基于格子Boltzmann方法的致密气藏微尺度效应研究

Micro-scale effect in tight gas reservoir based on lattice Boltzmann method

 吴子森¹ 董平川¹ 袁忠超² 张雪娇¹ 曹耐¹ 杨书¹

中国石油大学（北京）石油工程教育部重点实验室，北京 102249 中海油研究总院开发研究院，北京 100027）

MOE Key Laboratory of Petroleum Engineering, China University of Petroleum, Beijing 102249, China CNOOC Research Institute, Beijing 100027, China)

 致密储层孔隙结构复杂，气体在致密孔喉中的流动存在微尺度效应，宏观流动规律难以准确描述其渗流特征。针对致密多孔介质孔隙主要分布在微纳米尺度的特点，建立修正克努森数（Kn）、固体边界处考虑镜面反弹（边界滑移效应）的格子Boltzmann模型。通过模拟压差驱动下的二维平板流动，验证了模型的正确性，并分析了克努森数对流动速度的影响。基于随机生长四参数生成法，对致密储层的二维微观孔隙结构进行了重构，利用修正格子Boltzmann模型进行流动模拟。结果表明：气体在致密储层中的流动存在微尺度效应，滑脱效应使得通道中间部分流体速度增大；在一定的压力梯度下，渗透率随着克努森数的增加而呈线性增加；克努森数不变时，渗透率随着平均压力倒数的增加而呈线性增加，即随着平均压力的增加，岩心的绝对渗透率减小。

 The micro?-pore structure of tight gas reservoir is complex, and gas flow in tight reservoir can lead to micro?-scale effect which can′t be described by flowing law of macro fluid. Considering the micro-nano scale pores in tight sandstone, a lattice Boltzmann model (LBM) amended by Knudsen number has been established with a specular bounceback condition (slippage effect) on the solid boundary. The correctness of the new model is verified by the simulation of two parallel plates flow forced by differential pressure. The influence of Knudsen number on velocity was analyzed. With the multi-parameter random generation growth method (MRGGM), a 2D digital core of tight reservoir was reconstructured and the fluid flow behavior in this core was studied by the LBM. The results show that there exists micro-scale effect when gas flows in tight reservoir and the predicted flow velocity in the middle of the flat for the novel model will become larger because of the slippage effect. Under a certain pressure gradient, the permeability increases linearly with the increase of Knudsen number; when the Knudsen number is constant, the permeability increases linearly with the reciprocal of the average pressure, which means the absolute permeability of core decreases with the increase of average pressure.

10.6056/dkyqt201606022