2. 中国石油西南油气田分公司川西北气矿, 四川 江油 621700
2. Sichuan Northwest Gas Mine of Southwest Oil and Gas Field Branch, PetroChina, Jiangyou, Sichuan 621700, China
裂缝性气藏储层多为致密储层,裂缝是该类储层中重要的气体储存空间与传输通道。裂缝系统形态与体积决定了裂缝性气藏气井的产能与稳产能力[1]。对于该类型气藏的试井模型研究方法主要分为4类:第1类研究方法为使用连续双重介质描述裂缝性气藏非均质储层,结合渗流力学理论,建立裂缝性气藏试井模型,模拟气体在裂缝性油气藏内的流动,该类方法无法描述裂缝系统形态与试井压力动态曲线的关系[2-4];第2类研究方法是基于数值试井理论方法,利用离散裂缝网络(DFN)描述裂缝性油气藏的大尺度裂缝,模拟其试井时的压力变化规律,该类方法的缺点在于仅能模拟大尺度裂缝,受限于计算机处理能力与内存限制,无法描述小尺寸分支裂缝及其形成的网络系统[5-7];第3类研究方法是使用分形连续双重介质描述不同尺度下储层的非均质性,该类方法同样存在裂缝形态描述上的问题[8-10];第4类方法使用分形参数控制不同长度的裂缝,形成平行或相交网络,嵌入储层基质中,形成具有多尺度分形性质的天然裂缝性油气藏模型[11-13],该方法能够很好地表征裂缝网络的形态与分布,但该类裂缝网络以直线和相交的直线为主,并不能完全模拟趋向井底的径向流动[14-15]。
本文利用树状分形网络对趋向井底的径向流动模拟的优越性,使用树状分形网络模拟气藏裂缝系统,并将树状分形网络嵌入到基质中,提出基于树状分形网络的裂缝性气藏试井模型,分析基于树状分形网络的裂缝性气藏压力动态特征的影响因素,为裂缝性气藏的动态描述及试井分析提供了一种新方法。
1 物理模型树状分形网络由一系列分叉结构组合而成,考虑到网络的对称性,可以在计算时只分析网络的一个单元,如图 1所示。生成网络之前,需要生成多个不同级(总分叉级数
本文研究的是裂缝性气藏圆形地层,井位于圆心
气藏储层由多个不同级(总分叉级数
$ {{l}_{k}}={{\alpha }^{k}}{{l}_{0}} $ | (1) |
式中:
单条
$ {{d}_{k}}={{\beta }^{k}}{{d}_{0}} $ | (2) |
式中:
径向距离为井到各区域界面的距离,由式(1),可得
$ {{r}_{k}}=\sum\limits_{i=0}^{k}{{{l}_{i}}\cos \theta }={{l}_{0}}\left[1+\dfrac{\alpha \left( 1-{{\alpha }^{k}} \right)\cos \theta }{1-\alpha } \right] $ | (3) |
式中:
Xu等将单条
$ {{K}_{k}}=10^{-12}\dfrac{d_{k}^{2}}{32}\dfrac{1}{{{T}_{k}}} $ | (4) |
式中:
区域
$ {{T}_{k}}=\dfrac{{{l}_{k}}}{{{r}_{k}}-{{r}_{k-1}}}=\left\{ \begin{array}{*{35}{l}}1, {\kern 32pt} k=0 \\ \sec \theta, {\kern 18pt} k>0 \\\end{array} \right. $ | (5) |
联立式(2)~式(5),得到区域
$ {{K}_{{\rm f}k}}=\left\{ \begin{array}{*{35}{l}}\dfrac{10^{-12}Nd_{0}^{2}}{32}, {\kern 52pt} k=0 \\[8pt] \dfrac{10^{-12}N{{n}^{k}}{{\beta }^{2k}}d_{0}^{2}\cos \theta }{32}, {\kern 10pt} k>0 \\\end{array} \right. $ | (6) |
式中:
区域
$ {{V}_{{\rm t}k}}=\left\{ \begin{array}{*{35}{l}} \pi hr_{0}^{2}, {\kern 48pt} k=0 \\ \pi h\left( r_{k}^{2}-r_{k-1}^{2} \right), {\kern 10pt} k>0 \\ \end{array} \right. $ | (7) |
式中:
区域
$ {{V}_{{\rm ft}k}}=N{{n}^{k}}\dfrac{\pi {{l}_{k}}d_{k}^{2}}{4}=\dfrac{N\pi {{n}^{k}}{{\alpha }^{k}}{{\beta }^{2k}}{{l}_{0}}d_{0}^{2}}{4} $ | (8) |
式中:
区域
$ {{V}_{{\rm mt}k}}={{\phi }_{{\rm mp}}}\left( {{V}_{{\rm t}k}}-{{V}_{{\rm tf}k}} \right) $ | (9) |
式中:
联立式(7)、式(8),区域
$ {{\phi }_{{\rm f}k}}=\dfrac{{{V}_{{\rm ft}k}}}{{{V}_{{\rm t}k}}}=\left\{ \begin{array}{*{35}{l}}\dfrac{Nd_{0}^{2}}{4h{{l}_{0}}}, {\kern 65pt} k=0 \\[6pt] \dfrac{N{{n}^{k}}{{\alpha }^{k}}{{\beta }^{2k}}{{l}_{0}}d_{0}^{2}}{4h\left( r_{k}^{2}-r_{k-1}^{2} \right)} k=0, {\kern 5pt} k>0 \\\end{array} \right. $ | (10) |
式中:
联立式(7)~式(10),区域
$ {{\phi }_{{\rm m}k}}=\dfrac{{{V}_{{\rm mt}k}}}{{{V}_{{\rm t}k}}}={{\phi }_{{\rm mp}}}\left( 1-{{\phi }_{{\rm f}k}} \right) $ | (11) |
式中:
在双分叉结构下,裂缝性气藏各区域裂缝系统渗透率、裂缝体积相等的条件为
当
$ \left\{ \begin{array}{*{35}{l}} {{K}_{{\rm f}k}}\left( \dfrac{{{\partial }^{2}}{{\psi }_{{\rm f}k}}}{\partial {{r}^{2}}}+\dfrac{1}{r}\dfrac{\partial {{\psi }_{{\rm f}k}}}{\partial r} \right)+a{{K}_{{\rm m}}}\left( {{\psi }_{{\rm m}k}}-{{\psi }_{{\rm f}k}} \right)= \dfrac{\mu {{\phi }_{{\rm f}k}}{{C}_{{\rm tf}}}}{3.6}\dfrac{\partial {{\psi }_{{\rm f}k}}}{\partial t}, {\kern 28pt} \\ {{r}_{k-1}}\leqslant r \leqslant {{r}_{k}} \\ -a{{K}_{{\rm m}}}\left( {{\psi }_{{\rm m}k}}-{{\psi }_{{\rm f}k}} \right)=\dfrac{\mu {{\phi }_{{\rm m}k}}{{C}_{{\rm tm}}}}{3.6}\dfrac{\partial {{\psi }_{{\rm m}k}}}{\partial t}, {\kern 112pt} \\ {{r}_{k-1}}\leqslant r\leqslant {{r}_{k}} \\ {{\psi }_{{\rm f}k}}(r, 0)={{\psi }_{{\rm m}k}}(r, 0)={{\psi }_{{\rm i}}}, {\kern 158pt} \\ k=0, 1, \cdots, M \\ {{\left. \left( r\dfrac{\partial {{\psi }_{{\rm f}k}}}{\partial r} \right) \right|}_{{{r}_{{\rm e}}}={{r}_{{\rm w}}, k =1}}}{\rm =}-\left( 1-C\dfrac{{\rm d}{{\psi }_{{\rm wf}}}}{{\rm d}t} \right), {\kern 120pt} \\ {{\psi }_{{\rm wf}}}={{\left. {{\psi }_{{\rm f}k}} \right|}_{k=1, r={{r}_{{\rm w}}}{{{\rm e}}^{-S}}}} \\ {{\left. {{\psi }_{{\rm f}k}} \right|}_{r={{r}_{k}}}}={{\left. {{\psi }_{{\rm f}\left( k+1 \right)}} \right|}_{r={{r}_{k}}}}, {\kern 175pt} \\ k=0, 1, \cdots, M-1 \\[6pt] {{\left. \dfrac{\partial {{\psi }_{{\rm f}k}}}{\partial r} \right|}_{r={{r}_{k}}}}={{\left. \dfrac{{{K}_{{\rm f}\left( k+1 \right)}}}{{{K}_{{\rm f}k}}}\dfrac{\partial {{\psi }_{{\rm f}\left( k+1 \right)}}}{\partial r} \right|}_{r={{r}_{k}}}}, {\kern 131pt} \\ k=0, 1, \cdots, M-1 \\ {{\psi }_{{\rm f}k}}\left( t \right)={{\psi }_{{\rm i}}}, {\kern 217pt} \\ r\to \infty, k= M \\ \end{array} \right. $ | (12) |
式中:
裂缝系统和基质系统的拟压力可以分别表示为
$ {\psi _{{\text{f}}k}} = \int_{{p_0}}^{{p_{{\text{f}}k}}} {\frac{{2p}}{{\mu Z}}{\text{d}}p}, \;\;\;\;\;\;{r_{k-1}} \leqslant r \leqslant {r_k} $ | (13) |
$ {\psi _{{\text{m}}k}} = \int_{{p_0}}^{{p_{{\text{m}}k}}} {\frac{{2p}}{{\mu Z}}{\text{d}}p}, \;\;\;\;\;\;{r_{k-1}} \leqslant r \leqslant {r_k} $ | (14) |
式中:
为简化数学模型及求解方便,定义下列无因次变量[21]。
区域
$ {{\psi }_{{\rm Df}k}}=\dfrac{78.489{{K}_{{\rm f}k}}h}{T{{q}_{{\rm sc}}}}\left( {{\psi }_{{\rm i}}}-{{\psi }_{{\rm f}k}} \right) $ | (15) |
式中:
区域
$ {{\psi }_{{\rm Dm}k}}=\dfrac{78.489{{K}_{{\rm m}k}}h}{T{{q}_{{\rm sc}}}}\left( {{\psi }_{{\rm i}}}-{{\psi }_{{\rm m}k}} \right) $ | (16) |
式中:
无因次有效半径为
$ {{r}_{{\rm De}}}=\dfrac{r}{{{r}_{{\rm w}}}}{{{\rm e}}^{S}} $ | (17) |
式中:
无因次有效界面半径为
$ {{r}_{{\rm De}k}}=\dfrac{{{r}_{k}}}{{{r}_{{\rm w}}}}{{{\rm e}}^{S}} $ | (18) |
式中:
无因次有效时间为
$ {{t}_{{\rm De}}}={\dfrac{{3.6{K_{{\rm{f}}0}}t{{\rm{e}}^{2S}}}}{{{\phi _{{\rm{fm0}}}}{C_{{\rm{tfm0}}}}\mu r_{\rm{w}}^2}}} $ | (19) |
式中:
无因次有效井筒储积系数为
$ {{C}_{{\rm De}}}=\dfrac{C{{{\rm e}}^{2S}}}{2\pi h{\phi _{{\rm{fm0}}}}{C_{{\rm{tfm0}}}}r_{{\rm w}}^{2}} $ | (20) |
式中:
区域
$ {{\omega }_{k}}=\dfrac{{{\phi }_{{\rm f}k}}{{C}_{{\rm ft}}}}{{{\phi }_{{\rm m}k}}{{C}_{{\rm tm}}}+{{\phi }_{{\rm f}k}}{{C}_{{\rm ft}}}} $ | (21) |
式中:
区域
$ {{\lambda }_{k}}=a\dfrac{{{K}_{\rm m}}}{{{K}_{{\rm f}k}}}r_{\rm w}^{2} $ | (22) |
式中:
无因次的渗流数学模型为
$ \left\{ \begin{array}{*{35}{l}} \dfrac{{{\partial }^{2}}{{\psi }_{{\rm Df}k}}}{\partial r_{{\rm De}}^{2}}+\dfrac{1}{{{r}_{{\rm De}}}}\dfrac{\partial {{\psi }_{{\rm Df}k}}}{\partial {{r}_{{\rm De}}}}+{{\lambda }_{k}}{{{\rm e}}^{-2S}}\left( \dfrac{{{K}_{{\rm f}k}}}{{{K}_{{\rm m}}}}{{\psi }_{{\rm Dm}k}}-{{\psi }_{{\rm Df}k}} \right)=\\ \dfrac{{{\omega }_{k}}}{{{C}_{{\rm De}}}}\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}\dfrac{\partial {{\psi }_{{\rm Df}k}}}{\partial \left( {{{t}_{{\rm De}}}}/{{{C}_{{\rm De}}}}\; \right)}, {\kern 10pt} {{r}_{{\rm De}\left( k-1 \right)}}\leqslant {{r}_{{\rm De}}}\leqslant {{r}_{{\rm De}k}} \\ -{{\lambda }_{k}}{{{\rm e}}^{-2S}}\left( {{\psi }_{{\rm Dm}k}}-\dfrac{{{K}_{{\rm m}}}}{{{K}_{{\rm f}k}}}{{\psi }_{{\rm Df}k}} \right)=\dfrac{{\rm 1}-{{\omega }_{k}}}{{{C}_{{\rm De}}}}\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}\dfrac{\partial {{\psi }_{{\rm Dm}k}}}{\partial \left( {{{t}_{{\rm De}}}}/{{{C}_{{\rm De}}}}\; \right)}, {\kern 86pt} \\ {{r}_{{\rm De}\left( k-1 \right)}}\leqslant {{r}_{{\rm De}}}\leqslant {{r}_{{\rm De}k}} \\ {{\psi }_{{\rm Df}k}}({{r}_{{\rm De}}}, 0)={{\psi }_{{\rm Dm}k}}({{r}_{{\rm De}}}, 0)=0, {\kern 178pt}\\ k=0, 1, \cdots, M \\ \dfrac{{\rm d}{{\psi }_{{\rm wD}}}}{{\rm d}\left( {{{t}_{{\rm De}}}}/{{{C}_{{\rm De}}}}\; \right)}-{{\left. \left( {{r}_{{\rm De}}}\dfrac{\partial {{\psi }_{{\rm Df}0}}}{\partial {{r}_{{\rm De}}}} \right) \right|}_{{{r}_{{\rm De}}}=1}}=1, {\kern 156pt} \\ {{\psi }_{{\rm wD}}}={{\left. {{\psi }_{{\rm Df0}}} \right|}_{{{r}_{{\rm De}}}=1}} \\[6pt] {{\left. {{\psi }_{{\rm Df}k}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}={{\left. {{\psi }_{{\rm Df}\left( k+1 \right)}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}, {\kern 185pt}\\ k=0, 1, \cdots, M-1 \\[8pt] {{\left. \dfrac{\partial {{\psi }_{{\rm Df}k}}}{\partial {{r}_{{\rm D}}}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}=\dfrac{{{K}_{{\rm f}\left( k+1 \right)}}}{{{K}_{{\rm f}k}}}{{\left. \dfrac{\partial {{\psi }_{{\rm Df}\left( k+1 \right)}}}{\partial {{r}_{{\rm De}}}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}, {\kern 140pt} \\ k=0, 1, \cdots, M-1 \\[8pt] {{\psi }_{{\rm Df}k}}\left( {{t}_{{\rm De}}} \right)=0, {\kern 251pt} \\ {{r}_{{\rm De}}}\to \infty; k = M \\\end{array} \right. $ | (23) |
将式(23)进行基于
$ \left\{ \begin{array}{*{35}{l}}\dfrac{{{\rm d}^{2}}{{{\bar{\psi }}}_{{\rm Df}k}}}{{\rm d}r_{{\rm De}}^{2}}+\dfrac{1}{{{r}_{{\rm De}}}}\dfrac{{\rm d}{{{\bar{\psi }}}_{{\rm Df}k}}}{{\rm d}{{r}_{{\rm De}}}}+{{\lambda }_{k}}{{{\rm e}}^{-2S}}\left( \dfrac{{{K}_{{\rm f}k}}}{{{K}_{{\rm m}}}}{{{\bar{\psi }}}_{{\rm Dm}k}}-{{{\bar{\psi }}}_{{\rm Df}k}} \right)=\dfrac{{{\omega }_{k}}}{{{C}_{{\rm De}}}}\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}z{{{\bar{\psi }}}_{{\rm Df}k}}, {\kern 35pt} \\ {{r}_{{\rm De}\left( k-1 \right)}}\leqslant {{r}_{{\rm De}}}\leqslant {{r}_{{\rm De}k}} \\ -{{\lambda }_{k}}{{{\rm e}}^{-2S}}\left( {{{\bar{\psi }}}_{{\rm Dm}k}}-\dfrac{{{K}_{{\rm m}}}}{{{K}_{{\rm f}k}}}{{{\bar{\psi }}}_{{\rm Df}k}} \right)=\dfrac{1-{{\omega }_{k}}}{{{C}_{{\rm De}}}}\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}z{{{\bar{\psi }}}_{{\rm Dm}k}}, {\kern 108pt} \\ {{r}_{{\rm De}\left( k-1 \right)}}\leqslant {{r}_{{\rm De}}}\leqslant {{r}_{{\rm De}k}} \\ {{{\bar{\psi }}}_{{\rm Df}k}}({{r}_{{\rm De}}}, 0)={{{\bar{\psi }}}_{{\rm Dm}k}}({{r}_{{\rm De}}}, 0)=0, {\kern 173pt}\\ k=0, 1, \cdots, M \\ z{{{\bar{\psi }}}_{{\rm wD}}}-{{\left. \left( {{r}_{{\rm De}}}\dfrac{d{{{\bar{\psi }}}_{{\rm Df}0}}}{d{{r}_{{\rm De}}}} \right) \right|}_{{{r}_{{\rm De}}}=1}}=\dfrac{1}{z}, {\kern 180pt} \\ {{{\bar{\psi }}}_{{\rm wD}}}={{\left. {{{\bar{\psi }}}_{{\rm Df0}}} \right|}_{{{r}_{{\rm De}}}=1}} \\ {{\left. {{{\bar{\psi }}}_{{\rm Df}k}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}={{\left. {{{\bar{\psi }}}_{{\rm Df}\left( k+1 \right)}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}, {\kern 180pt} \\ k=0, 1, \cdots, M-1 \\[8pt] {{\left. \dfrac{{\rm d}{{{\bar{\psi }}}_{{\rm Df}k}}}{{\rm d}{{r}_{{\rm De}}}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}=\dfrac{{{K}_{{\rm f}\left( k+1 \right)}}}{{{K}_{{\rm f}k}}}{{\left. \dfrac{{\rm d}{{{\bar{\psi }}}_{{\rm Df}\left( k+1 \right)}}}{{\rm d}{{r}_{{\rm De}}}} \right|}_{{{r}_{{\rm De}}}={{r}_{{\rm De}k}}}}, {\kern 135pt} \\ k=0, 1, \cdots, M-1 \\[8pt] {{{\bar{\psi }}}_{{\rm Df}k}}\left( z \right)=0, {\kern 254pt} \\ {{r}_{{\rm De}}}\to \infty ; k = M \\ \end{array} \right. $ | (24) |
式中:
式(24)中,
$ {{\bar{\psi }}_{{\rm Df}k}}={{A}_{k}}{{I}_{0}}\left( {{r}_{{\rm De}k}}\sqrt{{{S}_{k}}\left( z \right)} \right)+{{B}_{k}}{{K}_{0}}\left( {{r}_{{\rm De}k}}\sqrt{{{S}_{k}}\left( z \right)} \right), \quad k=0, 1, \cdots, M $ | (25) |
式中:
对式(25)求导,有
$ \dfrac{{\rm d}{{{\bar{\psi }}}_{{\rm Df}k}}}{{\rm d}{{r}_{{\rm De}}}}=\sqrt{{{S}_{k}}\left( z \right)}{{A}_{k}}{{I}_{1}}\left( {{r}_{{\rm De}k}}\sqrt{{{S}_{k}}\left( z \right)} \right)-\sqrt{{{S}_{k}}\left( z \right)}{{B}_{k}}{{K}_{1}}\left( {{r}_{{\rm De}k}}\sqrt{{{S}_{k}}\left( z \right)} \right),\\ \quad k=0, 1, \cdots, M $ | (26) |
将式(26)、(25)代入式(24),求取
$ \left\{ {\begin{array}{*{20}{l}} {z{{\bar \psi }_{{\rm{wfD}}}} - \sqrt {{S_0}\left( z \right)} {A_0}{I_1}\left( {\sqrt {{S_0}\left( z \right)} } \right) + \sqrt {{S_0}\left( z \right)} {B_0}{K_1}\left( {\sqrt {{S_0}\left( z \right)} } \right) = \dfrac{1}{z}} \\ {{{\bar \psi }_{{\rm{wfD}}}} = {A_0}{I_0}\left( {\sqrt {{S_0}\left( z \right)} } \right) + {B_0}{K_0}\left( {\sqrt {{S_0}\left( z \right)} } \right)}&{}&{}\\ {A_k}{I_0}\left( {{r_{{\rm{De}}k}}\sqrt {{S_k}\left( z \right)} } \right) + {B_k}{K_0}\left( {{r_{{\rm{De}}k}}\sqrt {{S_k}\left( z \right)} } \right) = {A_{k + 1}}{I_0}\left( {{r_{{\rm{De}}k}}\sqrt {{S_{k + 1}}\left( z \right)} } \right) + \\{\kern 20pt}{B_{k + 1}}{K_0}\left( {{r_{{\rm{De}}k}}\sqrt {{S_{k + 1}}\left( z \right)} } \right), \\ {k = 1, 2, \cdots, M - 1}\\ {A_k}\sqrt {{S_k}\left( z \right)} {I_1}\left( {{r_{{\rm{De}}k}}\sqrt {{S_k}\left( z \right)} } \right) - {B_k}\sqrt {{S_k}\left( z \right)} {K_1}\left( {{r_{{\rm{De}}k}}\sqrt {{S_k}\left( z \right)} } \right) = \\ \dfrac{{{k_{{\rm{f}}\left( {k + 1} \right)}}}}{{{k_{{\rm{f}}k}}}} {A_{k + 1}}\cdot \\{\kern 20pt}\sqrt {{S_k}\left( z \right)} {I_1}\left( {{r_{{\rm{De}}k}}\sqrt {{S_k}\left( z \right)} } \right) - \dfrac{{{K_{{\rm{f}}\left( {k + 1} \right)}}}}{{{K_{{\rm{f}}k}}}}{B_{k + 1}}\sqrt {{S_k}\left( z \right)} {K_1}\left( {{r_{{\rm{De}}k}}\sqrt {{S_k}\left( z \right)} } \right), \\ {k = 1, 2, \cdots, M - 1}\\ {{A_M} = 0} \end{array}} \right. $ | (27) |
式中:
式(27)中,参数无因次有效界面半径
由式(3)和式(17),得到无因次界面有效半径的表达式
$ {{r}_{{\rm De}k}}=\dfrac{{{l}_{0}}}{{{r}_{{\rm w}}}}\left[1+\dfrac{\alpha \left( 1-{{\alpha }^{k}} \right)\cos \theta }{1-\alpha } \right]{{{\rm e}}^{S}} $ | (28) |
由式(6),渗透率比的表达式为
$ \dfrac{{{K}_{{\rm f}\left( k+1 \right)}}}{{{K}_{{\rm f}k}}}=\left\{ \begin{array}{*{35}{l}}n{{\beta }^{2}}\cos \theta, {\kern 20pt}k=0 \\n{{\beta }^{2}}, {\kern 43pt} k>0 \end{array} \right. $ | (29) |
$ {{S}_{k}}\left( z \right)=\dfrac{\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}{{\lambda }_{k}}\left( 1-{{\omega }_{k}} \right)z}{\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}\left( 1-{{\omega }_{k}} \right){{{\rm e}}^{2S}}z+{{\lambda }_{k}}{{C}_{{\rm De}}}}+ \\ {\kern 40pt}\dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}\dfrac{{{\omega }_{k}}}{{{C}_{{\rm De}}}}z $ | (30) |
其中
$ \dfrac{{{K}_{{\rm f}0}}}{{{K}_{{\rm f}k}}}={{\left( n{{\beta }^{2}} \right)}^{-k}} $ | (31) |
$ {{\lambda }_{k}}=\left\{ \begin{array}{*{35}{l}}\dfrac{32a{{K}_{{\rm m}}}r_{{\rm w}}^{2}}{Nd_{0}^{2}},&{\quad}k=0 \\ \dfrac{32a{{K}_{{\rm m}}}r_{{\rm w}}^{2}}{N{{n}^{k}}{{\beta }^{2k}}d_{0}^{2}\cos \theta },& {\quad}k>0 \\ \end{array} \right. $ | (32) |
对式(27)进行求解,可得到拉氏空间内无因次井底拟压力
树状分形网络裂缝性气藏中,各区域裂缝系统渗透率、裂缝体积相等的树状分形裂缝性气藏典型曲线,即满足式(13)。裂缝系统分形网络的参数取值为
图 3为长度比
由图 3可见,长度比
图 4为直径比
由图 4可见,
图 5为分叉角度
由图 5可见,分叉角度
图 6、图 7分别为
由图 6、图 7可见,总分叉级数
图 8为初始裂缝数
由图 8可见,初始裂缝数
利用树状分形网络模拟裂缝系统,并将树状分形网络嵌入到基质中,提出了基于树状分形网络的裂缝性气藏试井模型,作出了树状分形网络的裂缝性气藏拟压力动态特征典型曲线。分析了长度比
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