Dynamic calculation method for geothermal reserves

Abstract

The invention discloses a dynamic calculation method for geothermal reserves, belongs to the technical field of geothermal reserve estimation, and can solve the problem that an existing calculation mode cannot accurately reflect complex dynamic characteristics of geothermal reservoirs, and consequently the error between a reserve calculation result and the actual situation is large. The method comprises the following steps: S1, determining the current heat storage temperature of a target area at a target depth, and determining a temperature influence coefficient of the porosity of heat storage rock in the target area according to the current heat storage temperature; s2, determining a pressure influence coefficient and a fluid influence coefficient of the porosity, and determining the current porosity of the thermal storage rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; and S3, determining the current geothermal reserves of the target area according to the current thermal storage temperature and the current porosity. The method is used for estimating geothermal reserves.

Description

Technical Field

[0001] The invention relates to a dynamic calculation method of geothermal reserves, belonging to the technical field of geothermal reserves estimation. Background Art

[0002] The existing geothermal reserve calculation formula is as follows: ; ; ; ; ; ;in: is the amount of heat stored in the heat storage (J); is the heat stored in the rock (J); is the amount of water stored in the heat storage (m 3 ); is the static storage volume of hot water in the heat reservoir pores up to the calculation time (m 3 ); is the amount of water released from the thermal storage when the water level drops to the current water extraction capacity limit depth (m 3 ); is the heat stored in water (J); is the area of ​​the calculation area (m 2 ); is the heat reservoir thickness (m); is the density of thermal reservoir rock (kg / m 3 ); is the specific heat of the heat storage rock (J / kg.℃); is the porosity of the reservoir rock; is the heat storage temperature (°C); is the local annual average temperature (℃); is the density of geothermal water (kg / m 3 ); is the hydraulic conductivity; is the height above the calculation starting point (m); is the specific heat of water (J / kg.℃).

[0003] The above calculation formula cannot accurately reflect the complex dynamic characteristics of geothermal reservoirs, resulting in a large error between the reserve calculation results and the actual situation. Specifically, (1) the formula assumes that the thermal reservoir temperature is fixed, which is inconsistent with the actual situation. In practical applications, the temperature of the heat reservoir will change with time and depth. Especially in the process of geothermal development, heat transfer will cause temperature changes. (2) This formula assumes that the porosity is a constant, which is not true in practice. With the changes in pressure and temperature, as well as the process of fluid loss, the porosity will change dynamically, thus affecting the calculation of geothermal reserves. This formula does not take into account the impact of fluid loss on porosity and reserves, especially during the development process, when fluid loss may lead to changes in porosity, thus affecting the available heat of the thermal reservoir. This allows for a more accurate calculation of thermal reserves. Summary of the invention

[0004] The present invention provides a dynamic calculation method for geothermal reserves, which can solve the problem that the existing calculation method cannot accurately reflect the complex dynamic characteristics of the geothermal reservoir, resulting in a large error between the reserve calculation result and the actual situation.

[0005] The present invention provides a method for dynamically calculating geothermal reserves, the method comprising: S1. Determine the current heat storage temperature of the target area at the target depth, and determine the temperature influence coefficient of the porosity of the heat storage rock in the target area according to the current heat storage temperature; S2, determining the pressure influence coefficient and the fluid influence coefficient of the porosity, and determining the current porosity of the thermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; S3. Determine the current geothermal reserve of the target area according to the current heat reservoir temperature and the current porosity.

[0006] Optionally, the determining of the current heat storage temperature of the target area at the target depth in S1 specifically includes: Determine the temperature distribution model of the target area according to the heat diffusion equation; The current heat reservoir temperature of the target area at the target depth is determined according to the temperature distribution model.

[0007] Optionally, the temperature distribution model of the target area is determined according to the heat diffusion equation, specifically: A general solution of the heat diffusion equation is obtained, and the general solution is used as a temperature distribution model of the target area.

[0008] Optionally, determining the current heat storage temperature of the target area at the target depth according to the temperature distribution model specifically includes: Acquiring an initial temperature and a steady-state temperature of the target area at a target depth; The current heat reservoir temperature of the target area at the target depth is determined according to the target depth, the initial temperature, the steady-state temperature and the temperature distribution model.

[0009] Optionally, determining the temperature influence coefficient of the porosity of the heat reservoir rock in the target area according to the current heat reservoir temperature in S1 specifically includes: Calculating a first difference between the current thermal storage temperature and a reference temperature; The first product of the first difference and the temperature expansion coefficient is calculated, and the sum of the first product and 1 is used as the temperature influence coefficient of the porosity of the thermal reservoir rock in the target area.

[0010] Optionally, the pressure influence coefficient for determining the porosity in S2 is specifically: The pressure influence coefficient of the porosity is determined according to the current pressure of the target area at the target depth and the pore compressibility coefficient.

[0011] Optionally, determining the pressure influence coefficient of the porosity according to the current pressure of the target area at the target depth and the pore compressibility coefficient specifically includes: Calculating a second difference between the current pressure of the target area at the target depth and the reference pressure; A second product of the second difference and the pore compressibility coefficient is calculated, and the difference between 1 and the second product is used as the pressure influence coefficient of the porosity.

[0012] Optionally, the fluid influence coefficient for determining the porosity in S2 is specifically: The fluid influence coefficient of the porosity is determined according to the fluid loss amount and the fluid loss coefficient of the target area per unit time.

[0013] Optionally, the fluid influence coefficient of the porosity is determined according to the fluid loss amount and the fluid loss coefficient of the target area per unit time, specifically: The third product of the fluid loss amount per unit time in the target area and the fluid loss coefficient is calculated, and the difference between 1 and the third product is used as the fluid influence coefficient of the porosity.

[0014] Optionally, the step of determining the current porosity of the thermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient in S2 specifically includes: Calculating a fourth product of the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; The product of the fourth product and the reference porosity is calculated as the current porosity of the thermal reservoir rock.

[0015] The beneficial effects that the present invention can produce include: The dynamic calculation method of geothermal reserves provided by the present invention considers the influence of changes in formation pressure, temperature, fluid loss and time on the porosity of thermal reservoir rocks, introduces temperature influence coefficient, pressure influence coefficient and fluid influence coefficient, so that the calculation of porosity is more accurate, and thus the calculation result of geothermal reserves is more accurate.

[0016] The dynamic calculation method of geothermal reserves provided by the present invention takes into account dynamic change factors such as temperature and porosity, and uses the heat diffusion equation and porosity optimization model to reflect the changes in geothermal reservoirs in real time and provide a more accurate reserve assessment. This method combines the advantages of numerical simulation and physical models, and improves the accuracy and real-time performance of geothermal reserve estimation through multi-variable and multi-physical field coupled calculation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for dynamically calculating geothermal reserves provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention is described in detail below in conjunction with embodiments, but the present invention is not limited to these embodiments.

[0019] The embodiment of the present invention provides a method for dynamically calculating geothermal reserves, such as Figure 1 As shown, the method includes: S1. Determine the current heat reservoir temperature of the target area at the target depth, and determine the temperature influence coefficient of the porosity of the heat reservoir rock in the target area according to the current heat reservoir temperature.

[0020] Wherein, determining the current heat storage temperature of the target area at the target depth specifically includes: (1) Determine the temperature distribution model of the target area based on the heat diffusion equation.

[0021] Specifically: obtain the general solution of the heat diffusion equation and use the general solution as the temperature distribution model of the target area.

[0022] The existing formula assumes a fixed thermal storage temperature However, the change of heat reservoir temperature with time and depth cannot be ignored in actual situations. Therefore, the present invention dynamically describes the temperature change of the heat reservoir by establishing a temperature distribution model, considering the heat diffusion equation as: , take its general solution As the temperature distribution model, represents the initial temperature, is the target depth The steady-state temperature at is the thermal diffusivity, is the density of the rock, is the specific heat capacity, It is the thermal conductivity of rock, a physical quantity that describes the thermal conductivity of materials. It can measure the ability of heat to pass through a unit area in a unit time. represents the error function, which describes the diffusion process of heat in the reservoir and the dynamic response of temperature as it changes over time. In smaller cases, , which means that when the depth is shallow or the time is short, the heat diffusion has not yet reached the deep layer. In larger cases, , indicating that the heat has diffused to this depth and the temperature has stabilized.

[0023] (2) Determine the current heat reservoir temperature of the target area at the target depth based on the temperature distribution model.

[0024] Specifically, the method includes: first obtaining the initial temperature and steady-state temperature of the target area at the target depth; and then determining the current heat storage temperature of the target area at the target depth according to the target depth, initial temperature, steady-state temperature and temperature distribution model.

[0025] In the embodiment of the present invention, the temperature distribution model is used To calculate the current thermal reservoir temperature of the target area at the target depth.

[0026] Since the prior art assumes that the temperature of the heat reservoir is fixed, it ignores the fact that the temperature of the heat reservoir changes with time and depth in practice. The present invention can dynamically calculate the temperature distribution by introducing the heat diffusion equation, and accurately reflect the temperature changes in the geothermal reservoir. Especially in the process of geothermal development, temperature is a dynamically changing factor, and the heat diffusion equation can take this change into account.

[0027] Among them, the temperature influence coefficient of the porosity of the heat reservoir rock in the target area is determined according to the current heat reservoir temperature, specifically including: first calculating the first difference between the current heat reservoir temperature and the reference temperature; then calculating the first product of the first difference and the temperature expansion coefficient, and taking the sum of the first product and 1 as the temperature influence coefficient of the porosity of the heat reservoir rock in the target area.

[0028] The specific calculation formula is as follows:

[0029] In the formula, is the temperature influence coefficient, is the temperature expansion coefficient, which indicates the effect of temperature change on porosity; is the current heat storage temperature, is a reference temperature (e.g. land surface temperature).

[0030] High temperatures tend to cause rocks to expand, reducing their porosity, while low temperatures may cause rocks to shrink and increase their porosity. This relationship can be explained by the temperature expansion coefficient The effect of temperature on porosity is usually linear, but under certain high temperature conditions, more complex nonlinear models can also be considered.

[0031] S2. Determine the pressure influence coefficient and fluid influence coefficient of porosity, and determine the current porosity of the thermal reservoir rock based on the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient.

[0032] The pressure influence coefficient of the porosity is determined by: determining the pressure influence coefficient of the porosity according to the current pressure of the target area at the target depth and the pore compressibility coefficient.

[0033] Specifically: firstly, the second difference between the current pressure of the target area at the target depth and the reference pressure is calculated; then, the second product of the second difference and the pore compressibility coefficient is calculated, and the difference between 1 and the second product is used as the pressure influence coefficient of the porosity.

[0034] The specific calculation formula is as follows:

[0035] In the formula, is the pressure influence coefficient, is the pore compressibility coefficient, which indicates the effect of pressure change on porosity; For the current pressure, is the reference pressure (e.g. surface pressure).

[0036] The porosity of rock changes with the change of formation pressure. Generally, the greater the pressure, the more compacted the rock will be and the porosity will decrease. This change can be described by a linear relationship or a more complex nonlinear relationship. It describes the effect of pressure change on porosity, where is the pore compressibility coefficient.

[0037] The fluid influence coefficient of the porosity is determined by: determining the fluid influence coefficient of the porosity according to the fluid loss amount and the fluid loss coefficient of the target area per unit time.

[0038] Specifically: the third product of the fluid loss in the target area per unit time and the fluid loss coefficient is calculated, and the difference between 1 and the third product is used as the fluid influence coefficient of the porosity.

[0039] The specific calculation formula is as follows:

[0040] In the formula, is the fluid influence coefficient, is the fluid loss coefficient, which indicates the effect of fluid loss on porosity; is the amount of fluid lost per unit time.

[0041] The fluid loss and porosity , Current Pressure The specific calculation formula is as follows:

[0042] In the formula, is the porosity The permeability of the rock under the condition of (unit: Darcy), is the viscosity of the fluid (unit: Pa·s), is the flow area (unit: m 2 ), is the reference pressure (in Pa), is the current pressure (unit: Pa), is the length of the flow path (in meters).

[0043] Fluid loss results in a decrease in the amount of fluid available in the pores, thus changing the porosity. It may be related to factors such as porosity, pressure, and rock permeability. Fluid loss will lead to an increase in porosity, especially during extraction or over-exploitation, where the porosity changes significantly. This effect can be measured by the fluid loss coefficient To quantify.

[0044] Among them, the current porosity of the thermal reservoir rock is determined according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient, specifically including: first calculating the fourth product of the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; then calculating the product of the fourth product and the reference porosity as the current porosity of the thermal reservoir rock.

[0045] Porosity of thermal reservoir rocks During the development process, the porosity will change with the change of pressure, temperature and fluid loss. The present invention uses the following formula to calculate the porosity: Make optimizations.

[0046]

[0047] Where: is the reference porosity (usually the reference pressure and reference temperature porosity under is the pore compressibility coefficient, which indicates the effect of pressure change on porosity (unit: 1 / Pa); is the current pressure (unit: Pa); is the reference pressure (e.g. surface pressure); is the thermal expansion coefficient, which indicates the effect of temperature change on porosity (unit: 1 / °C); is the current heat storage temperature (unit: °C); is the reference temperature (e.g., surface temperature); is the fluid loss coefficient, which indicates the effect of fluid loss on porosity (unit: m³ / Pa); It is the amount of fluid lost per unit time (unit: m³ / s).

[0048] The existing technology assumes that porosity is a constant, which cannot reflect the actual impact of pressure, temperature and fluid loss on porosity. By introducing a dynamic porosity update model, the present invention can accurately calculate the dynamic changes of porosity according to the changes in formation pressure, temperature, fluid loss and time, thereby improving the accuracy of reserve calculation.

[0049] S3. Determine the current geothermal reserve of the target area according to the current heat reservoir temperature and the current porosity.

[0050] After the current heat reservoir temperature and the current porosity are determined, the current geothermal reserves of the target area can be calculated using the existing geothermal reserve calculation formula. The present invention does not limit the specific calculation formula.

[0051] The present invention achieves higher accuracy and real-time performance in geothermal reserve estimation by considering the dynamic changes of factors such as temperature and porosity, and combining the advantages of numerical simulation and physical models. Compared with the prior art, the present invention can better reflect the complex characteristics of geothermal reservoirs, especially the dynamic changes during geothermal development, thereby effectively improving the accuracy and reliability of geothermal reserve estimation.

[0052] The present invention provides a specific calculation process of geothermal reserves, which mainly includes the following steps: 1. Enter initial data.

[0053] Calculate the area of ​​the target region (Unit: m²), reservoir thickness (Unit: m), surface pressure (reference pressure, unit: Pa), initial temperature (reference temperature, unit: °C); geothermal water density (Unit: kg / m³); Physical parameters of thermal reservoir rocks: rock density (Unit: kg / m³), rock specific heat (Unit: J / kg·℃); specific heat of water (Unit: J / kg·℃); Fluid loss (Unit: m³ / s); Reference porosity obtained through testing , fluid loss coefficient , pore compressibility coefficient and temperature expansion coefficient .

[0054] 2. Calculate the current heat storage temperature.

[0055] The temperature distribution at each depth and time point is solved by the heat diffusion equation , the error function model is used to dynamically update the current thermal storage temperature of the reservoir.

[0056] 3. Calculate the current porosity.

[0057] According to the actual current formation pressure , Current heat storage temperature and fluid loss , dynamically update the current porosity:

[0058] 4. Calculate the current geothermal reserves.

[0059] Use the updated current thermal storage temperature and current porosity Calculating heat storage in rocks and water and . Summarize the reserve data of each region to obtain the total current geothermal reserve.

[0060]

[0061] In the formula, is the current geothermal reserve, The heat stored in the rock, The heat stored in the water.

[0062] 5. Dynamically update parameters.

[0063] As time goes by, the current thermal storage temperature is updated in real time and current porosity , dynamically correcting the current estimate of geothermal reserves through numerical simulation.

[0064] Since the traditional geothermal reserve calculation formula cannot be dynamically modified, the present invention can continuously adjust the calculation parameters as the geothermal development progresses through numerical simulation and dynamic correction methods, provide real-time geothermal reserve estimation results, and improve the real-time and accuracy of the estimation method.

[0065] In addition, the present invention combines the coupled calculations of multiple physical fields such as thermal diffusion and porosity optimization, and can comprehensively consider the mutual influence of factors such as temperature, porosity, and fluid loss, thereby obtaining more accurate geothermal reserve estimation results.

[0066] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for dynamic calculation of geothermal reserves, characterized in that: The method comprises: S1. Determine the current heat storage temperature of the target area at the target depth, and determine the temperature influence coefficient of the porosity of the heat storage rock in the target area according to the current heat storage temperature; S2, determining the pressure influence coefficient and the fluid influence coefficient of the porosity, and determining the current porosity of the thermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; S3. Determine the current geothermal reserve of the target area according to the current heat reservoir temperature and the current porosity.

2. The method according to claim 1, characterized in that The step of determining the current heat storage temperature of the target area at the target depth in S1 specifically includes: Determine the temperature distribution model of the target area according to the heat diffusion equation; The current heat reservoir temperature of the target area at the target depth is determined according to the temperature distribution model.

3. The method according to claim 2, characterized in that The temperature distribution model of the target area is determined according to the heat diffusion equation, specifically: A general solution of the heat diffusion equation is obtained, and the general solution is used as a temperature distribution model of the target area.

4. The method according to claim 2, characterized in that: Determining the current heat storage temperature of the target area at the target depth according to the temperature distribution model specifically includes: Acquiring an initial temperature and a steady-state temperature of the target area at a target depth; The current heat reservoir temperature of the target area at the target depth is determined according to the target depth, the initial temperature, the steady-state temperature and the temperature distribution model.

5. The method according to claim 1, characterized in that Determining the temperature influence coefficient of the porosity of the heat reservoir rock in the target area according to the current heat reservoir temperature in S1 specifically includes: Calculating a first difference between the current thermal storage temperature and a reference temperature; The first product of the first difference and the temperature expansion coefficient is calculated, and the sum of the first product and 1 is used as the temperature influence coefficient of the porosity of the thermal reservoir rock in the target area.

6. The method according to claim 1, characterized in that The pressure influence coefficient for determining the porosity in S2 is specifically: The pressure influence coefficient of the porosity is determined according to the current pressure of the target area at the target depth and the pore compressibility coefficient.

7. The method according to claim 6, characterized in that The step of determining the pressure influence coefficient of the porosity according to the current pressure of the target area at the target depth and the pore compressibility coefficient specifically includes: Calculating a second difference between the current pressure of the target area at the target depth and the reference pressure; A second product of the second difference and the pore compressibility coefficient is calculated, and the difference between 1 and the second product is used as the pressure influence coefficient of the porosity.

8. The method according to claim 1, characterized in that The fluid influence coefficient for determining the porosity in S2 is specifically: The fluid influence coefficient of the porosity is determined according to the fluid loss amount and the fluid loss coefficient of the target area per unit time.

9. The method according to claim 8, characterized in that The fluid influence coefficient of the porosity is determined according to the fluid loss amount and the fluid loss coefficient of the target area per unit time, specifically: The third product of the fluid loss amount per unit time in the target area and the fluid loss coefficient is calculated, and the difference between 1 and the third product is used as the fluid influence coefficient of the porosity.

10. The method according to claim 1, characterized in that Determining the current porosity of the thermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient in S2 specifically includes: Calculating a fourth product of the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; The product of the fourth product and the reference porosity is calculated as the current porosity of the thermal reservoir rock.

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