Heavy oil reservoir underground electric heating energy supply and demand matching calculation method and device

Abstract

The embodiment of the invention provides a heavy oil reservoir underground electric heating energy supply and demand matching calculation method and device and a storage medium. The method comprises the steps that a thickened oil starting temperature and pressure chart is obtained, and the thickened oil starting temperature and pressure chart defines a starting temperature threshold value and a starting pressure gradient threshold value needed by thickened oil to start flowing under the condition of specific reservoir permeability and temperature; establishing a heat transfer and seepage coupling numerical model from the shaft to the target stratum; the starting temperature threshold value and the starting pressure gradient threshold value serve as target conditions, iterative calculation is conducted through a heat transfer and seepage coupling numerical model, and the minimum thermal power input by a shaft and needed for enabling the temperature and the pressure of the target stratum to reach the target conditions is solved; according to the minimum heat power, heat loss from the ground to the target stratum is subjected to compensation calculation, and the matched operation power needing to be provided by the ground electric heating system is determined.

Description

Technical Field

[0001] This application relates to the field of heavy oil reservoir development technology, specifically to a method, device, and storage medium for calculating the energy supply and demand matching of downhole electric heating in heavy oil reservoirs. Background Technology

[0002] In the development of heavy oil reservoirs, downhole electric heating technology, as a novel low-carbon thermal recovery method, focuses on the precise conversion of electrical energy into heat energy, directly acting on the wellbore and near-wellbore reservoir to reduce the viscosity of heavy oil and initiate its flow. Existing technical solutions typically consist of three parts: first, obtaining the starting pressure gradient of heavy oil under different temperature and permeability conditions through laboratory core displacement experiments; second, estimating the maximum electric heating power required to maintain a certain temperature in the wellbore based on simplified steady-state heat conduction models or empirical formulas; and finally, setting a fixed heating power or adjusting it empirically based on geological and engineering parameters. This technical approach, to a certain extent, addresses the basic requirement of heating and reducing the viscosity of heavy oil, forming the main basis for current downhole electric heating design and operation.

[0003] However, the existing technical solutions described above characterize the start-up capability of heavy oil in an isolated and static manner. The "start-up pressure gradient" parameter obtained from experiments is not dynamically coupled to the real-time calculation model of the formation temperature and pressure field, making it impossible to scientifically define the spatially and temporally varying temperature and pressure threshold conditions necessary for "heavy oil to truly begin flowing." Secondly, the energy transfer process from the wellbore to the formation is greatly simplified. Existing steady-state models or empirical formulas fail to simultaneously couple the complex physical processes of non-isothermal flow within the wellbore, radial unsteady heat transfer, and non-Darcy flow in the reservoir. This results in severe distortion in the calculation of the heat input from the wellbore to the formation for effective utilization, making it impossible to solve for the minimum accurate thermal power required to meet the start-up conditions. When determining the surface electric heating power, existing methods lack a systematic calculation method that uses the minimum formation heat demand as a constraint and accurately compensates for the heat loss throughout the entire process. They can only make rough estimates or "over-match" designs, failing to achieve real-time, accurate, and adaptive matching between the dynamic demand for underground thermal energy and the supply of surface electric energy. Summary of the Invention

[0004] The purpose of this application is to overcome the problem of energy supply and demand mismatch caused by the inability to couple dynamic start-up conditions and multi-physics field energy transmission in the traditional energy calculation method based on steady-state heat conduction model or empirical formula during the development of heavy oil by downhole electric heating, and to provide a method, device and storage medium for calculating energy supply and demand matching of downhole electric heating in heavy oil reservoirs.

[0005] To achieve the above objectives, this application provides a method for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs, including: Obtain the heavy oil start-up temperature and pressure chart, which defines the start-up temperature threshold and start-up pressure gradient threshold required for heavy oil to begin flowing under specific reservoir permeability and temperature conditions. Establish a numerical model of heat transfer and seepage coupling from the wellbore to the target formation; Using the start-up temperature threshold and start-up pressure gradient threshold as target conditions, the minimum thermal power input from the wellbore is calculated through iterative calculation using a coupled heat transfer and seepage numerical model to achieve the target formation temperature and pressure. Based on the minimum thermal power, the heat loss from the ground to the target stratum is compensated by calculation, and the matching operating power that the ground electric heating system needs to provide is determined.

[0006] In this embodiment, the coupled heat transfer and seepage numerical model includes a wellbore axial one-dimensional energy conservation model. This model considers convective heat transfer of the fluid within the wellbore, radial heat conduction through the tubing and formation, and the latent heat of vapor condensation phase change. The expression for the wellbore axial one-dimensional energy conservation model is as follows:

[0007] in, Temperature of the fluid in the wellbore, in Kelvin (K). The coupling temperature of the outer surface of the wellbore is in K; t is time in seconds; z is the axial coordinate of the wellbore in meters. The density of the fluid is expressed in kg·m³. -3 A represents the cross-sectional area of ​​the fluid flow within the wellbore, in meters (m²). 2 ; The specific heat capacity at constant pressure of a fluid is expressed in J·kg. -1 ·K -1 Q represents volumetric flow rate, in cubic meters per second (m³). 3 ·s -1 U is the overall heat transfer coefficient after adjusting for convection within the well and radial heat conduction from the casing / cement sheath / near-wellbore formation, expressed in W·m³. -2 · K -1 P represents the circumference of the inner wall, in meters (m). The latent heat of steam condensation is expressed in J·kg. -1 ; This represents the mass of water that changes from steam to liquid water per unit length of wellbore per unit time, and the unit is kg·m. -1 ·s -1 .

[0008] In this embodiment of the application, the coupled heat transfer and seepage numerical model further includes a radial unsteady heat transfer model from the wellbore to the formation. The radial unsteady heat transfer model is used to solve for the wellbore coupling temperature and the near-wellbore formation temperature field. The expression of the radial unsteady heat transfer model is as follows:

[0009]

[0010] in, This represents the convective heat transfer coefficient inside the wellbore, with units of W·m. -2 ·K -1 ; This represents the external convective heat transfer coefficient of the wellbore, with units of W·m. -2 ·K -1 ; This represents the outer radius of the j-th wellbore, in meters. The radius of the inner layer of the wellbore is represented by j, in meters; L represents the friction length of the wellbore, in meters. This represents the thermal conductivity of the j-th layer, in W·m. -1 ·K -1 ; Density of rock is expressed in kg·m³. -3 ; Specific heat capacity of rock is expressed in J·kg. -1 ·K -1 T represents formation temperature, in Kelvin (K); t represents time, in seconds (s). The density of the fluid is expressed in kg·m³. -3 ; Specific heat capacity of a fluid is expressed in J·kg. -1 ·K -1 ; Radial seepage velocity, in m·s -1 ; Represents radial coordinates, in meters (m). A heat source generated by an electric heating element or a chemical reaction, measured in W·m. -3 ;in The effective thermal conductivity is expressed in W·m. -1 ·K -1 ; , Temperature of the fluid in the wellbore, in Kelvin (K). The coupling temperature of the outer surface of the wellbore is expressed in Kelvin (K).

[0011] In this embodiment of the application, the coupled numerical model of heat transfer and seepage further includes a formation radial seepage pressure drop model, which is used to calculate the near-wellbore formation pressure distribution. The expression of the formation radial seepage pressure drop model is as follows:

[0012] in, Indicates formation porosity; This represents the overall compressibility factor, with units of Pa. -1 ; This represents formation pressure, measured in Pa. This indicates viscosity, and the unit is mPa·s; k Reservoir permeability is expressed in mD. Represents radial coordinates, in meters (m). The equivalent "pressure source term" represents the rate of pressure change per unit time and unit volume of formation due to fluid injection or production, measured in Pa·s. -1 .

[0013] In this embodiment of the application, the process of determining the minimum thermal power input from the wellbore required to bring the temperature and pressure of the target formation to the target conditions includes: setting multiple surface heating powers as initial input values; calculating the temperature and pressure distribution of the target formation under each heating power based on a coupled heat transfer and seepage numerical model; determining whether the temperature distribution reaches the start-up temperature threshold and whether the pressure distribution reaches the start-up pressure gradient threshold; and iteratively adjusting the surface heating power until the minimum thermal power that simultaneously satisfies the temperature and pressure thresholds is found, which is then taken as the minimum thermal power.

[0014] In this embodiment of the application, the heat loss compensation calculation from the ground to the target stratum is performed based on the minimum thermal power, including: using the minimum thermal power as the effective heat demand of the target stratum; establishing an energy transmission link model from the ground to the target stratum, the model being used to calculate the total heat loss of the energy supplied from the ground during the transmission to the target stratum; adding the minimum thermal power to the total heat loss calculated by the model to obtain the theoretical thermal power that the ground electric heating system needs to provide; and converting the theoretical thermal power into an equivalent electric power value as the matching operating power of the ground electric heating system.

[0015] In this embodiment of the application, obtaining the heavy oil start-up temperature-pressure map includes: measuring the start-up pressure gradient of heavy oil in the core under different displacement rates and temperatures through core displacement experiments; establishing a curve relating injection rate to pressure gradient based on the experimental data, and determining the proposed start-up pressure gradient by the intersection of the reverse extension of the curve with the pressure gradient coordinate axis; repeating the experiment with cores of different permeabilities and under different temperature conditions to obtain multiple sets of proposed start-up pressure gradient data; and constructing the heavy oil start-up temperature-pressure map based on the gradient data.

[0016] A second aspect of this application provides a calculation device for the supply and demand matching of downhole electric heating energy in heavy oil reservoirs, the device comprising: The memory is configured to store instructions; The processor is configured to retrieve instructions from memory and, when executing instructions, to implement any of the above-mentioned methods for calculating the supply and demand of downhole electric heating energy in heavy oil reservoirs.

[0017] In this embodiment of the application, the apparatus further includes an experimental device for determining the starting pressure of heavy oil, the experimental device including: a high-precision injection pump; a piston container; a constant temperature chamber; a pressure monitoring system; a six-way valve; a core holder; a metering test tube; and a confining pressure pump.

[0018] A third aspect of this application provides a machine-readable storage medium storing instructions, characterized in that, when executed by a processor, the instructions cause the processor to be configured to perform any of the above-described methods for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs.

[0019] Through the above technical solution, this application can address the problem of difficulty in accurately matching energy supply and demand during the development of heavy oil reservoirs by downhole electric heating due to unclear dynamic start-up conditions and complex energy transmission paths. It integrates calculations of heavy oil start-up capability and multi-physics field coupling simulation, and verifies the seepage law that "heavy oil needs to reach critical temperature and pressure conditions to effectively start flow". This significantly improves the accuracy of solving for the minimum thermal power required for formation start-up, enhances the economy and operating efficiency of energy configuration of the electric heating system, and provides a scientific and accurate theoretical basis for energy supply and demand matching for the design and optimization of downhole electric heating development schemes for heavy oil reservoirs.

[0020] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings: Figure 1 The schematic diagram illustrates a flow chart of a method for calculating the energy supply and demand matching of downhole electric heating in heavy oil reservoirs according to an embodiment of this application; Figure 2 A schematic diagram illustrating the injection rate-pressure gradient relationship curve according to an embodiment of this application is shown. Figure 3 A schematic diagram of a pressure-time curve according to an embodiment of this application is shown. Figure 4 A schematic diagram illustrating the relationship between flow rate and pressure gradient according to an embodiment of this application is shown. Figure 5 The illustration schematically shows the heavy oil start-up pressure gradient at different temperatures and permeabilities, as experimentally measured according to embodiments of this application. Figure 6 A schematic diagram illustrating the heavy oil start-up pressure and temperature according to an embodiment of this application is shown. Figure 7 A schematic diagram illustrating the heat conduction temperature diffusion distance according to an embodiment of this application is shown. Figure 8 This illustration schematically shows the change of total heat in the injected reservoir over time according to an embodiment of this application; Figure 9 The schematic diagram illustrates a flow chart of a method for calculating the energy supply and demand matching of downhole electric heating in heavy oil reservoirs according to another embodiment of this application; Figure 10 This illustration schematically shows a calculation diagram of the supply-side energy required for heavy oil mobilization according to an embodiment of this application; Figure 11 An experimental apparatus for determining the starting pressure of heavy oil is illustrated schematically according to an embodiment of this application; Figure 12 The diagram illustrates the internal structure of a computer device according to an embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0024] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0025] Figure 1The illustration schematically shows a flowchart of a method for calculating the energy supply and demand matching of downhole electric heating in heavy oil reservoirs according to an embodiment of this application. Figure 1 As shown in one embodiment of this application, a method for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs is provided, including the following steps: Step 101: Obtain the heavy oil start-up temperature and pressure map. The heavy oil start-up temperature and pressure map defines the start-up temperature threshold and start-up pressure gradient threshold required for heavy oil to begin flowing under specific reservoir permeability and temperature conditions.

[0026] The heavy oil start-up temperature and pressure chart refers to a quantitative relationship chart or data set established through analysis and calculation based on systematic indoor core displacement experimental data, which can clearly characterize the critical conditions required for heavy oil to start flowing under different reservoir properties and temperature environments.

[0027] In one embodiment, the initiation pressure gradient of heavy oil in the core is measured under different displacement rates and temperatures through core displacement experiments; based on the experimental data, such as Figure 2 As shown, an injection rate versus pressure gradient curve was established, and the proposed start-up pressure gradient was determined by the intersection of the reverse extension of the curve with the pressure gradient coordinate axis. The experiment was repeated with cores of different permeabilities and under different temperature conditions to obtain multiple sets of proposed start-up pressure gradient data. Based on the gradient data, a heavy oil start-up temperature-pressure chart was constructed.

[0028] In one embodiment, firstly, fluid is driven into the core inlet under very low displacement conditions to gradually build up the inlet pressure, while closely monitoring the core outlet. When the first appearance of liquid (heavy oil) at the outlet is observed, the inlet pressure at this point is recorded; this pressure is the minimum start-up pressure under these conditions. After the pressure data stabilizes, the stable injection pressure is recorded. By systematically changing different displacement flow rates (i.e., injection velocities) and repeating the above process, a set of data on the correspondence between start-up pressure and injection velocity can be obtained. Based on these experimental data, a curve showing the relationship between injection velocity and pressure gradient can be plotted. By finding the intersection of the backward extension of the straight line segment of this curve with the pressure gradient coordinate axis, the intended start-up pressure gradient under these experimental conditions can be accurately determined. Finally, these massive gradient data are comprehensively analyzed, regressed, and graphically processed to form a heavy oil start-up temperature-pressure chart that clearly defines the dual thresholds of "temperature-pressure" for heavy oil start-up.

[0029] Step 102: Establish a numerical model of heat transfer and seepage coupling from the wellbore to the target formation.

[0030] After determining the threshold temperature and threshold pressure for heavy oil mobilization, based on the heavy oil start-up temperature and pressure chart, the minimum energy input required to bring the temperature within the target wellbore's influence range to the threshold temperature for heavy oil mobilization and the pressure to the threshold pressure is determined through the heat transfer and pressure drop equations coupled between the wellbore and the near-wellbore formation.

[0031] In one embodiment, the coupled heat transfer and seepage numerical model includes a wellbore axial one-dimensional energy conservation model. This model considers convective heat transfer of the fluid within the wellbore, radial heat conduction through the tubing and formation, and latent heat of vapor condensation phase change. The expression for the wellbore axial one-dimensional energy conservation model is as follows:

[0032] in, Temperature of the fluid in the wellbore, in Kelvin (K). The coupling temperature of the outer surface of the wellbore is in K; t is time in seconds; z is the axial coordinate of the wellbore in meters. The density of the fluid is expressed in kg·m³. -3 A represents the cross-sectional area of ​​the fluid flow within the wellbore, in meters (m²). 2 ; The specific heat capacity at constant pressure of a fluid is expressed in J·kg. -1 ·K -1 Q represents volumetric flow rate, in cubic meters per second (m³). 3 ·s -1 U is the overall heat transfer coefficient after adjusting for convection within the well and radial heat conduction from the casing / cement sheath / near-wellbore formation, expressed in W·m³. -2 · K -1 P represents the circumference of the inner wall, in meters (m). The latent heat of steam condensation is expressed in J·kg. -1 ; This represents the mass of water that changes from steam to liquid water per unit length of wellbore per unit time, and the unit is kg·m. -1 ·s -1 .

[0033] In this embodiment of the application, the coupled heat transfer and seepage numerical model further includes a radial unsteady heat transfer model from the wellbore to the formation. The radial unsteady heat transfer model is used to solve for the wellbore coupling temperature and the near-wellbore formation temperature field. The expression of the radial unsteady heat transfer model is as follows:

[0034]

[0035] in, This represents the convective heat transfer coefficient inside the wellbore, with units of W·m. -2 ·K -1 ; This represents the external convective heat transfer coefficient of the wellbore, with units of W·m. -2 ·K -1 ; This represents the outer radius of the j-th wellbore, in meters. The radius of the inner layer of the wellbore is represented by j, in meters; L represents the friction length of the wellbore, in meters. This represents the thermal conductivity of the j-th layer, in W·m. -1 ·K -1 ; Density of rock is expressed in kg·m³. -3 ; Specific heat capacity of rock is expressed in J·kg. -1 ·K -1 T represents formation temperature, in Kelvin (K); t represents time, in seconds (s). The density of the fluid is expressed in kg·m³. -3 ; Specific heat capacity of a fluid is expressed in J·kg. -1 ·K -1 ; Radial seepage velocity, in m·s -1 ; Represents radial coordinates, in meters (m). A heat source generated by an electric heating element or a chemical reaction, measured in W·m. -3 ;in The effective thermal conductivity is expressed in W·m. -1 ·K -1 ; , Temperature of the fluid in the wellbore, in Kelvin (K). The coupling temperature of the outer surface of the wellbore is expressed in Kelvin (K).

[0036] In this embodiment of the application, the coupled numerical model of heat transfer and seepage further includes a formation radial seepage pressure drop model, which is used to calculate the near-wellbore formation pressure distribution. The expression of the formation radial seepage pressure drop model is as follows:

[0037] in, Indicates formation porosity; This represents the overall compressibility factor, with units of Pa. -1 ; This represents formation pressure, measured in Pa. This indicates viscosity, and the unit is mPa·s; k Reservoir permeability is expressed in mD. Represents radial coordinates, in meters (m). The equivalent "pressure source term" represents the rate of pressure change per unit time and unit volume of formation due to fluid injection or production, measured in Pa·s. -1 .

[0038] In one embodiment, a one-dimensional mechanical energy equation is used within the wellbore, as shown in the following formula:

[0039] in, Indicates the friction factor; This indicates the inner diameter of the wellbore, in meters (m). This indicates the density of the fluid inside the wellbore, with units of kg·m³. -3 g represents gravitational acceleration, and its unit is m·s². -2 p represents pressure, and the unit is MPa; The j-th segment represents the seepage resistance; v represents the seepage velocity, in m·s. -1 ; This represents the size of the j-th grid in the z-direction, in meters (m).

[0040] Step 103: Using the start-up temperature threshold and start-up pressure gradient threshold as target conditions, iterative calculations are performed using a coupled heat transfer and seepage numerical model to determine the minimum thermal power input from the wellbore required to bring the temperature and pressure of the target formation to the target conditions.

[0041] In one embodiment, determining the minimum thermal power input from the wellbore required to bring the temperature and pressure of the target formation to the target conditions includes: setting multiple surface heating powers as initial input values; calculating the temperature and pressure distribution of the target formation at each heating power based on a coupled heat transfer and seepage numerical model; determining whether the temperature distribution reaches the start-up temperature threshold and whether the pressure distribution reaches the start-up pressure gradient threshold; and iteratively adjusting the surface heating power until the minimum thermal power that simultaneously satisfies the temperature and pressure thresholds is found, which is then taken as the minimum thermal power.

[0042] In one embodiment, based on the permeability of the target reservoir and the expected development temperature, the corresponding start-up temperature threshold and start-up pressure gradient threshold are determined from the heavy oil start-up temperature-pressure map. Next, a set of initial candidate values ​​for surface heating power are set and substituted into the coupled heat transfer and seepage numerical model as input conditions. For each candidate power, the model calculates the temperature distribution and pressure gradient distribution of the target formation. The model evaluates whether the current power meets the heavy oil start-up requirements by determining whether the calculated temperature is not lower than the start-up temperature threshold and whether the pressure gradient is not lower than the start-up pressure gradient threshold. If so, the power is reduced to find a smaller feasible solution. Through iterative iteration, the minimum thermal power value that simultaneously satisfies the temperature and pressure start-up conditions is finally determined. This value is the minimum thermal energy input required to ensure effective heavy oil flow and can be directly used to guide the power configuration and operation strategy formulation of the surface electric heating system.

[0043] Step 104: Based on the minimum thermal power, calculate the compensation for heat loss from the ground to the target stratum to determine the matching operating power that the ground electric heating system needs to provide.

[0044] In one embodiment, the heat loss compensation calculation from the ground to the target stratum is performed based on the minimum thermal power, including: using the minimum thermal power as the effective heat demand of the target stratum; establishing an energy transmission link model from the ground to the target stratum, the model being used to calculate the total heat loss of the energy supplied from the ground during the transmission to the target stratum; adding the minimum thermal power to the total heat loss calculated by the model to obtain the theoretical thermal power that the ground electric heating system needs to provide; and converting the theoretical thermal power into an equivalent electric power value as the matching operating power of the ground electric heating system.

[0045] This application provides a method for calculating the energy supply and demand matching of downhole electric heating in heavy oil reservoirs based on the start-up capability of heavy oil. By establishing a temperature and pressure chart for heavy oil start-up and combining it with a numerical model of the entire heat transfer and seepage coupling from the wellbore to the reservoir, the minimum energy input required for heavy oil start-up is accurately quantified. This method links the physical conditions for heavy oil start-up, namely temperature and pressure, with the energy supply of the electric heating system. It can dynamically adjust the surface power supply according to the heat and pressure conditions required for heavy oil utilization, significantly improving energy utilization efficiency and providing a reliable theoretical basis and technological guidance for the green and low-carbon development of heavy oil.

[0046] In one specific embodiment, a core displacement experiment was conducted using the method of this application to determine the starting pressure gradient of the heavy oil. The core samples used in the experiment were 6.5 cm artificial sandstone cores with permeabilities of 928 mD, 3025 mD, and 4632 mD, respectively. The heavy oil used was extra-heavy oil with a viscosity of 83730 mPa·s at 50°C.

[0047] The starting pressure gradient of heavy oil was determined using the method described above. At 90℃, the pressure rise of a 3025 mD core sample was monitored to determine the starting pressure gradient at different stages. Pressure changes were measured at flow rates of 0.025 mL / min, 0.05 mL / min, 0.1 mL / min, 0.15 mL / min, 0.3 mL / min, and 0.5 mL / min. The injection pressure values ​​at different times were recorded, and time-pressure curves were plotted as shown below. Figure 3 As shown in the figure. The pressure gradient at different flow rates is calculated based on the injection pressure at which the pressure stabilizes, and the relationship curve between flow rate and pressure gradient is plotted as follows. Figure 4 As shown. By fitting the later line segment, the linear equation can be obtained as y = 0.3152x - 0.0765. Calculating the intersection of the fitted line with the pressure gradient coordinate axis, the pseudo-start-up pressure gradient under the experimental conditions is found to be 0.2427 MPa / m. The experiment was repeated to measure the pseudo-start-up pressure gradient at different temperatures (50-140℃) and different permeabilities (928 mD, 3029 mD, 4632 mD). The results are as follows. Figure 5 As shown. Based on the experimental results, a startup chart for extra-heavy oil, considering the combined temperature, permeability, and startup pressure gradients, is plotted as follows. Figure 6 As shown.

[0048] Assuming the basic physical properties of the reservoir are a permeability of 928 mD, a reservoir temperature of 50°C, a viscosity of 83730 mPa·s for heavy oil at 50°C, and a vertical depth of 1000 m, the required reservoir temperature, injected steam temperature, downhole electric heating time, and downhole electric heating power can be calculated based on the calculation steps proposed in this patent. The calculation steps are as follows.

[0049] Based on the heavy oil start-up pressure and temperature charts, the lower limits of the electric heating temperature and pressure were determined to be 100℃ and 0.0962 MPa / m, respectively. After 1000 days of electric heat conduction, the near-wellbore temperature rose to 320℃, decreasing with heat conduction. The furthest heat conduction distance was 13.7 m. The heat conduction temperature diffusion distance is as follows... Figure 7 As shown.

[0050] Injection wells at 2×10 8 J / m 3 The energy density propagates heat into the reservoir, and within 30 days, the temperature diffuses to a location 8m from the injection well, where the heat reaches 1×10⁻⁶. 8 J / m 3 During heat conduction, green electric heat and steam heat are continuously transferred into the reservoir, and the total heat injected into the reservoir reaches 1.6 × 10⁻⁶ days. 13 J. Based on the experimentally obtained heavy oil driving pressure and start-up temperature charts, the required start-up temperature for heavy oil is 388.15 K, and the calculated heat required is 1.56 × 10⁻⁶ K.12 J, electric heating can provide 48% of the heat in 30 days. After 60 days, the heat input by electric heating will be converted into latent heat of steam for energy supply. The total heat injected into the reservoir changes over time as follows: Figure 8 As shown.

[0051] Figure 9 A schematic diagram illustrating a method for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs, according to another embodiment of this application, is shown. Figure 9 As shown, the steps include: S1. Conduct core displacement experiments to determine the starting pressure gradient of heavy oil, establish a velocity-pressure gradient chart, and calculate the proposed starting pressure gradient.

[0052] Under extremely low-velocity conditions, liquid was displaced to the inlet end of the core sample to establish inlet pressure. When liquid appeared at the outlet end of the core sample, this pressure was recorded as the minimum starting pressure. Once the pressure data stabilized, the injection pressure was recorded. Starting pressure gradient measurements were performed using different displacement flow rates, and the injection pressure was recorded when the pressure stabilized. Based on the experimental results, the starting pressure gradient at different injection rates was calculated, and the relationship curve between injection rate and pressure gradient was plotted. The proposed starting pressure gradient under this condition was determined by the intersection of the backward extension of the straight line segment and the pressure gradient coordinate axis.

[0053] S2, Establish a heavy oil start-up chart that takes into account reservoir permeability and temperature.

[0054] By changing the core samples with different experimental temperatures and permeabilities, the seepage curves at different permeabilities and temperatures were calculated to determine the proposed start-up pressure gradient, and a heavy oil start-up chart considering reservoir permeability and temperature was established to determine the heavy oil start-up limit.

[0055] S3, calculate the radial unsteady heat transfer temperature field of the wellbore-casing-cement sheath-near-wellbore formation.

[0056] The formula is as follows:

[0057] in, This represents the convective heat transfer coefficient inside the wellbore, with units of W·m. -2 ·K -1 ; This represents the external convective heat transfer coefficient of the wellbore, with units of W·m. -2 ·K -1 ; This represents the outer radius of the j-th wellbore, in meters. The radius of the inner layer of the wellbore is represented by j, in meters; L represents the friction length of the wellbore, in meters. This represents the thermal conductivity of the j-th layer, in W·m. -1 ·K-1 .

[0058] S4, calculate the radial unsteady heat transfer distribution within the reservoir.

[0059] The formula is as follows:

[0060] in, Density of rock is expressed in kg·m³. -3 ; This indicates the specific heat capacity of rocks, measured in J·kg. -1 ·K -1 T represents formation temperature, in Kelvin (K); t represents time, in seconds (s). The density of the fluid is expressed in kg·m³. -3 ; Specific heat capacity of a fluid is expressed in J·kg. -1 ·K -1 ; Radial seepage velocity, in m·s -1 ; Represents radial coordinates, in meters (m). A heat source generated by an electric heating element or a chemical reaction, measured in W·m. -3 ;in The effective thermal conductivity is expressed in W·m. -1 ·K -1 ; , Temperature of the fluid in the wellbore, in Kelvin (K). The coupling temperature of the outer surface of the wellbore is expressed in Kelvin (K).

[0061] S5 converts the heat supply value into the electrical energy supply of the electric heating system, enabling flexible allocation of heat demand and electrical energy supply.

[0062] Figure 10 This illustration schematically shows a calculation diagram of the supply-side energy required for heavy oil mobilization according to an embodiment of this application. For example... Figure 10 The image shows a comparison and optimization scheme of heating technologies for heavy oil reservoir development. The core objective is to solve the problem of heavy oil's difficulty in extraction due to its viscosity (requiring heating to reduce viscosity). This can be broken down into three parts: (1) Prerequisite for choosing between the two heating methods: Heavy oil extraction requires a high-temperature environment. Traditionally, there are two methods: electric heating and steam heating. However, the core requirement of "the temperature required for heavy oil reservoir development" must be considered.

[0063] (2) The pain points of traditional steam heating (left side of the process): The traditional method is to generate high-temperature steam through a surface steam generator and then inject it into the underground heavy oil reservoir through the wellbore. However, it will experience three serious heat losses: surface steam heat loss: the steam cools down during the transportation from the generator to the wellhead; wellbore steam heat loss: the heat is absorbed by the surrounding formation when the steam is transported underground along the wellbore; reservoir steam heat loss: after the steam enters the reservoir, the heat is dispersed into the reservoir rock. These losses will result in insufficient "dryness (steam purity)" when the steam reaches the reservoir, and it will be unable to effectively heat the heavy oil.

[0064] (3) Optimization scheme: downhole electric heating (right side process): In order to make up for the heat loss of steam, the scheme adds "electric heating" in the horizontal well section (the area directly in contact with heavy oil): steam is first injected through the traditional process, and then combined with the downhole electric heater to directly heat the steam / heavy oil in the reservoir area, reduce heat waste, accurately increase the reservoir temperature, and make the heavy oil easier to extract after viscosity reduction.

[0065] In one embodiment, a downhole electric heating energy supply and demand matching calculation device for heavy oil reservoirs is provided, comprising: The memory is configured to store instructions; The processor is configured to retrieve instructions from memory and, when executing instructions, to implement any of the above-mentioned methods for calculating the supply and demand of downhole electric heating energy in heavy oil reservoirs.

[0066] In this embodiment, the apparatus further includes an experimental device for determining the starting pressure of heavy oil. The experimental device includes: 1-high-precision injection pump, 2-piston container, 3-thermal chamber, 4-pressure monitoring system, 5-six-way valve, 6-core holder, 7-metering test tube, 8-containing pressure pump, etc. Figure 11 It is composed of the method shown.

[0067] In one embodiment, a machine-readable storage medium is provided, on which instructions are stored, which, when executed by a processor, cause the processor to be configured to perform any of the above-described methods for calculating the supply and demand of downhole electric heating energy in heavy oil reservoirs.

[0068] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 12As shown in the figure, the computer device includes a processor A01, a network interface A02, a display screen A04, an input device A05, and a memory (not shown) connected via a system bus. The processor A01 provides computing and control capabilities. The memory includes internal memory A03 and a non-volatile storage medium A06. The non-volatile storage medium A06 stores an operating system B01 and a computer program B02. The internal memory A03 provides an environment for the operation of the operating system B01 and the computer program B02 stored in the non-volatile storage medium A06. The network interface A02 is used for communication with external terminals via a network connection. When the computer program is executed by the processor A01, it implements a method for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs. The display screen A04 can be an LCD screen or an e-ink display screen. The input device A05 can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device casing, or an external keyboard, touchpad, or mouse.

[0069] Those skilled in the art will understand that Figure 12 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0070] This application provides a computer (electronic) device, which includes a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps of any of the above methods for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs.

[0071] This application also provides a computer program product that, when executed on a data processing device, is suitable for executing a program that initializes a method for calculating the supply and demand matching of downhole electric heating energy in heavy oil reservoirs.

[0072] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0073] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0074] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0075] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0076] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0077] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0078] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0079] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0080] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for calculating the energy supply and demand matching of downhole electric heating in heavy oil reservoirs, characterized in that, The method includes: Obtain a heavy oil start-up temperature and pressure chart, which defines the start-up temperature threshold and start-up pressure gradient threshold required for heavy oil to begin flowing under specific reservoir permeability and temperature conditions. Establish a numerical model of heat transfer and seepage coupling from the wellbore to the target formation; Using the starting temperature threshold and the starting pressure gradient threshold as target conditions, the minimum thermal power input from the wellbore is obtained by iterative calculation through the heat transfer and seepage coupling numerical model to make the temperature and pressure of the target formation reach the target conditions. Based on the minimum thermal power, a compensation calculation is performed for the heat loss from the ground to the target stratum to determine the matching operating power that the ground electric heating system needs to provide.

2. The method according to claim 1, characterized in that, The coupled heat transfer and seepage numerical model includes a one-dimensional energy conservation model along the wellbore axis. This model considers convective heat transfer of the fluid within the wellbore, radial heat conduction through the tubing and formation, and latent heat of vapor condensation phase change. The expression for this one-dimensional energy conservation model is as follows: in, This refers to the temperature of the fluid in the wellbore, measured in Kelvin (K). The coupling temperature of the outer surface of the wellbore is in K; t is time in seconds; z is the axial coordinate of the wellbore in meters. The density of the fluid is expressed in kg·m³. -3 A represents the cross-sectional area of ​​the fluid flow within the wellbore, in meters (m²). 2 ; The specific heat capacity at constant pressure of a fluid is expressed in J·kg. -1 ·K -1 Q represents volumetric flow rate, in cubic meters per second (m³). 3 ·s -1 U is the overall heat transfer coefficient after adjusting for convection within the well and radial heat conduction from the casing / cement sheath / near-wellbore formation, expressed in W·m³. -2 · K -1 P represents the circumference of the inner wall, in meters (m). The latent heat of steam condensation is expressed in J·kg. -1 ; This represents the mass of water that changes from steam to liquid water per unit length of wellbore per unit time, and the unit is kg·m. -1 ·s -1 .

3. The method according to claim 1, characterized in that, The coupled heat transfer and seepage numerical model also includes a radial unsteady heat transfer model from the wellbore to the formation. This radial unsteady heat transfer model is used to solve for the wellbore coupling temperature and the near-wellbore formation temperature field. The expression for the radial unsteady heat transfer model is as follows: in, This represents the convective heat transfer coefficient inside the wellbore, with units of W·m. -2 ·K -1 ; This represents the external convective heat transfer coefficient of the wellbore, with units of W·m. -2 ·K -1 ; This represents the outer radius of the j-th wellbore, in meters. The radius of the inner layer of the wellbore is represented by j, in meters; L represents the friction length of the wellbore, in meters. This represents the thermal conductivity of the j-th layer, in W·m. -1 ·K -1 ; Density of rock is expressed in kg·m³. -3 ; Specific heat capacity of rock is expressed in J·kg. -1 ·K -1 T represents formation temperature, in Kelvin (K); t represents time, in seconds (s). The density of the fluid is expressed in kg·m³. -3 ; Specific heat capacity of a fluid is expressed in J·kg. -1 ·K -1 ; Radial seepage velocity, in m·s -1 ; Represents radial coordinates, in meters (m). A heat source generated by an electric heating element or a chemical reaction, measured in W·m. -3 ;in The effective thermal conductivity is expressed in W·m. -1 ·K -1 ; , This refers to the temperature of the fluid in the wellbore, measured in Kelvin (K). The coupling temperature of the outer surface of the wellbore is expressed in Kelvin (K).

4. The method according to claim 1, characterized in that, The coupled heat transfer and seepage numerical model also includes a formation radial seepage pressure drop model, which is used to calculate the near-wellbore formation pressure distribution. The expression for the formation radial seepage pressure drop model is as follows: in, Indicates formation porosity; This represents the overall compressibility factor, with units of Pa. -1 ; This represents formation pressure, measured in Pa. This indicates viscosity, and the unit is mPa·s; k Reservoir permeability is expressed in mD. Represents radial coordinates, in meters (m). The equivalent "pressure source term" represents the rate of pressure change per unit time and per unit volume of formation due to fluid injection or production, measured in Pa·s. -1 .

5. The method according to claim 1, characterized in that, The minimum thermal power input from the wellbore required to achieve the target temperature and pressure conditions of the target formation includes: Set multiple ground heating power outputs as initial input values; Based on the aforementioned heat transfer and seepage coupling numerical model, the temperature and pressure distribution of the target formation under each heating power is calculated. Determine whether the temperature distribution reaches the start-up temperature threshold and whether the pressure distribution reaches the start-up pressure gradient threshold; By iteratively adjusting the ground heating power, the minimum heat power that simultaneously satisfies the temperature threshold and pressure threshold is found, and this minimum heat power is taken as the minimum heat power.

6. The method according to claim 1, characterized in that, The calculation of heat loss compensation from the ground to the target formation based on the minimum thermal power includes: The minimum thermal power is taken as the effective thermal demand of the target formation; An energy transmission link model is established from the ground to the target stratum, and the model is used to calculate the total heat loss of energy supplied from the ground during the transmission to the target stratum; Add the minimum thermal power to the total heat loss calculated by the model to obtain the theoretical thermal power that the ground electric heating system needs to provide; The theoretical thermal power is converted into an equivalent electrical power value, which is used as the matching operating power of the ground electric heating system.

7. The method according to claim 1, characterized in that, The process of obtaining the heavy oil start-up temperature and pressure chart includes: Through core displacement experiments, the initiation pressure gradient of heavy oil in the core was measured under different displacement rates and temperatures. Based on experimental data, a curve relating injection rate to pressure gradient was established, and the proposed initiation pressure gradient was determined by the intersection of the reverse extension of the curve with the pressure gradient coordinate axis. Experiments were repeated with cores of different permeabilities and under different temperature conditions to obtain multiple sets of proposed initiation pressure gradient data; Based on the gradient data, construct the heavy oil start-up temperature and pressure chart.

8. A device for calculating the supply and demand of electric heating energy in heavy oil reservoirs, characterized in that, The device includes: The memory is configured to store instructions; The processor is configured to retrieve the instructions from the memory and, when executing the instructions, to implement the method for calculating the supply and demand matching of downhole electric heating energy for heavy oil reservoirs according to any one of claims 1 to 7.

9. The apparatus according to claim 8, characterized in that, The apparatus further includes an experimental device for determining the heavy oil start-up pressure, the experimental device comprising: High-precision injection pumps; piston containers; constant temperature chambers; pressure monitoring systems; six-way valves; core holders; metering test tubes; confining pressure pumps.

10. A machine-readable storage medium storing instructions thereon, characterized in that, When executed by a processor, this instruction causes the processor to be configured to perform the method for calculating the supply and demand matching of downhole electric heating energy for heavy oil reservoirs according to any one of claims 1 to 7.

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