CN104594872A - Method for optimizing fracture conductivity of tight gas-reservoir fractured horizontal well - Google Patents

Abstract

The invention relates to fracturing reformation in the field of oil-gas field development, in particular to a method for optimizing fracture conductivity of a tight gas-reservoir fractured horizontal well. The method mainly comprises the following steps of (1) collecting basic parameters of a reservoir, fluid property and a horizontal well shaft; (2) collecting basic parameters of fractures of the fractured horizontal well; (3) evenly dividing each fracture of the fractured horizontal well into line congruence with equal length along the fracture length direction; (4) building a reservoir permeability model for a tight gas-reservoir fractured horizontal well fracture system; (5) building a flowing decompression model of gas in the fractures; (6) building a flowing model of coupled gas in the reservoir permeability and the fractures, and forming a yield calculation model of the tight gas-reservoir fractured horizontal well; (7) optimizing the fracture conductivity of the tight gas reservoir fractured horizontal well. By utilization of the method for optimizing the fracture conductivity of the tight gas-reservoir fractured horizontal well provided by the invention, the shortages of the prior art can be conquered, and the problem of optimizing non-constant fracture conductivity of the fractured horizontal well along the fracture length direction is effectively solved, so that reasonable basis is provided for the optimization design of reservoir reformation, and the reservoir reformation effect is improved.

Description

A kind of method optimizing tight gas reservoir pressure break horizontal well fracture condudtiviy

Technical field

The present invention relates to the fracturing reform in oil-gas field development field, more specifically relating to the method for optimizing tight gas reservoir pressure break horizontal well fracture condudtiviy.

Background technology

Staged fracturing of horizontal well is the effective measures of exploitation tight gas reservoir.Fracturing a kind of makes formation fracture by injecting high-pressure fluid to stratum being greater than in the imbibition ability situation of stratum; Inject the mulling liquid containing proppant subsequently, impel crack to extend to reservoir deep further; After construction terminates, due to the supporting role of proppant fracture wall, fracture surface is made to close completely and still to keep certain flow conductivity.These cracks with flow conductivity guarantee that reservoir hydrocarbons can Channel Group, thus make Oil/gas Well obtain volume increase and improve recovery ratio; The horizontal well yield of tight gas reservoir pressure break can be significantly improved by the flow conductivity optimizing tight gas reservoir pressure break horizontal well crack.

The method of optimization tight gas reservoir pressure break horizontal well fracture condudtiviy conventional is at present: first set up pressure break horizontal well production computation model; Then based on the pressure break horizontal well production computation model set up, under the condition of given reservoir basic parameter, gas parameter, horizontal well parameter and fracture parameters, the pressure break horizontal well production under different fracture condudtiviy is simulated; Finally carry out preferred fracture condudtiviy according to cumulative production under the certain hour of simulation.Accurately preferably the key of tight gas reservoir pressure break horizontal well fracture condudtiviy sets up correct pressure break horizontal well production computation model.At present, the model calculated about pressure break horizontal well production is broadly divided into two classes: a class adopts commercial numerical simulation software, computational analysis (Zhou Zhumei is carried out in production forecast fractured horizontal well being formed to many cracks, Lang Zhaoxin. the Finite Element Method [J] of Horizontal Well Reservoir Numerical Simulation. hydrodynamics research and advances A collects .1996, and 11 (3): 261-270; Zhang Xuewen, Fang Hongchang, Qiu Yinan, etc. low-permeability oil deposit Factors affecting production capacity of fractured horizontal wells [J]. petroleum journal, 1999,20 (4): 51-54).Another kind of is adopt Analytic Calculation Method, according to the thought that source is converged, is divided into by the flow process of tight gas reservoir pressure break horizontal well gas in Reservoir Seepage and crack and flows two stages, set up corresponding Mathematical Modeling respectively and describe its flow process; Then the equation that flows in Reservoir Seepage and crack of coupled gas, solves the flow conductivity in the horizontal well yield of tight gas reservoir pressure break and preferred crack.Its basic process solved comprises five basic steps:

The first step: pressure break horizontal well crack single-blade is divided into the equal congruence of length, the production of each congruence approximate processing can become the production of a bite straight well, utilize principle of stacking, set up when multiple congruence is produced simultaneously at drop of pressure (Aissa Zerzar.Interpretation of Multiple Hydraulically Fractured Horizontal Wells in Closed Systems [R] SPE 84888,2003 that crack tip produces; Zeng Fanhui, Guo Jianchun, Zhao Jinzhou, etc. affect the factor analysis [J] of fractured horizontal well's productivity. Petroleum finance, 2007,34 (4): 474-477; Sun Hai, Yao Jun, Lian Peiqing, etc. consider the pressure break horizontal well unsteady Model [J] of basement rock to pit shaft feed flow. petroleum journal, 2012,33 (1): 117-122).

Second step: solve the pressure drop equation that gas flows in crack.At present for the flowing of gas in crack, be processed into along the invariable miniature planar radial flow (Zeng Fanhui of seam length direction flow conductivity, Guo Jianchun, Zhao Jinzhou, Deng. affect the factor analysis [J] of fractured horizontal well's productivity. Petroleum finance .2007,34 (4): 474-477; Sun Hai, Yao Jun, Lian Peiqing, Deng. consider the pressure break horizontal well unsteady Model [J] of basement rock to pit shaft feed flow. petroleum journal, 2012,33 (1): 117-122), be processed into along the invariable sheet flow model (Gringarten of seam length direction flow conductivity, A.C., Ramey, H.I.Jr., Raghavan, R.Unsteady State PressureDistributions Created by a Well with a Single Infinite-Conductivity Vertical Fracture [J]: SPEJ, 1974:347-60).

3rd step: meet when utilizing gas to flow in Reservoir Seepage and crack that pressure is equal, flow continuous print basic principle, set up containing with each congruence output for variable and the tight gas reservoir pressure break horizontal well production equation equal with the several number of total congruence, because the number of equation is equal with the variable number of congruence output, the output solving and obtain each congruence can be closed.

4th step: the output of each congruence added up, obtains the horizontal well yield of whole pressure break.

5th step: by changing the fracture condudtiviy distribution of pressure break horizontal well, contrasting different fracture condudtiviy and dividing the pressure break horizontal well crack output distribotion and cumulative production that plant, the fracture condudtiviy of Optimum Fracturing horizontal well.

The method of the tight gas reservoir of these methods optimization at present pressure break horizontal well fracture condudtiviy has following remarkable shortcoming:

Suppose that fracture condudtiviy is long invariable along seam, cause the result optimized can only be average crack flow conductivity (Zeng Fanhui, Guo Jianchun, Zhao Jinzhou, Deng. affect the factor analysis [J] of fractured horizontal well's productivity. Petroleum finance .2007,34 (4): 474-477; Sun Hai, Yao Jun, Lian Peiqing, etc. consider the pressure break horizontal well unsteady Model [J] of basement rock to pit shaft feed flow. petroleum journal, 2012,33 (1): 117-122; Wang Xiaodong, Zhang Yitang, Liu Ciqun. vertical fracture well capacity and flow conductivity optimizing research [J] Petroleum finance, 2004,31 (6): 78-81), this and tight gas reservoir horizontal well are in hydraulic fracturing process, and the non-constant flow conductivity distribution along seam length direction that the factor such as laid concentration difference, fracturing fluid residue due to proppant causes exists marked difference.

In order to realize the fracture condudtiviy optimization of tight gas reservoir pressure break horizontal well under real conditions, the flowing of the gas of tight gas reservoir pressure break horizontal well is divided in Reservoir Seepage and crack the process of two couplings of flowing by the present invention, consider that gas is along the actual conditions becoming fracture condudtiviy in the non-homogeneous inflow on fracture surface and crack, adopt room and time discrete technology, utilize the general principles such as instantaneous point source function and barrier layer add, first establish the unstable state Production rate model of tight gas reservoir pressure break horizontal well; And divide the output condition planted, the fracture condudtiviy of preferred tight gas reservoir pressure break horizontal well further by the different fracture condudtiviy of contrast.

Summary of the invention

The object of the present invention is to provide a kind of method of quantitative optimization tight gas reservoir pressure break horizontal well fracture condudtiviy, the method is utilized to overcome the deficiencies in the prior art, effective solution pressure break horizontal well is along the optimization problem of the non-constant fracture condudtiviy of seam length direction, thus provide rational basis for the optimal design of reservoir reconstruction, improve reservoir reconstruction effect.

Optimize a method for tight gas reservoir pressure break horizontal well fracture condudtiviy, mainly comprise the following steps:

1) reservoir, fluid properties, horizontal well pit shaft basic parameter is collected;

2) pressure break horizontal well crack basic parameter is collected;

3) crack of pressure break horizontal well is on average divided into the equal congruence of length along seam length direction;

4) the Reservoir Seepage model of tight gas reservoir pressure break horizontal well Fracture System is set up;

5) Pressure Drop Model that gas flows in crack is set up;

6) set up the flow model of coupled gas in Reservoir Seepage and crack, form the Production rate model of tight gas reservoir pressure break horizontal well;

7) fracture condudtiviy of tight gas reservoir pressure break horizontal well is optimized.

In the present invention, described step 1) middle collection reservoir, fluid properties, horizontal well pit shaft basic parameter, specifically comprise Original strata stress direction, reservoir thickness, degree of porosity, permeability, gas viscosity, gas critical pressure, deviation factor for gas, reservoir temperature, gas critical-temperature, horizontal well orientation, Horizontal Well tube length degree.

In the present invention, described step 2) in collect pressure break horizontal well crack basic parameter and comprise: hydraulic fracture orientation, Number of Fractures, fracture interval, crack location, fracture length.

In the present invention, described step 3) in by the crack of pressure break horizontal well along seam length direction be on average divided into the equal congruence of length.

In the present invention, described step 4) set up the Reservoir Seepage model calculating tight gas reservoir pressure break horizontal well Fracture System, comprise following basic step:

(1) physical model of pressure break horizontal well is set up as Fig. 1, go to the bottom a bite pressure break horizontal well in closed infinitely great reservoir in upper top, horizontal well is divided into some sections by the fracturing fracture penetrating reservoir completely, and first reservoir gas flows to crack and flow to horizontal wellbore through crack again.Horizontal well radius is r _w, length is L, and well is (x in reservoir center position coordinates ₀, y ₁, z ₀)-(x ₀, y ₂, z ₀), and parallel with y-axis.Reservoir homogeneous isotropism, thickness is h, degree of porosity φ, permeability K are constant; Horizontal wellbore is infinite fluid diversion, and reservoir initial pressure is constant p _i.Because fracturing fracture runs through oil reservoir, therefore the flowing of infinitely great formation breakdown horizontal well whole system can be reduced to the Radial Flow in plane oil reservoir, crack can be reduced to a congruence (Li Junshi. pressure break horizontal well Research of Dynamic Analysis [D]. Beijing: China University of Geosciences, 2005).

(2) for the ease of solving, kth crack single-blade is divided into ns section, every segment length is Δ x _fk, Δ x _fk=x _fk/ ns; Each congruence can be processed into a bite straight well and produce consideration (Fig. 2).Straight well in process of production output constantly changes, if but will obtain in the time interval very little, can be similar to and think that output is definite value within this period, the whole production phase t of pressure break horizontal well is divided into the equal time interval Δ t of m spacing, t=m Δ t.

Being located at kth crack has a congruence i (output is q _{fk, i}) be positioned at M (x _{fk, i}, y _fk) place, crack k+1 has a point of observation O (x _{fk+1, j}, y _fk+1), when considering fluid volume coefficient, the drop of pressure that congruence i produces at O point after production time Δ t is (Fig. 2):

$p_i-p_{\mathrm{fk}+1,j}=\frac{q_{\mathrm{fk},i}\mathrm{\μB}}{4\mathrm{\πKh}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}---\left(1\right)$

In formula: p _ifor original formation pressure, MPa; p _{fk+1, j}for the pressure at kth+1 crack jth congruence sides of fracture place, MPa; q _{fk, i}for the output of i-th congruence on kth crack, m ³/ s; μ is viscosity of crude, mPa.s; B is volume factor, zero dimension; (x _{fk, i}, y _fk) be the coordinate (m, m) of i-th congruence on kth crack; (x _{fk+1, j}, y _fk+1) be the coordinate (m, m) of the jth congruence on kth+1 crack; K is reservoir permeability, 10 ^?3μm ²; H is reservoir thickness, m; η is piezometric conductivity, μm ²/ (mPas × MPa ^-1), η=K/ μ c φ; C is stratum system compressibility, MPa ^?1; φ is reservoir porosity, zero dimension; Δ t is the production time, s; K is crack numbering; I, j are crack congruence numbering.

(3) when crack k containing multiple continuous congruence, the drop of pressure produced at point of observation O place when each congruence of k crack is produced simultaneously can be obtained according to principle of stacking; After the same method, also can obtain pressure break horizontal well and form N crack, at the drop of pressure of O point simultaneously when N × 2ns the crack congruence is produced altogether:

$p_i-p_{\mathrm{fk}+1,j}=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\frac{q_{\mathrm{fk},i}\mathrm{\μB}}{4\mathrm{\πKh}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}---\left(2\right)$

In formula: N is pressure break horizontal well Number of Fractures, bar; Ns is crack single-blade congruence number.

(4) when reservoir fluid is gas, according to definition and the actual gas state equation of pressure function, and gas yield (Ning Zhengfu underground output converted in ground standard situation, Han Shugang, Cheng Linsong, etc. Low permeable oil and gas reservoirs method of productivity calculation for fractured horizontal well [J]. petroleum journal, 2002,23 (2): 68 ?71), formula (2) can be written as:

$p_i^2-p_{\mathrm{fk}+1,j}^2=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\frac{q_{\mathrm{fk},i}{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{2\mathrm{\πKh}{T}_{\mathrm{sc}}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}---\left(3\right)$

In formula: μ _gfor gas viscosity, mPas; p _scfor gas critical pressure, MPa; Z is deviation factor for gas, zero dimension; T is reservoir temperature, DEG C; T _scfor gas critical-temperature, DEG C.

Formula (3) be exactly all slits congruence simultaneously after production time Δ t at the drop of pressure equation of O point generation, this equation considers the mutual interference effect between each congruence in crack and crack.

In the present invention, described step 5) calculate the Pressure Drop Model that gas flows in crack, comprise following basic step:

(1) consider that hydraulic fracture width narrows gradually along seam length direction, by crack section processing in echelon, kth+1 crack root width is w _{fk+1, max}, end portion width is w _{fk+1, min}, as shown in Figure 3.For the ease of calculating, each congruence being processed into rectangle and calculating, line taking remittance central point width is congruence width.With the intersection point of crack and horizontal wellbore for initial point, distance horizontal wellbore x _jthe width of a jth congruence at place is:

w _fk+1,j＝w _fk+1,min+(w _fk+1,max-w _fk+1,min)×(x _fk+1-x _fk+1,j)/x _fk+1(4)

The average crack width w of a jth congruence _{fk+1, averj}for:

w _fk+1,averj＝(w _fk+1,j+w _fk+1,j-1)/2 (5)

In formula: w _{fk+1, j}for the crack width of kth+1 crack jth congruence, m; w _{fk+1, max}for kth+1 crack root width, m; w _{fk+1, min}for kth+1 crack end portion width, m; x _fk+1for kth+1 crack single slot is long, m; x _{fk+1, j}for kth+1 crack jth congruence is in the x-direction apart from the distance of pit shaft, m; w _{fk+1, averj}for kth+1 crack jth congruence mean breadth, m.

(2) consider that gas meets linear flow in crack, calculate (the some O of congruence j on kth+1 crack according to Darcy's law _{fk+1, j}) pressure loss that flow to horizontal wellbore is:

$\begin{array}{c}{p}_{\mathrm{fk}+1,j}^2-p_{\mathrm{fk}+\mathrm{1,0}}^2=\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}{q}_{\mathrm{fk}+\mathrm{1,1}}+\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}{w}_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,2}}}{w_{\mathrm{fk}+1,\mathrm{aver}2}})q_{\mathrm{fk}+\mathrm{1,2}}+...\\ +\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,2}}}{w_{\mathrm{fk}+1,\mathrm{aver}2}}+...+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{averj}}})q_{\mathrm{fk}+1,j}\\ +\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,2}}}{w_{\mathrm{fk}+1,\mathrm{aver}2}}+...+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{averj}}})q_{\mathrm{fk}+1,j+1}+...\\ +\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,2}}}{w_{\mathrm{fk}+1,\mathrm{aver}2}}+...+\frac{\mathrm{\Δ}{x}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{averj}}})q_{\mathrm{fk}+1,\mathrm{ns}}\\ =\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}\{\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\left(q_{\mathrm{fk}+1,i}\underset{j=1}{\overset{i}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{averj}}}\right)+\underset{n=j+1}{\overset{\mathrm{ns}}{\mathrm{\Σ}}}[q_{\mathrm{fk}+1,n}\left(\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,i}}{w_{\mathrm{fk}+1,\mathrm{averj}}}\right)\left]\right\}\end{array}$

$\left(6\right)$

In formula: p _fk+1,0for the pressure of kth+1 crack and horizontal wellbore intersection, MPa; k _fk+1for the permeability in kth+1 crack, 10 ^?3μm ².

In the present invention, described step 6) calculate the pressure break horizontal well production of tight gas reservoir, comprise following basic step:

(1) set up reservoir Shen Liu ?the coupling model of flowing in crack

The process that gas flows to horizontal wellbore from reservoir can be divided in gas reservoir seepage flow and crack two processes that flow, and formula (3), formula (6) have established corresponding descriptive equation; Consider gas store up when intrastratal flow and fluid flow in crack equal at the pressure at wall place, crack, can build-up pressure continuity equation; Due to hypothesis pit shaft infinite fluid diversion, each crack with horizontal wellbore intersection O ₀pressure equal, stable bottom hole pressure (p _wf) produce time fringe conditions be:

p _fk+1,0＝p _wf(7)

In formula: p _wffor horizontal wellbore flowing bottomhole pressure (FBHP), MPa;

Simultaneous equations (3), (6), (7) arrange obtain kth+1 crack jth congruence Qi Zang ?crack coupling flow equation:

$\begin{array}{c}{p}_i^2-p_{\mathrm{wf}}^2=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\frac{q_{\mathrm{fk},i}{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{2\mathrm{\πKh}{T}_{\mathrm{sc}}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}\\ +\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}\{\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\left(q_{\mathrm{fk}+1,i}\underset{j=1}{\overset{i}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{averj}}}\right)+\underset{n=j+1}{\overset{\mathrm{ns}}{\mathrm{\Σ}}}[q_{\mathrm{fk}+1,n}\left(\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,i}}{w_{\mathrm{fk}+1,\mathrm{averj}}}\right)\left]\right\}\end{array}---\left(8\right)$

In formula (8), variable is the output of each congruence, so just establishes the Transient Flow Mathematical Modeling that pressure break horizontal well crack is coupled with gas reservoir.Due to bottom pressure p _wfknown, according to the system of linear equations of N × 2ns the linear equation formation that formula (8) is set up, the output of each congruence can be tried to achieve.

(2) the transient state output of tight gas reservoir pressure break horizontal well is calculated

Owing to considering that gas only flow into horizontal wellbore by crack, so the total output of pressure break horizontal well is the sum of all congruence output on a pressure break horizontal well crack:

$Q=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}{q}_{\mathrm{fk},i}---\left(9\right)$

The horizontal well yield of tight gas reservoir pressure break can be tried to achieve according to formula (9).

(3) the unstable state output of tight gas reservoir pressure break horizontal well is calculated

The computational methods of equation (8), (9) each congruence and pressure break horizontal well production under establishing the Δ t time; For each congruence, because output can change with the production time, at this moment need to utilize the time to superpose the value of trying to achieve any time.If time step is Δ t, as t=m Δ t (m time period ending), then (Lian Peiqing can be obtained to kth+1 crack jth point sink, Cheng Linsong, Cao Renyi, etc.. unsteady Model [J] Computational Physics that low-permeability oil deposit pressure break horizontal well pit shaft is coupled with oil reservoir, 2010,27 (2): 203 ?210):

$\begin{array}{c}{p}_i^2-p_{\mathrm{wf}}^2=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\{q_{\mathrm{fk},i}\left(\mathrm{\Δt}\right)F_{\mathrm{ki},k+1j}\left(\mathrm{m\Δt}\right)\\ +\underset{g=2}{\overset{m}{\mathrm{\Σ}}}[q_{\mathrm{fk},i}\left(\mathrm{g\Δt}\right)-q_{\mathrm{fk},i}\left((g-1)\mathrm{\Δt}\right)]F_{\mathrm{ki},k+1j}\left[(m-g+1)\mathrm{\Δt}\right]\}\end{array}---\left(10\right)$

In formula: $F_{\mathrm{ki},k+1j}\left(\mathrm{\Δt}\right)=\frac{{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{2\mathrm{\πKh}{T}_{\mathrm{sc}}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}$

The same with the Production rate producing Δ t time span, according to bottom pressure constraint and total output constraint, composition Closure equation group solves, and from the 1st time Δ t step-length, circulation solves, until calculate the Production rate result under m Δ t step-length.

In the present invention, described step 7) optimize the fracture condudtiviy of tight gas reservoir pressure break horizontal well, comprise following basic step:

(1) different fracture condudtiviy distribution schemes is set along seam length direction;

(2) calculate different fracture condudtiviy and divide the crack planted output distribotion situation;

(3) calculate the cumulative production that different fracture condudtiviy divides the pressure break horizontal well planted to produce 360 days, consider engineering condition, preferred best fracture condudtiviy distribution scheme in conjunction with cumulative production result;

Compared with prior art, beneficial effect of the present invention:

Technical scheme of the present invention can realize the fracture condudtiviy quantitative optimization to tight gas reservoir pressure break horizontal well, utilize the method according to underlying parameters such as the physical parameter of reservoir, fluid properties, horizontal wellbore and fracturing fractures, the quantitative optimization of tight gas reservoir pressure break horizontal well fracture condudtiviy along seam length direction can be realized.Thus overcome in prior art and can only realize the average crack flow conductivity optimization of fracture flow conductivity along whole seam length direction, improve validity and the effect of tight gas reservoir fractured horizontal well transformation.

Accompanying drawing explanation

Fig. 1 is go to the bottom closed infinitely great gas reservoir pressure break horizontal well physical model schematic diagram in upper top;

Fig. 2 is the segmentation of two dimensional surface crack and discretization schematic diagram;

Fig. 3 is gas flow schematic diagram in gas reservoir pressure break horizontal well single-blade crack;

Fig. 4 is that different flow conductivity divides the yield spatial distribution map planted when the 1st crack produces 1 day;

Fig. 5 is the cumulative production comparison diagram produced under different fracture condudtiviy distribution scheme 360 days;

Fig. 6 is the fracture condudtiviy optimum results of example pressure break horizontal well.

Detailed description of the invention

Illustrate the Optimization Design utilizing the present invention specifically how to realize a certain tight gas reservoir pressure break horizontal well fracture condudtiviy below further, specific as follows:

A certainly treat that fracturing stratum reservoir, fluid and crack basic parameter are as follows:

Certain tight gas reservoir horizontal well buried depth 2800m, horizontal section length is 500m, and effective thickness is 25m, and degree of porosity is 12.0%, and permeability is 0.75 × 10 ^-3μm ², gas-bearing formation temperature is 68 DEG C, and gas viscosity is 0.035mPas, and deviation factor for gas is 0.89, gas critical pressure 4.64MPa, gas critical-temperature 88 DEG C; Stratum system compressibility is 3.5 × 10 ^-4mPa ^-1, strata pressure is 30MPa, flowing bottomhole pressure (FBHP) is 25MPa.Evenly press off formation 4 crack along horizontal well pit shaft, fracture length 75.0m, fracture permeabgility is 200 μm ².

1) fracture condudtiviy distribution scheme design

The fracture condudtiviy of pressure break horizontal well is the product (Li Yingchuan edits, petroleum production engineering [J] petroleum industry publishing house, 2009) of crack width and reservoir buried depth closure stress condition lower support agent permeability after pressure break.Proppant permeability under reservoir buried depth is determined by the proppant type selected, and the key of therefore fracture condudtiviy optimization is exactly the optimization of hydraulic fracture width.

For the ease of optimizing the crack width of tight gas reservoir pressure break horizontal well, assuming that crack width is along seam length direction linear gradient: namely the crack width of pressure break horizontal well pit shaft place (crack root) maximum, diminish gradually along seam length direction crack width, suppose 4 kinds of crack width change programmes, scheme I:w _max=w _min=2.75mm; Scheme II:w _max=3mm, w _min=2.5mm; Scheme III:w _max=4mm, w _min=1.5mm; Scheme IV:w _max=5mm, w _min=0.5mm.

2) the 1st crack output distribotion under different fracture condudtiviy distribution scheme is calculated

Crack output distribotion curve when Fig. 4 is pressure break horizontal well the 1st crack production 1d.Can find out, in crack there is local peaking in root production, this is because the closer to root, in crack, pressure is lower causes; As can be seen from the crack volume analysis of contrast fracture condudtiviy distribution scheme I, II, III, IV, along with crack root width increases, the output peak value of root reduces; Output distribotion on whole crack presents " double-H groove weld " type distribution characteristics, and show as typical non-homogeneous aerogenesis feature, gas is mainly through crack root and end output; Along with crack root width increases, crack interlude output increases, and trends towards the feature of evenly producing along whole crack section, is conducive to well production of improving the standard.

3) cumulative production that different fracture condudtiviy divides the pressure break horizontal well planted to produce 360 days is calculated

Fig. 5 is the cumulative production comparison diagram that pressure break horizontal well produces 360d under seam length direction 4 kinds of width distribution schemes.Can find out, under identical average seam wide (being 2.75mm) condition, due to the distributional difference of crack width, cause 360d cumulative production to there are larger difference (scheme I:1534.50 × 10 ⁴m ³, scheme IV:1564.06 × 10 ⁴m ³), this shows to improve pressure break horizontal well production by optimizing the wide distribution of seam.From the impact of changes of slit length on output, along with root and end portion width difference increase, pressure break horizontal well increases; But difference is increased to a certain degree, output increasing degree reduces, and there is the distribution of preferred crack width.In this example, consider in long-term production process, because the factors such as proppant is crushed, fracturing fluid residue cause crack effective width to narrow, preferred crack root width is 4mm, fracture tip width is 1.5mm, that is to say that crack root flow conductivity is 200 μm ²× 4mm=80 μm ².cm, fracture tip width is 200 μm ²× 1.5mm=30 μm ².cm.

Fig. 6 is the fracture condudtiviy optimum results of example well.

4) this optimisation technique at the scene 10 mouthfuls of water horizontal wells carried out field conduct.The method that the present invention optimizes tight gas reservoir pressure break horizontal well fracture condudtiviy makes crack inner support agent distribution more trend towards the laid of optimization, obtains better steady production ability: obtain average temperature output 3.52 × l0 after 10 mouthfuls of wells transformations ⁴m ³/ d, higher than 3.30 × l0 before optimization ⁴m ³/ d, effect of increasing production is obvious.Describe applicability of the present invention and reliability.

Claims (8)

1. optimize a method for tight gas reservoir pressure break horizontal well fracture condudtiviy, mainly comprise the following steps:

1) reservoir, fluid properties, horizontal well pit shaft basic parameter is collected;

2) pressure break horizontal well crack basic parameter is collected;

3) crack of pressure break horizontal well is on average divided into the equal congruence of length along seam length direction;

4) the Reservoir Seepage model of tight gas reservoir pressure break horizontal well Fracture System is set up;

5) Pressure Drop Model that gas flows in crack is set up;

6) set up the flow model of coupled gas in Reservoir Seepage and crack, form the Production rate model of tight gas reservoir pressure break horizontal well;

7) fracture condudtiviy of tight gas reservoir pressure break horizontal well is optimized.

2. the method for claim 1, it is characterized in that, described step 1) middle collection reservoir, fluid properties, horizontal well pit shaft basic parameter, specifically comprise Original strata stress direction, reservoir thickness, degree of porosity, permeability, gas viscosity, gas critical pressure, deviation factor for gas, reservoir temperature, gas critical-temperature, horizontal well orientation, Horizontal Well tube length degree.

3. the method for claim 1, is characterized in that, described step 2) in collect pressure break horizontal well crack basic parameter and comprise: hydraulic fracture orientation, Number of Fractures, fracture interval, crack location, fracture length.

4. the method for claim 1, is characterized in that, described step 3) in by the crack of pressure break horizontal well along seam length direction be on average divided into the equal congruence of length.

5. the method for claim 1, is characterized in that, described step 4) set up the Reservoir Seepage model calculating tight gas reservoir pressure break horizontal well Fracture System, comprise following basic step:

(1) set up the physical model of pressure break horizontal well, go to the bottom a bite pressure break horizontal well in closed infinitely great reservoir in upper top, horizontal well is divided into some sections by the fracturing fracture penetrating reservoir completely, and first reservoir gas flows to crack and flow to horizontal wellbore through crack again.Horizontal well radius is r _w, length is L, and well is (x in reservoir center position coordinates ₀, y ₁, z ₀)-(x ₀, y ₂, z ₀), and parallel with y-axis.Reservoir homogeneous isotropism, thickness is h, degree of porosity φ, permeability K are constant; Horizontal wellbore is infinite fluid diversion, and reservoir initial pressure is constant p _i.Because fracturing fracture runs through oil reservoir, therefore the flowing of infinitely great formation breakdown horizontal well whole system can be reduced to the Radial Flow in plane oil reservoir, and crack can be reduced to a congruence.

(2) for the ease of solving, kth crack single-blade is divided into ns section, every segment length is Δ x _fk, Δ x _fk=x _fk/ ns; Each congruence can be processed into a bite straight well and produce consideration.Straight well in process of production output constantly changes, if but will obtain in the time interval very little, can be similar to and think that output is definite value within this period, the whole production phase t of pressure break horizontal well is divided into the equal time interval Δ t of m spacing, t=m Δ t.

Being located at kth crack has a congruence i (output is q _{fk, i}) be positioned at M (x _{fk, i}, y _fk) place, crack k+1 has a point of observation O (x _{fk+1, j}, y _fk+1), when considering fluid volume coefficient, the drop of pressure that congruence i produces at O point after production time Δ t is:

$p_i-p_{\mathrm{fk}+1,j}=\frac{q_{\mathrm{fk},i}\mathrm{\μB}}{4\mathrm{\πKh}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}---\left(1\right)$

In formula: p _ifor original formation pressure, MPa; p _{fk+1, j}for the pressure at kth+1 crack jth congruence sides of fracture place, MPa; q _{fk, i}for the output of i-th congruence on kth crack, m ³/ s; μ is viscosity of crude, mPa.s; B is volume factor, zero dimension; (x _{fk, i}, y _fk) be the coordinate (m, m) of i-th congruence on kth crack; (x _{fk+1, j}, y _fk+1) be the coordinate (m, m) of the jth congruence on kth+1 crack; K is reservoir permeability, 10 ^-3μm ²; H is reservoir thickness, m; η is piezometric conductivity, μm ²/ (mPas × MPa ^-1), η=K/ μ c φ; C is stratum system compressibility, MPa ^-1; φ is reservoir porosity, zero dimension; Δ t is the production time, s; K is crack numbering; I, j are crack congruence numbering.

(3) when crack k containing multiple continuous congruence, the drop of pressure produced at point of observation O place when each congruence of k crack is produced simultaneously can be obtained according to principle of stacking; After the same method, also can obtain pressure break horizontal well and form N crack, at the drop of pressure of O point simultaneously when N × 2ns the crack congruence is produced altogether:

$p_i-p_{\mathrm{fk}+1,j}=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\frac{q_{\mathrm{fk},i}\mathrm{\μB}}{4\mathrm{\πKh}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}---\left(2\right)$

In formula: N is pressure break horizontal well Number of Fractures, bar; Ns is crack single-blade congruence number.

(4) when reservoir fluid is gas, according to definition and the actual gas state equation of pressure function, and convert underground output to gas yield in ground standard situation, formula (2) can be written as:

$p_i^2-p_{\mathrm{fk}+1,j}^2=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\frac{q_{\mathrm{fk},i}{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{2\mathrm{\πKh}{T}_{\mathrm{sc}}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}---\left(3\right)$

In formula: μ _gfor gas viscosity, mPas; p _scfor gas critical pressure, MPa; Z is deviation factor for gas, zero dimension; T is reservoir temperature, DEG C; T _scfor gas critical-temperature, DEG C.

Formula (3) be exactly all slits congruence simultaneously after production time Δ t at the drop of pressure equation of O point generation, this equation considers the mutual interference effect between each congruence in crack and crack.

6. the method for claim 1, is characterized in that, described step 5) calculate the Pressure Drop Model that flows in crack of gas, comprise following basic step:

(1) consider that hydraulic fracture width narrows gradually along seam length direction, by crack section processing in echelon, kth+1 crack root width is w _{fk+1, max}, end portion width is w _{fk+1, min}.For the ease of calculating, each congruence being processed into rectangle and calculating, line taking remittance central point width is congruence width.With the intersection point of crack and horizontal wellbore for initial point, distance horizontal wellbore x _jthe width of a jth congruence at place is:

w _fk+1,j＝w _fk+1,min+(w _fk+1,max-w _fk+1,min)×(x _fk+1-x _fk+1,j)/x _fk+1(4)

The average crack width w of a jth congruence _{fk+1, averj}for:

w _{fk+1,aver j}＝(w _fk+1,j+w _fk+1,j-1)/2 (5)

In formula: w _{fk+1, j}for the crack width of kth+1 crack jth congruence, m; w _{fk+1, max}for kth+1 crack root width, m; w _{fk+1, min}for kth+1 crack end portion width, m; x _fk+1for kth+1 crack single slot is long, m; x _{fk+1, j}for kth+1 crack jth congruence is in the x-direction apart from the distance of pit shaft, m; w _{fk+1, aver j}for kth+1 crack jth congruence mean breadth, m.

(2) consider that gas meets linear flow in crack, calculate (the some O of congruence j on kth+1 crack according to Darcy's law _{fk+1, j}) pressure loss that flow to horizontal wellbore is:

$\begin{array}{c}{p}_{\mathrm{fk}+1,j}^2-p_{\mathrm{fk}+\mathrm{1,0}}^2=\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver\; l}}}{q}_{\mathrm{fk}1,1}+\frac{2{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}{w}_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver\; l}}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,2}}}{w_{\mathrm{fk}+1,\mathrm{aver}2}})q_{\mathrm{fk}+\mathrm{1,2}}+...\\ +\frac{{2\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,2}}{q_{\mathrm{fk}+1,\mathrm{sver}2}}+...+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{aver\; j}}})q_{\mathrm{fk}+1,j}\\ +\frac{{2\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,2}}{w_{\mathrm{fk}+1,\mathrm{aver}2}}+...+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+,\mathrm{aver\; j}}})q_{\mathrm{fk}+1j+1}+...---\left(6\right)\\ +\frac{{2\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}(\frac{{\mathrm{\Δx}}_{\mathrm{fk}+\mathrm{1,1}}}{w_{\mathrm{fk}+1,\mathrm{aver}1}}+\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,2}}{w_{\mathrm{fk}+1,\mathrm{aver\; j}}})q_{\mathrm{fk}+1,\mathrm{ns}}\\ =\frac{{2\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}\{\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\left(q_{\mathrm{fk}+1,i}\underset{j=1}{\overset{i}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{aver\; j}}}\right)+\underset{n=j+1}{\overset{\mathrm{ns}}{\mathrm{\Σ}}}[q_{\mathrm{fk}+1,n}\left(\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,i}}{w_{\mathrm{fk}+1,\mathrm{aver\; j}}}\right)\left]\right\}\end{array}$

In formula: p _fk+1,0for the pressure of kth+1 crack and horizontal wellbore intersection, MPa; k _fk+1for the permeability in kth+1 crack, 10 ^-3μm ².

7. the method for claim 1, is characterized in that, described step 6) calculate the pressure break horizontal well production of tight gas reservoir, comprise following basic step:

(1) coupling model of flowing in Reservoir Seepage-crack is set up

The process that gas flows to horizontal wellbore from reservoir can be divided in gas reservoir seepage flow and crack two processes that flow, and formula (3), formula (6) have established corresponding descriptive equation; Consider gas store up when intrastratal flow and fluid flow in crack equal at the pressure at wall place, crack, can build-up pressure continuity equation; Due to hypothesis pit shaft infinite fluid diversion, each crack with horizontal wellbore intersection O ₀pressure equal, stable bottom hole pressure (p _wf) produce time fringe conditions be:

p _fk+1,0＝p _wf(7)

In formula: p _wffor horizontal wellbore flowing bottomhole pressure (FBHP), MPa;

Simultaneous equations (3), (6), (7) arrange the flow equation obtaining kth+1 crack jth congruence gas reservoir-crack coupling:

$\begin{array}{c}{p}_i^2-p_{\mathrm{wf}}^2=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\frac{q_{\mathrm{fk},i}{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{2\mathrm{\πKh}{T}_{\mathrm{sc}}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\\ +\frac{{2\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{K_{\mathrm{fk}+1}h{T}_{\mathrm{sc}}}\{\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\left(q_{\mathrm{fk}+1,i}\underset{j=1}{\overset{i}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,j}}{w_{\mathrm{fk}+1,\mathrm{aver\; j}}}\right)+\underset{n=j+1}{\overset{\mathrm{ns}}{\mathrm{\Σ}}}[q_{\mathrm{fk}+1,n}\left(\underset{i=1}{\overset{j}{\mathrm{\Σ}}}\frac{{\mathrm{\Δx}}_{\mathrm{fk}+1,i}}{w_{\mathrm{fk}+1,\mathrm{aver\; j}}}\right)\left]\right\}\end{array}---\left(8\right)$

In formula (8), variable is the output of each congruence, so just establishes the Transient Flow Mathematical Modeling that pressure break horizontal well crack is coupled with gas reservoir.Due to bottom pressure p _wfknown, according to the system of linear equations of N × 2ns the linear equation formation that formula (8) is set up, the output of each congruence can be tried to achieve.

(2) the transient state output of tight gas reservoir pressure break horizontal well is calculated

Owing to considering that gas only flow into horizontal wellbore by crack, so the total output of pressure break horizontal well is the sum of all congruence output on a pressure break horizontal well crack:

$Q=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}{q}_{\mathrm{fk},i}---\left(9\right)$

The horizontal well yield of tight gas reservoir pressure break can be tried to achieve according to formula (9).

(3) the unstable state output of tight gas reservoir pressure break horizontal well is calculated

The computational methods of equation (8), (9) each congruence and pressure break horizontal well production under establishing the Δ t time; For each congruence, because output can change with the production time, at this moment need to utilize the time to superpose the value of trying to achieve any time.If time step is Δ t, as t=m Δ t (m time period ending), then can obtain kth+1 crack jth point sink:

$\begin{array}{c}{p}_i^2-p_{\mathrm{wf}}^2=\underset{k=1}{\overset{N}{\mathrm{\Σ}}}\underset{i=1}{\overset{2\mathrm{ns}}{\mathrm{\Σ}}}\{q_{\mathrm{fk},i}\left(\mathrm{\Δt}\right)F_{\mathrm{ki},k+1j}\left(\mathrm{m\Δt}\right)\\ +\underset{g=2}{\overset{m}{\mathrm{\Σ}}}[q_{\mathrm{fk},i}\left(\mathrm{g\Δt}\right)-q_{\mathrm{fk},i}\left((g-1)\mathrm{\Δt}\right)]F_{\mathrm{ki},k+1j}\left[(m-g+1)\mathrm{\Δt}\right]\}\end{array}---\left(10\right)$

In formula: $F_{\mathrm{ki},k+1j}\left(\mathrm{\Δt}\right)=\frac{{\mathrm{\μ}}_g{p}_{\mathrm{sc}}\mathrm{ZT}}{2\mathrm{\πKh}{T}_{\mathrm{sc}}}\{-\mathrm{Ei}(-\frac{{(x_{\mathrm{fk},i}-x_{\mathrm{fk}+1,j})}^2+{(y_{\mathrm{fk}}-y_{\mathrm{fk}+1})}^2}{4\mathrm{\η\Δt}})\}$

The same with the Production rate producing Δ t time span, according to bottom pressure constraint and total output constraint, composition Closure equation group solves, and from the 1st time Δ t step-length, circulation solves, until calculate the Production rate result under m Δ t step-length.

8. the method for claim 1, is characterized in that, described step 7) optimize the fracture condudtiviy of tight gas reservoir pressure break horizontal well, comprise following basic step:

(1) different fracture condudtiviy distribution schemes is set along seam length direction;

(2) calculate different fracture condudtiviy and divide the crack planted output distribotion situation;

(3) calculate the cumulative production that different fracture condudtiviy divides the pressure break horizontal well planted to produce 360 days, consider engineering condition, preferred best fracture condudtiviy distribution scheme in conjunction with cumulative production result.