Economic evaluation method and system for in-situ conversion of medium-low mature shale

Abstract

The invention relates to an economic evaluation method and system for in-situ conversion of medium and low-cooked shale, and belongs to the technical field of shale oil development. Comprising the following steps: 1) establishing a medium-low mature shale in-situ conversion geological model; 2) constructing a three-dimensional heat conduction equation, setting a definite solution condition, and solving the three-dimensional heat conduction equation in combination with the thermophysical parameters to obtain a temperature field on each time-space node in the medium-low mature shale in-situ conversion geological model; the method comprises the steps of (1) obtaining a dynamic hydrocarbon generation process, (2) obtaining a hydrocarbon generation kinetic parameter, (3) obtaining a total energy output, (5) obtaining a total energy input in a heating process, and (6) calculating an energy consumption ratio (ER), and carrying out economic feasibility evaluation of a shale in-situ conversion technology. The method can calculate a dynamic hydrocarbon generation process at any time and position in a shale bed in real time, and obviously improves the prediction precision of the hydrocarbon generation amount.

Description

Technical Field

[0001] The present invention relates to a method and system for evaluating the economy of in-situ conversion of medium-low maturity shale, belonging to the technical field of shale oil development. Background Art

[0002] The in-situ conversion technology of medium-low maturity shale is a technical means of heating the effective shale section by using horizontal wells or vertical wells, so that the kerogen and retained oil in the shale are cracked into light oil and natural gas and developed. After being tested by pilot tests at home and abroad, its technical feasibility has been recognized by the academic and industrial circles. However, due to the huge energy consumption in the heating process of this technology, its economic feasibility remains to be discussed. The in-situ conversion technology of medium-low maturity shale involves many aspects such as geology, geophysics, and geological engineering, and requires integrated geological-engineering consideration to establish a scientific and reasonable economic feasibility evaluation method.

[0003] The existing research mainly focuses on solving the problem of how to have better heating efficiency and greater oil and gas production under the deployment of heating and production well patterns, lacking the consideration of energy input and time scale in the heating process. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention proposes a method for evaluating the economy of in-situ conversion of medium-low maturity shale; Based on numerical simulation, through the coupling of hydrocarbon generation kinetics and solid heat transfer, the dynamic hydrocarbon generation process of in-situ conversion of medium-low maturity shale is simulated. From the perspective of energy input and output, the energy consumption ratio is used to characterize the economic feasibility of this technology.

[0005] Based on the principle of energy conservation, the present invention conducts numerical simulation on the in-situ conversion technology of medium-low maturity shale. By quantitatively calculating the energy output (the energy contained in the produced oil and gas) and energy input (the energy consumption for kerogen pyrolysis and environmental heat loss, that is, the synchronous heat absorption and energy consumption of the surrounding rock, shale minerals, and water molecules) in the process of in-situ conversion of medium-low maturity shale, the energy consumption ratio is used to characterize the economic feasibility of this technology. First, a solid heat transfer model for in-situ shale conversion is constructed. Based on the thermal physical parameters such as the thermal conductivity and specific heat capacity of shale, the dynamic distribution characteristics of the temperature field in the geological body during the heating process are simulated. Based on open / closed system thermal simulation experiments, the hydrocarbon generation kinetic parameters for the primary and secondary cracking of organic matter to generate oil and gas are obtained through calibration of the hydrocarbon generation kinetic model. The solid heat transfer model and the hydrocarbon generation kinetic model are coupled to realize the simulation of the dynamic hydrocarbon generation process of shale during the heating process, and the hydrocarbon generation amount at each time node in the shale is calculated. On this basis, combined with the output amount and calorific value of the oil and gas components, the energy contained in the produced oil and gas is calculated; the energy consumption is calculated based on the average activation energy of kerogen cracking and the change in the temperature field during the heating process of shale and the surrounding rock; finally, the energy consumption ratio (total energy obtained / total energy consumed) is constructed to provide a scientific basis for the economic feasibility evaluation of the in-situ shale conversion technology.

[0006] The present invention also provides a system for evaluating the economic feasibility of in-situ conversion of medium-low maturity shale.

[0007] The technical solution of the present invention is as follows: A method for evaluating the economic feasibility of in-situ conversion of medium-low maturity shale, comprising: 1) Establishing a geological model for in-situ conversion of medium-low maturity shale and assigning relevant geochemical and thermophysical parameters; 2) Based on the law of conservation of energy and Fourier's law of heat conduction, constructing a three-dimensional heat conduction equation and setting definite solution conditions, and solving the three-dimensional heat conduction equation in combination with thermophysical parameters to obtain the temperature field at each space-time node in the geological model of in-situ conversion of medium-low maturity shale; 3) Using open / closed system thermal simulation experiments to obtain the temperature-conversion curves of primary and secondary cracking of kerogen, and calibrating them with a hydrocarbon generation kinetic model to obtain hydrocarbon generation kinetic parameters: activation energy, pre-exponential factor, and reaction fraction; 4) Coupling the hydrocarbon generation kinetic model with the temperature field to calculate the kerogen hydrocarbon generation conversion rate at any space-time node in the geological model of in-situ conversion of medium-low maturity shale, further calculating the oil and gas production, and then multiplying them by the corresponding calorific values respectively to obtain the total energy output; 5) Calculating the energy consumption for kerogen cracking based on the average activation energy or bond energy difference of kerogen cracking; calculating the environmental heat loss based on the change in the temperature field during the heating process of shale and its surrounding rocks; summing the energy consumption for kerogen cracking and the environmental heat loss to obtain the total energy input during the heating process; 6) Combining the total energy input and the total energy output, further calculating the energy consumption ratio ER, and using the energy consumption ratio ER as an index to evaluate the economic feasibility of the in-situ conversion technology of shale.

[0008] Preferably according to the present invention, for horizontal well electric heating, a geological model for in-situ conversion of horizontal well electric heating is established, including: In the geological model for in-situ conversion of horizontal well electric heating, shale is in the middle, and the surrounding rocks are above and below. The wellbore radius is r, and the well spacing between the production well and the heating well is d; Four models of three-well heating, four-well heating, six-well heating, and well pattern heating are established respectively; Preferably according to the present invention, based on the law of conservation of energy and Fourier's law of heat conduction, for the heat conduction process of shale layers and surrounding rock layers, the following control equations, namely three-dimensional heat conduction equations, are established respectively: For the shale layer region, i.e., -y1 < y < y1: (1); For the surrounding rock layer region, i.e., y1 < y < y2 or -y2 < y < -y1: (2); Where: ρ iis the material density, kg / m³; k i is the material thermal conductivity, W / (m·K); c pi is the specific heat capacity, J / (kg·K); T i is the temperature field function, °C; i = 1 for the shale layer, i = 2 for the surrounding rock layer; Based on the constructed geological model, the following definite solution conditions are determined: Initial condition: (3); In the formula, is the reference temperature at the surface, °C; G is the geothermal gradient; h is the depth from the surface, m, refers to the initial temperature of the formation, that is, the temperature at the point (x, y, z) in the geological model before artificial heating; Boundary conditions, including the following: A. Heating wellbore boundary: The area near the heating well, that is The temperature is constant at the heat source temperature: (4); In the formula, is the wellbore radius, m; is the heating temperature, °C; refers to the temperature at the point (x, y, z) in the geological model after artificial heating to time t; B. Lateral symmetry boundaries at x = -x1 and x = x1: (5); In the formula, x1 refers to the length of the heating well; C. Outer boundary of the surrounding rock: Assume that the outer boundary of the formation is an adiabatic boundary and the heat flux is zero; (6); Interface connection condition: At the interface between the shale and the surrounding rock, that is the conditions of temperature and heat flux density continuity are satisfied: (7); (8); Based on the geological model and its geochemical and thermal physical parameters, using the COMSOL Multiphysics numerical simulation platform, setting the initial conditions, boundary conditions and interface connection conditions, solving the three-dimensional heat conduction equation, the temperature T(x, y, z) at any point (x, y, z) in the geological model at time t can be obtained, so as to obtain the temperature field in the formation, that is, the temperature field at each space-time node in the in-situ conversion geological model of medium-low maturity shale.

[0009] Preferably according to the present invention, the process for obtaining hydrocarbon generation kinetic parameters is as follows: The parallel first-order reaction model assumes that the hydrocarbon generation process of kerogen includes N parallel first-order reactions, and the activation energy corresponding to each parallel first-order reaction is E i , and the pre-exponential factor is A i , and it is assumed that the reaction fraction corresponding to each parallel first-order reaction is X io , i = 1, 2, 3, … N. At a certain reaction time t, the hydrocarbon generation amount of the i-th parallel first-order reaction is , then there is: (9); (10); In the formula, K i is the reaction rate constant of the i-th kerogen hydrocarbon generation reaction; R is the gas constant; T is the absolute temperature, K; When the open / closed system thermal simulation experiment is heated at a constant rate; (11); wherein, D is the heating rate; Combining the above formula, we get: (12); Integrating the above formula from T0→T, the hydrocarbon generation amount of the i-th reaction is obtained : (13); The total hydrocarbon generation amount of N parallel first-order reactions is: (14); By simulating the primary cracking and secondary cracking processes of kerogen through open-system and closed-system thermal simulation experiments respectively, the hydrocarbon generation amounts within each temperature range and the total hydrocarbon generation amount are obtained, and then the hydrocarbon generation conversion rate of kerogen at each temperature point is calculated; using the temperature and the corresponding hydrocarbon generation conversion rate data of kerogen as input data, and using the pyrolysis kinetic parameter calibration module in TMMI for parameter calibration, that is, the activation energy E i , the pre-exponential factor A i , and the reaction fraction X io are obtained.

[0010] Preferably according to the present invention, the hydrocarbon generation kinetic model is coupled with the temperature field to obtain the hydrocarbon generation conversion rate XH(x,y,z,t) of kerogen at the t moment of any spatio-temporal node (x, y, z) in the in-situ conversion geological model of medium-low maturity shale, and further calculate the amounts of oil and gas generated, and then multiply them by the corresponding calorific values respectively, that is, the total energy output is obtained E out ; including: Heat for time t, and the kerogen hydrocarbon generation conversion rate XH(x, y, z, t) at time t for any space-time node (x, y, z): (15); In the formula, H is any one of the four reaction types KO, KG, OG, and NG; for each reaction type, NH is the number of corresponding parallel first-order reactions, and the activation energy corresponding to each reaction is EH i , and the pre-exponential factor is AH i , and the original hydrocarbon generation potential of kerogen for each reaction is XH i0 , i = 1, 2, 3, ……, NH ; The net oil generation in shale is the difference between the oil generated by kerogen cracking and the oil consumed by gas generation from oil: (16); The net gas generation in shale is the sum of the gas generated by kerogen cracking and the gas generated from oil: (17); In the formula: ρ is the rock density, kg / m 3 ; TOC is the total organic carbon content of the rock; HI is the hydrocarbon generation potential of organic matter, mg / g·TOC -1 ; r O、 r G is the proportion of the oil and gas parts generated by kerogen; X KO , X KG、 X OG are the kerogen oil generation conversion rate, the kerogen gas generation conversion rate, and the liquid hydrocarbon cracking conversion rate respectively; n is the proportion of oil participating in cracking; The total energy output during in-situ heating of shale: (18); In the formula, m o 、m g are the masses of the generated oil and gas, g respectively; M o ，M g are the molar masses of oil and gas, g / mol respectively; q oil is the calorific value per mole of oil; q oil is the calorific value per mole of natural gas.

[0011] Preferably according to the present invention, the total energy input E during the heating process in The calculation process is as follows: From the perspective of the product, the energy consumption E for the bond breakage of kerogen K is obtained by multiplying the molar masses of the oil and gas generated by the cracking of kerogen by the activation energy required for the generation of unit molar mass of oil and gas: (19); In the formula: m o , m g , m ng are the masses of the oil, hydrocarbon gas, and non-hydrocarbon gas generated by the cracking of kerogen, respectively, in g; M o , M g , M ng are the molar masses of the oil, hydrocarbon gas, and non-hydrocarbon gas, respectively, in g / mol; E KO , E KG , E NG are the average activation energies for the generation of oil, hydrocarbon gas, and non-hydrocarbon gas from kerogen, respectively, in KJ / mol; (20); (21); In the formula: is the mass of the bond-breaking kerogen in the shale layer, in g; 0.84 is the conversion coefficient between TOC and kerogen; M k is the molar mass of kerogen, in g / mol; q k is the energy consumed for the bond breakage of each mole of kerogen, in KJ / mol; Environmental heat loss, that is, the synchronous heat absorption and energy consumption of rock minerals and water molecules in the shale and surrounding rocks Er， is the total heat absorbed by the shale and surrounding rocks in the geological model from the initial temperature to the pyrogenic temperature field: (22); In the formula: , are the specific heat capacities of the shale and surrounding rocks, respectively, in J / (kg·K); , are the densities of the shale and surrounding rocks, respectively, in kg / m 3 ; , which are the temperature change amounts of the shale and the surrounding rock heated to time t, in K; Assume that during the heating process, electrical energy is completely converted into the energy consumption for kerogen cracking and environmental heat loss. Then the total energy input during the in-situ conversion process is: (23).

[0012] According to the preference of the present invention, the energy consumption ratio ER is calculated; (24); In the formula, γ is the recovery rate.

[0013] According to the preference of the present invention, taking the energy consumption ratio ER as an index, an economic feasibility evaluation of the shale in-situ conversion technology is carried out; including: when the energy consumption ratio ER > 1, it has economic feasibility; otherwise, it does not have economic feasibility.

[0014] A system for evaluating the economy of in-situ conversion of medium-low maturity shale includes: A geological model establishment module, configured to: establish a geological model for in-situ conversion of medium-low maturity shale and assign relevant geochemical and thermophysical parameters; A temperature field calculation module, configured to: based on the law of conservation of energy and Fourier's law of heat conduction, construct a three-dimensional heat conduction equation and set the definite solution conditions, and solve the three-dimensional heat conduction equation in combination with the thermophysical parameters to obtain the temperature field at each space-time node in the geological model for in-situ conversion of medium-low maturity shale; A hydrocarbon generation kinetic parameter calculation module, configured to: use open / closed system thermal simulation experiments to obtain the temperature-conversion rate curves of primary and secondary cracking of kerogen, and calibrate them through a hydrocarbon generation kinetic model to obtain hydrocarbon generation kinetic parameters: activation energy, pre-exponential factor, reaction fraction; A total energy output calculation module, configured to: couple the hydrocarbon generation kinetic model with the temperature field, calculate the kerogen hydrocarbon generation conversion rate at any space-time node in the geological model for in-situ conversion of medium-low maturity shale, further calculate the oil and gas production, and then multiply them by the corresponding calorific values respectively to obtain the total energy output; A total energy input module, configured to: obtain the energy consumption for kerogen cracking based on the average activation energy or bond energy difference of kerogen cracking; calculate the environmental heat loss based on the temperature field change amount during the heating process of the shale and the surrounding rock; sum up the energy consumption for kerogen cracking and the environmental heat loss to obtain the total energy input during the heating process; An economic feasibility evaluation module, configured to: combine the total energy input and the total energy output, further calculate the energy consumption ratio ER, and take the energy consumption ratio ER as an index to carry out an economic feasibility evaluation of the shale in-situ conversion technology.

[0015] The beneficial effects of the present invention are: 1. The hydrocarbon generation kinetics model is dynamically coupled with the three-dimensional temperature field to construct an integrated simulation framework of geology-solid heat transfer-hydrocarbon generation kinetics, which can calculate the dynamic hydrocarbon generation process at any time and position within the shale layer in real time, significantly improving the accuracy of hydrocarbon generation prediction.

[0016] 2. Based on the law of conservation of energy, quantitatively calculate the energy input during the in-situ heating transformation process and the energy contained in the produced oil and gas, and scientifically evaluate the economic feasibility of the in-situ conversion technology for medium-low maturity shale from the perspective of energy consumption ratio. Brief Description of the Drawings

[0017] Figure 1 It is the flow chart of the economic evaluation method for in-situ conversion of medium-low maturity shale of the present invention; Figure 2 It is the schematic diagram of the geological model for in-situ conversion by horizontal well electric heating; Figure 3 It is the schematic diagram of well layout; Figure 4 It is the graph showing the relationship between the average kerogen hydrocarbon generation conversion rate in shale and time; Figure 5 It is the graph showing the relationship between the average temperature of shale and heating time; Figure 6 It is the graph showing the relationship between energy consumption ratio and heating time (TOC = 15%); Figure 7 It is the graph showing the relationship between energy consumption ratio and easyRo during heating of shale with different TOC contents (well pattern - 5m - 600°C). Detailed Embodiments

[0018] The present invention will be further defined below in conjunction with the drawings of the specification and embodiments, but not limited thereto.

[0019] Term Explanation: 1. Open system (PY-GC / Rock-Eval) and closed system (gold tube) thermal simulation experiments: The hydrocarbon generation thermal simulation experiment of source rocks is an experimental method that uses the "time-temperature complementarity" principle to simulate the thermal evolution and hydrocarbon generation process of organic matter under geological conditions.

[0020] In the open system thermal simulation experiment, in a high-temperature and high-pressure reaction vessel, the kinetic energy is provided by the carrier gas (nitrogen or inert gas) or the power generated by hydrocarbon generation pressurization, so that the products generated by the reaction are directly transported to the supporting instruments for geochemical analysis. Commonly used analytical instruments include rock pyrolysis instrument (Rock-Eval), pyrolysis gas chromatography (PY-GC), etc. The open system experiment can better reflect the relationship between temperature and different products, and has the advantages of fast analysis speed and low experimental cost. The disadvantage is that the influence of pressure and water on the reaction process cannot be considered during the experiment, and it can be used for the study of the primary cracking of source rocks.

[0021] Closed systems can explore the effects of factors such as pressure and formation water on the thermal evolution process of hydrocarbon generation during the hydrocarbon generation process of organic matter. Commonly used experimental equipment includes quartz tubes, gold tubes, and MSSV, which can be used to study phenomena such as secondary cracking and continuous hydrocarbon generation of source rocks, and are applicable to research such as hydrocarbon generation kinetics and isotope simulation.

[0022] 2. Parallel first-order reaction model: During the cracking process of kerogen, reactions occur simultaneously through multiple different and independent reaction paths, and each reaction path is a parallel first-order reaction.

[0023] Example 1 A method for evaluating the economic feasibility of in-situ conversion of medium-low maturity shale includes: 1) Establish a geological model for in-situ conversion of medium-low maturity shale and assign relevant geochemical (total organic carbon TOC, hydrogen index HI) and thermophysical parameters (thermal conductivity k , specific heat capacity c, thermal diffusivity K); 2) Based on the law of conservation of energy and Fourier's law of heat conduction, construct a three-dimensional heat conduction equation and set the definite solution conditions, and solve the three-dimensional heat conduction equation in combination with the thermophysical parameters to obtain the temperature field at each space-time node in the geological model of in-situ conversion of medium-low maturity shale; 3) Use open / closed system thermal simulation experiments to obtain the temperature-conversion rate curves of primary and secondary cracking of kerogen, and calibrate them with a hydrocarbon generation kinetics model to obtain hydrocarbon generation kinetics parameters: activation energy E i , pre-exponential factor A i , reaction fraction X io ; 4) Couple the hydrocarbon generation kinetics model with the temperature field to calculate the kerogen hydrocarbon generation conversion rate XH(x, y, z, t) at any space-time node (x, y, z) at time t in the geological model of in-situ conversion of medium-low maturity shale, further calculate the oil and gas production, and then multiply by the corresponding calorific values to obtain the total energy output Eout ; 5) Calculate the energy consumption E k for kerogen cracking based on the average activation energy or bond energy difference of kerogen cracking; calculate the environmental heat loss Er based on the change in the temperature field during the heating process of shale and its surrounding rocks; sum the energy consumption of kerogen cracking and the environmental heat loss to obtain the total energy input E in during the heating process; 6) Combine the total energy input and the total energy output, and further calculate the energy consumption ratio ER, and use the energy consumption ratio ER as an index to evaluate the economic feasibility of the shale in-situ conversion technology.

[0024] Example 2 According to the method for evaluating the economic feasibility of in-situ conversion of medium-low maturity shale described in Example 1, the difference is: Based on the principle of energy conservation, this invention conducts numerical simulations on the in-situ conversion technology of medium-low maturity shale. By quantitatively calculating the energy output and energy input during the in-situ conversion of medium-low maturity shale, the energy consumption ratio is used to characterize the economic feasibility of this technology, and the realization is carried out according to the process as Figure 1 , and the specific implementation steps are as follows: For horizontal well electric heating, establish a geological model for in-situ conversion of horizontal well electric heating; including: As Figure 2 shown, taking the starting point of the oil production well at the center of the shale as the origin, the positive directions of the x and y axes are as shown respectively, and the positive direction of the z axis is the extension direction of the horizontal well. The horizontal length of the heating well is L. Taking six-well heating as an example, the middle is shale, the upper and lower are surrounding rocks. Horizontal wells are drilled in the shale, and the six surrounding wells are heated while oil is produced in the middle. In the geological model for in-situ conversion of horizontal well electric heating, the middle is shale, the upper and lower are surrounding rocks, the wellbore radius is r, and the well spacing between the oil production well and the heating well is d;

[0025] Establish four models of three-well heating, four-well heating, six-well heating, and well pattern heating respectively (attached Figure 2 ); On the basis of constructing the geometric model, relevant thermophysical properties of the rock need to be input, such as specific heat capacity (c), thermal conductivity ( k ), and thermal diffusivity (K) under different temperature conditions, which can be measured by a laser thermal conductivity meter. In addition, the thermal diffusivity and thermal conductivity are anisotropic. Due to the development of microscopic laminations in shale, its thermal conductivity in the horizontal direction is usually higher than that in the vertical direction, and sandstone also has the same property. The detailed modeling data are shown in Table 1 and Table 2.

[0026] Table 1 Parameters related to simulation calculation;

[0027] Table 2 Thermophysical properties of rocks;

[0028] When the temperature distribution inside an object is uneven, the process of heat flowing from high temperature to low temperature regions (T is a function of space and time). According to the law of conservation of energy and Fourier's law of heat conduction, for the heat conduction processes of the shale layer and the surrounding rock layer, the following control equations, namely three-dimensional heat conduction equations, are established respectively: For the shale layer region, i.e., -y1 < y < y1: (1); For the surrounding rock layer region, i.e., y1 < y < y2 or -y2 < y < -y1: (2); In the formula: ρ i is the material density, kg / m³; ki is the thermal conductivity of the material, W / (m·K); c pi is the specific heat capacity, J / (kg·K); T i is the temperature field function, °C; i = 1 for the shale layer, i = 2 for the surrounding rock layer; This equation can characterize the change of temperature with time in three-dimensional space.

[0029] Based on the constructed geological model, the following definite solution conditions are determined: Initial condition: (3); In the formula, is the reference temperature on the ground surface, °C; G is the geothermal gradient, which is 0.033 °C / m; h is the depth from the ground surface, m, refers to the initial temperature of the formation, that is, the temperature at the point (x, y, z) in the geological model before artificial heating; Boundary conditions, including the following: A. Heating wellbore boundary (heat source): The area near the heating well, that is the temperature is constant at the heat source temperature: (4); In the formula, is the wellbore radius, m; is the heating temperature, °C; refers to the temperature at the point (x, y, z) in the geological model after artificial heating to time t; B. Lateral symmetry boundaries at x = -x1 and x = x1: Due to the symmetry of the model, there is no heat flow passing through both sides: (5); In the formula, x1 refers to the length of the heating well; C. Outer boundary of the surrounding rock: Assume that the outer boundary of the formation is an adiabatic boundary and the heat flow is zero; that is, when the thickness of the surrounding rock is large enough, the top and bottom interfaces are not affected by the artificial thermal field: (6); Interface connection condition: At the interface between the shale and the surrounding rock, that is the conditions of temperature and heat flux density continuity are satisfied: (7); (8); Based on the geological model and its geochemical and thermal physical parameters, using the COMSOL Multiphysics numerical simulation platform, setting the initial conditions, boundary conditions, and interface connection conditions, and solving the three-dimensional heat conduction equation, the temperature T(x, y, z) at any point (x, y, z) in the geological model at time t can be obtained, thereby obtaining the temperature field in the formation, that is, the temperature field at each space-time node in the in-situ conversion geological model of medium-low maturity shale. As Figure 4 shown. The more heating wells, the smaller the well spacing, and the higher the heating temperature, the shorter the time required for kerogen to reach the same hydrocarbon generation conversion rate.

[0030] The process of obtaining the hydrocarbon generation kinetic parameters is as follows: The parallel first-order reaction model assumes that the hydrocarbon generation process of kerogen includes a series of N parallel first-order reactions, and the activation energy corresponding to each parallel first-order reaction is E i , and the pre-exponential factor is A i , and it is assumed that the reaction fraction corresponding to each parallel first-order reaction is X io , i = 1, 2, 3,... N. At a certain reaction time t, the hydrocarbon generation amount of the i-th parallel first-order reaction is , then there is: (9); (10); In the formula, K i is the reaction rate constant of the i-th kerogen hydrocarbon generation reaction; R is the gas constant, 8.31441 J / (mol·K); T is the absolute temperature, K; When the open / closed system thermal simulation experiment (or geological conditions) is heated at a constant rate; (11); Among them, D is the heating rate; Combining the above formula, we get: (12); Integrating the above formula from T0→T, the hydrocarbon generation amount of the i-th reaction is obtained : (13); The total hydrocarbon generation amount of N parallel first-order reactions is: (14); By means of open-system (PY-GC / Rock-Eval) and closed-system (gold tube) pyrolysis experiments, the primary and secondary cracking processes of kerogen are simulated respectively to obtain the hydrocarbon generation amounts in each temperature range and the total hydrocarbon generation amount, and further calculate the hydrocarbon generation conversion rate of kerogen at each temperature point. Taking the temperature and the corresponding hydrocarbon generation conversion rate data of kerogen as input data, the pyrolysis kinetic parameter calibration module in TMMI (in-situ pyrolysis kinetics software for oil shale) is used for parameter calibration, that is, the activation energy E i , the pre-exponential factor A i , and the reaction fraction X io are obtained.

[0031] As shown in Table 3 and Table 4: Table 3 Hydrocarbon generation kinetic parameters;

[0032] Table 4 Hydrocarbon generation kinetic parameters;

[0033] Couple the hydrocarbon generation kinetic model with the temperature field to obtain the hydrocarbon generation conversion rate XH(x, y, z, t) of kerogen at time t at any spatio-temporal node (x, y, z) in the in-situ conversion geological model of medium-low maturity shale, further calculate the amounts of oil and gas generated, and then multiply by the corresponding calorific values respectively to obtain the total energy output E out ; including: The hydrocarbon generation conversion rate XH(x, y, z, t) of kerogen at time t at any spatio-temporal node (x, y, z) after heating for t time: (15); In the formula, H is any one of the four reaction types of KO (kerogen to oil), KG (kerogen to gas), OG (oil cracking to gas), and NG (kerogen to non-hydrocarbon gas); for each reaction type, NH is the number of parallel first-order reactions corresponding, and the activation energy corresponding to each reaction is EH i , the pre-exponential factor is AH i , the original hydrocarbon generation potential of kerogen for each reaction is XH i0 , i=1, 2, 3, ……, NH ; The net oil generation amount of shale is the difference between the oil generation amount from kerogen cracking and the oil consumption for oil to gas conversion: (16); The net gas generation amount of shale is the sum of the gas generation amount from kerogen cracking and the gas generation amount from oil: (17); Wherein: ρ is the rock density, kg / m 3 ; TOC is the total organic carbon content of the rock; HI is the hydrocarbon generation potential of the organic matter, mg / g·TOC -1 ; r O、 r G are the proportions of the oil- and gas-generating parts of kerogen, taking 85% and 15% respectively, determined from the data of the gold tube thermal simulation experiment; X KO and X KG、 X OG are the oil-generation conversion rate of kerogen, the gas-generation conversion rate of kerogen, and the liquid hydrocarbon cracking conversion rate respectively; n is the proportion of oil and gas participating in cracking, taking 50%; Total energy output during in-situ heating of shale: (18); Wherein, m o 、m g are the masses of the generated oil and gas, g respectively; M o ，M g are the molar masses of oil and gas, g / mol respectively; q oil is the calorific value per mole of oil, 7233.84 KJ / mol; q oil is the calorific value per mole of natural gas, 890.3 KJ / mol.

[0034] Total energy input E during the heating process in The calculation process is as follows: Starting from the perspective of the products, the energy consumption E for the bond breaking of kerogen K is obtained by multiplying the molar masses of the oil and gas (hydrocarbon gas and non-hydrocarbon gas) generated by the cracking of kerogen by the activation energy required for the generation of unit molar mass of oil and gas: (19); Wherein: m o and m g and m ng are the masses of the oil, hydrocarbon gas, and non-hydrocarbon gas generated by the cracking of kerogen, g respectively; M o and M g and Mng are the molar masses of oil, hydrocarbon gas, and non-hydrocarbon gas, respectively, in g / mol; E KO , E KG , E NG are the average activation energies of kerogen oil generation, hydrocarbon gas, and non-hydrocarbon gas, respectively, in KJ / mol; From the perspective of reactants, based on the chemical reaction equation of kerogen cracking, the energy consumption for bond breaking per unit molar mass of kerogen is determined, and by multiplying it by the amount of substance of the bond-breaking kerogen, the energy consumption for kerogen bond breaking (E K ) can be obtained. <![CDATA[

[0035] ]]>The energy consumption for kerogen cracking (E K ) is the product of the energy consumption for bond breaking per unit molar mass of kerogen and the amount of kerogen cracking during the heating process; <![CDATA[ ]]> (20); <![CDATA[ ]]> (21); In the formula: is the mass of the bond-breaking kerogen in the shale layer, in g; 0.84 is the conversion coefficient between TOC and kerogen; M k is the molar mass of kerogen, in g / mol; q k is the energy required to break bonds per mole of kerogen, in KJ / mol; The environmental heat loss, that is, the synchronous heat absorption and energy consumption of rock minerals and water molecules in the shale and surrounding rocks Er， is the total heat absorbed by the shale and surrounding rocks in the geological model from the initial temperature to the pyrogenic temperature field: <![CDATA[ ]]> (22); In the formula: , are the specific heat capacities of the shale and surrounding rocks, respectively, in J / (kg·K); , are the densities of the shale and surrounding rocks, respectively, in kg / m 3 ; , are the temperature change amounts of the shale and surrounding rocks at time t during heating, respectively, in K; Assume that during the heating process, electrical energy is completely converted into the energy consumption for kerogen cracking and environmental heat loss, and the energy loss in the actual electric heating process is not considered for the time being. Then the total energy input during the in-situ conversion process: <![CDATA[ ]]> (23). <![CDATA[

[0036] ]]>Calculate the energy consumption ratio ER; Through the above calculations, the magnitudes of the energy consumed and obtained during the shale heating process are clarified, and the energy consumption ratio ER can be further calculated as follows: (24); In the formula, γ is the recovery rate, which represents the proportion of the actually recoverable oil and gas in the total generated oil and gas, and is taken as 65%.

[0037] Taking the energy consumption ratio ER as an index, the economic feasibility of the in-situ shale conversion technology is evaluated, including Theoretically, from an energy perspective, when the energy consumption ratio ER > 1, it is economically feasible; and the higher the ER, the higher the energy efficiency. However, the current method does not consider engineering costs, such as drilling, equipment, environmental protection, etc. (lack of corresponding data). Generally speaking, under the condition of considering engineering costs, when the energy consumption ratio ER ≥ 3, large-scale implementation can be carried out to spread the costs and achieve economically viable development. Otherwise, it is not economically feasible.

[0038] Figure 3 It is a schematic diagram of the well layout in the geological model. In the heating of three wells, four wells, and six wells, d is the distance between the heating well and the oil production well; in the well pattern, d is the distance between the heating wells. According to the above calculation method and parameters, the energy consumption ratios at each time node during the in-situ heating process are calculated for different well layouts, well spacings, and heating temperatures when TOC = 15%, so as to determine which well layout and heating conditions are more economical. The results are shown in Table 5 Figure 5 As shown. The more heating wells, the smaller the well spacing, and the higher the heating temperature, the faster the temperature field changes, and the shorter the time required for kerogen to reach the same hydrocarbon generation conversion rate.

[0039] Table 5 Calculation results of energy consumption ratio

[0040] According to the above calculation method and parameters, the energy consumption ratios, average shale temperatures, and easyRo at each time node are calculated respectively under the conditions of well pattern heating, well spacing of 5 m, and heating temperature of 600 °C when TOC = 5 / 10 / 15 / 20%, and an intersection diagram is drawn to further determine the average shale temperature and the corresponding thermal maturity interval when the economy is optimal. The results are as Figure 6 shown. As the heating time increases, the energy consumption ratio generally shows a trend of first increasing and then decreasing. From the heating of three wells, four wells, and six wells to well pattern heating, the maximum energy consumption ratio increases successively, and the time required to reach the maximum energy consumption ratio is shorter; when the heating well temperature is 550 °C, the energy consumption ratio is the highest; reducing the well spacing of the heating wells slightly increases the energy consumption ratio, but significantly reduces the time to reach the maximum energy consumption ratio.

[0041] Figure 7Relationship diagram of energy consumption ratio and easyRo during heating of shales with different TOC contents (well pattern - 5m - 600°C). The higher the TOC content, the stronger the hydrocarbon generation ability of the shale. When reaching the highest energy consumption ratio, the required heating time is shorter and the degree of thermal evolution is lower. When heated to about 300 - 320°C, it has the highest energy consumption ratio, and the corresponding easyRo is about 0.8% - 1.2%.

[0042] Example 3 A system for evaluating the economic feasibility of in-situ conversion of medium-low maturity shale, comprising: A geological model establishment module, configured to: establish a geological model for in-situ conversion of medium-low maturity shale and assign relevant geochemical and thermophysical parameters; A temperature field calculation module, configured to: based on the law of conservation of energy and Fourier's law of heat conduction, construct a three-dimensional heat conduction equation and set the definite solution conditions, and solve the three-dimensional heat conduction equation in combination with the thermophysical parameters to obtain the temperature field at each space-time node in the geological model for in-situ conversion of medium-low maturity shale; A hydrocarbon generation kinetic parameter calculation module, configured to: use open / closed system thermal simulation experiments to obtain the temperature-conversion curves of kerogen primary and secondary cracking, and calibrate them with a hydrocarbon generation kinetic model to obtain hydrocarbon generation kinetic parameters: activation energy, pre-exponential factor, reaction fraction; A total energy output calculation module, configured to: couple the hydrocarbon generation kinetic model with the temperature field, calculate the kerogen hydrocarbon generation conversion rate at any space-time node in the geological model for in-situ conversion of medium-low maturity shale, further calculate the oil and gas production, and then multiply them by the corresponding calorific values respectively to obtain the total energy output; A total energy input module, configured to: obtain the energy consumption for kerogen cracking based on the average activation energy of kerogen cracking or the bond energy difference; calculate the environmental heat loss based on the change in the temperature field during the heating process of the shale and its surrounding rock; sum up the energy consumption for kerogen cracking and the environmental heat loss to obtain the total energy input during the heating process; An economic feasibility evaluation module, configured to: combine the total energy input and the total energy output, further calculate the energy consumption ratio ER, and use the energy consumption ratio ER as an indicator to evaluate the economic feasibility of the in-situ conversion technology of shale.

Claims

1. A method for evaluating the economy of in-situ conversion of medium-low maturity shale, characterized in that, Including: 1) Establish a geological model for in-situ conversion of medium-low maturity shale and assign relevant geochemical and thermophysical parameters; 2) Based on the law of conservation of energy and Fourier's law of heat conduction, construct a three-dimensional heat conduction equation and set the definite solution conditions, and solve the three-dimensional heat conduction equation in combination with the thermophysical parameters to obtain the temperature field at each space-time node in the geological model of in-situ conversion of medium-low maturity shale; 3) Use open / closed system thermal simulation experiments to obtain the temperature-conversion rate curves of kerogen primary and secondary cracking, and calibrate them with a hydrocarbon generation kinetic model to obtain hydrocarbon generation kinetic parameters: activation energy, pre-exponential factor, reaction fraction; 4) Couple the hydrocarbon generation kinetic model with the temperature field to calculate the hydrocarbon generation conversion rate of kerogen at any space-time node in the geological model of in-situ conversion of medium-low maturity shale, further calculate the oil and gas production, and then multiply by the corresponding calorific values respectively to obtain the total energy output; 5) Calculate the energy consumption for kerogen cracking based on the average activation energy or bond energy difference of kerogen cracking; calculate the environmental heat loss based on the change in the temperature field during the heating process of shale and its surrounding rocks; sum up the energy consumption for kerogen cracking and the environmental heat loss to obtain the total energy input during the heating process; 6) Combine the total energy input and the total energy output, further calculate the energy consumption ratio ER, and use the energy consumption ratio ER as an index to evaluate the economic feasibility of the in-situ conversion technology of shale.

2. The economic evaluation method for in-situ conversion of medium and low maturity shale according to claim 1, wherein For horizontal well electric heating, establish a geological model for in-situ conversion of horizontal well electric heating; including: In the geological model of in-situ conversion of horizontal well electric heating, the middle is shale, the upper and lower are surrounding rocks, the wellbore radius is r, and the well spacing between the production well and the heating well is d; Establish four models of three-well heating, four-well heating, six-well heating, and well pattern heating respectively.

3. The in-situ conversion economic evaluation method for medium-low maturity shale according to claim 1, characterized in that, According to the law of conservation of energy and Fourier's law of heat conduction, for the heat conduction process of the shale layer and the surrounding rock layer, establish the following control equations, namely the three-dimensional heat conduction equation: Shale layer area, i.e., -y1 < y < y1: （1）； Surrounding rock layer area, i.e., y1 < y < y2 or -y2 < y < -y1: （2）； Where: ρ i is the material density, kg / m³; k i is the material thermal conductivity, W / (m·K); c pi is the specific heat capacity, J / (kg·K); T i is the temperature field function, °C; i = 1 for the shale layer, i = 2 for the surrounding rock layer; Based on the constructed geological model, determine the following definite solution conditions: Initial condition: （3）； In the formula, is the surface reference temperature, in °C; G is the geothermal gradient; h is the depth from the surface, in m, refers to the initial formation temperature, that is, the temperature at the point (x, y, z) in the geological model before artificial heating; Boundary conditions, including the following: A. Heating wellbore boundary: The area near the heating well is where the temperature is constantly the heat source temperature: （4）； In the formula, is the wellbore radius, in m; is the heating temperature, in °C; refers to the temperature at the point (x, y, z) in the geological model at time t after artificial heating; B. When the lateral symmetric boundaries are x = -x1 and x = x1: （5）； In the formula, x1 refers to the length of the heating well; C. Outer boundary of the surrounding rock: Assume that the outer boundary of the formation is an adiabatic boundary and the heat flux is zero; （6）； Interface connection condition: At the interface between the shale and the surrounding rock, namely the conditions of temperature and heat flux density continuity are satisfied: （7）； （8）； Based on the geological model and its geochemical and thermophysical parameters, use the COMSOL Multiphysics numerical simulation platform to set the initial conditions, boundary conditions, and interface connection conditions, solve the three-dimensional heat conduction equation, and obtain the temperature T(x, y, z) at any point (x, y, z) in the geological model at time t, so as to obtain the temperature field in the formation, that is, the temperature field at each space-time node in the geological model of in-situ conversion of medium-low maturity shale.

4. The in-situ conversion economic evaluation method for medium-low maturity shale according to claim 1, characterized in that The process of obtaining hydrocarbon generation kinetic parameters is as follows: The parallel first-order reaction model assumes that the kerogen hydrocarbon generation process includes N parallel first-order reactions, and the activation energy corresponding to each parallel first-order reaction is E i , and the pre-exponential factor is A i . It is also assumed that the reaction fraction corresponding to each parallel first-order reaction is X io , i = 1, 2, 3, … N. At a certain reaction time t, the hydrocarbon generation amount of the i-th parallel first-order reaction is . Then we have: （9）； （10）； where K i is the reaction rate constant of the hydrocarbon generation reaction of the i-th kerogen; R is the gas constant; T is the absolute temperature, K; When the open / closed system thermal simulation experiment is heating at a constant rate; （11）； Among them, D is the heating rate; Combined with the above formula, we get: （12）； Integrating the above formula from T0 to T gives the hydrocarbon generation amount of the i-th reaction : （13）； The total hydrocarbon generation amount of N parallel first-order reactions is: （14）； The primary cracking and secondary cracking processes of kerogen are simulated through open-system and closed-system thermal simulation experiments respectively to obtain the hydrocarbon generation amounts in each temperature range and the total hydrocarbon generation amount, and then the hydrocarbon generation conversion rate of kerogen at each temperature point is calculated. The temperature and the corresponding hydrocarbon generation conversion rate data of kerogen are used as input data, and the pyrolysis kinetic parameter calibration module in TMMI is used for parameter calibration, that is, the activation energy E i , the pre-exponential factor A i , and the reaction fraction X io are obtained.

5. The in-situ conversion economic evaluation method for medium-low maturity shale according to claim 1, wherein, Couple the hydrocarbon generation kinetics model with the temperature field to obtain the kerogen hydrocarbon generation conversion rate XH(x, y, z, t) at any space-time node (x, y, z) at time t within the in-situ conversion geological model of medium- to low-maturity shale. Further calculate the oil and gas production, and then multiply by the corresponding calorific values respectively to obtain the total energy output E out ; Including: Heating for t time, the hydrocarbon generation conversion rate XH(x, y, z, t) of kerogen at the t moment of any space-time node (x, y, z): （15）； where H is any one of the four reaction types KO, KG, OG, and NG; for each reaction type, NH is the corresponding number of parallel first-order reactions, and the activation energy for each reaction is EH i , and the pre-exponential factor is AH i , and the original hydrocarbon generation potential of kerogen for each reaction is XH i0 , i = 1, 2, 3, ……, NH ; The net oil generation volume of shale is the difference between the oil generation volume by kerogen pyrolysis and the oil consumption volume for gas generation: （16）； The net gas generation volume of shale is the sum of the gas generation volume by kerogen pyrolysis and the gas generation volume for oil generation: （17）； In the formula: ρ is the rock density, kg / m 3 ; TOC is the total organic carbon content of the rock; HI is the hydrocarbon generation potential of organic matter, mg / g·TOC -1 ; r O、 r G is the proportion of the oil- and gas-generating parts of kerogen; X KO and X KG、 X OG are the oil-generation conversion rate of kerogen, the gas-generation conversion rate of kerogen, and the cracking conversion rate of liquid hydrocarbons, respectively; n is the proportion of oil and gas participating in cracking; The total energy output during the in-situ heating process of shale: （18）； In the formula, m o 、m g are the masses of the generated oil and gas, respectively, in g; M o ，M g are the molar masses of the oil and gas, respectively, in g / mol; q oil is the calorific value per mole of oil; q oil is the calorific value per mole of natural gas.

6. The in-situ conversion economic evaluation method for medium-low maturity shale according to claim 1, wherein Total energy input E during the heating process in The calculation process is as follows: From the perspective of the product, the energy consumption E for the cleavage of chemical bonds in kerogen K is obtained by multiplying the molar mass of oil and gas generated by the cleavage of kerogen by the activation energy required for the generation of unit molar mass of oil and gas: （19）； In the formula: m o , m g , m ng are the masses of oil, hydrocarbon gas, and non-hydrocarbon gas generated by the cracking of kerogen, respectively, in g; M o , M g , M ng are the molar masses of oil, hydrocarbon gas, and non-hydrocarbon gas, respectively, in g / mol; E KO , E KG , E NG are the average activation energies of kerogen for oil generation, hydrocarbon gas generation, and non-hydrocarbon gas generation, respectively, in KJ / mol; （20）； （21）； In the formula: is the mass of broken - bond kerogen in the shale layer, g; 0.84 is the conversion coefficient between TOC and kerogen; M k is the molar mass of kerogen, g / mol; q k is the energy required to break the bonds per mole of kerogen, KJ / mol; Environmental heat loss, that is, the synchronous heat absorption and energy consumption of rock minerals and water molecules in shale and surrounding rocks Er， It is the sum of the heat absorbed by shale and surrounding rocks in the geological model when heated from the initial temperature to the pyrogenic temperature field: （22）； In the formula: , are the specific heat capacities of shale and surrounding rock respectively, J / (kg·K); , are the densities of shale and surrounding rock respectively, kg / m 3 ; are the temperature change amounts of shale and surrounding rock heated to time t respectively, K; Assume that during the heating process, electrical energy is completely converted into the energy consumption for kerogen pyrolysis and environmental heat loss. Then the total energy input during the in-situ conversion process: （23）。 7. The in-situ conversion economic evaluation method for medium-low maturity shale according to claim 1, wherein Calculate the energy consumption ratio ER; （24）； In the formula, γ is the recovery rate.

8. A method for evaluating the economy of in-situ conversion of medium-low maturity shale according to any one of claims 1-7, characterized in that, Taking the energy consumption ratio ER as an index, conduct an economic feasibility evaluation of the in-situ conversion technology of shale; including: when the energy consumption ratio ER > 1, it has economic feasibility; otherwise, it does not have economic feasibility.

9. A system for evaluating the economy of in-situ conversion of medium-low maturity shale, which is used to implement an economy evaluation method for in-situ conversion of medium-low maturity shale according to any one of claims 1-8, characterized in that, Including: The geological model establishment module is configured to: establish an in-situ conversion geological model of medium-low maturity shale and assign relevant geochemical and thermophysical parameters; The temperature field calculation module is configured to: based on the law of conservation of energy and Fourier's law of heat conduction, construct a three-dimensional heat conduction equation and set the definite solution conditions, and solve the three-dimensional heat conduction equation in combination with the thermophysical parameters to obtain the temperature field at each space-time node in the in-situ conversion geological model of medium-low maturity shale; The hydrocarbon generation kinetic parameter calculation module is configured to: use open / closed system thermal simulation experiments to obtain the temperature-conversion rate curves of the primary and secondary pyrolysis of kerogen, and calibrate them through the hydrocarbon generation kinetic model to obtain the hydrocarbon generation kinetic parameters: activation energy, pre-exponential factor, reaction fraction; The total energy output calculation module is configured to: couple the hydrocarbon generation kinetic model with the temperature field, calculate the hydrocarbon generation conversion rate of kerogen at any space-time node in the in-situ conversion geological model of medium-low maturity shale, further calculate the oil and gas generation volumes, and then multiply them by the corresponding calorific values respectively to obtain the total energy output; The total energy input module is configured to: obtain the energy consumption for kerogen pyrolysis based on the average activation energy or bond energy difference of kerogen pyrolysis; calculate the environmental heat loss based on the change in the temperature field during the heating process of shale and its surrounding rocks; sum up the energy consumption for kerogen pyrolysis and the environmental heat loss to obtain the total energy input during the heating process; The economic feasibility evaluation module is configured to: combine the total energy input and the total energy output, further calculate the energy consumption ratio ER, and take the energy consumption ratio ER as an index to conduct an economic feasibility evaluation of the in-situ conversion technology of shale.

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