基于水平集方法的低渗砂岩数字岩心气水两相渗流模拟

doi:10.19596/j.cnki.1001-246x.8322

摘要/Abstract

摘要：

低渗致密砂岩气藏孔喉结构复杂，气水流动及分布规律表征难，常规岩心实验精细刻画困难。基于真实低渗砂岩岩心，利用Micro-CT扫描技术构建储层三维数字岩心，提取连通孔隙结构并建立非结构化四面体网格模型。结合水平集法与N-S方程，建立气水两相流数学模型并利用有限元方法进行求解，研究低渗砂岩气水两相流动中的水驱气过程、残余气分布特征、岩石润湿性对两相流的影响以及并联通道中的窜流特征。结果表明：利用水平集方法能清晰地观察到气水两相分布特征与驱替前缘的运移规律；岩石润湿性对两相流过程影响较大，水湿条件下采出程度更高；并联通道中的窜流现象明显，大通道中水相优先突破并形成优势流动通道，狭小通道中的流动受毛管现象影响，存在较大的附加阻力。

关键词: 低渗砂岩, 数字岩心, 水平集法, 两相流, 润湿性

Abstract:

The pore throat structure of low permeability tight sandstone gas reservoir is complex. It is difficult to characterize the flow and distribution of gas and water in it. Based on real low-permeability sandstone core, micro-CT scanning technology was used to construct three-dimensional digital core of the reservoir. Connected pore structure was extracted and unstructured tetrahedral mesh model was established. With level-set method and N-S equation, a mathematical model of gas-water two-phase flow is established which is solved by finite element method. Water drive gas process, residual gas distribution, influence of rock wettability on two-phase flow in low-permeability sandstone gas-water two-phase flow, and interflow characteristics in parallel channels are studied. It shows that level-set method provides clearly gas-water two-phase distribution and migration of the displacement front. Rock wettability has great influence on two-phase flow process, and production degree is higher under water-wet conditions. Interflow phenomenon is obvious in parallel channels. Water phase in the large channel breaks through first and forms a dominant flow channel, while flow in the narrow channel is affected by capillary phenomenon and has great additional resistance.

Key words: low permeability sandstone, digital rock, level-set method, two phase flow, wettability

中图分类号:

TE312

赵玉龙, 周厚杰, 李洪玺, 文涛, 张芮菡, 张烈辉. 基于水平集方法的低渗砂岩数字岩心气水两相渗流模拟[J]. 计算物理, 2021, 38(5): 585-594.

Yulong ZHAO, Houjie ZHOU, Hongxi LI, Tao WEN, Ruihan ZHANG, Liehui ZHANG. Gas-water Two-phase Flow Simulation of Low-permeability Sandstone Digital Rock: Level-set Method[J]. Chinese Journal of Computational Physics, 2021, 38(5): 585-594.

图/表 9

图1 (a) 低渗砂岩灰度图片；(b)非局部均质滤波法得到的图像；(c)孔隙分割结果(xy平面)；(d)连通孔隙空间；(e)表征单元体；(f)非结构化四面体网格；(g)入口分布(紫色面)；(h)出口分布(紫色面)

Fig.1 (a)Gray image of low permeability sandstone; (b)Image obtained with non-local-means filter; (c)Pore segmentation results(xy plane); (d)Connected pore space; (e)Representative elementary volume; (f)Unstructured tetrahedral mesh; (g)Inlet; (h)Outlet

图2 两相流模拟结果

Fig.2 Two-phase flow simulation results

图3 驱替前缘的形状随驱替过程的变化(a)凸型驱替前缘(s=5)；(b)凹型驱替前缘(s=13)

Fig.3 Shape of the displacement front in the displacement process (a)convex displacement front (s=5);(b)concave displacement front (s=13)

图4 残余气的两种分布

Fig.4 Two distributions of residual gas

图5 饱和度随时间变化

Fig.5 Saturation over time

图6 不同润湿角下的水驱气过程模拟(a) θw=30°; (b) θw=60°; (c) θw=90°; (d) θw=120°

Fig.6 Simulation of water drive gas process at different wetting angles (a) θw=30°; (b) θw=60°; (c) θw=90°; (d) θw=120°

图7 不同润湿条件下采出程度与驱替时间的关系

Fig.7 Relation of recovery degree and displacement time under different wetting conditions

图8 (a) 并联模型网格划分；(b)两相流入口分布(紫色面)；(c)两相流出口分布(紫色面)

Fig.8 (a)Grid division of parallel model; (b)Inlet(purple face); (c)Outlet(purple face)

图9 并联通道中的驱替过程

Fig.9 Process of displacing in parallel channels

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