A method for evaluating reservoir pressure field during in-situ heated shale oil extraction

Abstract

A method for evaluating the reservoir pressure field during in-situ heated shale oil extraction is applied in the petroleum development field. The method comprises the following steps: ① Constructing a three-dimensional grid model of the shale oil reservoir between two horizontal wells; ② Evaluating the porosity of each reservoir grid unit after compression based on the temperature field, porosity, and volumetric thermal expansion coefficient of the reservoir skeleton; ③ Evaluating the volume of each fluid in each reservoir grid unit under constant pore fluid pressure based on the reservoir temperature field, fluid saturation, fluid thermal expansion coefficient, and natural gas solubility characteristics in oil; ④ Evaluating the pore fluid pressure in each reservoir grid unit based on the compressibility coefficient of each fluid at the corresponding temperature, combined with the reduction in porosity and the volume of each fluid after thermal expansion, thereby obtaining the pressure field of the shale oil reservoir.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration and development technology, and to a method for evaluating the reservoir pressure field during in-situ heated extraction of shale oil. Background Technology

[0002] my country possesses enormous shale oil resource potential, but its extraction has not been entirely successful, primarily due to issues such as high investment costs, low production, and rapid decline in production per well during horizontal well volumetric fracturing. Numerous scholars both domestically and internationally have proposed technologies like in-situ heating and refining, and in-situ heating and conversion, for shale oil extraction. This involves in-situ heating of the underground shale oil reservoir (without bringing the reservoir to the surface) to reduce reservoir fluid viscosity, increase reservoir fluid pressure, create fractures to increase permeability, and potentially promote small-scale hydrocarbon generation from organic matter. This aims to increase shale oil well production and reduce extraction costs—essentially, reducing viscosity, increasing pressure, enhancing permeability, increasing volume, increasing production, and reducing costs. This method eliminates the need for large-scale hydraulic fracturing and holds promise for overcoming the technological bottlenecks in shale oil extraction.

[0003] In-situ heating methods for shale oil extraction mainly include three types: heat conduction (electric heating rods, steam circulation pipes, dielectric heating, etc.), convection + conduction (injection of steam, hot organic gases, and CO2), and radiation + conduction (electric fields, electromagnetic waves, and microwaves, etc.). Due to the low permeability of shale oil reservoirs, injecting hot fluids into them is difficult and costly. Numerous scholars both domestically and internationally have conducted research on heating unconventional oil and gas reservoirs such as heavy oil, oil sands, shale oil, and shale gas using low-frequency electric fields (a type of dielectric heating), microwaves, and high-frequency electromagnetic fields. Oil companies such as Shell have already conducted field trials in several blocks using heating pipes to heat shale oil reservoirs on a large scale for shale oil extraction.

[0004] A core issue remains to be addressed in in-situ heated shale oil extraction: how the pressure field of the shale oil reservoir changes during the temperature rise process. This controls whether overpressure fractures can form, their location, and the characteristics of highly efficient permeable channels during the heating process, ultimately determining the success of in-situ heated shale oil extraction.

[0005] Therefore, this invention proposes a method for evaluating the reservoir pressure field during in-situ heated extraction of shale oil. This method can quantitatively evaluate the characteristics of the shale oil reservoir pressure field changing with temperature during in-situ heated extraction, providing important technical parameters for in-situ heated reforming and extraction of shale oil, and supporting the overcoming of technical bottlenecks in shale oil extraction. Summary of the Invention

[0006] The purpose of this invention is to provide a method for evaluating the reservoir pressure field during in-situ heating and extraction of shale oil, enabling quantitative evaluation of the characteristics of shale oil reservoir pressure field changes with temperature field during in-situ heating and extraction of shale oil, providing important technical parameters for in-situ heating and upgrading of shale oil, and supporting the breakthrough of shale oil extraction technology bottlenecks.

[0007] The technical solution adopted in this invention is: a method for evaluating the reservoir pressure field during in-situ heated shale oil extraction, characterized in that:

[0008] Step 1: Construct a 3D mesh model of the shale oil reservoir between the two horizontal wells. Each 3D mesh cell has a length, width, and height of 1m. The length of the 3D mesh model is equal to the length of the horizontal section of the two wells, the width is not less than twice the distance between the horizontal sections of the two wells, and the height is equal to the thickness of the shale oil reservoir. Determine the initial temperature T of each mesh cell. x,y,z,0 Initial temperature P x,y,z,0 Initial porosity Ф x,y,z,0 Initial oil saturation S o,x,y,z,0 Initial gas saturation S g,x,y,z,0 Initial water saturation S w,x,y,z,0 Initial crude oil dissolved natural gas volume V dis-g,x,y,z,0 The initial rock skeleton's volumetric thermal expansion coefficient β r,x,y,z,0 Initial crude oil thermal expansion coefficient β o,x,y,z,0 Initial thermal expansion coefficient of natural gas β g,x,y,z,0 and the initial hydrothermal expansion coefficient β w,x,y,z,0 x, y, and z are all integers, representing the mesh cell numbers on the x, y, and z axes in 3D space, respectively. Temperature is measured in Kelvin (K), pressure in MPa (MPa), porosity in % (%), and oil saturation, gas saturation, and water saturation in % (%). The unit for dissolved natural gas in crude oil is m³. 3 / m 3 The unit of the coefficient of volumetric thermal expansion is K. -1 ;

[0009] Step 2: Based on the temperature field, porosity, and reservoir skeleton volumetric thermal expansion coefficient during in-situ heating of the shale oil reservoir, evaluate the porosity of each reservoir grid unit after the original pores are squeezed due to the volumetric thermal expansion of the reservoir skeleton. That is, within a unit time interval from t0 to t, the temperature of each grid unit changes from T... x,y,z,0 Change to T x,y,z The porosity of each grid cell is determined by Ф x,y,z,0 Change to Ф x,y,z The porosity at time t is given by the following formula, where the unit time can be 1 hour, 1 minute, or 1 second.

[0010] Ф x,y,z =Ф x,y,z,0 –β r,x,y,z(T x,y,z –T x,y,z,0 )(1–Ф x,y,z,0 ) / Ф x,y,z,0

[0011] In the formula, Ф x,y,z and Ф x,y,z,0 The porosity β of reservoir grid cells numbered x, y, and z at times t and t0 during in-situ heating of shale oil reservoirs. r,x,y,z T is the volumetric thermal expansion coefficient of the rock skeleton of reservoir grid cells numbered x, y, and z at time t. x,y,z and T x,y,z,0 The temperatures of reservoir grid cells numbered x, y, and z at times t and t0 during in-situ heating of the shale oil reservoir are given. The porosity is expressed as a percentage (%), and the thermal expansion coefficient of the rock skeleton is expressed as Kelvin (K). -1 The unit of temperature is K, and x, y, and z are all integers, which are the numbers of the mesh cells on the x-axis, y-axis, and z-axis in three-dimensional space, respectively.

[0012] Step 3: Based on the reservoir temperature field, the saturation of each fluid, the thermal expansion coefficient of each fluid, and the solubility characteristics of natural gas in oil, evaluate the volume V' of oil, gas, and water in each reservoir grid cell at time t under constant pore fluid pressure. o,x,y,z V' g,x,y,z and V' w,x,y,z The volumes of oil, gas, and water in each reservoir grid cell under constant pore fluid pressure are given by the following formulas;

[0013] V' o,x,y,z =(1+β) o,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S o,x,y,z

[0014] V' g,x,y,z =(1+β) g,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S g,x,y,z

[0015] V' w,x,y,z =(1+β) w,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S w,x,y,z

[0016] in,

[0017] S o,x,y,z =S o,x,y,z,0 (1+β o,x,y,z (Tx,y,z –T x,y,z,0 ))

[0018] S g,x,y,z =(S g,x,y,z,0 (1+β g,x,y,z (T x,y,z –T x,y,z,0 ))+ΔV dis-g,x,y,z / Ф x,y,z )

[0019] S w,x,y,z =S w,x,y,z,0 (1+β w,x,y,z (T x,y,z –T x,y,z,0 ))

[0020] ΔV dis-g,x,y,z =(V dis-g,x,y,z,0 –V dis-g,x,y,z )﹒ Ф x,y,z S o,x,y,z P c T x,y,z / P x,y,z,0 / T c

[0021] V dis-g,x,y,z =2.4ρ rel-g (P x,y,z ﹒ exp(1.77 / ρ oil -0.001638T x,y,z –1.67)) 1.205

[0022] In the formula, V' o,x,y,z V' g,x,y,z and V' w,x,y,z These represent the volumes of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, under constant pore fluid pressure, respectively. β o,x,y,z β g,x,y,z and β w,x,y, z represents the volumetric thermal expansion coefficients of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, respectively. x,y,z and T x,y,z,0 These are the temperatures of reservoir grid cells numbered x, y, and z at times t and t0, respectively, P. x,y,z and P x,y,z,0 These are the pressures of reservoir grid cells numbered x, y, and z at times t and t0, respectively, and Ф x,y,z and Ф x,y,z,0 These are the porosity of the reservoir grid cells at times t and t0, respectively, S o,x,y,z S g,x,y,z and S w,x,y,zThese represent the saturation levels of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, respectively. o,x,y,z,0 S g,x,y,z,0 and S w,x,y,z,0 These are the saturations of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t0, respectively, ΔV dis-g,x,y,z V is the volume of natural gas that transitions from a dissolved state to a free state in the crude oil within a reservoir grid cell, under the reservoir temperature and pressure conditions from time t0 to t. dis-g,x,y,z V is the volume of dissolved natural gas in crude oil under standard conditions in reservoir grid cells numbered x, y, and z at time t. dis-g,x,y,z,0 ρ is the volume of dissolved natural gas in crude oil under standard conditions in reservoir grid cells numbered x, y, and z at time t0. rel-g and ρ oil These are the relative densities of natural gas and crude oil, respectively, with values ​​of 0.55 and 0.85. (P) c and T c Pressure and temperature under standard conditions, respectively; the unit of fluid volume is m³. 3 / m 3 This unit represents the volume of fluid in one cubic meter of reservoir under standard conditions, and the unit of the volumetric thermal expansion coefficient is K. -1 Temperature is measured in Kelvin (K), pressure in MPa (MPa), porosity in % (%), oil, gas, and water saturation in % (%), and natural gas volume in m³ (m³). 3 / m 3 The unit represents the volume of natural gas in the reservoir under standard conditions per cubic meter. The relative density of natural gas and the relative density of crude oil are dimensionless parameters. The pressure unit is MPa. x, y and z are all integers, which are the numbers of the grid cells on the x-axis, y-axis and z-axis in three-dimensional space, respectively.

[0023] Step 4: Based on the compressibility coefficient of each fluid at the corresponding temperature, combined with the porosity of the reservoir skeleton after thermal expansion and compression of pores evaluated in Step 2 and the volume of each fluid after thermal expansion under constant pore fluid pressure evaluated in Step 3, the pore fluid pressure in each reservoir grid unit is evaluated using the following formula to obtain the pressure field of the in-situ heated shale oil reservoir.

[0024] P x,y,z =(V' o,x,y,z +V' g,x,y,z +V' w,x,y,z –Ф x,y,z ) / (Z o V' o,x,y,z +Z g V' g,x,y,z +Z w V' w,x,y,z )+Px,y,z,0

[0025] In the formula, P x,y,z and P x,y,z,0 These are the pore fluid pressures, V', in reservoir grid cells numbered x, y, and z at times t and t0, respectively. o,x,y,z V' g,x,y,z and V' w,x,y,z These represent the volumes of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, under constant pore fluid pressure, respectively. Ф x,y,z Z represents the porosity of reservoir grid cells numbered x, y, and z at time t. o Z g and Z w These are the compressibility coefficients of oil, gas, and water in the reservoir, respectively. The unit for pore fluid pressure is MPa, and the unit for fluid volume is m³. 3 / m 3 This unit represents the volume of fluid in one cubic meter of reservoir under standard conditions. Porosity is measured in % (percentage in centimeters). The compressibility coefficients of oil, gas, and water are measured in MPa (percentage in centimeters). -1 x, y, and z are all integers, which are the numbers of the mesh cells on the x-axis, y-axis, and z-axis in three-dimensional space, respectively.

[0026] The beneficial effects of this invention are as follows: This invention provides a method for evaluating the reservoir pressure field during in-situ heating and extraction of shale oil. This method is easy to operate and implement. This method can quantitatively evaluate the changes in the reservoir pressure field with temperature field during in-situ heating of shale oil reservoirs, providing important technical parameters for in-situ heating and upgrading of shale oil, and supporting the breakthrough of technological bottlenecks in shale oil extraction. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the method for evaluating the reservoir pressure field during in-situ heated shale oil extraction according to the present invention.

[0028] Figure 2 This is a diagram of a horizontal well layout scheme for extracting shale oil using in-situ heating with a low-frequency electric field.

[0029] Figure 3 It is the temperature field of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after the shale oil reservoir has been heated in situ by a low-frequency electric field for 1 hour.

[0030] Figure 4 It is the porosity characteristic of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after 1 hour of in-situ heating of the shale oil reservoir with a low-frequency electric field.

[0031] Figure 5It is the volume of oil in a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane, assuming that the pore fluid pressure remains constant after 1 hour of in-situ heating of the shale oil reservoir by a low-frequency electric field.

[0032] Figure 6 It is the volume of gas in a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane, assuming that the pore fluid pressure remains constant after 1 hour of in-situ heating of a shale oil reservoir with a low-frequency electric field.

[0033] Figure 7 It is the volume of water in a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane, assuming that the pore fluid pressure remains constant after 1 hour of in-situ heating of a shale oil reservoir with a low-frequency electric field.

[0034] Figure 8 It is the pressure field result of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after the shale oil reservoir is heated in situ by a low-frequency electric field for 1 hour. Detailed Implementation

[0035] Example 1: As Figure 1 The method for evaluating the reservoir pressure field during in-situ heated shale oil extraction includes the following steps:

[0036] Step 1: Construct a 3D mesh model of the shale oil reservoir between two horizontal wells. Each 3D mesh cell has a length, width, and height of 1m. The length of the 3D mesh model is equal to the length of the horizontal section of the two wells, and the width is not less than twice the distance between the horizontal sections of the two wells, which is 60m. The height is equal to the thickness of the shale oil reservoir. The length, width, and height of this 3D mesh model are 1000m, 200m, and 200m, respectively. Determine the initial temperature T of each mesh cell. x,y,z,0 The initial pressure is 363.15 K and P. x,y,z,0 30 MPa, initial porosity Ф x,y,z,0 2% and initial oil saturation S o,x,y,z,0 50%, initial gas saturation S g,x,y,z,0 0%, initial water saturation S w,x,y,z,0 50%, initial crude oil dissolved natural gas volume V dis-g,x,y,z,0 50m 3 / m 3 The initial rock skeleton's volumetric thermal expansion coefficient β r,x,y,z,0 3.0×10 -7 K -1 Initial crude oil thermal expansion coefficient β o,x,y,z,0 2.0×10 -4 K -1 Initial thermal expansion coefficient of natural gas β g,x,y,z,0 2.0×10 -3 K -1 and the initial hydrothermal expansion coefficient βw,x,y,z,0 3.0×10 -4 K -1 x, y, and z are all integers, representing the mesh cell numbers on the x, y, and z axes in 3D space, respectively. Temperature is measured in Kelvin (K), pressure in MPa (MPa), porosity in % (%), and oil saturation, gas saturation, and water saturation in % (%). The unit for dissolved natural gas in crude oil is m³. 3 / m 3 The unit of the coefficient of volumetric thermal expansion is K. -1 .

[0037] Step 2: Figure 3 This refers to the temperature field of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after one hour of in-situ heating of a shale oil reservoir with a low-frequency electric field. This temperature field was obtained through the invention patent "A Method for Evaluating the Temperature Field of a Shale Oil Reservoir Heated by a Low-Frequency Electric Field" (patent number 202111529967.5). Based on the temperature field, porosity, and volumetric thermal expansion coefficient of the shale oil reservoir, the porosity of each reservoir grid unit after the original pores are compressed due to the volumetric thermal expansion of the reservoir skeleton is evaluated. In other words, within a unit time interval from t0 to t, the temperature of each grid unit changes from T... x,y,z,0 Change to T x,y,z The porosity of each grid cell is determined by Ф x,y,z,0 Change to Ф x,y,z The porosity at time t is given by the following formula, where the unit time is 1 hour. Figure 4 It is the porosity characteristics of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after the shale oil reservoir has been heated in situ for 1 hour by a low-frequency electric field.

[0038] Ф x,y,z =Ф x,y,z,0 –β r,x,y,z (T x,y,z –T x,y,z,0 )(1–Ф x,y,z,0 ) / Ф x,y,z,0

[0039] In the formula, Ф x,y,z and Ф x,y,z,0 The porosity β of reservoir grid cells numbered x, y, and z at times t and t0 during in-situ heating of shale oil reservoirs. r,x,y,z T is the volumetric thermal expansion coefficient of the rock skeleton of reservoir grid cells numbered x, y, and z at time t. x,y,z and T x,y,z,0 The temperatures of reservoir grid cells numbered x, y, and z at times t and t0 during in-situ heating of the shale oil reservoir are given. The porosity is expressed as a percentage (%), and the thermal expansion coefficient of the rock skeleton is expressed as Kelvin (K). -1The temperature is measured in Kelvin (K), and x, y, and z are all integers, representing the grid cell numbers on the x, y, and z axes in three-dimensional space, respectively.

[0040] Step 3: Based on the reservoir temperature field, the saturation of each fluid, the thermal expansion coefficient of each fluid, and the solubility characteristics of natural gas in oil, evaluate the volume V' of oil, gas, and water in each reservoir grid cell at time t under constant pore fluid pressure. o,x,y,z V' g,x,y,z and V' w,x,y,z The volumes of oil, gas, and water in each reservoir grid cell under constant pore fluid pressure are given by the following formulas: Figure 5 , Figure 6 and Figure 7 These represent the volumes of oil, gas, and water in a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane, assuming constant pore fluid pressure.

[0041] V' o,x,y,z =(1+β) o,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S o,x,y,z

[0042] V' g,x,y,z =(1+β) g,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S g,x,y,z

[0043] V' w,x,y,z =(1+β) w,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S w,x,y,z

[0044] in,

[0045] S o,x,y,z =S o,x,y,z,0 (1+β o,x,y,z (T x,y,z –T x,y,z,0 ))

[0046] S g,x,y,z =(S g,x,y,z,0 (1+β g,x,y,z (T x,y,z –T x,y,z,0 ))+ΔV dis-g,x,y,z / Ф x,y,z )

[0047] S w,x,y,z =S w,x,y,z,0 (1+βw,x,y,z (T x,y,z –T x,y,z,0 ))

[0048] ΔV dis-g,x,y,z =(V dis-g,x,y,z,0 –V dis-g,x,y,z )﹒ Ф x,y,z S o,x,y,z P c T x,y,z / P x,y,z,0 / T c

[0049] V dis-g,x,y,z =2.4ρ rel-g (P x,y,z ﹒ exp(1.77 / ρ oil -0.001638T x,y,z –1.67)) 1.205

[0050] In the formula, V' o,x,y,z V' g,x,y,z and V' w,x,y,z These represent the volumes of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, under constant pore fluid pressure, respectively. β o,x,y,z β g,x,y,z and β w,x,y, z represents the volumetric thermal expansion coefficients of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, respectively. x,y,z and T x,y,z,0 These are the temperatures of reservoir grid cells numbered x, y, and z at times t and t0, respectively, P. x,y,z and P x,y,z,0 These are the pressures of reservoir grid cells numbered x, y, and z at times t and t0, respectively, and Ф x,y,z and Ф x,y,z,0 These are the porosity of the reservoir grid cells at times t and t0, respectively, S o,x,y,z S g,x,y,z and S w,x,y,z These represent the saturation levels of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, respectively. o,x,y,z,0 S g,x,y,z,0 and S w,x,y,z,0 These are the saturations of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t0, respectively, ΔV dis-g,x,y,z V is the volume of natural gas that transitions from a dissolved state to a free state in the crude oil within a reservoir grid cell, under the reservoir temperature and pressure conditions from time t0 to t. dis-g,x,y,z V is the volume of dissolved natural gas in crude oil under standard conditions in reservoir grid cells numbered x, y, and z at time t.dis-g,x,y,z,0 ρ is the volume of dissolved natural gas in crude oil under standard conditions in reservoir grid cells numbered x, y, and z at time t0. rel-g and ρ oil These are the relative densities of natural gas and crude oil, respectively, with values ​​of 0.55 and 0.85. (P) c and T c Pressure and temperature under standard conditions, respectively; the unit of fluid volume is m³. 3 / m 3 The volumetric thermal expansion coefficient is the volume of fluid in each cubic meter of reservoir under standard conditions, and its unit is K. -1 Temperature is measured in Kelvin (K), pressure in MPa (MPa), porosity in % (%), oil, gas, and water saturation in % (%), and natural gas volume in m³ (m³). 3 / m 3 , which is the volume of natural gas in the reservoir under standard conditions per cubic meter. The relative density of natural gas and the relative density of crude oil are dimensionless parameters. The unit of pressure is MPa. x, y and z are all integers, which are the numbers of the grid cells on the x-axis, y-axis and z-axis in three-dimensional space, respectively.

[0051] Step 4: Based on the compressibility coefficients of each fluid at the corresponding temperatures, combined with the porosity of the reservoir skeleton after thermal expansion and compression of pores evaluated in Step 2, and the volume of each fluid after thermal expansion under constant pore fluid pressure evaluated in Step 3, the pore fluid pressure in each reservoir grid cell is evaluated using the following formula. This yields the pressure field of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after 1 hour of in-situ heating of the shale oil reservoir with a low-frequency electric field. Figure 8 The pressure field of a two-dimensional reservoir grid profile perpendicular to the projection of the horizontal well section plane after one hour of in-situ heating of a shale oil reservoir by a low-frequency electric field.

[0052] P x,y,z =(V' o,x,y,z +V' g,x,y,z +V' w,x,y,z –Ф x,y,z ) / (Z o V' o,x,y,z +Z g V' g,x,y,z +Z w V' w,x,y,z )+P x,y,z,0

[0053] In the formula, P x,y,z and P x,y,z,0 These are the pore fluid pressures, V', in reservoir grid cells numbered x, y, and z at times t and t0, respectively. o,x,y,z V' g,x,y,z and V' w,x,y,zThese represent the volumes of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, under constant pore fluid pressure, respectively. Ф x,y,z Z represents the porosity of reservoir grid cells numbered x, y, and z at time t. o Z g and Z w These are the compressibility coefficients of oil, gas, and water in the reservoir, respectively, with values ​​of 0.0004 MPa. -1 0.0323MPa -1 and 0.0003MPa -1 The unit for pore fluid pressure is MPa, and the unit for fluid volume is m³. 3 / m 3 Porosity is the volume of fluid in a reservoir per cubic meter under standard conditions. The unit for porosity is %, and the unit for the compressibility of oil, gas, and water is MPa. -1 x, y, and z are all integers, which are the numbers of the mesh cells on the x-axis, y-axis, and z-axis in three-dimensional space, respectively.

Claims

1. A method for evaluating the reservoir pressure field during in-situ heated shale oil extraction, characterized in that: Step 1: Construct a 3D mesh model of the shale oil reservoir between the two horizontal wells. Each 3D mesh cell has a length, width, and height of 1m. The length of the 3D mesh model is equal to the length of the horizontal section of the two wells, the width is not less than twice the distance between the horizontal sections of the two wells, and the height is equal to the thickness of the shale oil reservoir. Determine the initial temperature T of each mesh cell. x,y,z,0 Initial temperature P x,y,z,0 Initial porosity Ф x,y,z,0 Initial oil saturation S o,x,y,z,0 Initial gas saturation S g,x,y,z,0 Initial water saturation S w,x,y,z,0 Initial crude oil dissolved natural gas volume V dis-g,x,y,z,0 The initial rock skeleton's volumetric thermal expansion coefficient β r,x,y,z,0 Initial crude oil thermal expansion coefficient β o,x,y,z,0 Initial thermal expansion coefficient of natural gas β g,x,y,z,0 and the initial hydrothermal expansion coefficient β w,x,y,z,0 x, y, and z are all integers, representing the mesh cell numbers on the x, y, and z axes in 3D space, respectively. Temperature is measured in Kelvin (K), pressure in MPa (MPa), porosity in % (%), and oil saturation, gas saturation, and water saturation in % (%). The unit for dissolved natural gas in crude oil is m³. 3 / m 3 The unit of the coefficient of volumetric thermal expansion is K. -1 ; Step 2: Based on the temperature field, porosity, and reservoir skeleton volume thermal expansion coefficient during in-situ heating of shale oil reservoirs, evaluate the porosity of each reservoir grid unit after the original pores are squeezed due to the volume thermal expansion of the reservoir skeleton. Step 3: Based on the reservoir temperature field, the saturation of each fluid, the thermal expansion coefficient of each fluid, and the solubility characteristics of natural gas in oil, evaluate the volume V of oil, gas, and water in each reservoir grid cell at time t under constant pore fluid pressure. ’ o,x,y,z V ’ g,x,y,z and V ’ w,x,y,z The volumes of oil, gas, and water in each reservoir grid cell under constant pore fluid pressure are given by the following formulas: V ’ o,x,y,z =(1+β o,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S o,x,y,z V ’ g,x,y,z =(1+β g,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S g,x,y,z V ’ w,x,y,z =(1+β w,x,y,z (T x,y,z –T x,y,z,0 ))Ф x,y,z,0 S w,x,y,z in, S o,x,y,z =S o,x,y,z,0 (1+β o,x,y,z (T x,y,z –T x,y,z,0 )) S g,x,y,z =(S g,x,y,z,0 (1+b g,x,y,z (T x,y,z –T x,y,z,0 ))+ΔV dis-g,x,y,z / F x,y,z ) S w,x,y,z =S w,x,y,z,0 (1+β w,x,y,z (T x,y,z –T x,y,z,0 )) ΔV dis-g,x,y,z =(V dis-g,x,y,z,0 –V dis-g,x,y,z )﹒Ф x,y,z S o,x,y,z P c T x,y,z / P x,y,z,0 / T c V dis-g,x,y,z =2.4p rel-g (P x,y,z ﹒exp(1.77 / ρ oil –0.001638T x,y,z –1.67)) 1.205 In the formula, V ’ o,x,y,z V ’ g,x,y,z and V ’ w,x,y,z These represent the volumes of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, under constant pore fluid pressure, respectively, and β. o,x,y,z β g,x,y,z and β w,x,y, z represents the volumetric thermal expansion coefficients of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, respectively. x,y,z and T x,y,z,0 These are the temperatures of reservoir grid cells numbered x, y, and z at times t and t0, respectively, P x,y,z and P x,y,z,0 These are the pressures of reservoir grid cells numbered x, y, and z at times t and t0, respectively, and Ф x,y,z and Ф x,y,z,0 These are the porosity of the reservoir grid cells at times t and t0, respectively, S o,x,y,z S g,x,y,z and S w,x,y,z These represent the saturation levels of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, respectively. o,x,y,z,0 S g,x,y,z,0 and S w,x,y,z,0 These are the saturations of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t0, respectively, ΔV dis-g,x,y,z V is the volume of natural gas that transitions from a dissolved state to a free state in the crude oil within a reservoir grid cell, under the reservoir temperature and pressure conditions from time t0 to t. dis-g,x,y,z V is the volume of dissolved natural gas in crude oil under standard conditions in reservoir grid cells numbered x, y, and z at time t. dis-g,x,y,z,0 ρ is the volume of dissolved natural gas in crude oil under standard conditions in reservoir grid cells numbered x, y, and z at time t0. rel-g and ρ oil These are the relative densities of natural gas and crude oil, respectively, with values ​​of 0.55 and 0.

85. (P) c and T c Pressure and temperature under standard conditions, respectively; the unit of fluid volume is m³. 3 / m 3 m 3 / m 3 The unit represents the volume of fluid in one cubic meter of reservoir under standard conditions; the unit of the volumetric thermal expansion coefficient is K. -1 Temperature is measured in Kelvin (K), pressure in MPa (MPa), porosity in % (%), oil, gas, and water saturation in % (%), and natural gas volume in m³ (m³). 3 / m 3 m 3 / m 3 The unit represents the volume of natural gas in the reservoir under standard conditions per cubic meter. The relative density of natural gas and the relative density of crude oil are dimensionless parameters. The unit of pressure is MPa. x, y and z are all integers, which are the numbers of the grid cells on the x-axis, y-axis and z-axis in three-dimensional space, respectively. Step 4: Based on the compressibility coefficient of each fluid at the corresponding temperature, combined with the porosity of the reservoir skeleton after thermal expansion and compression of pores evaluated in Step 2 and the volume of each fluid after thermal expansion under constant pore fluid pressure evaluated in Step 3, determine the pressure field of the in-situ heated shale oil reservoir.

2. The method for evaluating the reservoir pressure field during in-situ heated shale oil extraction according to claim 1, characterized in that: The method for evaluating the porosity of each reservoir grid cell after the original pores are compressed due to the volumetric thermal expansion of the reservoir skeleton in step 2 is as follows: Within a unit time interval from t0 to t, the temperature of each grid cell changes from T... x,y,z,0 Transform into T x,y,z The porosity of each grid cell is determined by Ф x,y,z,0 Change to Ф x,y,z The unit of time can be 1 hour, 1 minute, or 1 second. F x,y,z =Ф x,y,z,0 –β r,x,y,z (T x,y,z –T x,y,z,0 )(1–F x,y,z,0 ) / F x,y,z,0 In the formula, Ф x,y,z and Ф x,y,z,0 The porosity β of reservoir grid cells numbered x, y, and z at times t and t0 during in-situ heating of shale oil reservoirs, respectively. r,x,y,z T represents the volumetric thermal expansion coefficient of the rock skeleton in reservoir grid cells numbered x, y, and z at time t. x,y,z and T x,y,z,0 The temperatures of reservoir grid cells numbered x, y, and z at times t and t0 during in-situ heating of the shale oil reservoir are given. The porosity is expressed as a percentage (%), and the thermal expansion coefficient of the rock skeleton is expressed as Kelvin (K). -1 The temperature is measured in Kelvin (K), and x, y, and z are all integers, representing the grid cell numbers on the x, y, and z axes in three-dimensional space, respectively.

3. The method for evaluating the reservoir pressure field during in-situ heated shale oil extraction according to claim 1, characterized in that: The method for determining the pore fluid pressure in each reservoir grid cell in step 4 is as follows: P x,y,z =(V ’ o,x,y,z +V ’ g,x,y,z +V ’ w,x,y,z –Ф x,y,z ) / (Z o In ’ o,x,y,z +Z g In ’ g,x,y,z +Z w In ’ w,x,y,z )+P x,y,z,0 In the formula, P x,y,z and P x,y,z,0 These are the pore fluid pressures (V) in reservoir grid cells numbered x, y, and z at times t and t0, respectively. ’ o,x,y,z V ’ g,x,y,z and V ’ w,x,y,z These represent the volumes of oil, gas, and water in reservoir grid cells numbered x, y, and z at time t, under constant pore fluid pressure, respectively. Ф x,y,z Z represents the porosity of reservoir grid cells numbered x, y, and z at time t. o Z g and Z w These are the compressibility coefficients of oil, gas, and water in the reservoir, respectively. The unit for pore fluid pressure is MPa, and the unit for fluid volume is m³. 3 / m 3 m 3 / m 3 The unit represents the volume of fluid in one cubic meter of reservoir under standard conditions. Porosity is measured in % (percentage in centimeters). The compressibility coefficients of oil, gas, and water are measured in MPa (per unit of pressure). -1 x, y, and z are all integers, which are the numbers of the mesh cells on the x-axis, y-axis, and z-axis in three-dimensional space, respectively.

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