CN114429011B - Method, device and medium for calculating heat exchange total surface of dry-heat rock heat storage fracturing crack - Google Patents

Abstract

The present invention discloses a method, device and medium for calculating the total heat exchange area of the hydraulic fractures of a hot dry rock thermal reservoir. The method comprises: obtaining a reasonable flow rate M of a circulating heat-collecting medium in the thermal reservoir; calculating the bottom hole temperature _Tr,in of the injection well based on a one-dimensional flow heat transfer mathematical model of the medium in the wellbore of the injection well and a reasonable flow rate M of the heat-collecting medium; calculating the bottom hole temperature _Tr,out of the production well based on a one-dimensional flow heat transfer mathematical model of the medium in the wellbore of the production well and a reasonable flow rate M of the heat-collecting medium; and calculating the total heat exchange area A of the hydraulic fractures based on the bottom hole temperature _Tr,in of the injection well and the bottom hole temperature Tr _,out of the production well. The present invention establishes a relationship between the power generation of the ground system and the parameters of the hydraulic fractures of the underground thermal reservoir, and establishes a method for calculating the total heat exchange area of the hydraulic fractures of the hot dry rock thermal reservoir under the coupling constraints of multiple factors such as the thermal reservoir characteristics and the power generation, thereby solving the problem that the existing hydraulic fracture network design of the hot dry rock thermal reservoir has no basis and the capacity of the hydraulic fracture network cannot be estimated.

Description

Method, device and medium for calculating total heat transfer area of fractures in hot dry rock thermal storage

Technical Field

The invention belongs to the technical field of hot dry rock development, and in particular relates to a method for calculating the total heat exchange area of hot dry rock thermal storage fracturing cracks based on power generation.

Background Art

In recent years, the growing demand for energy and the highly valued environmental issues have made the development and utilization of clean and renewable energy an important way for the healthy and sustainable development of the national economy. Hot dry rock is a hot rock body buried 3 to 10 km from the surface, with a rock temperature of 150 to 650 ° C, almost no water or steam in the rock layer, and extremely low porosity and permeability. Hot dry rock is widely distributed in my country and has abundant resources. As an important technology for the development and utilization of hot dry rock resources, the Enhanced Geothermal System (EGS) uses hydraulic fracturing and other technical means to transform reservoirs with low permeability, construct heat exchange channels in the reservoir, and enable the heat extraction medium to extract a certain amount of heat from the reservoir for power generation and other purposes. Due to the temperature and pressure environment of the hot dry rock thermal reservoir, numerical simulations and laboratory physical simulation experiments have shown that hydraulic fracturing produces one more crack, but as the main heat exchange channel, one crack is far from meeting the long-term effective extraction of heat, thermal breakthrough will occur in advance, and the temperature of the production well will drop sharply.

In order to ensure that heat can be extracted efficiently and that the production water temperature does not experience thermal breakthrough, the hot dry rock thermal reservoir fracturing needs to design enough artificial fractures to meet the installed power generation of the ground power generation system. Regarding the published patents for the enhanced geothermal system fracturing network, they are all about the design of the positional relationship between the fracturing fractures in the hot dry rock thermal reservoir and the injection and production wells. For example, the patent (CN 201710136534.0) provides a method for designing a multi-stage and multi-segment hydraulic fracturing network for horizontal wells in an enhanced geothermal system, but does not involve the evaluation of the power generation capacity of such a fracturing network. The heat exchange area of the fracturing fracture is an important parameter guiding the design of fracturing engineering, but there is no calculation method for the heat exchange area of the hot dry rock thermal reservoir fracturing network based on the installed power generation target in the existing patents and literature, and it is impossible to achieve the optimized design of the fracture network of the enhanced geothermal system.

In summary, there is a particular need for a method for calculating the total heat exchange area of dry hot rock thermal reservoir fracturing cracks based on power generation, which can calculate the required parameters of the fracturing network in the thermal reservoir, provide a reference basis for the design of fracturing projects, and solve the problem of no corresponding relationship between the existing fracturing network design and ground power generation.

Summary of the invention

The purpose of the present invention is to propose a method, device, medium and electronic equipment for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation, so as to solve the problem that there is no corresponding relationship between the existing fracturing network design and ground power generation.

In order to achieve the above-mentioned purpose, the present invention provides a method for calculating the total heat exchange area of a hot dry rock thermal reservoir fracturing crack based on power generation, comprising: obtaining a reasonable flow rate M of a circulating heat recovery medium in the thermal reservoir; calculating the bottom hole temperature _Tr,in of the injection well based on a one-dimensional flow heat transfer mathematical model of the medium in the wellbore of the injection well and the reasonable flow rate M of the heat recovery medium; calculating the bottom hole temperature _Tr,out of the production well based on a one-dimensional flow heat transfer mathematical model of the medium in the wellbore of the production well and the reasonable flow rate M of the heat recovery medium; calculating the total heat exchange area A of the fracturing crack based on the bottom hole temperature _Tr,in of the injection well and the bottom hole temperature _{Tr,out of} the production well.

Optionally, the following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium:

P＝η·M·c _p ·(T _pro -T _inj )

Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage.

Optionally, the one-dimensional flow heat transfer mathematical model is:

For injection wells, the solution condition of the above equation is

x＝0,T＝T _inj ；x＝L,

For production wells, the solution condition of the above equation is

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.

Optionally, the total heat exchange area A of the fracturing cracks is calculated using the following formula:

Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system.

Optionally, the ground power generation system is determined according to the temperature and depth of the heat storage; and the waste temperature of the heat recovery medium after ground utilization, ie, the ground wellhead temperature _Tinj of the injection well, is determined according to the characteristics of the power generation system.

Optionally, the surface wellhead temperature T _pro of the production well is estimated according to the heat storage depth and temperature of the hot dry rock heat storage resource and the insulation condition of the production well.

Optionally, the density of the thermal reservoir rock matrix is obtained based on the physical property test of the thermal reservoir core.

In a second aspect, the present invention further proposes an electronic device, comprising: a memory storing executable instructions; a processor, the processor running the executable instructions in the memory to implement the above-mentioned method for calculating the total surface area of heat exchange of hot dry rock thermal reservoir fracturing cracks based on power generation.

In a third aspect, the present invention further proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-mentioned method for calculating the total heat exchange area of dry hot rock thermal reservoir fracturing cracks based on power generation.

In a fourth aspect, the present invention further proposes a device for calculating the total area of heat exchange of hot dry rock thermal reservoir fracturing cracks based on power generation, including: a reasonable flow acquisition module, which acquires a reasonable flow M of the circulating heat recovery medium in the thermal reservoir; an injection well bottom hole temperature calculation module, which calculates the injection well bottom hole temperature _Tr,in based on a one-dimensional flow heat transfer mathematical model of the medium in the injection well wellbore and the reasonable flow M of the heat recovery medium; a production well bottom hole temperature calculation module, which calculates the production well bottom hole temperature _Tr,out based on a one-dimensional flow heat transfer mathematical model of the medium in the production well wellbore and the reasonable flow M of the heat recovery medium; a fracturing crack total heat exchange area calculation module, which calculates the fracturing crack total heat exchange area A based on the injection well bottom hole temperature _Tr,in and the production well bottom hole temperature Tr _,out .

Optionally, the following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium:

P＝η·M·c _p ·(T _pro -T _inj )

Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage.

Optionally, the one-dimensional flow heat transfer mathematical model is:

For injection wells, the solution condition of the above equation is

x＝0,T＝T _inj ；x＝L,

For production wells, the solution condition of the above equation is

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.

Optionally, the total heat exchange area A of the fracturing cracks is calculated using the following formula:

Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system.

Optionally, the ground power generation system is determined according to the temperature and depth of the heat storage; and the waste temperature of the heat recovery medium after ground utilization, ie, the ground wellhead temperature _Tinj of the injection well, is determined according to the characteristics of the power generation system.

Optionally, the surface wellhead temperature T _pro of the production well is estimated according to the heat storage depth and temperature of the hot dry rock heat storage resource and the insulation condition of the production well.

The beneficial effects of the present invention are as follows: the method for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation of the present invention establishes the relationship between the power generation of the ground system and the parameters of the artificial fractures of the underground thermal storage fracturing. Under the coupling constraints of multiple factors such as thermal storage characteristics, power generation, and system stable operation time, a method for calculating the total heat exchange area of dry hot rock thermal storage fracturing artificial fractures is established, which solves the problem that the existing dry hot rock thermal storage fracturing network design has no basis and cannot estimate the production capacity of the fracturing network. The calculation method is simple and the inversion result is reliable, which proposes a design target and a production capacity prediction method for dry hot rock thermal storage fracturing.

The present invention has other features and advantages, which will be apparent from or will be described in detail in the accompanying drawings and the following specific embodiments incorporated herein, which together serve to explain the specific principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

FIG1 shows a flow chart of a method for calculating the total heat exchange area of a hot dry rock thermal reservoir fracture based on power generation according to an embodiment of the present invention.

FIG2 shows a block diagram of a device for calculating the total heat exchange area of dry hot rock thermal reservoir fractures based on power generation according to an embodiment of the present invention.

Reference numerals

102. Reasonable flow acquisition module; 104. Injection well bottom temperature calculation module; 106. Production well bottom temperature calculation module; 108. Fracturing crack total heat exchange area calculation module.

DETAILED DESCRIPTION

The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

The present invention provides a method for calculating the total heat exchange area of a hot dry rock thermal reservoir fracturing crack based on power generation, comprising: obtaining a reasonable flow rate M of a circulating heat recovery medium in the thermal reservoir; calculating the bottom hole temperature _Tr,in of the injection well based on a one-dimensional flow heat transfer mathematical model of the medium in the wellbore of the injection well and the reasonable flow rate M of the heat recovery medium; calculating the bottom hole temperature _Tr,out of the production well based on a one-dimensional flow heat transfer mathematical model of the medium in the wellbore of the production well and the reasonable flow rate M of the heat recovery medium; and calculating the total heat exchange area A of the fracturing crack based on the bottom hole temperature Tr _,in of the injection well and the bottom hole temperature _Tr,out of the production well.

Specifically, according to the target of power generation capacity and the selection of ground power generation system, reasonable production temperature and reinjection temperature are proposed, and the reasonable flow rate of heat recovery working fluid in the heat storage is calculated. The bottom temperature of the injection well is calculated based on the one-dimensional flow heat transfer mathematical model of the working fluid in the wellbore of the injection well and the reasonable flow rate of the heat recovery working fluid. The bottom temperature of the production well is calculated based on the one-dimensional flow heat transfer mathematical model of the working fluid in the wellbore of the production well and the reasonable flow rate of the heat recovery working fluid. On the basis of the known physical properties of the target heat extraction layer section of the heat storage, the total heat exchange area of the heat storage fracture network under the joint constraints of power generation and system effective operation time is calculated.

According to an exemplary implementation, a method for calculating the total heat exchange area of hot dry rock thermal reservoir fracturing cracks based on power generation established a relationship between the power generation of the ground system and the parameters of artificial fractures in underground thermal reservoir fracturing. Under the coupled constraints of multiple factors such as thermal reservoir characteristics, power generation, and system stable operation time, a method for calculating the total heat exchange area of artificial fractures in hot dry rock thermal reservoir fracturing was established, which solved the problem that the existing hot dry rock thermal reservoir fracturing network design has no basis and cannot estimate the production capacity of the fracturing network. The calculation method is simple and the inversion results are reliable, which proposes design goals and production capacity prediction methods for hot dry rock thermal reservoir fracturing.

As an optional solution, the following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium:

P＝η·M·c _p ·(T _pro -T _inj )

Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage.

Specifically, the type of power generation system is selected according to the requirements of ground power generation, and the waste temperature of the heat recovery medium after ground use, that is, the reinjection medium temperature T _inj at the injection well, is determined. According to the dry hot rock thermal reservoir resource endowment conditions (heat reservoir burial depth and temperature) and the insulation conditions of the production well, the wellhead working medium temperature T _pro of the production well is estimated. After preliminarily determining the injection well reinjection temperature T _inj and the wellhead temperature T _pro of the production well, the following formula (1) is used to give a reasonable flow rate M of the heat recovery medium in the heat storage internal circulation under the system target power generation installed capacity P requirements according to the selected power generation system heat utilization efficiency η and the ground water pump head as a constraint.

P＝η·M·c _p ·(T _pro -T _inj ) (1)

Where, P is the output power of the generator set, η is the thermal efficiency of the power generation system, and the thermal efficiency of the dual working fluid cycle is in the range of 10% to 13%. _{T inj} and T _pro are the surface wellhead temperatures of the injection well and the production well, respectively, in units of °C. M is the reasonable flow rate of the heat recovery medium, in units of kg/s, and _cp is the specific heat capacity of the heat recovery medium in the heat storage, in units of J/kg/K.

As an alternative, the one-dimensional flow heat transfer mathematical model is:

For injection wells, the solution condition of the above equation is

x＝0,T＝T _inj ；x＝L,

For production wells, the solution condition of the above equation is

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.

Specifically, considering the transient heat exchange between the fluid in the wellbore and the surrounding formations, under the assumption that the loss of the heat recovery medium flow in the heat reservoir is not considered, the mathematical model of one-dimensional flow heat transfer of the working fluid in the injection wellbore of formula (2)-formula (4) is established, where formula (3) is the injection well reinjection temperature _Tinj and the heat recovery medium flow rate M obtained by calculation, which are used as the boundary conditions of the differential equation (2) of the one-dimensional flow heat transfer model of the fluid in the wellbore, x = 0 is the wellhead of the injection well, and x = L is the bottom of the injection well. Formula (4) represents the instantaneous heat exchange heat q between the wellbore and the surrounding formations, which is included in the heat transfer model of formula (2) as a heat source term. Solving the following wellbore mathematical model, the temperature _Tr,in at the bottom of the injection well (heat reservoir inlet) can be calculated.

x＝0,T＝T _inj ；x＝L,

in is the thermal diffusion coefficient of the thermal reservoir rock matrix, in m ² /s, λ _r , ρ _r , _cr are the thermal conductivity of the thermal reservoir rock matrix, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. _{λ f} , ρ _f and c _p are the thermal conductivity of the heat extraction medium in the wellbore, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. r ₀ is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, and L is the injection well depth.

Considering the heat dissipation effect of the high-temperature fluid in the wellbore of the production well to the surrounding formations, the mathematical model of one-dimensional flow heat transfer of the working fluid in the wellbore of the production well is established in equations (5) to (7). In equation (6), the calculated wellhead temperature T _pro and heat recovery working fluid flow rate M of the production well are used as the boundary conditions of the differential equation (5) of the one-dimensional flow heat transfer model of the fluid in the wellbore. The position x = 0 is the wellhead of the production well, and x = L is the bottom of the production well. Equation (7) represents the instantaneous heat exchange heat q between the wellbore and the surrounding formations, which is included in the heat transfer model of equation (5) as a heat dissipation term. Solving the following wellbore mathematical model, the bottom (heat storage outlet) temperature _Tr,out of the production well can be calculated.

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, in m ² /s, λ _r , ρ _r , and _cr are the thermal conductivity of the thermal reservoir rock matrix, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. _{λ f} , ρ _{f ,} and c _p are the thermal conductivity of the heat extraction medium in the wellbore, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. _{r 0} is the radius of the well, t is the time, _Tr,i is the well wall temperature, i.e., the formation temperature gradient distribution, and L is the depth of the production well.

As an optional solution, the following formula is used to calculate the total heat exchange area A of the fracturing fracture:

Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system.

The matrix temperature _Tro and the physical property parameters of the target thermal reservoir layer, thermal conductivity _λr , density _ρr , and heat capacity _cr , are obtained. The bottom hole fluid temperature _{Tr,in of} the injection well and the bottom hole temperature _Tr,out of the production well are taken as input parameters. According to the economic requirements of the effective operating life _t0 of the hot dry rock mining system, the total heat exchange area A of the fractures required to meet the minimum stable power generation is calculated using formula (8).

Wherein, _Tr,in , _Tr,out and _Tro are the bottom hole temperature of the injection well, the bottom hole temperature of the production well and the matrix temperature of the target layer of the thermal reservoir, respectively, in °C. _cp is the specific heat capacity of the fluid at constant pressure, in J/kg/K, _ρr is the density of the thermal reservoir rock matrix, in kg/ ^m3 , _λr is the thermal conductivity of the thermal reservoir rock matrix, in W/m/K, _cr is the specific heat capacity of the thermal reservoir rock matrix, in J/kg/K, and M is the flow rate of the circulating working fluid in the thermal reservoir, in kg/s.

As an optional solution, the ground power generation system is determined according to the temperature and depth of the heat storage; according to the characteristics of the power generation system, the waste temperature of the heat recovery medium after ground utilization, that is, the ground wellhead temperature _Tinj of the injection well is determined.

As an optional solution, the surface wellhead temperature T _pro of the production well is estimated according to the heat storage depth and temperature of the hot dry rock heat storage resource and the insulation condition of the production well.

As an optional solution, the density of the thermal reservoir rock matrix can be obtained based on the physical property test of the thermal reservoir core.

In a second aspect, the present invention further proposes an electronic device, which includes: a memory storing executable instructions; a processor running the executable instructions in the memory to implement the above-mentioned method for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation.

In a third aspect, the present invention further proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-mentioned method for calculating the total heat exchange area of dry hot rock thermal reservoir fracturing cracks based on power generation.

In a fourth aspect, the present invention further proposes a device for calculating the total area of heat exchange of hot dry rock thermal reservoir fracturing cracks based on power generation, including: a reasonable flow acquisition module, which acquires a reasonable flow M of the circulating heat recovery medium in the thermal reservoir; an injection well bottom hole temperature calculation module, which calculates the injection well bottom hole temperature _Tr,in based on a one-dimensional flow heat transfer mathematical model of the medium in the injection well bore and a reasonable flow M of the heat recovery medium; a production well bottom hole temperature calculation module, which calculates the production well bottom hole temperature _Tr,out based on a one-dimensional flow heat transfer mathematical model of the medium in the production well bore and a reasonable flow M of the heat recovery medium; a fracturing crack total heat exchange area calculation module, which calculates the fracturing crack total heat exchange area A based on the injection well bottom hole temperature _Tr,in and the production well bottom hole temperature _Tr,out .

Specifically, according to the target of power generation capacity and the selection of ground power generation system, reasonable production temperature and reinjection temperature are proposed, and the reasonable flow rate of heat recovery working fluid in the heat storage is calculated. The bottom temperature of the injection well is calculated based on the one-dimensional flow heat transfer mathematical model of the working fluid in the wellbore of the injection well and the reasonable flow rate of the heat recovery working fluid. The bottom temperature of the production well is calculated based on the one-dimensional flow heat transfer mathematical model of the working fluid in the wellbore of the production well and the reasonable flow rate of the heat recovery working fluid. On the basis of the known physical properties of the target heat extraction layer section of the heat storage, the total heat exchange area of the heat storage fracture network under the joint constraints of power generation and system effective operation time is calculated.

According to an exemplary implementation, a method for calculating the total heat exchange area of hot dry rock thermal reservoir fracturing cracks based on power generation established a relationship between the power generation of the ground system and the parameters of artificial fractures in underground thermal reservoir fracturing. Under the coupled constraints of multiple factors such as thermal reservoir characteristics, power generation, and system stable operation time, a method for calculating the total heat exchange area of artificial fractures in hot dry rock thermal reservoir fracturing was established, which solved the problem that the existing hot dry rock thermal reservoir fracturing network design has no basis and cannot estimate the production capacity of the fracturing network. The calculation method is simple and the inversion results are reliable, which proposes design goals and production capacity prediction methods for hot dry rock thermal reservoir fracturing.

As an optional solution, the following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium:

P＝η·M·c _p ·(T _pro -T _inj )

Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage.

Specifically, the type of power generation system is selected according to the requirements of ground power generation, and the waste temperature of the heat recovery medium after ground use, that is, the reinjection medium temperature T _inj at the injection well, is determined. According to the dry hot rock thermal reservoir resource endowment conditions (heat reservoir burial depth and temperature) and the insulation conditions of the production well, the wellhead working medium temperature T _pro of the production well is estimated. After preliminarily determining the injection well reinjection temperature T _inj and the wellhead temperature T _pro of the production well, the following formula (1) is used to give a reasonable flow rate M of the heat recovery medium in the heat storage internal circulation under the system target power generation installed capacity P requirements according to the selected power generation system heat utilization efficiency η and the ground water pump head as a constraint.

P＝η·M·c _p ·(T _pro -T _inj ) (1)

Where, P is the output power of the generator set, η is the thermal efficiency of the power generation system, and the thermal efficiency of the dual working fluid cycle is in the range of 10% to 13%. _{T inj} and T _pro are the surface wellhead temperatures of the injection well and the production well, respectively, in units of °C. M is the reasonable flow rate of the heat recovery medium, in units of kg/s, and _cp is the specific heat capacity of the heat recovery medium in the heat storage, in units of J/kg/K.

As an alternative, the one-dimensional flow heat transfer mathematical model is:

For injection wells, the solution condition of the above equation is

x＝0,T＝T _inj ；x＝L,

For production wells, the solution condition of the above equation is

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.

Specifically, considering the transient heat exchange between the fluid in the wellbore and the surrounding formations, under the assumption that the loss of the heat recovery medium flow in the heat reservoir is not considered, the mathematical model of one-dimensional flow heat transfer of the working fluid in the injection wellbore of formula (2)-formula (4) is established, where formula (3) is the injection well reinjection temperature _Tinj and the heat recovery medium flow rate M obtained by calculation, which are used as the boundary conditions of the differential equation (2) of the one-dimensional flow heat transfer model of the fluid in the wellbore, x = 0 is the wellhead of the injection well, and x = L is the bottom of the injection well. Formula (4) represents the instantaneous heat exchange heat q between the wellbore and the surrounding formations, which is included in the heat transfer model of formula (2) as a heat source term. Solving the following wellbore mathematical model, the temperature _Tr,in at the bottom of the injection well (heat reservoir inlet) can be calculated.

x＝0,T＝T _inj ；x＝L,

in is the thermal diffusion coefficient of the thermal reservoir rock matrix, in m ² /s, λ _r , ρ _r , _cr are the thermal conductivity of the thermal reservoir rock matrix, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. _{λ f} , ρ _f and c _p are the thermal conductivity of the heat extraction medium in the wellbore, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. r ₀ is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, and L is the injection well depth.

Considering the heat dissipation effect of the high-temperature fluid in the wellbore of the production well to the surrounding formations, the mathematical model of one-dimensional flow heat transfer of the working fluid in the wellbore of the production well is established in equations (5) to (7). In equation (6), the calculated wellhead temperature T _pro and heat recovery working fluid flow rate M of the production well are used as the boundary conditions of the differential equation (5) of the one-dimensional flow heat transfer model of the fluid in the wellbore. The position x = 0 is the wellhead of the production well, and x = L is the bottom of the production well. Equation (7) represents the instantaneous heat exchange heat q between the wellbore and the surrounding formations, which is included in the heat transfer model of equation (5) as a heat dissipation term. Solving the following wellbore mathematical model, the bottom (heat storage outlet) temperature _Tr,out of the production well can be calculated.

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, in m ² /s, λ _r , ρ _r , and _cr are the thermal conductivity of the thermal reservoir rock matrix, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. _{λ f} , ρ _{f ,} and c _p are the thermal conductivity of the heat extraction medium in the wellbore, in W/m/K, density, in kg/m ³ , and heat capacity, in J/kg/K. _{r 0} is the radius of the well, t is the time, _Tr,i is the well wall temperature, i.e., the formation temperature gradient distribution, and L is the depth of the production well.

As an optional solution, the following formula is used to calculate the total heat exchange area A of the fracturing fracture:

Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system.

The matrix temperature _Tro and the physical property parameters of the target thermal reservoir layer, thermal conductivity _λr , density _ρr , and heat capacity _cr , are obtained. The bottom hole fluid temperature _{Tr,in of} the injection well and the bottom hole temperature _Tr,out of the production well are taken as input parameters. According to the economic requirements of the effective operating life _t0 of the hot dry rock mining system, the total heat exchange area A of the fractures required to meet the minimum stable power generation is calculated using formula (8).

Wherein, _Tr,in , _Tr,out and _Tro are the bottom hole temperature of the injection well, the bottom hole temperature of the production well and the matrix temperature of the target layer of the thermal reservoir, respectively, in °C. _cp is the specific heat capacity of the fluid at constant pressure, in J/kg/K, _ρr is the density of the thermal reservoir rock matrix, in kg/ ^m3 , _λr is the thermal conductivity of the thermal reservoir rock matrix, in W/m/K, _cr is the specific heat capacity of the thermal reservoir rock matrix, in J/kg/K, and M is the flow rate of the circulating working fluid in the thermal reservoir, in kg/s.

As an optional solution, the ground power generation system is determined according to the temperature and depth of the heat storage; according to the characteristics of the power generation system, the waste temperature of the heat recovery medium after ground utilization, that is, the ground wellhead temperature _Tinj of the injection well is determined.

As an optional solution, the surface wellhead temperature T _pro of the production well is estimated according to the heat storage depth and temperature of the hot dry rock heat storage resource and the insulation condition of the production well.

As an optional solution, the density of the thermal reservoir rock matrix can be obtained based on the physical property test of the thermal reservoir core.

Embodiment 1

FIG1 shows a flow chart of a method for calculating the total heat exchange area of a hot dry rock thermal reservoir fracture based on power generation according to an embodiment of the present invention.

As shown in FIG1 , the method for calculating the total heat exchange area of dry hot rock thermal storage fracturing fractures based on power generation includes:

Step 1: Obtain the reasonable flow rate M of the heat storage internal circulation heat extraction medium;

The following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium:

P＝η·M·c _p ·(T _pro -T _inj )

Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage.

Step 2: Calculate the injection well bottom temperature _Tr,in based on the one-dimensional flow heat transfer mathematical model of the working fluid in the injection wellbore and the reasonable flow rate M of the heat recovery working fluid;

Step 3: Calculate the bottom hole temperature _Tr,out of the production well based on the one-dimensional flow heat transfer mathematical model of the working fluid in the production well bore and the reasonable flow rate M of the heat recovery working fluid;

Among them, the one-dimensional flow heat transfer mathematical model is:

For injection wells, the solution condition of the above equation is

x＝0,T＝T _inj ；x＝L,

For production wells, the solution condition of the above equation is

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.

The ground power generation system is determined according to the temperature and depth of the heat storage; the waste temperature of the heat recovery medium after ground utilization, ie, the surface wellhead temperature _Tinj of the injection well, is determined according to the characteristics of the power generation system.

The surface wellhead temperature T _pro of the production well is estimated according to the heat storage depth and temperature of the hot dry rock heat storage resource and the insulation condition of the production well.

Among them, the density of the thermal reservoir rock matrix is obtained based on the physical property test of the thermal reservoir core.

Step 4: Calculate the total heat exchange area A of the hydraulic fracture based on the bottom hole temperature Tr _,in of the injection well and the bottom hole temperature _Tr,out of the production well.

The total heat exchange area A of the fracturing crack is calculated using the following formula:

Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system.

Taking a hot dry rock thermal reservoir in a certain area (temperature 200℃, depth 3700m) as an example, the system goal is to ensure stable power generation of 2MW for 20 years. The total heat exchange area of the hot dry rock thermal reservoir fracturing fracture is calculated using the method of this application:

According to the temperature and depth of the heat storage, the ground power generation system adopts an organic Rankine cycle power generation system. According to the characteristics of the power generation system, the waste temperature of the heat recovery medium after ground utilization is determined to be 87°C, that is, the temperature of the reinjected medium at the injection well. Under the constraints of the ground power generation system and the heat storage temperature, the working temperature of the production well still needs to be guaranteed to be 150-180°C after 20 years of continuous mining. According to the thermal utilization efficiency of the power generation system of 11%, the flow rate of the heat recovery medium in the heat storage is obtained, see Table 1.

Considering the transient heat exchange between the fluid in the wellbore and the surrounding formations, under the assumption that the loss of the heat recovery fluid flow in the heat reservoir is not considered, a mathematical model of one-dimensional flow heat transfer of the fluid in the injection wellbore is established. The injection well reinjection temperature _Tinj and the heat recovery fluid flow rate M are used as the boundary conditions of the differential equation of the one-dimensional flow heat transfer model of the fluid in the wellbore. The position x=0 is the wellhead of the injection well, and x=L is the bottom of the injection well. The heat q representing the transient heat exchange between the wellbore and the surrounding formations is included in the heat transfer model as a heat source term. Solving the following wellbore mathematical model, the temperature of the bottom of the injection well (heat reservoir inlet) Tr _,in can be calculated, as shown in Table 1.

Considering the heat dissipation effect of the high-temperature fluid in the wellbore of the production well to the surrounding formations, a mathematical model of one-dimensional flow heat transfer of the working fluid in the wellbore of the production well is established. The wellhead temperature T _pro of the production well and the heat recovery working fluid flow rate M are used as the boundary conditions of the differential equation of the one-dimensional flow heat transfer model of the fluid in the wellbore. The position x = 0 is the wellhead of the production well on the ground, and x = L is the bottom of the production well. The heat q representing the instantaneous heat exchange between the wellbore and the surrounding formations is included in the heat transfer model as a heat dissipation term. By solving the following wellbore mathematical model, the bottom (heat storage outlet) temperature of the production well _Tr,out can be calculated, as shown in Table 1.

According to the core physical property test of thermal reservoir, the density of thermal reservoir matrix rock is 2670kg/m ³ , the specific heat capacity is 950J/m/K, and the thermal conductivity is 3W/m/K. According to the reasonable flow rate and the bottom hole fluid temperature of the injection and production wells, the total heat exchange area A of the thermal reservoir fracture required to meet the goal of stable 2MW power generation for 20 years is calculated.

Table 1 Total heat exchange area of cracks (heat storage temperature 200℃)

Embodiment 2

FIG2 shows a block diagram of a device for calculating the total heat exchange area of dry hot rock thermal reservoir fractures based on power generation according to an embodiment of the present invention.

As shown in FIG2 , the total heat exchange area calculation device for dry hot rock thermal storage fracturing cracks based on power generation includes:

A reasonable flow acquisition module 102 is used to acquire a reasonable flow M of the heat storage internal circulation heat extraction medium;

The injection well bottom temperature calculation module 104 calculates the injection well bottom temperature _Tr,in based on the one-dimensional flow heat transfer mathematical model of the working fluid in the injection well bore and the reasonable flow rate M of the heat extraction working fluid;

The production well bottom temperature calculation module 106 calculates the production well bottom temperature _Tr,out based on the one-dimensional flow heat transfer mathematical model of the working fluid in the production well bore and the reasonable flow rate M of the heat extraction working fluid;

The total heat exchange area calculation module 108 of the hydraulic fractures calculates the total heat exchange area A of the hydraulic fractures based on the bottom hole temperature _Tr,in of the injection well and the bottom hole temperature _Tr,out of the production well.

The following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium:

P＝η·M·c _p ·(T _pro -T _inj )

Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage.

Among them, the one-dimensional flow heat transfer mathematical model is:

For injection wells, the solution condition of the above equation is

x＝0,T＝T _inj ；x＝L,

For production wells, the solution condition of the above equation is

x＝0,T＝T _pro ；x＝L,

in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.

The total heat exchange area A of the fracturing crack is calculated using the following formula:

Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system.

The ground power generation system is determined according to the temperature and depth of the heat storage; the waste temperature of the heat recovery medium after ground utilization, ie, the surface wellhead temperature _Tinj of the injection well, is determined according to the characteristics of the power generation system.

The surface wellhead temperature T _pro of the production well is estimated according to the heat storage depth and temperature of the hot dry rock heat storage resource and the insulation condition of the production well.

Embodiment 3

The present disclosure provides an electronic device, which includes: a memory storing executable instructions; a processor, which runs the executable instructions in the memory to implement the above-mentioned method for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation.

An electronic device according to an embodiment of the present disclosure includes a memory and a processor.

The memory is used to store non-temporary computer-readable instructions. Specifically, the memory may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and/or non-volatile memory. The volatile memory may, for example, include random access memory (RAM) and/or cache memory (cache), etc. The non-volatile memory may, for example, include read-only memory (ROM), hard disk, flash memory, etc.

The processor may be a central processing unit (CPU) or other forms of processing units having data processing capabilities and/or instruction execution capabilities, and may control other components in the electronic device to perform desired functions. In one embodiment of the present disclosure, the processor is used to run the computer-readable instructions stored in the memory.

Those skilled in the art should be able to understand that in order to solve the technical problem of how to obtain a good user experience, the present embodiment may also include well-known structures such as a communication bus and an interface, and these well-known structures should also be included in the protection scope of the present disclosure.

For detailed description of this embodiment, reference may be made to the corresponding descriptions in the aforementioned embodiments, which will not be repeated here.

Embodiment 4

The present disclosure provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-mentioned method for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation.

According to the computer-readable storage medium of the embodiment of the present disclosure, non-transitory computer-readable instructions are stored thereon. When the non-transitory computer-readable instructions are executed by a processor, all or part of the steps of the above-mentioned methods of each embodiment of the present disclosure are executed.

The above-mentioned computer-readable storage media include, but are not limited to: optical storage media (e.g., CD-ROM and DVD), magneto-optical storage media (e.g., MO), magnetic storage media (e.g., magnetic tape or mobile hard disk), media with built-in rewritable non-volatile memory (e.g., memory card) and media with built-in ROM (e.g., ROM box).

The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims (8)

1. A method for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation, characterized by comprising: Obtain the reasonable flow rate M of the heat storage internal circulation heat extraction medium; Based on the one-dimensional flow heat transfer mathematical model of the working fluid in the injection wellbore and the reasonable flow rate M of the heat recovery working fluid, the bottom temperature of the injection well _Tr,in is calculated; Calculate the bottom hole temperature _Tr,out of the production well based on the one-dimensional flow heat transfer mathematical model of the working fluid in the production well bore and the reasonable flow rate M of the heat recovery working fluid; Calculate the total heat exchange area A of the fracturing fracture based on the bottom hole temperature _Tr, in of the injection well and the bottom hole temperature _Tr,out of the production well; The following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium: P＝η·M·c _p ·(T _pro -T _inj ) Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage; Among them, the one-dimensional flow heat transfer mathematical model is: For injection wells, the solution condition of the above equation is For production wells, the solution condition of the above equation is in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth. 2. The method for calculating the total heat exchange area of the hot dry rock thermal reservoir fractures based on power generation according to claim 1 is characterized in that the total heat exchange area A of the fractures is calculated using the following formula: Among them, _Tro is the matrix temperature of the target layer of the heat reservoir, and _t0 is the effective operating life of the hot dry rock mining system. 3. The method for calculating the total heat exchange area of the hot dry rock thermal reservoir fracturing cracks based on power generation according to claim 1, characterized in that the ground power generation system is determined according to the temperature and depth of the thermal reservoir; According to the characteristics of the power generation system, the discard temperature of the heat recovery medium after being used on the ground, that is, the surface wellhead temperature _Tinj of the injection well, is determined. 4. The method for calculating the total heat exchange area of dry hot rock thermal reservoir fracturing cracks based on power generation according to claim 1 is characterized in that the surface wellhead temperature T _pro of the production well is estimated according to the heat reservoir burial depth and temperature of the dry hot rock thermal reservoir resource and the insulation condition of the production well. 5. The method for calculating the total heat exchange area of dry hot rock thermal reservoir fracturing cracks based on power generation according to claim 1 is characterized in that the density of the thermal reservoir rock matrix is obtained based on the physical property test of the thermal reservoir core. 6. An electronic device, characterized in that the electronic device comprises: A memory storing executable instructions; A processor, wherein the processor runs the executable instructions in the memory to implement the method for calculating the total heat exchange area of hot dry rock thermal storage fracturing cracks based on power generation according to any one of claims 1 to 5. 7. A computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program, which, when executed by a processor, implements the method for calculating the total heat exchange area of a hot dry rock thermal reservoir fracture based on power generation according to any one of claims 1 to 5. 8. A device for calculating the total heat exchange area of dry hot rock thermal storage fracturing cracks based on power generation, characterized by comprising: Reasonable flow acquisition module, to obtain the reasonable flow M of the heat storage internal circulation heat extraction medium; The injection well bottom temperature calculation module calculates the injection well bottom temperature _Tr,in based on the one-dimensional flow heat transfer mathematical model of the working fluid in the injection well and the reasonable flow rate M of the heat recovery working fluid; The bottom hole temperature calculation module of the production well calculates the bottom hole temperature _Tr,out of the production well based on the one-dimensional flow heat transfer mathematical model of the working fluid in the wellbore of the production well and the reasonable flow rate M of the heat-collecting working fluid; A module for calculating the total heat exchange area of the hydraulic fractures, which calculates the total heat exchange area A of the hydraulic fractures based on the bottom hole temperature _Tr,in of the injection well and the bottom hole temperature _Tr,out of the production well; The following formula is used to calculate the reasonable flow rate M of the heat storage internal circulation heat extraction medium: P＝η·M·c _p ·(T _pro -T _inj ) Wherein, P is the output power of the generator set, η is the thermal utilization efficiency of the power generation system, _Tinj is the surface wellhead temperature of the injection well, _Tpro is the surface wellhead temperature of the production well, and _cp is the specific heat capacity of the heat extraction medium in the heat storage; Among them, the one-dimensional flow heat transfer mathematical model is: For injection wells, the solution condition of the above equation is For production wells, the solution condition of the above equation is in, is the thermal diffusion coefficient of the thermal reservoir rock matrix, _λr is the thermal conductivity of the thermal reservoir rock matrix, _ρr is the density of the thermal reservoir rock matrix, _cr is the heat capacity of the thermal reservoir rock matrix, _λf is the thermal conductivity of the heat extraction fluid in the barrel, _ρf is the density of the heat extraction fluid in the wellbore, _r0 is the radius of the well, t is the time, _Tr,i is the well wall temperature, that is, the formation temperature gradient distribution, L is the injection well depth, _Tr,in is the injection well bottom temperature, T is the temperature, q is the instantaneous heat exchange heat between the wellbore and the surrounding formation, and x is the well depth.