A thermal reservoir engineering evaluation method for geothermal resources

Abstract

A method for evaluating geothermal reservoir engineering for geothermal resources, the steps of which include: 1) analyzing the existing geothermal well pumping test reports in the area based on pumping test data; 2) establishing a geothermal numerical model of the study area using existing parameters; 3) simulating the maximum reinjection volume of reinjection wells under different wellhead reinjection pressure conditions using the numerical model to determine the maximum reinjection volume of reinjection wells in the area; 4) determining the optimal well spacing of geothermal wells using the numerical model; 5) selecting the minimum well spacing of production and injection wells using the numerical simulation method; 6) flexibly selecting the well network form in combination with the actual ground conditions; 7) calculating the recoverable heat capacity per square kilometer based on the principle of combining the ground and underground; 8) calculating the heat capacity rate; the advantages are: strong operability, design and optimization of the optimal well spacing of production and injection wells, production and injection volume, and clear parameters such as the reasonable water intake of geothermal wells, well spacing, reinjection temperature, and heat capacity rate. The invention comprehensively uses a variety of methods such as theoretical formulas, empirical formulas, and numerical simulations.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal resource development, and in particular to a heat storage engineering evaluation method for geothermal resources. Background Art

[0002] Geothermal resources refer to renewable heat energy stored inside the earth. Under the current situation of energy shortage and serious air pollution in my country, geothermal resources have attracted widespread attention with their advantages of cleanliness, renewable energy, large energy, and relatively simple development and utilization equipment. More and more companies have joined the army of geothermal resource heating development. Although there are many geothermal resource evaluation projects in my country in recent years, as an underground resource development, developers often pay more attention to the amount of geothermal resources. A lot of research work has been carried out on the evaluation of geothermal resource quantity, but there is a lack of research on thermal storage engineering for geothermal resource development. There is no unified and reasonable thermal storage engineering evaluation method in the existing technical system. The lack of a complete method system guidance has led to a strong randomness in the deployment of mining and injection wells during the implementation of geothermal projects, unreasonable setting of mining and injection well development parameters, rapid decline in geothermal heat storage pressure, reduced water temperature of geothermal wells, ground subsidence and other problems, resulting in a waste of geothermal resources and poor economic benefits of geothermal resource development. Summary of the invention

[0003] The present invention provides a geothermal resource heat storage engineering evaluation method for solving the defects of the prior art.

[0004] The technical solution of the present invention is:

[0005] A method for evaluating geothermal resources thermal storage engineering, the steps comprising:

[0006] 1) Establish the relationship between water inflow and water level drawdown based on the pumping test data, and analyze the existing geothermal well pumping test reports in the area;

[0007] 2) Use the existing drilling, measurement and recording data and the geological structure, lithology, thermophysical properties and other parameters of the thermal reservoir to establish a geothermal numerical model of the study area, and use numerical simulation to calculate the relationship between the thermal reservoir thickness and the stable water inflow at different water level drawdowns, so as to determine the stable water inflow of different geothermal wells;

[0008] 3) Use numerical models to simulate the maximum recharge volume of the recharge wells under different wellhead recharge pressure conditions while keeping the heat reservoir energy relatively stable and the geothermal wells maintaining stable production capacity; then determine the maximum recharge volume of the recharge wells in the study area based on the ground recharge equipment conditions and geothermal well production conditions;

[0009] 4) Use numerical models to simulate the distribution characteristics of thermal reservoir pressure field under different geothermal well spacings, and determine the optimal geothermal well spacing based on empirical formulas;

[0010] 5) Using numerical simulation methods, calculate the distance of the cold front edge of the reinjection well within a set heating cycle under different reinjection temperatures and different production and injection well distances, and select the distance where the cold front edge cannot reach the geothermal well heating area as the minimum production and injection well distance;

[0011] 6) Determine the ratio of production and injection wells according to the demand for geothermal resources, the stable water inflow of geothermal wells and reinjection conditions, and flexibly select the well network form based on the actual ground conditions;

[0012] 7) Based on the principle of combining above-ground and underground, the water-heat balance method is used to calculate the recoverable heat capacity per square kilometer;

[0013] 8) Calculate the heat capacity and reserve the peak load design.

[0014] In the step 1), the permeability coefficient is calculated by analyzing the existing geothermal well pumping test report in the area. The calculation formula is: ; Where: K—permeability coefficient, m / d; R—influence radius, m; Q—geothermal well water yield, m 3 / d; S—stable water level drawdown, m; M—thermal reservoir thickness, m; r—wellbore radius, m.

[0015] The empirical formula in step 4) is: ;

[0016] Where: R is the influence radius of the geothermal well, m; S is the stable water level drawdown, m; M is the thickness of the thermal reservoir, m; K is the permeability coefficient, m / d.

[0017] The geothermal well layout in step 6) includes two-point, four-point, and six-point well networks.

[0018] The water-heat balance method in step 7) is calculated as follows: ;

[0019] Where: Qw—recoverable heat capacity per square kilometer, J / km 2 ; Q—hot water well production, m 3 / d; Cw—average specific heat capacity of hot water, J / m 3 ℃; Tw—average temperature of geothermal water, ℃; T0—reinjection temperature, ℃; n—number of geothermal wells, group; A—available heat storage area, km 2 .

[0020] The heat capacity in step 8) is the regional carrying capacity of geothermal resources.

[0021] The heat capacity rate calculation in the step 8) includes: the ratio of the heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities to the heat load required by the ground buildings within a heating season; the planned building area of ​​a single community is divided by the community plot ratio to obtain the surface area of ​​the community, and the geothermal heat load that can be extracted from the geothermal reservoir within the surface area of ​​a single community within a heating season is calculated; all planned communities are accumulated to obtain the total heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities within a heating season; the total heating load is divided by the ground heat load required of all communities to obtain the heat capacity rate of the area.

[0022] The advantages of the present invention are as follows: the heat storage engineering evaluation method for geothermal resources in the present invention is applicable to geothermal blocks to be developed that have certain exploration data and relatively solid geothermal resources. In view of the irregular and unreasonable geothermal well layout and implementation in the existing geothermal resource development system, a complete set of heat storage engineering research methods for geothermal resource evaluation projects is proposed. The method is highly operational, and the optimal production and injection well spacing, production and injection volume are designed and optimized, and parameters such as reasonable water intake of geothermal wells, well spacing, reinjection temperature, and heat capacity are clarified. In addition, the invention comprehensively uses theoretical formulas, empirical formulas, numerical simulations and other methods to ensure the reliability of the results, which has practical guiding significance for the planning and feasibility study of geothermal resource evaluation projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a geothermal concept numerical model in a specific embodiment of the present invention.

[0024] Figure 2 This is a diagram showing the relationship between reservoir thickness and stable water inflow at different water level drawdowns in a specific embodiment of the present invention.

[0025] Figure 3 This is a chart showing the maximum recharge volume of a recharge well under different wellhead recharge pressures at different thermal reservoir thicknesses in a specific embodiment of the present invention.

[0026] Figure 4 This is a diagram showing the advancement of the front edge of the recharge water cooling front under different production and injection well distance conditions in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0028] A method for evaluating geothermal resources thermal storage engineering, the steps comprising:

[0029] 1) Establish the relationship between water inflow and water level drawdown based on the pumping test data, and analyze the existing geothermal well pumping test reports in the area;

[0030] 2) Use the existing drilling, measurement and recording data and the geological structure, lithology, thermophysical properties and other parameters of the thermal reservoir to establish a geothermal numerical model of the study area, and use numerical simulation to calculate the relationship between the thermal reservoir thickness and the stable water inflow at different water level drawdowns, so as to determine the stable water inflow of different geothermal wells;

[0031] 3) Use numerical models to simulate the maximum recharge volume of the recharge wells under different wellhead recharge pressure conditions while keeping the heat reservoir energy relatively stable and the geothermal wells maintaining stable production capacity; then determine the maximum recharge volume of the recharge wells in the study area based on the ground recharge equipment conditions and geothermal well production conditions;

[0032] 4) Use numerical models to simulate the distribution characteristics of thermal reservoir pressure field under different geothermal well spacings, and determine the optimal geothermal well spacing based on empirical formulas;

[0033] 5) Using numerical simulation methods, calculate the distance of the cold front edge of the reinjection well within a set heating cycle under different reinjection temperatures and different production and injection well distances, and select the distance where the cold front edge cannot reach the geothermal well heating area as the minimum production and injection well distance;

[0034] 6) Determine the ratio of production and injection wells according to the demand for geothermal resources, the stable water inflow of geothermal wells and reinjection conditions, and flexibly select the well network form based on the actual ground conditions;

[0035] 7) Based on the principle of combining above-ground and underground, the water-heat balance method is used to calculate the recoverable heat capacity per square kilometer;

[0036] 8) Calculate the heat capacity and reserve the peak load design.

[0037] In the step 1), the permeability coefficient is calculated by analyzing the existing geothermal well pumping test report in the area. The calculation formula is: ; Where: K—permeability coefficient, m / d; R—influence radius, m; Q—geothermal well water yield, m 3 / d; S—stable water level drawdown, m; M—thermal reservoir thickness, m; r—wellbore radius, m.

[0038] The empirical formula in step 4) is: Where: R is the influence radius of the geothermal well, m; S is the stable water level drawdown, m; M is the thickness of the thermal reservoir, m; K is the permeability coefficient, m / d.

[0039] The geothermal well layout in step 6) includes two-point, four-point, and six-point well networks.

[0040] The water-heat balance method in step 7) is calculated as follows: ; Where: Qw—recoverable heat capacity per square kilometer, J / km 2 ; Q—hot water well production, m 3 / d; Cw—average specific heat capacity of hot water, J / m 3 ℃; Tw—average temperature of geothermal water, ℃; T0—reinjection temperature, ℃; n—number of geothermal wells, group; A—available heat storage area, km 2 .

[0041] The heat capacity in step 8) is the regional carrying capacity of geothermal resources.

[0042] The heat capacity rate calculation in the step 8) includes: the ratio of the heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities to the heat load required by the ground buildings within a heating season; the planned building area of ​​a single community is divided by the community plot ratio to obtain the surface area of ​​the community, and the geothermal heat load that can be extracted from the geothermal reservoir within the surface area of ​​a single community within a heating season is calculated; all planned communities are accumulated to obtain the total heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities within a heating season; the total heating load is divided by the ground heat load required of all communities to obtain the heat capacity rate of the area.

Claims

1. A method for evaluating geothermal thermal storage engineering, characterized in that: The steps include: 1) Establish the relationship between water inflow and water level drawdown based on pumping test data, and analyze existing geothermal well pumping test reports; 2) Use the existing drilling, measurement and recording data and the geological structure, lithology, thermophysical properties and other parameters of the thermal reservoir to establish a geothermal numerical model of the study area, and use numerical simulation to calculate the relationship between the thermal reservoir thickness and the stable water inflow at different water level drawdowns, so as to determine the stable water inflow of different geothermal wells; 3) Use numerical models to simulate the maximum recharge volume of the recharge wells under different wellhead recharge pressure conditions while maintaining the thermal reservoir energy stability and the geothermal wells maintaining stable production capacity; then determine the maximum recharge volume of the recharge wells in the study area based on the ground recharge equipment conditions and geothermal well production conditions; 4) Use numerical models to simulate the distribution characteristics of thermal reservoir pressure field under different geothermal well spacings, and determine the optimal geothermal well spacing based on empirical formulas; 5) Using numerical simulation methods, calculate the distance of the cold front edge of the reinjection well within a set heating cycle under different reinjection temperatures and different production and injection well distances, and select the distance where the cold front edge cannot reach the geothermal well heating area as the minimum production and injection well distance; 6) Determine the ratio of production and injection wells according to the demand for geothermal resources, the stable water inflow of geothermal wells and reinjection conditions, and flexibly select the well network form based on the actual ground conditions; 7) Based on the principle of combining above-ground and underground, the water-heat balance method is used to calculate the recoverable heat capacity per square kilometer; 8) Calculate the heat capacity and reserve the peak load design; The empirical formula in step 4) is: ; Where: R—geothermal well influence radius, m; S—stable water level drawdown, m; M—thermal reservoir thickness, m; K—permeability coefficient, m / d; The heat capacity in step 8) is the regional carrying capacity of geothermal resources; The heat capacity rate calculation in step 8) includes: the ratio of the total heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities in the region to the heat load required by the ground buildings within a heating season; the specific steps are: the planned building area of ​​a single community in the region is divided by the community's plot ratio to obtain the surface area of ​​the community, and the geothermal heat load that can be extracted from the geothermal reservoir within the surface area of ​​a single community within a heating season is calculated; all planned communities are accumulated to obtain the total heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities in the region within a heating season; the total heating load that can be provided by the geothermal reservoir within the area of ​​all planned communities in the region is divided by the heat load required by the ground buildings to obtain the heat capacity rate of the region.

2. A geothermal resource heat storage engineering evaluation method according to claim 1, characterized in that: In the step 1), the permeability coefficient is calculated by analyzing the existing geothermal well pumping test report in the area. The calculation formula is: ; Where: K—permeability coefficient, m / d; R—geothermal well influence radius, m; Q—geothermal well water yield, m 3 / d; S—stable water level drawdown, m; M—thermal reservoir thickness, m; r—wellbore radius, m.

3. A geothermal resource heat storage engineering evaluation method according to claim 1, characterized in that: The geothermal well layout in step 6) includes two-point, four-point, and six-point well networks.

4. A geothermal resource heat storage engineering evaluation method according to claim 1, characterized in that: The water-heat balance method in step 7) is calculated as follows: ; Where: Qw—recoverable heat capacity per square kilometer, J / km 2 ; Q—geothermal well water yield, m 3 / d; Cw—average specific heat capacity of hot water, J / m 3 ℃; Tw—average temperature of geothermal water, ℃; T0—reinjection temperature, ℃; n—number of geothermal wells, group; A—available heat storage area, km 2 .

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