulsion efficiency, the more saturated hydrocarbons are lost in the residual hydrocarbons and the greater the difference between (S / A)r and (S / A)0, the formula is derived as follows:

[0087] η = (1 (S / A) r (S / A)0) × 100%

[0088] Furthermore, other geochemical parameters can be used for verification, such as the psarcosane / phytane ratio (Pr / Ph). Pr is more easily expelled than Ph, indicating higher hydrocarbon expulsion efficiency and a lower Pr / Ph ratio in the residual hydrocarbons. Carbon isotopes (δ13C) also play a role – hydrocarbons with lighter carbon isotopes (12C) are more easily expelled during hydrocarbon expulsion, while the residual hydrocarbons have a heavier δ13C content. The degree of δ13C shift can be used to semi-quantitatively assess hydrocarbon expulsion efficiency. This method is cost-effective and has a short experimental cycle, making it suitable for rapid screening of hydrocarbon expulsion efficiency in the early stages of shale exploration when hydrocarbon generation potential or organic carbon data is lacking.

[0089] 5. Experimental simulation method, i.e., thermal simulation of semi-closed systems.

[0090] This method reproduces the entire process of hydrocarbon generation and expulsion in shale under geological conditions through laboratory simulation, thereby directly quantifying hydrocarbon expulsion efficiency. Its core lies in constructing a controllable and observable experimental system to overcome the irreversibility of geological processes.

[0091] The key to the experimental design lies in constructing a semi-closed reaction system: a high-pressure reactor is used as the container, and the shale sample is placed inside. The heating rate is controlled by a programmed temperature controller to simulate the temperature rise during geological burial, typically set at 1-5℃ / h. Simultaneously, the reactor pressure is controlled to simulate formation pressure. The system is designed to allow hydrocarbon expulsion but limit excessive escape; that is, the generated hydrocarbons are discharged to a collection device, such as a liquid nitrogen cold trap, through conduits, while residual hydrocarbons in the sample inside the reactor are retained, achieving simulation of the entire "generation-expulsion-residue" process. Specifically, the shale sample used must be in block or powder form, maintaining the integrity of its organic matter and pore structure.

[0092] The core steps of implementing the method include:

[0093] (1) Determine the amount of hydrocarbons emitted (Q) 排 , 实 During the experiment, the collected effluent hydrocarbons were qualitatively and quantitatively analyzed by gas chromatography or gas chromatography-mass spectrometry to obtain the amount of effluent hydrocarbons per unit mass of sample.

[0094] (2) Determination of residual hydrocarbon content (Q) 残 , 实 After the experiment, the shale sample inside the reactor was removed, and the residual hydrocarbons were extracted using the Soxhlet extraction method, or the residual hydrocarbon generation potential was determined using a Rock-Eval pyrolysis instrument and converted into the amount of residual hydrocarbons.

[0095] (3) Calculation of hydrocarbon expulsion efficiency: Based on the balance relationship of total hydrocarbon generation = hydrocarbon expulsion + residual hydrocarbon, the formula is derived as follows:

[0096] η = (Q) 排 , 实 +Q 残 , 实 ) / Q排 , 实 ×100%

[0097] The core advantage of this method lies in the controllability of experimental conditions. By changing single variables such as heating rate, pressure, and pore structure, the influence mechanism of various factors on hydrocarbon expulsion efficiency can be studied. At the same time, it can serve as a "calibration tool" to provide experimental verification and correction for empirical parameters in geological methods such as the hydrocarbon generation potential difference method and organic carbon balance method, such as the original hydrocarbon generation potential and carbon conversion coefficient. It is suitable for the study of shale hydrocarbon expulsion mechanism and the reliability verification of geological calculation methods.

[0098] The methods described above are commonly used calculation methods. However, these existing methods typically employ empirical "threshold" models to handle the initial hydrocarbon expulsion process. The fundamental flaw of this empirical method lies in its lack of a solid physical foundation, leading to significant subjectivity and uncertainty in the selection of the hydrocarbon expulsion threshold value. This has become a critical technical bottleneck that urgently needs to be overcome in the current field of shale gas resource evaluation. To address this issue, this embodiment provides a method for calculating shale hydrocarbon expulsion efficiency. The flowchart of this method is shown below. Figure 1 As shown, the method may include:

[0099] Step 110: Construct a digital core model based on the target rock sample.

[0100] First, target rock samples consistent with the geological background of the shale strata to be evaluated are collected to ensure that the samples are representative.

[0101] For example, if the research object is deltaic facies shale in a basin, core samples from the same shale strata in the basin but at different depths and maturity levels should be selected to avoid model distortion due to differences between the samples and the actual geological bodies. At the same time, the samples must ensure structural integrity, without obvious artificial damage or large natural cracks, to accurately reflect the original porosity and framework characteristics of the shale matrix.

[0102] The target rock samples were macroscopically cut and cleaned to remove surface impurities and drilling fluid residues, and processed into dimensions that met experimental standards, such as cylinders with a diameter of 2.5 cm and a length of 5 cm, to facilitate subsequent experimental testing. Simultaneously, some samples underwent microscopic preparation, for example, using focused ion beam scanning electron microscopy or nano-CT scanning to obtain nanoscale pore images of the target rock samples, providing direct evidence for the microstructural reconstruction of the digital core model.

[0103] The remaining samples were tested for physical, mechanical, and hydrocarbon generation parameters to obtain corresponding data, ensuring that each digital core model is supported by real sample data.

[0104] After processing the target rock samples, data such as matrix permeability, hydrocarbon density, pore hydrocarbon saturation, and total organic carbon content are obtained to construct a corresponding digital core model. During model construction, the model needs to be assigned corresponding microscopic tensile strength, Biot coefficient, and minimum principal stress at the corresponding burial depth to simulate the actual stress environment of the shale.

[0105] The constructed model sets the simulation temperature and time conditions based on the geological evolution history of the shale to which the target rock sample belongs, ensuring that the simulation process is synchronized with actual geological conditions. Simultaneously, relevant data from the simulation process are recorded to obtain simulation data.

[0106] Optionally, during the simulation process, multiple sets of simulation data can be obtained by changing the initial original organic carbon content and the minimum effective principal stress.

[0107] Step 120: Solve the predetermined set of microscopic control equations based on the digital core model to simulate the hydrocarbon expulsion process.

[0108] Step 130: Based on the solution results, obtain the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs.

[0109] When solving the predetermined set of microscopic governing equations, the burial history and thermal history of the target rock sample are used as boundary conditions.

[0110] To accurately simulate the initiation conditions of the hydrocarbon expulsion process, this embodiment innovatively establishes a shale gas-induced fracturing hydrocarbon expulsion criterion. This criterion differs from traditional methods that use pore fluid pressure or hydrocarbon saturation as the initiation condition for the hydrocarbon expulsion process. Instead, it determines whether shale is generating gas and expelling hydrocarbons by observing changes in the effective principal stress of the shale. Based on this criterion, the timing of shale gas-induced hydrocarbon expulsion can be scientifically determined, improving the accuracy of shale hydrocarbon expulsion efficiency calculations.

[0111] Therefore, the embodiments of the present invention use the effective principal stress of the shale to which the target rock sample belongs as the control basis to simulate the micromechanical fracture of the rock caused by gas generation. On this basis, the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs is solved and calculated. After obtaining the hydrocarbon expulsion efficiency of the shale based on the method provided by the present invention, the shale gas resource evaluation is carried out accordingly. The process and results are more scientific and accurate.

[0112] The following describes in detail the shale gas-induced fracturing hydrocarbon expulsion criteria and the set of microscopic governing equations provided in this embodiment through some optional examples.

[0113] In an alternative embodiment, the shale gas-induced fracturing hydrocarbon expulsion criterion is determined based on the minimum principal stress of the shale, pore fluid pressure, and microscopic tensile strength.

[0114] The shale gas-induced fracturing and hydrocarbon expulsion criterion describes that when gas generation from kerogen causes an increase in pore fluid pressure, making the minimum effective principal stress of the shale change to tensile stress, and the magnitude of the tensile stress exceeds the microscopic tensile strength, tensile fracturing occurs in the shale, initiating hydrocarbon expulsion.

[0115] Correspondingly, the mathematical expression for the shale gas-induced fracturing and hydrocarbon expulsion criterion is:

[0116]

[0117] In the formula, It is tensile stress; The minimum effective principal stress; The Biot coefficient; Pore ​​fluid pressure; This refers to the microscopic tensile strength.

[0118] The shale gas-induced fracturing and hydrocarbon expulsion criterion provided in this embodiment clarifies the critical conditions for the initial hydrocarbon expulsion of shale gas, replacing the traditional subjective experience threshold; the digital core model based on this shale gas-induced fracturing and hydrocarbon expulsion criterion can simulate the gas-fracturing-hydrocarbon expulsion process.

[0119] In order to apply the above-mentioned shale gas-induced cracking hydrocarbon expulsion criterion, it is necessary to add corresponding auxiliary formulas. That is, in an optional embodiment, the pre-determined set of micro-control equations also includes a gas mass conservation equation; the gas mass conservation equation is determined based on the gas generation rate of kerogen.

[0120] Accordingly, the gas mass conservation equation is expressed as:

[0121]

[0122] In the formula, Porosity; The density of the gas; Indicates gradient operation; Darcy velocity; Anger rate.

[0123] In this embodiment, The hydrocarbon generation kinetic model provides a dynamic activation that increases with temperature, offering a gas source for the rise in pore fluid pressure. This equation is used to describe the dynamic relationship of gas generation, migration, and conservation within the digital core, reflecting both the replenishment of gas by kerogen gas and the consumption of gas through seepage in the pores, thus maintaining gas mass balance.

[0124] In an optional embodiment, the predetermined set of microscopic governing equations also includes solid mechanical equilibrium equations.

[0125] The equilibrium equations in solid mechanics are expressed as follows:

[0126]

[0127] In the formula, Indicates effective stress; This indicates the change in void pressure.

[0128] This equation describes the equilibrium relationship of the effective stress σ′ of shale under varying pore pressure P.

[0129] This equation describes the dynamic relationship between pore fluid pressure changes and effective stress in the rock skeleton, quantifies the impact of pressure increase on rock stress state, and provides a mechanical calculation basis for determining whether the gas-induced cracking and hydrocarbon expulsion criterion is met, i.e. whether the minimum effective principal stress reaches the fracture threshold.

[0130] In an optional embodiment, the predetermined set of microscopic governing equations also includes a damage function. The damage function describes the degree of fracturing at which the shale begins to fracture after the shale gas-induced fracturing and hydrocarbon expulsion criterion is met.

[0131] Correspondingly, the damage function is expressed as:

[0132]

[0133] In the formula, This represents the permeability of the shale matrix before fractures are formed. This is a damage mechanics variable, with a value between 0 and 1, used to describe the degree of fracture. This represents the permeability of shale when fractures form.

[0134] After the gas-induced fracturing and hydrocarbon expulsion criterion is met, the rock begins to fracture. To describe the degree of rock fracture at this point, this embodiment introduces a damage function. This function is used to quantitatively describe the degree of rock fracture, where 0 represents no fracture and 1 represents complete fracture. This function can correlate with abrupt changes in permeability; that is, when the fracturing criterion is met, the variable increases with the development of fracture, driving the permeability from the matrix nanodarcy level to the fracture microdarcy level. This function enables the reproduction of the physical processes of fracturing and the opening of hydrocarbon expulsion channels.

[0135] Based on the above equations, during the digital core model simulation, as the temperature increases, the gas generation rate source term is activated, leading to a rapid increase in local pore pressure. Under these circumstances, the minimum effective principal stress changes. When the local pore pressure rises to a certain critical value, the minimum effective stress satisfies the shale gas generation-induced fracturing and hydrocarbon expulsion criterion.

[0136] After satisfying the shale gas-induced fracture hydrocarbon expulsion criterion, the damage variable D begins to increase, and the permeability undergoes a sudden change, with the order of magnitude jumping from nano-Darcy to micro-Darcy. A large amount of gas is expelled along the formed micro-fracture network, and the hydrocarbon expulsion process is completed. Based on this process, the digital core model gives the final hydrocarbon expulsion efficiency.

[0137] In an optional embodiment, after obtaining the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs based on the solution results in step 130, the method further includes:

[0138] Regression analysis was performed on the shale hydrocarbon expulsion efficiency under different simulation data to obtain the micro-fractured hydrocarbon expulsion efficiency function.

[0139] Among them, the micro-crack-induced hydrocarbon expulsion efficiency function is used for basin simulation to evaluate shale gas resources within the target basin.

[0140] Figure 2 This is a flowchart illustrating the implementation of the basin simulation application provided in this embodiment of the invention. The following is a summary of the process. Figure 2 This embodiment will be described.

[0141] The solution result is the simulation process performed by the digital core model. During the simulation, the initial conditions, namely TOC and the minimum principal stress, can be changed to obtain different simulation data. Specifically, the TOC can be adjusted between 2% and 6%, and the minimum principal stress can be adjusted between 50 MPa and 80 MPa.

[0142] Regression analysis or machine learning is performed on different simulation data and the corresponding shale hydrocarbon expulsion efficiency to establish a micro-fracture-induced hydrocarbon expulsion efficiency function.

[0143] The microscopic cracking hydrocarbon expulsion efficiency function can be expressed as:

[0144]

[0145] In the formula, The reflectance of vitrinite is expressed in % (%). This represents the microscopic tensile strength, expressed in MPa.

[0146] The obtained micro-fracture-induced hydrocarbon expulsion efficiency function is used to replace the hydrocarbon expulsion module in the basin simulation to obtain a new basin model. This model ensures that the function covers the main geological conditions of the shale in the study area and improves the accuracy of subsequent basin simulation applications. This model can reproduce the geological evolution process, more accurately calculate shale gas retention and effective hydrocarbon expulsion, and significantly improve the accuracy of judging the abundance of sweet spot resources and evaluating the amount of movable resources.

[0147] In an optional embodiment, the method further includes:

[0148] Based on the shale gas-induced fracturing and hydrocarbon expulsion criterion, hydraulic fracturing predictions are performed in various regions within the target basin.

[0149] Regions that meet the criteria for hydrocarbon expulsion caused by gas-induced fracturing in shale are considered regions prone to gas-induced fracturing.

[0150] In this embodiment, within the target basin, areas that meet the shale gas-induced fracturing and hydrocarbon expulsion criteria indicate that these areas are prone to gas-induced fracturing. Therefore, these areas can be used as a benchmark to identify areas prone to gas-induced fracturing. This approach allows for early prediction of areas with potential fracturing, enabling timely implementation of appropriate countermeasures.

[0151] In summary, this invention provides a shale gas-induced fracturing hydrocarbon expulsion criterion. This criterion transforms the initial hydrocarbon expulsion from a vague overpressure seepage problem into a clear, rock-physical-based mechanical failure problem. Based on this criterion, this invention combines damage evolution and permeability abrupt changes to perform simulations, achieving a quantitative reproduction of the entire "gas-fracturing-hydrocarbon expulsion" process, freeing the calculation of hydrocarbon expulsion efficiency from subjective and empirical constraints. Finally, by applying the obtained microscopic fracturing hydrocarbon expulsion efficiency function to basin simulation, the amount of shale gas retained and the effective hydrocarbon expulsion can be calculated more accurately, significantly improving the accuracy of judging the abundance of "sweet spots" resources and evaluating the amount of movable resources. Furthermore, based on this function, this embodiment can not only predict areas with high hydrocarbon expulsion efficiency but also identify areas that meet the shale gas-induced fracturing hydrocarbon expulsion criterion as the areas most prone to gas-induced fracturing, providing a new and more physically meaningful direct criterion for predicting "sweet spots" and selecting fracturing sites in shale gas exploration.

[0152] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0153] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0154] This invention also provides an electronic device, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described in the above method embodiments.

[0155] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0156] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for calculating shale hydrocarbon expulsion efficiency, characterized in that, include: Construct a digital core model based on the target rock sample; Based on the digital core model, the predetermined set of microscopic control equations are solved to simulate the hydrocarbon expulsion process; Based on the solution results, the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs is obtained; The predetermined set of microscopic control equations includes a shale gas-induced fracturing hydrocarbon expulsion criterion; the shale gas-induced fracturing hydrocarbon expulsion criterion is used to characterize the initial hydrocarbon expulsion initiation conditions of shale and is controlled by the effective principal stress of the shale to which the target rock sample belongs; The predetermined set of microscopic control equations also includes a gas mass conservation equation; the gas mass conservation equation is determined based on the gas generation rate of kerogen. The gas mass conservation equation is expressed as: In the formula, Porosity; The density of the gas; This represents gradient operation; Darcy velocity; Anger rate; The predetermined set of microscopic control equations also includes solid mechanics equilibrium equations; The solid mechanical equilibrium equation is as follows: In the formula, Indicates effective stress; This indicates the change in pore pressure; For Biot coefficient; The solid mechanics equilibrium equation is used to describe the equilibrium relationship of the effective stress σ′ of shale under the action of varying pore pressure P. The predetermined set of microscopic control equations also includes a damage function; The damage function is used to describe the degree of fracturing of the shale after the shale gas-induced fracturing and hydrocarbon expulsion criterion is met. The damage function is expressed as: In the formula, This represents the permeability of the shale matrix before fractures are formed. This is a damage mechanics variable, with a value between 0 and 1, used to describe the degree of fracture. This represents the permeability of shale when fractures form.

2. The method for calculating shale hydrocarbon expulsion efficiency according to claim 1, characterized in that, The shale gas-induced cracking hydrocarbon expulsion criterion is determined based on the minimum principal stress, pore fluid pressure, and microscopic tensile strength of the shale. The shale gas-induced fracturing and hydrocarbon expulsion criterion describes that when kerogen gas causes an increase in pore fluid pressure, making the minimum effective principal stress of the shale change to tensile stress and the magnitude of the tensile stress exceeds the microscopic tensile strength, the shale undergoes tensile fracturing, and hydrocarbon expulsion is initiated.

3. The method for calculating shale hydrocarbon expulsion efficiency according to claim 2, characterized in that, The mathematical expression for the shale gas-induced fracturing and hydrocarbon expulsion criterion is as follows: In the formula, The tensile stress is mentioned above; This is the minimum effective principal stress; For Biot coefficient; The pore fluid pressure; The microscopic tensile strength is given.

4. The method for calculating shale hydrocarbon expulsion efficiency according to claim 1, characterized in that, After obtaining the hydrocarbon expulsion efficiency of the shale to which the target rock sample belongs based on the solution results, the method further includes: By performing regression analysis on the shale hydrocarbon expulsion efficiency under different simulation data, the micro-fractured hydrocarbon expulsion efficiency function is obtained. The microscopic cracking hydrocarbon expulsion efficiency function is used for basin simulation to evaluate shale gas resources within the target basin.

5. The method for calculating shale hydrocarbon expulsion efficiency according to claim 4, characterized in that, The method further includes: Based on the shale gas-induced fracturing and hydrocarbon expulsion criteria, hydraulic fracturing predictions are performed for each region within the target basin. Regions that meet the shale gas-induced fracturing and hydrocarbon expulsion criteria are considered as regions prone to gas-induced fracturing.

6. An electronic device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 5.

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