致密油气藏微纳米孔喉滑移机理及表征方法

Oil and gas in tight sandstone reservoirs are reliable alternative resources. Sandstones of tight reservoirs are tight and micro-nano throats are widely distributed. Environment and mechanism of flow in porous media are complex. Traditional flow theory cannot be applied to tight oil and gas reservoirs. Molecular motion affects boundary slip greatly. Boundary slip results from interaction between fluid and rock. Continuum mechanics, Darcy Equation and traditional flow parameters cannot be applied to flow in micro-nano throats. In this study, micrometer tube experiments are conducted and dissipative particle dynamics is modified to study flow behavior in micro-nano throats. These two methods are based on micro pore and throat characteristics and can describe interaction between fluid and rock. Boundary slip characteristics and velocity profile characteristics are studied. The mechanism of boundary slip is revealed. Based on the micro flow behavior in micro-nano throats, a few new parameters are came up with and non-linear flow equation is built to describe flow behavior in tight sandstone. Future achievements of this study is significant to micro flow theory and they are also the theory foundation for development and enhancement recovery of tight oil and gas reservoirs.

非常规致密油气作为现实的接替资源，其岩性致密、微纳米孔喉发育，渗流环境和渗流机理更加复杂，传统渗流理论已不再适应。该类储层微纳米孔隙中分子运动对流体与岩石相互作用产生的壁面滑移（边界层或滑脱）影响显著，利用常规连续介质力学很难准确解释此现象，传统渗流参数和达西运动方程已不能准确反映致密储层中的渗流规律。本项目针对微纳米孔喉特征，采用微圆管实验和耗散粒子动力学的离散介质力学研究方法，真实反映微纳米尺度下不同流体介质与岩石特殊的相互作用机制，在微观尺度下研究纳米级孔喉中流体流动规律，分析微纳米孔喉中流动滑移和剖面特征，揭示微尺度下流动边界滑移机理；基于微纳米孔喉微尺度流动特征，由微观渗流机理解释和表征致密储层渗流现象，形成适合致密储层关键渗流参数新的表征方法，建立致密储层的非线性渗流方程。研究成果对发展完善微观渗流理论具有重要意义，也为非常规致密油气藏高效开发和提高采收率提供坚实的理论基础。

致密油藏中广泛发育微纳米喉道，受微尺度流动效应的影响，储层渗透率急剧下降。目前，微纳米喉道中的流动机理认识尚不充分。基于采用耗散粒子动力学实现了水在宽度为2-150nm狭缝中的流动模拟，研究结果表明固壁附近存在明显的流体高密度带，壁面附近的流体分子速度为零，存在边界层。搭建了微尺度流动实验平台，开展了去离子水在1.377-15.361μm熔融石英管中的流动实验，研究了压力梯度和喉道半径对流动的影响。然后，研究了致密油重要组分(正己烷、正辛烷、正十六烷)在微纳米喉道中的流动规律。揭示了烷烃在微尺度下的流速、流量、流动阻力和非线性流动规律，对比了不同碳链长度烷烃从非线性流动转化为线性流的规律，分析了碳链长度、喉道半径、压力梯度等因素对烷烃流动的影响。再次，研究了分子极性、润湿性、流固相互作用力强度对微尺度流动的影响。最后，基于微尺度流动规律的研究结果，给出了致密油藏关键渗流参数表征的新方法，并应用于致密油藏的数值模拟。本文的研究成果明确了微纳米级喉道内流体流动规律及非线性流动的产生机理，分析了流固相互作用力影响微尺度流动的机理，以及这种机理对致密油藏渗流规律的影响，为致密油藏的高效开发提供了理论基础。