CN-122021089-A - Method and system for determining convective heat effect of karst geothermal system

CN122021089ACN 122021089 ACN122021089 ACN 122021089ACN-122021089-A

Abstract

The invention discloses a method and a system for determining a convection heat effect of a karst geothermal system, wherein the method comprises the steps of measuring thermal property parameters of a rock sample taken from a target area, converting the thermal property parameters into a column coordinate system, forming a rock thermal property column, constructing a geothermal geological model, based on the rock thermal property column, combining flow characteristics and heat transfer characteristics of underground water in the target area, constructing a geothermal geological mathematical model, only configuring a thermal boundary condition on the mathematical model to obtain heat flux at a model boundary, simultaneously configuring the thermal boundary condition and a constant pressure boundary condition on the geothermal geological mathematical model, combining the heat flux to obtain a free convection heat collecting effect at the model boundary, further configuring the thermal boundary condition, the constant pressure boundary condition and a water head boundary condition on the mathematical model, and combining the free convection heat collecting effect to obtain a forced convection heat collecting effect at the model boundary. The invention realizes quantitative research on the heat accumulating mechanism of the karst geothermal system.

Inventors

FENG JIANBIN
ZHANG YING
LUO JUN
ZENG YAN
YUAN XIAORUI

Assignees

中国石油化工股份有限公司
中国石油化工股份有限公司石油勘探开发研究院

Dates

Publication Date: 20260512
Application Date: 20241111

Claims (10)

1. A method of determining convective heating effects in a karst geothermal system, comprising: Measuring thermal physical parameters of a rock sample taken from a target area, and converting the thermal physical parameters into a cylindrical coordinate system to form a rock thermal physical column; constructing a geothermal geological model by utilizing the rock thermophysical column, and constructing a geothermal geological mathematical model by combining the flow characteristics and the heat transfer characteristics of groundwater in the target area based on the geothermal geological model; configuring only the thermal boundary conditions to the mathematical model to obtain a heat flux at the model boundary; and simultaneously configuring the thermal boundary condition and the constant pressure boundary condition in the mathematical model, combining the thermal flux, acquiring the heat collecting effect of free convection at the model boundary as the free convection heat effect of the target area, further configuring the thermal boundary condition, the constant pressure boundary condition and the water head boundary condition in the mathematical model, combining the heat collecting effect of free convection, and acquiring the heat collecting effect of forced convection at the model boundary as the forced convection heat effect of the target area.
2. The method of claim 1, wherein in the step of constructing a geothermal geologic model using the rock thermophysical column, comprising: Dividing the target area into a plurality of rock stratum units according to geophysical logging data and drilling data, and integrating the rock thermophysical parameters with each rock stratum unit according to the dividing result, so as to construct the geothermal geological model, wherein the geothermal geological model is a two-dimensional model or a three-dimensional model.
3. The method according to claim 1 or 2, characterized in that the method further comprises: And (3) determining the coupling relation between the temperature field and the seepage field in the target area by equivalently using the target area as a porous medium and combining the change characteristics of the physical parameters of the underground water along with the temperature so as to obtain the flow characteristics and the heat transfer characteristics of the underground water in the target area.
4. A method according to claim 3, wherein the flow characteristics and heat transfer characteristics of groundwater in the target area are represented by the following expression: Wherein, the Represents the equivalent porosity of the porous medium, ρ w represents the density of groundwater, t represents time, Represents a gradient operator, q represents the velocity of groundwater, K represents a permeability coefficient, g represents gravitational acceleration, Representing the pressure gradient in the direction of gravity, Represents a high gradient, c w represents a specific heat capacity of groundwater, ρ ma represents a density of a porous medium, c ma represents a specific heat capacity of a porous medium, T represents a temperature, Represents the temperature gradient, lambda w represents the thermal conductivity of groundwater, lambda ma represents the thermal conductivity of porous media, and Q r represents the radioactive heat generation of rock.
5. The method of claim 4, wherein the change in physical parameters of the groundwater with temperature is characterized by the following expression: c w (T)＝12010.14-80.40T+0.31T 2 -5.38×10 -4 T 3 +3.63×10 -7 T 4 μ w (T)＝0.004-2.108×10 -5 T+3.858×10 -8 T 2 -2.397×10 -11 T 3 ρ w (T)＝1002.4-0.1905T-0.0025T 2 Wherein μ w represents the dynamic viscosity of groundwater.
6. The method according to any one of claims 1 to 5, wherein in the step of obtaining the heat flux at the model boundary, it comprises: and performing numerical simulation by using a geothermal geological mathematical model provided with the thermal boundary conditions, so as to obtain the geothermal gradient of the model only under the action of conduction and heat transfer, and further combining the geothermal gradient with the thermal conductivity of the model to calculate the heat flux at the boundary of the model.
7. The method of claim 6, wherein the step of obtaining the free convection heat effect at the model boundary as the free convection heat effect of the target region comprises: According to the simulation parameters which are the same as those of the geothermal geological mathematical model provided with the thermal boundary conditions, the geothermal geological mathematical model provided with the thermal boundary conditions and the constant pressure boundary conditions are utilized to carry out numerical simulation, so that the heat flux at the model boundary under the combined action of conduction heat transfer and fluid heat transfer, which is irrelevant to the fluctuation of the terrain, is obtained, and based on the simulation parameters, the free convection heat accumulation effect at the model boundary is calculated by combining the heat flux of the geothermal geological mathematical model provided with the thermal boundary conditions.
8. The method of claim 7, wherein the step of obtaining the heat accumulation effect of the forced convection at the model boundary as the forced convection heat effect of the target region comprises: According to the simulation parameters same as the geothermal geological mathematical model simultaneously provided with the thermal boundary condition and the constant pressure boundary condition, numerical simulation is carried out by utilizing the geothermal geological mathematical model simultaneously provided with the thermal boundary condition, the constant pressure boundary condition and the water head boundary condition, so that the heat flux at the model boundary under the combined action of conduction heat transfer and fluid heat transfer, which is related to the relief, is obtained, and based on the simulation parameters, the heat accumulation effect of forced convection at the model boundary is calculated by combining the heat accumulation effect of free convection at the model boundary.
9. The method of any one of claims 1-8, wherein after constructing the geothermal geological mathematical model, the method further comprises: And performing gridding treatment on the constructed geothermal geological model to obtain heat flux at the model boundary, free convection heat accumulation effect at the model boundary and forced convection heat accumulation effect at the model boundary, which are in accordance with reality, by utilizing the gridding geothermal geological model.
10. A system for determining convective heating effects of a karst geothermal system, the system comprising: The parameter acquisition module is used for measuring the thermophysical parameters of the rock sample taken from the target area and converting the thermophysical parameters into a column coordinate system to form a rock thermophysical column; the model construction module is used for constructing a geothermal geological model by utilizing the rock thermophysical columns, and based on the geothermal geological model, a geothermal geological mathematical model is constructed by combining the flow characteristics and the heat transfer characteristics of groundwater in the target area; a first thermal effect acquisition module for configuring only thermal boundary conditions to the mathematical model to obtain a heat flux at a model boundary; The second thermal effect obtaining module is configured to simultaneously configure the thermal boundary condition and the constant pressure boundary condition in the mathematical model, and combine the thermal flux to obtain a thermal gathering effect of free convection at a model boundary as a free convection thermal effect of the target area, and further simultaneously configure the thermal boundary condition, the constant pressure boundary condition and the water head boundary condition in the mathematical model, and combine the thermal gathering effect of free convection to obtain a thermal gathering effect of forced convection at the model boundary as a forced convection thermal effect of the target area.

Description

Method and system for determining convective heat effect of karst geothermal system Technical Field The invention belongs to the technical field of geothermal resource development, and particularly relates to a method and a system for determining a convective heating effect of a karst geothermal system. Background Geothermal resources are clean and renewable energy sources with great competitive power, have the advantages of large resource quantity, high energy utilization efficiency, low cost, good energy saving and emission reduction effects and the like, and are one of important alternative new energy sources in the future. The karst heat storage means heat storage composed of carbonate rock (limestone, dolomite, marble, etc.), sulfate rock (gypsum, anhydrite, mirabilite, etc.), and halide rock (rock salt, potassium salt, magnesium salt, etc.) in which developed rock is dissolved. The karst thermal reservoir has good vertical seepage and horizontal runoff conditions due to karst fracture development, the water yield is large, tail water after geothermal utilization is easy to recharge, and the karst thermal reservoir is the dominant reservoir with the most development potential. In karst geothermal systems, fluid convection rapidly transfers heat, causing localized significant thermal anomalies, forming "dessert areas" for geothermal field exploration and development. Therefore, the quantitative evaluation of the heat accumulation effect of the convection activity of the underground water has special significance for the geological evaluation and the causal mechanism research of the karst heat storage geothermal resource. In karst thermal storage, geological and hydrodynamic conditions are complex, deep temperature fields are affected by anisotropy of underground media and fluid activity, and a fluid flow system can evolve with time, so that forced convection driven by terrain and natural thermal convection driven by buoyancy tend to act on a geothermal system together. However, limited to research methods and scales, existing karst thermal storage temperature field structures and poly thermal mechanical studies remain dominated by qualitative analysis, and quantitative studies on the poly thermal mechanism of convection-conduction complex geothermal systems are lacking. In addition, in the few digital-analog simulation quantitative researches, the research scale is often limited to a certain secondary construction unit or geothermal field, the research on the heat accumulating mechanism of the river basin scale groundwater flow system is lacking, and particularly, the research on the combined action mode of the forced convection driven by terrain and the natural convection driven by buoyancy and the heat accumulating effect thereof is less. Therefore, a method for quantitatively evaluating the forced convection and natural convection heat effects of underground water in karst heat storage is needed, so that the heat accumulating mechanism of a karst geothermal system is scientifically known, and the karst heat Chu Gaowen and high-yield geothermal well position layout basis are determined. Disclosure of Invention In order to solve the problems, the embodiment of the invention provides a method for determining a convection heat effect of a karst geothermal system, which comprises the steps of measuring thermal property parameters of a rock sample taken from a target area and converting the thermal property parameters into a column coordinate system to form a rock thermal property column, constructing a geothermal geological model by utilizing the rock thermal property column, combining flow characteristics and heat transfer characteristics of groundwater in the target area based on the rock thermal property column, constructing a geothermal geological mathematical model, only configuring a thermal boundary condition to the mathematical model to obtain heat flux at a model boundary, simultaneously configuring the thermal boundary condition and a constant pressure boundary condition to the mathematical model, combining the heat flux to obtain a free convection heat effect of free convection at the model boundary as the free convection heat effect of the target area, and further simultaneously configuring the thermal boundary condition, the constant pressure boundary condition and a water head boundary condition to the mathematical model, and combining the free convection heat accumulation effect to obtain a forced convection heat accumulation effect at the model boundary as the forced convection heat effect of the target area. Preferably, the step of constructing the geothermal geologic model by using the rock thermophysical column comprises dividing the target region into a plurality of rock stratum units according to geophysical logging data and drilling data, and integrating the rock thermophysical parameters with each rock stratum unit according to the division result, thereby constructing the geotherma