Geothermal exploitation and injection well pattern design method

Abstract

The invention relates to a design method of a geothermal exploitation and injection well pattern, and belongs to the technical field of geothermal exploitation. The method specifically comprises the steps that S1, a mining and irrigation design is obtained; s2, establishing a geothermal geologic model; s3, the optimal single well water production amount is determined; s4, designing a mining and irrigation well pattern scheme; and S5, adopting a hydrothermal coupling simulation technology to optimize the mining and irrigation well pattern scheme. The invention aims to realize the maximization of the heat storage coverage area by reasonably utilizing the ground space, reduce the cost of new well drilling, ground construction, extraction and irrigation operation and the like, obtain the maximum geothermal energy and improve the heat energy utilization rate, thereby realizing the efficient and sustainable development and utilization of geothermal resources. In addition, thermal breakthrough can be avoided, the service life of the geothermal well is prolonged, and decision support is provided for large-scale development and utilization of geothermal resources. Meanwhile, the mining and filling design is easy to recombine and convert a well pattern, and later geothermal project adjustment is facilitated.

Description

Technical Field

[0001] This invention relates to a geothermal well network design method, belonging to the field of geothermal development technology. Background Technology

[0002] Geothermal energy is heat released from the Earth's interior. It is a common natural phenomenon deep within the Earth's crust, such as hot springs and geysers. Geothermal energy originates from the Earth's internal lava and exists in the form of heat, serving as the energy that causes volcanic eruptions and earthquakes. The temperature inside the Earth can reach as high as 7000 degrees Celsius, while at a depth of 80 to 100 kilometers, the temperature drops to 650 to 1200 degrees Celsius. Geothermal energy includes three types of shallow geothermal energy: soil-sourced, groundwater-sourced, and surface water-sourced, as well as hydrothermal medium-deep geothermal energy and dry hot rock geothermal resources.

[0003] Geothermal resources, as a valuable clean energy source, are receiving increasing attention for their development and utilization. Oilfield areas possess abundant geothermal resources, with enormous development potential in areas such as crude oil pipeline transportation, oilfield production, and residential heating. The development and utilization of geothermal energy involves two main approaches: utilizing produced water resources from oilfields and modifying geothermal wells.

[0004] In response to the current production and living needs of oilfields, and to better utilize geothermal resources comprehensively, we are actively conducting research on related technologies, including geothermal resource evaluation technology, sandstone formation reinjection technology, deep well heat exchange technology, and abandoned well conversion technology. Typically, we have established economic evaluation methods and models for oilfield geothermal development, developed geothermal resource evaluation software, and conducted detailed evaluations to select the best geothermal fields. Based on demonstration projects, we have developed absorption heat pump technology, sandstone formation reinjection technology, abandoned well conversion technology, deep well heat exchange technology, waste heat utilization technology for produced water in high water-cut oilfields, and combined gravity, magnetic, electrical, and seismic interpretation technology for geothermal exploration.

[0005] In the prior art, Chinese Utility Model Patent Application No. 202120046918.5 discloses a method for establishing a hydrothermal geothermal well factory, including geological model establishment; determination of stable geothermal well inflow; pressure field analysis and determination of geothermal well spacing; temperature field analysis and determination of production and irrigation well spacing; and well network deployment. Although this technology discloses the steps for well network optimization, it is not comprehensive, only considering two-point, four-point, and six-point well networks, which cannot match the actual site conditions to achieve the goal of sustainable development and utilization of geothermal resources.

[0006] For the development of geothermal resources, geothermal simulation methods are typically used to design extraction and injection schemes. In the process of geothermal energy development, reinjection is an essential step in the development of hydrothermal geothermal resources. However, reinjecting cold water may cause a thermal breakthrough, leading to a decrease in the water temperature of the extraction wells and a shortened lifespan of the geothermal field. Therefore, it is necessary to rationally plan the layout and design the parameters of geothermal extraction and reinjection wells to achieve the sustainable development and utilization of geothermal resources. Summary of the Invention

[0007] During the development and utilization of geothermal resources, the temperature and pressure of the reservoir decrease with the increase in extraction volume and time. The discharge of geothermal tailwater also causes thermal pollution to the environment. Reinjection of the reservoir can be an effective measure to solve these problems. Before geothermal development and utilization, scientifically and rationally planning the layout of extraction and injection wells, and exploring the optimal extraction and injection scheme to avoid premature thermal breakthroughs and achieve efficient utilization of geothermal resources, is beneficial to extending the service life of geothermal wells.

[0008] The ratio between geothermal extraction wells and reinjection wells determines the amount of reinjection water, while the distance between them affects the applied pressure during reinjection. To ensure that formation temperature does not exceed limits and to implement reinjection with minimal external pressure, a scientifically designed extraction and reinjection well network is essential. Hydrothermal coupling simulation is an effective method for understanding the reservoir response during geothermal development and has been widely applied in the planning and management of geothermal fields. For different reservoir types, suitable simulation software for geothermal temperature and pressure should be selected. For the actual geothermal heating area, different single-well extraction and reinjection volumes should be designed. The extraction and reinjection well network must be closely integrated with actual production needs. Combining economic evaluations of different methods, the most suitable and economical extraction and reinjection scheme should be selected to provide technical support for the rational exploitation of geothermal resources.

[0009] This invention provides a geothermal well network design method, aiming to maximize the geothermal reservoir coverage area through rational utilization of surface space, reduce costs associated with new well drilling, surface construction, and production / injection operations, obtain maximum geothermal energy, and improve thermal energy utilization efficiency, thereby achieving efficient and sustainable development and utilization of geothermal resources. Furthermore, this method can prevent thermal breakthrough, extend the service life of geothermal wells, and provide decision support for large-scale development and utilization of geothermal resources. Simultaneously, this production / injection design is easy to reorganize and convert, facilitating adjustments to geothermal projects in the future.

[0010] To ensure basic needs for industrial production and daily life, the design of geothermal extraction and irrigation is inherently linked to heating objectives in geothermal resource development. The potential for geothermal extraction is determined by numerous factors, such as the size of the reservoir, geological structure, hydrogeological conditions, and the design of the extraction and irrigation scheme. To achieve the above objectives, this invention provides a method for designing a geothermal extraction and irrigation well network, specifically including:

[0011] S1, obtain irrigation design;

[0012] S2, Establish a geothermal geological model;

[0013] S3, determine the optimal water extraction rate for a single well;

[0014] S4, Design the well network scheme for irrigation and extraction;

[0015] S5 uses hydrothermal coupling simulation technology to optimize the well network scheme for irrigation and extraction.

[0016] Furthermore, the extraction and irrigation design includes water extraction volume, extraction-to-irrigation well ratio, recharge volume, extraction-to-irrigation well spacing, and extraction-to-irrigation well network.

[0017] Furthermore, the establishment of the geothermal geological model specifically involves using geothermal simulation software to determine the reservoir characteristics of the geothermal field based on the obtained extraction and irrigation design, selecting key parameters, and thus obtaining the geothermal geological model.

[0018] Furthermore, the method for determining the optimal single-well water production is to determine the well location based on the geothermal geological model, and to conduct numerical simulations of different water production rates to obtain the drawdown corresponding to different water production rates. The relationship between water production rate and drawdown is analyzed, and the inflection point of the decrease in the rate of change of drawdown is taken as the optimal single-well water production rate of the geothermal geological model.

[0019] Furthermore, the drawdown is the numerical value of the decrease in water level in the well area during extraction.

[0020] Furthermore, the design of the production and irrigation well network scheme specifically involves using hydrothermal coupling simulation technology to select the optimal single-well water production volume, selecting a production and irrigation well network with one injection and one production, simulating and calculating the geothermal resource utilization rate of different production and irrigation well spacing and different production and irrigation well network schemes, and designing the production and irrigation well network scheme with reference to the economic indicators of a single well.

[0021] Furthermore, the range of different well spacings for extraction and irrigation is 200–700 m.

[0022] Furthermore, the different well spacings are specifically selected as 200m, 300m, 400m, 500m, 600m, and 700m, respectively.

[0023] Furthermore, the simulation calculation of geothermal resource utilization rate under different well spacing and well network schemes specifically involves designing five-point well networks, nine-point well networks, and oblique seven-point well networks, respectively, simulating and calculating the total heat recovery of each well spacing scheme several years into the geothermal development cycle, and comparing the total heat recovery of each well network scheme.

[0024] Furthermore, the oblique seven-point well network specifically has a production-to-injection well ratio of 1:2, and the length of the oblique side of the well network is 1.414 times the length of the right-angled side.

[0025] Furthermore, the total heat recovery is calculated using the STARS geothermal simulation software, and the calculation formula is: Total heat recovery = Cumulative time * Production volume * (Produced fluid temperature - Surface temperature).

[0026] This invention discloses a geothermal extraction and irrigation well network design method. Its beneficial effects include using geological modeling and numerical simulation, and applying hydrothermal coupling simulation technology to design a slanted seven-point well network based on the five-point and nine-point well network methods. Comparative analysis of the heat extraction effects of different extraction and irrigation designs reveals the optimal well network layout, improving the efficiency of geothermal resource recycling. This invention also maximizes the geothermal reservoir coverage area through rational utilization of surface space, reducing investment costs for new well drilling, surface construction, and extraction and irrigation operations, thereby maximizing the acquisition of geothermal energy. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the geothermal extraction and irrigation design method in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram showing the distribution of water extraction wells and recharge wells in a five-point square area well network according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram showing the distribution of water extraction wells and recharge wells in a nine-point square area well network according to an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram showing the distribution of water extraction wells and recharge wells in a square area well network using the oblique seven-point method in an embodiment of the present invention;

[0032] Figure 5 This is a structural block diagram of the geothermal extraction and irrigation design method device in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the hydrothermal coupling simulation technology circuit in an embodiment of the present invention;

[0034] Figure 7 This is a schematic diagram of the geothermal extraction and irrigation design parameter optimization technology in an embodiment of the present invention;

[0035] Figure 8 This is a graph showing the change of reservoir temperature over time under different irrigation and extraction schemes in this invention.

[0036] Figure 9 This is a comparison chart of heat extraction schemes under different irrigation and extraction methods in the embodiments of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] To further understand the invention, the technical solution will be further described below in conjunction with specific embodiments.

[0039] Example 1: A geothermal resource is of the hydrothermal type. A geothermal project replaces coal-fired boilers to provide clean energy for winter heating of 800,000 square meters of industrial production. The geothermal reservoir is an interbedded, high-permeability reservoir, with a burial depth of 800–2000 m and an average total thickness of 300 m. The reservoir temperature is 60–90℃. A geological conceptual model of the geothermal field is established based on geological structural data. The geothermal gradient is 3.0℃ / 100m, the surface isothermal zone is taken at 30m, and the temperature is taken as 12℃. Because the temperature within the reservoir is interconnected, the formation temperature is estimated based on the mid-depth location of the reservoir. Therefore, the estimated mid-depth temperature of the formation in the study area is 68–83℃. Figures 1-9 As shown, this embodiment provides a geothermal production and injection well network design method, specifically including: acquiring the geological foundation information for the production and injection design of the geothermal field; wherein, the production and injection design includes water production volume, production-injection well ratio, reinjection water volume, production-injection well spacing and well network, and establishing a geothermal geological model; determining the optimal single-well water production volume; the production and injection design is related to the geothermal field development plan; the geological foundation information determines the reservoir characteristics of the geothermal field, selects key parameters, and establishes a geothermal geological model. The selected key parameters include porosity, permeability, formation thickness, reservoir-to-land ratio, bottom layer temperature, tailwater temperature, and formation depth of the geothermal field in the study area; the production wells and reinjection wells in the production and injection scheme are selected as vertical wells. The geothermal geological model is established using the STARS simulator software for geothermal production simulation, and the establishment requires parameters such as rock thermal properties, geothermal gradient, and formation water properties. The three-dimensional geological model is directly imported from the Petrel fine geological model, and dynamic data of the wells are added. Based on research findings on tectonics and sedimentation in geothermal geological models, and adhering to the principles of good sand body connectivity and significant thickness, well locations for water extraction were determined within the established geothermal geological model. Numerical simulations were conducted using the established model to obtain the corresponding drawdown for different water extraction rates. The relationship between water extraction rate and drawdown was analyzed, and the inflection point of decreasing drawdown rate was taken as the optimal single-well water extraction rate for the geothermal geological model, thus determining the optimal single-well water extraction rate for the geothermal field in the study area. The drawdown is defined as the decrease in water level that occurs in the well area during extraction.

[0040] The spacing between injection and irrigation wells was then determined. When the water extraction volume was constant, a one-injection-one-extraction well network was selected as the basis for optimization. Hydrothermal coupling simulation technology was used to simulate and optimize different injection and irrigation well spacings. In heating projects, large-scale productive reinjection of low-temperature geothermal tailwater will significantly reduce the temperature of the surrounding geothermal reservoir, which will not recover to its original temperature by the next heating season. Therefore, alternating use of injection and irrigation wells is not feasible, and setting a reasonable well spacing to prevent thermal breakthroughs in a short period is essential. Based on the geothermal resource demand of the study area and considering the reinjection conditions, several schemes with injection and irrigation well spacings of 200m, 300m, 400m, 500m, 600m, and 700m were selected for simulation. The optimal single-well water extraction volume was chosen, and taking a 50-year development cycle as an example, the total heat extraction of each scheme was simulated and calculated 50 years into the geothermal development cycle. The total heat recovery was calculated using the STARS geothermal simulation software, with the formula: Total Heat Recovery = Cumulative Time * Production Rate * (Produced Fluid Temperature - Surface Temperature). Simulation results show that when the distance between the production well and the reinjection well is too small, thermal breakthrough is likely to occur, leading to low heat recovery in the production-injection scheme. Conversely, when the distance between the production and reinjection wells is too large, it is difficult to establish a production-injection balance, which is detrimental to coordinated pressure reduction between wells. The research results indicate that the scheme achieves the highest heat utilization rate when the production-injection well distance is 400-500m.

[0041] Compared with the common oil and water injection-production well patterns in oilfields, this well pattern is more reasonable and applicable to different geological conditions and reservoir distribution characteristics. Meanwhile, geothermal field development often closely follows oilfield development. In the later stages of oilfield development, utilizing old or abandoned wells, combined with the needs of oilfield industrial production and daily life, to develop deep geothermal fields within the reservoir is more economically viable.

[0042] Area well networks are further divided into triangular and square well networks. Based on the area well network form in oilfield development, several models for geothermal production and irrigation well networks are proposed. Among them, the triangular area well network has a lower average controlled area per well and higher geothermal field development investment costs, so its adoption is not recommended. The specific design of the production and irrigation well network scheme involves selecting the optimal single-well water production and production-irrigation well spacing, and designing square area well networks, including five-point and nine-point well networks, and simulating the total heat recovery of each scheme after a 50-year geothermal development cycle. Simulation calculations show that the nine-point well network has the highest heat recovery, while the five-point well network has a slightly lower heat recovery. From an economic evaluation perspective, the five-point well network has two production and irrigation wells (production-irrigation ratio of 1:1), while the nine-point well network has four production and irrigation wells (production-irrigation ratio of 1:3). The drilling investment for the nine-point well network is twice that of the five-point well network, but the total heat recovery of the nine-point well network design scheme is only 10% higher than that of the five-point well network design scheme, indicating that its economic benefits are not ideal.

[0043] Taking into account factors such as drilling investment cost, single-well thermal reservoir control area, low-temperature tailwater reinjection capacity, thermal energy utilization rate, and geothermal economic benefits, a honeycomb-like inclined seven-point production and injection well network design is proposed. This well network includes a production and injection well ratio of 1:2, meaning that one production and injection well group has one production well and two injection wells. The length of the hypotenuse of the well network is 1.414 times the length of the right-angled side, i.e., the interior angles are 90° and 135° respectively.

[0044] like Figure 5 As shown, the information acquisition module, reservoir geological feature determination module, data comprehensive analysis module, and scheme design module are all built-in functions of the STARS geothermal simulation software. The information acquisition module is mainly used to collect basic geological information of the geothermal field, the reservoir geological feature determination module is mainly used to obtain the main parameters, the data comprehensive analysis module is mainly used for numerical simulation, total heat recovery, and scheme comparison, and the scheme design module is mainly used for well network scheme design. The STARS simulator is existing technology, so it will not be described in detail.

[0045] Comparing the five-point, seven-point, and nine-point geothermal production and irrigation design schemes, all three well networks have the same controlled area per well and can be used as the foundation for production and irrigation. However, considering drilling investment costs and low-temperature tailwater reinjection capacity, the seven-point oblique well network is more economical and reasonable. A honeycomb-like seven-point oblique production and irrigation well network design is adopted, with a production-to-irrigation well ratio of 1:2, using... Figure 7 The diagram shows the design optimization process for geothermal extraction and irrigation parameters. The simulation calculates a geothermal development cycle of 50 years and determines a single-well water extraction volume of 80 m³. 3 / h, well spacing between extraction and irrigation is 400m, and the recharge volume per well is 960m³. 3 / d. (Attached) Figure 8 This indicates that the five-point well network and the inclined seven-point well network can be used for high-temperature water production for 24 years, with a slow temperature decline, and the temperature drop is less than 10℃ towards the end of the development period. Figure 9 As shown, the seven-point inclined well network design scheme has the highest total heat recovery, which is 10% higher than that of the five-point well network scheme. The research results show that when the well spacing is 400m, the right-angle side length of the seven-point inclined well network is 400m and the inclined side length is 565m, and this scheme has the highest heat utilization rate.

[0046] It should be noted that the specific distance between the extraction and irrigation wells is not limited to 200m, 300m, 400m, 500m, 600m, or 700m. It depends on the actual situation on site, as long as the simulation results ensure that the temperature of the extraction well does not exceed the maximum service life.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing a geothermal extraction and irrigation well network, characterized in that, S1, obtain irrigation design; S2, Establish a geothermal geological model; S3, determine the optimal water extraction rate for a single well; S4, Design the well network scheme for irrigation and extraction; S5 uses hydrothermal coupling simulation technology to optimize the well network scheme for irrigation and extraction.

2. The geothermal well network design method according to claim 1, characterized in that, The extraction and irrigation design includes the extraction volume, the ratio of extraction to irrigation wells, the recharge volume, the extraction-irrigation well spacing, and the well network.

3. The geothermal well network design method according to claim 1, characterized in that, The establishment of a geothermal geological model involves using geothermal simulation software to determine the reservoir characteristics of the geothermal field based on the obtained extraction and irrigation design, and selecting parameters such as porosity, permeability, formation thickness, reservoir-to-land ratio, bottom layer temperature, tailwater temperature, and mid-depth formation parameters of the geothermal field in the study area to obtain the geothermal geological model.

4. The geothermal well network design method according to claim 1, characterized in that, The method for determining the optimal single-well water production rate is to determine the well location based on the geothermal geological model, conduct numerical simulations of different water production rates, obtain the drawdown corresponding to different water production rates, analyze the relationship between water production rate and drawdown, and take the inflection point of the decrease in the rate of change of drawdown as the optimal single-well water production rate of the geothermal geological model.

5. The geothermal well network design method according to claim 4, characterized in that, Drawdown is the amount of water level reduction that occurs in the well area during extraction.

6. The geothermal well network design method according to claim 1, characterized in that, The design of the production and irrigation well network scheme specifically involves using hydrothermal coupling simulation technology to select the optimal single-well water production volume, selecting a production and irrigation well network with one injection and one production, simulating and calculating the geothermal resource utilization rate of different production and irrigation well spacing and different production and irrigation well network schemes, and designing the production and irrigation well network scheme with reference to the economic indicators of a single well.

7. The geothermal well network design method according to claim 6, characterized in that, The range of well spacing for different extraction and irrigation wells is 200–700m.

8. The geothermal well network design method according to claim 6, characterized in that, The simulation calculation of geothermal resource utilization rate under different well spacing and well network schemes specifically involves designing five-point well networks, nine-point well networks, and inclined seven-point well networks. The simulation calculation yields the total heat recovery of each well spacing scheme several years into the geothermal development cycle, and the total heat recovery of each well network scheme is compared.

9. The geothermal well network design method according to claim 8, characterized in that, The oblique seven-point well network has a production-to-injection well ratio of 1:2, and the length of the oblique side of the well network is 1.414 times the length of the right-angled side.

10. A geothermal well network design method according to claim 8, characterized in that, The total heat recovery was calculated using the STARS geothermal simulation software. The formula is: Total heat recovery = Cumulative time * Production rate * (Produced fluid temperature - Surface temperature).

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