基于数字岩心的含水合物石英砂微观渗流有限元分析

利用X射线计算机断层扫描系统（CT）获得不同饱和度下含水合物石英砂内部气、水、水合物各相态分布特征，通过有限元方法计算了不同水合物饱和度下石英砂液相渗透率变化，并模拟了流体在孔隙内的流动情况，获得了假定边界条件下孔隙流体的三维流速分布。研究结果表明，随着水合物饱和度的降低，渗透率逐渐增大，其中当水合物饱和度从56%下降到39%时，液相渗透率值增速最大；水合物分解末期，液相渗透率并未随着有效孔隙度的增大而快速升高，通过CT扫描图像显示，部分石英砂孔隙和喉道可见甲烷气泡滞留，由于气体的贾敏效应在一定程度上阻碍了液体的流动，从而导致液相渗透率增速降低。本研究建立了一种基于石英砂内部真实孔隙特征的液相渗透率和液体流速计算方法，可为水合物开采过程中储层微观渗流演化机理研究提供参考。

FINITE ELEMENT ANALYSIS OF MICRO-SEEPAGE IN HYDRATE-BEARING QUARTZ SANDS BASED ON DIGITAL CORES

In this study, the distribution characteristics of gas, water and hydrate in hydrate-bearing quartz sands under different saturation are acquired by X-ray computed tomography (CT). The change of liquid phase permeability is calculated using the finite element method. The flow of fluid in the pores is simulated and the three-dimensional velocity distribution of the pore fluid under the assumed boundary conditions is obtained. The results show that the liquid phase permeability in quartz sand increases gradually with the decrease of hydrate saturation. When the hydrate saturation decreases from 56% to 39%, the liquid phase permeability value of quartz sand increases to the maximum. At the end of hydrate decomposition, the permeability does not increase rapidly with the increase in effective porosity. The CT scan image shows that some methane bubbles are trapped in quartz sand pores and throat. Due to the Jamin effect, the flow of liquid is hindered to a certain extent, which leads to the decrease of liquid phase permeability growth rate. In this study, a calculation method of liquid phase permeability and liquid velocity based on the real pore characteristics of the hydrate-bearing quartz sand is established, which can provide a reference for the study of the evolution mechanism of micro seepage in the process of hydrate exploitation.