基于Lattice Boltzmann方法的页岩张性裂缝渗流特征研究

摘要

In order to deeply understand the fluid seepage characteristics in tension fractures structure,the seepage characteristics of fluid in shale tension fractures are systematically studied by combining physical experiment and numerical simulation. Split up the Barnett shale core into tensional fractures,collect the fracture surface data as a physical model,and at the same time,study fluid flow in tension fractures by using the D3Q19 model of LBM-BKG method. Research scale are whole,section,line,discrete element in turn. Investigate the distribution of seep-age field characteristic parameters under various scales and analyze the reasons.Research shows that:on the whole, pressure is linear distribution along the lateral and vertical of seepage,and it is fluctuant linear distribution on later-al lines,while nonlinear distribution on vertical lines;a recirculation zone is formed in the local region at the end of the joint surface,which is related to the roughness and the degree of roughness;velocity isosurface near average velocity are basically parallel,when the velocity is large,the velocity isosurface basically corresponds to the region with relatively smooth end surface;along the same streamline,there is a slight difference in seepage velocity;the whole seepage is steady,and it does not mean the velocity is equal everywhere in the seepage field,actually the seepage velocity of discrete seepage elements are different;the 3D roughness caused three dimensional distribution of seepage velocity,but mainly based on the flow direction and vertical seepage velocity. This study is of great sig-nificance for understanding the seepage of fractured system in fractured reservoirs such as shale.%为深入了解张性裂缝结构中流体渗流特征,采用物理实验和数值模拟相结合的方法,系统研究流体在页岩张性裂缝中的渗流特征.将Barnett页岩岩心劈裂成张性裂缝,并采集裂缝面数据,将其作为物理模型,同时采用LBM-BKG方法D3Q19模型研究流体在张性裂缝中的流动.研究尺度依次为整体、截面、截线、离散单元体,考察各尺度下渗流场特征参数分布,并分析原因.研究表明:整体上,沿渗流横向和纵向上压力均呈线性分布,横向各截线上压力呈波动式线性分布,纵向截线上压力分布呈非线性;缝面端部局部区域会产生回流区,回流区与粗糙性及粗糙性变化程度有关;近平均速度的速度等值面间基本呈平行分布,速度较大时,等值面基本对应于端面相对平缓的区域;沿同一流线,渗流速度略有差别;整体渗流为稳态,不代表渗流场各处速度相等,离散的渗流单元体的渗流速度各不相同;三维粗糙性造成了渗流速度的三维分布,但主要以渗流方向和垂向上渗流速度为主.该项研究对深入理解页岩等裂缝发育储层的裂缝系统渗流具有重要意义.