CN113935161A - Method for designing economic length of horizontal section of geothermal heating U-shaped butt-joint well - Google Patents
Method for designing economic length of horizontal section of geothermal heating U-shaped butt-joint well Download PDFInfo
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Abstract
The invention relates to the technical field of geothermal heating, in particular to a method for designing the economic length of a horizontal section of a U-shaped butt-jointed well of geothermal heating based on net present value, which comprises the following steps: firstly, inputting basic parameters of a U-shaped butt joint well; starting from the length of the horizontal segment of 0, calculating consumed pump work, calculating investment and determining cost every 1 segment of length; meanwhile, calculating the outlet temperature and the heat, and calculating the income; thirdly, calculating net present values NPV corresponding to different horizontal segment lengths according to the cost and income; fourthly, the maximum value of the calculated length NPV of the horizontal section is the optimal economic length of the horizontal section, and the length of the horizontal section of 0 in the NPV in the calculated length of the horizontal section is the economic limit of the length of the horizontal section. The invention determines the optimal horizontal segment length and the economic limit of the U-shaped butt-joint well from the economic perspective, and provides a certain theoretical basis for the design and the operation of the geothermal heating U-shaped butt-joint well.
Description
Technical Field
The invention relates to the technical field of geothermal heating, in particular to a method for designing the economic length of a horizontal section of a U-shaped butt-joint well for geothermal heating based on net present value.
Background
The U-shaped butt-joint well is a U-shaped pipe formed by steel sleeves in a vertical well and a horizontal engineering well, heat exchange is carried out by utilizing a shaft, the problems of reduction of underground water level, difficulty in recharging and environment pollution caused by geothermal tail water do not exist, and the U-shaped butt-joint well is green and environment-friendly. The device consists of three parts, namely a descending section, a horizontal section and an ascending section. Under the condition of a certain well depth, the heat exchange area of the circulating working medium can be increased by increasing the length of the horizontal section, and the heat taking capacity of the U-shaped butt-joint well can be effectively improved. However, the longer the horizontal section length also means the increase of the drilling cost, and how to technically and economically find the matching point of the length of the horizontal section of the U-shaped butt-jointed well so as to determine the economic length of the horizontal section is not solved at present.
Disclosure of Invention
It is an object of the present invention to provide a method of economically designing the length of the horizontal section of a geothermal heating U-shaped docking well that overcomes some or all of the disadvantages of the prior art.
The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt-jointed well is characterized by comprising the following steps of: the method comprises the following steps:
inputting basic parameters of a U-shaped butt joint well, including a well body structure, a well hole size and operation parameters;
starting from the length of the horizontal segment of 0, calculating consumed pump work, calculating investment and determining cost every 1 segment of length; meanwhile, calculating the outlet temperature and the heat, and calculating the income;
calculating net present values NPV corresponding to different horizontal segment lengths according to cost and income until the longest horizontal segment length which can be achieved in the prior art is calculated;
fourthly, the length of the horizontal section corresponding to the maximum value of the NPV in the calculated length of the horizontal section is the optimal economic length L of the horizontal sectionopteThe length of the horizontal segment whose corresponding NPV is 0 among the calculated lengths of the horizontal segments is the economic limit [ L ] of the length of the horizontal segmentmin，Lmax](ii) a That is, when the length of the horizontal segment is taken as LopteWhen the horizontal segment is L, the maximum benefit is obtainedmin，LmaxIn between, there is a gain. Preferably, the investment comprises U-shaped docking well engineering investment, U-shaped docking well fuel power cost and U-shaped docking well operation management cost.
Preferably, the U-butt well project investments include fixed investments and investments related to horizontal section length, namely:
COGC＝COGD+COBD；
in the formula, COGCInvestment for U-shaped butt joint well engineering; CO 2GDThe fixed investment is independent of the length of the horizontal section, and comprises the drilling cost of the vertical well section, the drilling cost of the inclined well section, other underground fixed investments except the drilling cost and the ground engineering construction investment cost; CO 2BDThe fixed investment related to the horizontal section mainly refers to the drilling cost of the horizontal section; if the drilling cost per meter of the horizontal section increases along with the extension of the horizontal section in an arithmetic progression, the drilling cost per meter of the horizontal section can be expressed as follows:
COH＝COH0+rHL；
then COBD＝COH·L＝COH0·L+rHL2；
In the above two formulae, COHThe drilling cost per meter of the horizontal section; l is the length of the horizontal segment; CO 2H0The basic value of the drilling cost per meter of the horizontal section is obtained; r isHThe drilling cost per meter of the horizontal section is increased by a factor.
Preferably, the fuel power cost of the U-shaped docking well is as follows:
where CE (t) is the fuel power cost of the U-shaped docking well; k is a radical of1The power consumption coefficient of the pump is taken as a reference; j is the service life of the U-shaped butt-joint well; t is the production life of the U-shaped butt-jointed well; t is t0The annual running time of the well is U-shaped butt joint; o is the electricity price; cpThe annual rate of increase of price; i is the reference yield.
Preferably, the operation and management cost of the U-shaped docking well is as follows:
in the formula, CM (t) is the operation management cost of the U-shaped butt-jointed well; cmgThe cost is managed for the production operation of the first year.
Preferably, the revenue includes sales revenue, government subsidies, and U-docking well operating taxes.
Preferably, the sales revenue calculation formula is:
in the formula, CISA(t) sales revenue from U-shaped docking well production to the t year; s is heat value; eta is heat extraction efficiency and is dimensionless; phi is heat quantity;
the government subsidy calculation formula is as follows:
CISU(t)＝kCOGC；
in the formula, CISU(t) a policy subsidy from the production of the U-shaped butt-jointed well to the t year; k is the proportion of one-time fund subsidies of the initial investment of the government on geothermal heating;
the calculation formula of the business tax of the U-shaped docking well is as follows:
CT(t)＝CISA(t)·β；
in the formula, CT (t) is tax paid by the U-shaped butt-jointed well from 1 st year to t th year of production; beta is the enterprise comprehensive tax rate.
Preferably, the net present value NPV is calculated by the formula:
let NPV equal to 0, the length of the horizontal segment is the minimum economic length L of the horizontal segment for generating profitminWith the maximum economic length L of the horizontal sectionmax；
Given any L, the corresponding NPV can be calculated, and the maximum NPV can be obtained after multiple calculations. Namely:
NPVmax＝Max(NPV1、NPV2、NPV3、……NPVn)；
NPVmaxthe length of the horizontal section of the corresponding geothermal heating U-shaped butt-joint well is the optimal economic length; substituting the heat function relationship into a calculation formula of the net present value NPV to obtain a function of the NPV as the horizontal segment length L, and solving a first derivative of the horizontal segment length L by the NPV, namely:
then let NPV solve the second derivative for the horizontal segment length L, i.e.:
C1<0, so that the second derivative of the NPV on the length L of the horizontal section is constantly less than 0, when the first derivative of the NPV on the length L of the horizontal section is 0, the obtained length of the horizontal section is the economic length L of the horizontal section of the U-shaped butt-jointed well corresponding to the maximum NPVopte。
The invention determines the optimal horizontal segment length and the economic limit of the U-shaped butt-joint well from the economic perspective, and provides a certain theoretical basis for the design and the operation of the geothermal heating U-shaped butt-joint well.
Drawings
FIG. 1 is a schematic view showing the working principle of a geothermal heating U-shaped docking well in embodiment 1;
FIG. 2 is a schematic view showing the change of the amount of heat extracted according to the length of a horizontal section in example 1;
FIG. 3 is a flow chart of the method for designing the economic length of the horizontal section of the U-shaped butt well for medium-heat heating in example 1.
Detailed Description
For a further understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings and examples. It is to be understood that the examples are illustrative of the invention and not limiting.
Example 1
Concept and working principle of geothermal heating U-shaped butt-joint well
Much of the literature on U-tube geothermal systems has focused on the use of shallow geothermal energy, which does not have long horizontal sections. For the geothermal resources in the middle and deep layers or the geothermal resources in the hot dry rock, most of previous researches mainly focus on two aspects, namely, (1) the heat exchange efficiency of a heat taking system using a concentric sleeve is low; (2) drilling a plurality of deep wells for producing and injecting water, adopting measures such as fracturing, acidizing and the like to connect a reservoir stratum. The process is complex, the stratum is communicated with a geothermal system, the system belongs to an open system, and the recovery rate of the working medium is low. In addition, the stratum is collapsed due to the large amount of underground water pumped, and the surface of the ground is polluted by environment and heat due to the discharge of geothermal water caused by unfavorable recharging.
Therefore, the embodiment provides a novel geothermal heating system with a U-shaped butt-jointed well, and the working process of the system is as follows: and injecting a low-temperature fluid medium into the U-shaped butt-joint well, transferring geothermal energy deep in the stratum to the low-temperature fluid in the pipe to heat the low-temperature fluid, extracting heat by a ground system, and injecting the artificial medium with the reduced temperature into the well again to form closed circulation. Because it has longer horizontal sections in higher temperature areas of the formation, its design allows for higher heating power and also isolates the formation from the geothermal system, with injected water recovery rates approaching 100%.
The U-shaped horizontal butt joint pipe consists of a descending section, a horizontal section and an ascending section, breaks through the limitation of low working flow of the concentric vertical well, and simultaneously increases the utilization of the heat energy of the high-temperature stratum at the deepest part of the well body. When the heat exchanger works, the fluid working medium finishes heat exchange with the stratum through the descending section, the horizontal section and the ascending section in sequence, and then enters the heat pump system to finish closed circulation. The working principle is shown in figure 1.
The U-shaped butt-joint well can be completed by butt-joint of a horizontal well and a vertical well depending on horizontal drilling technology, directional drilling technology and communication drilling technology.
U-shaped butt-joint well heat taking mathematical model
1. One-dimensional steady-state heat transfer model of shaft
The assumption of steady state heat transfer in the wellbore, that the heat transfer in the wellbore is calculated as the outer wall temperature of the cement sheath over time resulting from unsteady heat conduction of the formation, does not mean that the temperature throughout the wellbore does not change over time.
One-dimensional steady-state heat transfer is performed between the center of the working medium pipeline and the outer diameter of a cement sheath (an insulating layer), and the total heat transfer formula is as follows:
in the formula, phi is heat, W; t iswThe temperature of the interface of a shaft structure and a stratum is measured at the temperature of DEG C, if an insulating layer is arranged outside the shaft, the temperature of the outer edge of the insulating layer is measured, and if the insulating layer is not arranged outside the shaft, the temperature of the outer edge of the cement sheath is measured; t isfThe average temperature of the heat working medium is taken; r is total thermal resistance, (° C.m)/W, and the total thermal resistance R of the U-shaped horizontal butt well is as follows from inside to outside in sequence: heat resistance of convection heat transfer, heat conduction heat resistance of metal pipe wall, heat conduction heat resistance of cement sheath and heat conduction heat resistance of heat insulation layer (including heat insulation layer).
2. Stratum one-dimensional unsteady heat conduction and heat transfer model
In the same infinitesimal section of the steady-state heat transfer of the shaft, the unsteady-state heat conduction equation of the stratum is as follows:
in the formula, TeFormation temperature, deg.C; a is the thermal diffusion coefficient of the formation, m2/s。
Initial conditions:
Te＝Te|t＝0＝Tb+aTz (3)
in the formula, TbSurface temperature, deg.C; a isTIs the geothermal gradient, DEG C/m.
Boundary conditions:
r → ∞ time, then,
at the interface of the cement sheath and the formation, r ═ r3The method comprises the following steps:
at the interface of the insulating layer and the formation, r ═ r4The method comprises the following steps:
in the formula, λeThe formation thermal conductivity, W/(m.DEG C).
The following results were obtained using the semi-analytical method:
wherein f (t) is a dimensionless time function reflecting the formation thermal resistance, and can be obtained by adopting an IGSHPA method recommended by the International ground source heat pump Association.
3. Shaft and stratum heat transfer coupling model
Because the heat transfer is in a steady state in the wellbore and the heat transfer is balanced at the interface between the wellbore structure and the formation, there are
Can obtain the product
Wherein K is the total heat transfer coefficient, W/(m)2C.g. to be prepared into a preparation. Herein get
Model solving method
And dividing the U-shaped horizontal butt joint pipe into N sections with equal length for sectional calculation, wherein the bending part of the U-shaped well is subjected to sectional linear approximation. The initial inlet working medium temperature and the working medium flow are given, relevant geological parameters are substituted, iterative calculation is carried out on each section in sequence according to the working medium flow direction, the outlet working medium temperature of each section and the heat extraction quantity of the section can be obtained, and then the heat extraction quantity phi of the whole underground heat exchanger is obtained.
By varying the different horizontal segment lengths L, the relationship of the amount of heat extracted φ to the horizontal segment length can be obtained, as shown in FIG. 2.
As can be seen from fig. 2, the heat extraction of the geothermal well increases as the horizontal segment length increases. Wherein the heat extraction increases rapidly when the horizontal segment length is short. As the length of the horizontal segment continues to increase, the heat extraction increases more and more slowly. Fitting the data with enough samples, taking the relationship between the heat and the length of the horizontal segment to approximately satisfy the parabolic relationship with the opening downward, can be expressed by equation (11).
Φ＝C1L2+C2L+C3 (11)
In the formula, C1、C2、C3The fitting coefficients related to the technical parameters and the process parameters of the geothermal well are dimensionless.
U-shaped butt joint well horizontal section economic length mathematical model based on net present value
U-shaped docking well expenditure
Engineering investment of U-shaped butt well
The investment is divided into two parts, one part is the investment which is irrelevant to the length of the horizontal section and is called as fixed investment; the second is the investment related to the length of the horizontal segment, which means the investment will change correspondingly with the change of the length of the horizontal segment, i.e. the part of the investment is a function of the length L of the horizontal segment, and is called the variable investment. Namely:
COGC＝COGD+COBD (12)
in the formula, COGCInvestment for U-shaped butt joint well engineering is ten thousand yuan; CO 2GDThe method is a fixed investment irrelevant to the length of a horizontal section, and ten thousand yuan of the method comprises the drilling cost of a vertical well section, the drilling cost of an inclined well section, other underground fixed investments except the drilling cost, the investment cost of ground engineering construction and the like; CO 2BDThe method is mainly used for solving the problem that the drilling cost of the horizontal section is ten thousand yuan for the fixed investment related to the horizontal section.
The drilling cost per meter of the horizontal section is not constant, and the drilling cost is higher and higher along with the extension of the horizontal section, and the borne risk is higher and higher. For convenience, it can be assumed that the drilling cost per meter of the horizontal segment increases in an arithmetic progression with the extension of the horizontal segment, and the drilling cost per meter of the horizontal segment can be expressed as:
COH＝COH0+rHL (13)
then COBD＝COH·L＝COH0·L+rHL2 (14)
In the above two formulae, COHTen thousand yuan for the drilling cost per meter of the horizontal section; l is the length of the horizontal segment, m; CO 2H0The base value of the drilling cost per meter of the horizontal section is ten thousand yuan/m; r isHThe increment coefficient of the drilling cost per meter of the horizontal section is (ten thousand yuan/m)/m.
Fuel power cost for U-shaped docking well
The consumed pump work N is calculated by starting from a horizontal segment with the length of 0 and calculating the consumed pump work at intervals of the length.
N0Calculating the consumed basic pumping work, kW, of a certain horizontal segment length under a certain working condition of the geothermal heating U-shaped well;
delta p is the pressure loss of the inlet and the outlet of the geothermal heating U-shaped butt-joint well;
eta-pump efficiency, decimal.
qvCirculation displacement of geothermal heating U-shaped docking well, m3/s。
N0Calculating the consumed basic pumping work, kW, of a certain horizontal segment length under a certain working condition of the geothermal heating U-shaped well;
h is the length of the straight well section, m.
L0The length of the basic horizontal section of the geothermal heating U-shaped well is m.
Ls is the length of the inclined shaft section, m.
L-length of horizontal section of U-shaped butt-jointed well, m.
In order to drive the circulating working medium to circularly flow in the U-shaped butt-joint well, the system is provided with a high-pressure pump, and the energy provided by the high-pressure pump is used for overcoming the loss of the working medium flowing in the pipeline, so that certain power cost is consumed for the operation of the pump. The longer the length of the piping, the greater the on-way losses that occur, the more energy the pump is required to provide, and the higher the cost required, thus affecting the net present value. Which approximately satisfies a linear relationship with the horizontal segment length. Considering the cost of fuel power cost and the change of interest rate with time, according to the basic principle of technical economy, the fuel power cost of the U-shaped butt-jointed well is as follows:
wherein CE (t) is a U-shaped butt wellFuel power cost, ten thousand yuan; k is a radical of1The power consumption coefficient is a reference pump power consumption coefficient, W, and is obtained by pipeline hydraulic calculation; j is the service life of the U-shaped butt-joint well, year; t is the production age of the U-shaped butt-jointed well, year; t is t0The annual running time of the well is U-shaped butt joint; o is the electricity price, ten thousand yuan/(MkW h); cpThe price annual growth rate is decimal, ten thousand yuan/(MkW h); i is the benchmark yield, decimal.
U-shaped butt-joint well operation management cost
After the U-shaped docking well is put into operation, the operation cost, the labor cost, the management cost, the business cost and the like need to be put into operation every year in order to meet the requirements of daily management, maintenance, operation and the like. The operation and management cost of the U-shaped butt joint well is as follows:
in the formula, CM (t) is the management cost of U-shaped butt-jointed wells in ten thousand yuan; cmgThe cost is ten thousand yuan for the production, operation and management in the first year.
U-shaped docking well entry
Sales revenue
The sales income of the U-shaped butt-joint well refers to the capital value converted from the heat absorbed by the working medium from the stratum, and can be determined by the following formula.
In the formula, CISA(t) sales income from the production of the U-shaped butt-jointed well to the t year is ten thousand yuan; s is heat value, ten thousand yuan/(MkW h); eta is heat extraction efficiency and is dimensionless.
Government subsidy
The directive opinions about promoting the development and utilization of geothermal energy (hereinafter referred to as opinions) issued by the country in 2013 determine a development target for the development of the geothermal industry and make subsidy policies on geothermal heating and power generation. Referring to a subsidy policy for geothermal heating in a file 'implementation opinion about further accelerating application of a heat pump system and promoting clean heating' jointly formulated by 8 units such as Beijing Ministry of development and improvement and Ministry of municipal planning of natural resources, and the like: 30 to 50 percent of capital support is given according to the investment of engineering construction. Thus, the government subsidy after the U-docked well is put into operation may be determined by the following equation.
CISU(t)＝kCOGC (18)
In the formula, CISU(t) a policy subsidy from the production of the U-shaped butt-jointed well to the t year, ten thousand yuan; k is the proportion, decimal, of the one-time fund subsidy of the initial investment of the government for geothermal heating.
4.3U-shaped butt-joint well business tax
The business tax reflects the tax that the main business of enterprise operation should bear, mainly include value-added tax, resource tax, education fee additional tax, city maintenance construction tax and income tax, etc.. For convenience of research, the above tax names are referred to herein as general taxes. This tax is determined by the following equation.
CT(t)＝CISA(t)·β (19)
In the formula, CT (t) is tax paid from 1 st year to t th year of production of the U-shaped butt-jointed well, ten thousand yuan; beta is the comprehensive tax rate of the enterprise, decimal.
U-shaped butt joint well net present value model
Through the analysis, the cash flow flowing out and in of the geothermal heating U-shaped butt-joint well is determined, the cash flow flowing in is the sum of business income and national team geothermal energy industry subsidies, and the cash flow flowing out is the sum of initial investment, management cost and business tax of the geothermal heating U-shaped butt-joint well. The above formula is substituted into a detailed expression of the available geothermal heating U-shaped butt joint well net present value, which is:
from the above formula, it can be seen that, in addition to economic factors such as drilling cost, management and operation cost, tax, heating price, national subsidy, interest rate and the like, the net present value of the geothermal heating U-shaped butt-joint well is obtained, and the heat taking amount and the pump work consumed by the geothermal heating U-shaped butt-joint well directly influence the net present value of the geothermal heating U-shaped butt-joint wellThe heat quantity and the consumed pump work are closely related to variable technical parameters and operation parameters, including working medium circulation displacement, working medium inlet temperature and horizontal section length. Let NPV equal to 0, the length of the horizontal segment is the minimum economic length L of the horizontal segment for generating profitminWith the maximum economic length L of the horizontal sectionmax。
As shown in equation (20), when any given L is given, its corresponding NPV can be calculated, and the maximum NPV can be obtained after a plurality of calculations. Namely:
NPVmax＝Max(NPV1、NPV2、NPV3、……NPVn) (21)
apparently NPVmaxThe length of the corresponding horizontal section of the geothermal heating U-shaped butt-joint well is the optimal economic length. And substituting (20) the heat function relationship to obtain a function of the NPV as the length L of the horizontal section, and solving a first derivative of the length L of the horizontal section by the NPV, namely:
then let NPV solve the second derivative for the horizontal segment length L, i.e.:
according to the conclusions of the previous studies herein, C1<0, so that the second derivative of the NPV on the length L of the horizontal section is constantly less than 0, when the first derivative of the NPV on the length L of the horizontal section is 0, the obtained length of the horizontal section is the economic length L of the horizontal section of the U-shaped butt-jointed well corresponding to the maximum NPVopte。
Through the above formula, the net current value of the geothermal heating U-shaped butt joint well under different horizontal section lengths can be calculated under a certain operation parameter, so that the change rule of the net current value of the geothermal heating U-shaped butt joint well along with the horizontal section length can be obtained, and the optimal economic length of the horizontal section is obtained, wherein the process is as shown in fig. 3 and specifically as follows:
(1) inputting basic parameters of the U-shaped butt joint well, including a well body structure, a well hole size and operation parameters;
(2) starting from the length of a horizontal section of 0, calculating the consumed pump work by using a basic hydraulic calculation formula every 1 section of length (grid size), thereby calculating the investment by using an equation (12) to an equation (16) and determining the cost; meanwhile, the outlet temperature and the heat extraction amount are calculated by using a shaft heat transfer model of the U-shaped well butt joint well, so that the income is calculated by using the formula (17) to the formula (19);
(3) calculating the net present value NPV corresponding to each segment length by using a formula (20) until the horizontal segment length is the longest technically achieved horizontal segment length;
(4) the length of the horizontal segment corresponding to the maximum value of NPV in the calculated length of the horizontal segment is the optimal economic length L of the horizontal segmentopteThe horizontal segment length in which NPV is 0 (or close to 0) among the calculated horizontal segment lengths is the economic limit [ L ] of the horizontal segment lengthmin，Lmax]. That is, when the length of the horizontal segment is taken as LopteWhen the horizontal segment is L, the maximum benefit is obtainedmin，LmaxIn between, there is a gain.
In the embodiment, a geothermal heating U-shaped butt-joint well is taken as a research object, a U-shaped butt-joint well heat taking mathematical model is established, an NPV-based U-shaped butt-joint well horizontal section economic length model is established, the optimal horizontal section length and the economic limit of the U-shaped butt-joint well are determined from the economic perspective, and a certain theoretical basis is provided for the design and operation of the geothermal heating U-shaped butt-joint well.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.
Claims (8)
1. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt-joint well is characterized by comprising the following steps: the method comprises the following steps:
inputting basic parameters of a U-shaped butt joint well, including a well body structure, a well hole size and operation parameters;
starting from the length of the horizontal segment of 0, calculating consumed pump work, calculating investment and determining cost every 1 segment of length; meanwhile, calculating the outlet temperature and the heat, and calculating the income;
calculating net present values NPV corresponding to different horizontal segment lengths according to cost and income until the horizontal segment length is the longest horizontal segment length which can be achieved in the prior art;
fourthly, the length of the horizontal section corresponding to the maximum value of the NPV in the calculated length of the horizontal section is the optimal economic length L of the horizontal sectionopteThe horizontal segment length in which NPV is 0 among the calculated horizontal segment lengths is the economic limit [ L ] of the horizontal segment lengthmin，Lmax](ii) a That is, when the length of the horizontal segment is taken as LopteWhen the horizontal segment is L, the maximum benefit is obtainedmin，LmaxIn between, there is a gain.
2. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt well according to claim 1, wherein the method comprises the following steps: the investment comprises the U-shaped docking well engineering investment, the U-shaped docking well fuel power cost and the U-shaped docking well operation management cost.
3. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt well according to claim 2, wherein the method comprises the following steps: the U-shaped butt well engineering investment comprises fixed investment and investment related to the length of a horizontal section, namely:
COGC＝COGD+COBD；
in the formula, COGCInvestment for U-shaped butt joint well engineering; CO 2GDThe fixed investment is independent of the length of the horizontal section, and comprises the drilling cost of the vertical well section, the drilling cost of the inclined well section, other underground fixed investments except the drilling cost and the ground engineering construction investment cost; CO 2BDThe fixed investment related to the length of the horizontal section mainly refers to the drilling cost of the horizontal section;
if the drilling cost per meter of the horizontal section increases along with the extension of the horizontal section in an arithmetic progression, the drilling cost per meter of the horizontal section can be expressed as follows:
COH＝COH0+rHL；
then COBD＝COH·L＝COH0·L+rHL2；
In the above two formulae, COHThe drilling cost per meter of the horizontal section; l is the length of the horizontal segment; CO 2H0The basic value of the drilling cost per meter of the horizontal section is obtained; r isHThe drilling cost per meter of the horizontal section is increased by a factor.
4. A method of designing an economic length of a horizontal section of a geothermal heating U-shaped butted well as recited in claim 3 wherein: the fuel power cost of the U-shaped butt joint well is as follows:
where CE (t) is the fuel power cost of the U-shaped docking well; k is a radical of1The power consumption coefficient of the pump is taken as a reference; j is the service life of the U-shaped butt-joint well; t is the production life of the U-shaped butt-jointed well; t is t0The annual running time of the well is U-shaped butt joint; o is the electricity price; cpThe annual rate of increase of price; i is the reference yield.
5. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt-joint well according to claim 4, wherein the method comprises the following steps: the operation and management cost of the U-shaped butt joint well is as follows:
in the formula, CM (t) is the operation management cost of the U-shaped butt-jointed well; cmgThe cost is managed for the production operation of the first year.
6. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt well according to claim 5, wherein the method comprises the following steps: the income includes sales income, government subsidies and U-shaped docking well business taxes.
7. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt well according to claim 6, wherein the method comprises the following steps: the sales revenue calculation formula is:
in the formula, CISA(t) sales revenue from U-shaped docking well production to the t year; s is heat value; eta is heat extraction efficiency and is dimensionless; phi is heat quantity;
the government subsidy calculation formula is as follows:
CISU(t)＝kCOGC；
in the formula, CISU(t) a policy subsidy from the production of the U-shaped butt-jointed well to the t year; k is the proportion of one-time fund subsidies of the initial investment of the government on geothermal heating;
the calculation formula of the business tax of the U-shaped docking well is as follows:
CT(t)＝CISA(t)·β；
in the formula, CT (t) is tax paid by the U-shaped butt-jointed well from 1 st year to t th year of production; beta is the enterprise comprehensive tax rate.
8. The method for designing the economic length of the horizontal section of the geothermal heating U-shaped butt well according to claim 7, wherein the method comprises the following steps: the calculation formula of the net present value NPV is as follows:
let NPV equal to 0, the length of the horizontal segment is the minimum economic length L of the horizontal segment for generating profitminWith the maximum economic length L of the horizontal sectionmax；
Given any L, the corresponding NPV can be calculated, and the maximum NPV can be obtained after multiple calculations. Namely:
NPVmax＝Max(NPV1、NPV2、NPV3、……NPVn)；
NPVmaxthe length of the horizontal section of the corresponding geothermal heating U-shaped butt-joint well is the optimal economic length; substituting the heat function relationship into a calculation formula of the net present value NPV to obtain a function of the NPV as the horizontal segment length L, and solving a first derivative of the horizontal segment length L by the NPV, namely:
then let NPV solve the second derivative for the horizontal segment length L, i.e.:
C1<0, so that the second derivative of the NPV on the length L of the horizontal section is constantly less than 0, when the first derivative of the NPV on the length L of the horizontal section is 0, the obtained length of the horizontal section is the economic length L of the horizontal section of the U-shaped butt-jointed well corresponding to the maximum NPVopte。
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