基于复杂渗流机理的页岩气藏压后数值模拟研究

doi:10.13809/j.cnki.cn32-1825/te.2020.01.004

摘要/Abstract

摘要：

对于天然裂缝发育的页岩气藏,压后人工裂缝与天然裂缝相互沟通,传统的双重介质模型不能准确的反映天然裂缝对产量的影响。针对气体在纳米孔隙中运移的微尺度效应,建立了气体在基岩中黏性流动、Knudsen扩散、表面扩散、吸附层以及气体解吸附等复杂流动机理作用下的多段压裂水平井数学模型。通过离散裂缝模型对天然裂缝和压裂裂缝进行简化并采用有限元方法对模型进行求解,再运用数值模拟研究平桥区块页岩气多段压裂水平井产能的影响因素,结果表明,页岩气井早期产量主要来自裂缝系统游离气,吸附气采出程度平均只有10.1 %;储层未改造区域的存在使得基岩渗透率对累计产量的影响变大,裂缝密度和裂缝网络的连通性对气井产量和递减率影响也很大。

关键词: 平桥页岩气藏, 离散裂缝模型, 渗流机理, 产量递减, 压后模拟

Abstract:

In shale gas reservoirs with natural fractures, the artificial fractures and natural fractures communicate with each other after fracturing. The traditional dual media model can not accurately reflect the impact of natural fractures on well production. In order to investigate the influence on shale gas well productivity caused by gas transport in nanometer-size pores, the mathematical model of multi-stage fractured horizontal well in shale gas reservoir is built, which considers the influence of the complex flow mechanism such as the viscous flow, Knudsen diffusion, surface diffusion, adsorption layerand gas desorption. Discrete fracture model（DFM） is used to simplify the fracture and finite element method is applied to solve the model. The numerical simulation results of Pingqiao shale gas reservoir indicate that the free gas in fracture system mainly contributes to shale gas production in the early stage, and the average recovery of adsorbed gas is only 10.1 %. The existence of unmodified reservoir makes the influence of bedrock permeability on cumulative production greater. The density and connectivity of fracture networks have dominant effects on gas production and its decline trend.

Key words: Pingqiao shale gas reservoir, discrete fracture model, flow mechanism, production decline, post-fracturing simulation

中图分类号:

TE332

王伟,李阳,陈祖华,姚军,梅俊伟,任建华,马波. 基于复杂渗流机理的页岩气藏压后数值模拟研究[J]. 油气藏评价与开发, 2020, 10(1): 22-29.

WANG Wei,LI Yang,CHEN Zuhua,YAO Jun,MEI Junwei,REN Jianhua,MA Bo. Post-fracturing numerical simulation of shale gas reservoir based on complex flow mechanisms[J]. Reservoir Evaluation and Development, 2020, 10(1): 22-29.

图/表 10

图1

图2

表1

页岩气藏压裂水平井数值模拟基本参数"

参数	值
初始气藏压力 $p i$ /Pa	4.3×10⁷
井底压力 $p w$ /Pa	5×10⁶
基岩固有渗透率 $k ∞$ /m²	5×10^-20
基岩孔隙度 $? m$	0.05
基岩平均孔喉半径 $r i$ /m	5×10^-9
天然裂缝开度 $b$ /m	5×10^-6
天然裂缝间距 $a$ /m	0.1
人工裂缝半长 $x f$ /m	100
人工裂缝间距 $y f$ /m	75
人工裂缝开度 $d f$ /m	0.005
人工裂缝改造长度 $X e$ /m	300
气藏温度T/K	366.15
基岩颗粒密度 $ρ R$ /（kg·m^-3)	2 600
Langmuir体积 $V L$ /（m³·kg^-1）	0.004 1
Langmuir压力 $p L$ /Pa	4.7×10⁶
吸附气分子直径 $d m$ /m	3.8×10^-10
临界温度 $T c$ /K	191.05
临界压力P_c/Pa	4.64×10⁶
人工裂缝渗透率应力敏感系数d_F/（1·Pa^-1）	1×10^-6
天然裂缝渗透率应力敏感系数d_f/（1·Pa^-1）	1×10^-7
压裂段数	20

表1

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图9

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