波尔兹曼数字岩芯致密砂岩渗透率研究

致密砂岩渗透率在油气勘探开发、地应力测量及水库地质灾害等领域具有重要意义,但鉴于目前实验技术局限性,温压耦合渗透率测量尚无法通过实验手段实现. 在已有研究工作基础上,首次建立了基于D3Q27数字岩芯模型,并计算了高温压耦合低渗砂岩渗透率问题. 首先,以鄂尔多斯盆地某油田延长组致密砂岩为例,利用X射线CT断层成像技术岩芯获取10μm, 5μm, 2μm分辨率致密砂岩内部结构数据,应用基于量子力学第一性原理的D3Q27格子波尔兹曼数字岩芯模型建立数值模型. 进而,利用自编3DLBM程序分别计算了不同分辨率渗透率随围压(0～200MPa)、孔隙压(0～65MPa)和温度(25℃～180℃)变化规律,通过与Inc AUTOLAB2 000C岩石测试分析系统实验结果对比,验证了程序的可靠性,得到低渗砂岩断层最佳分辨率;最后,在并行CPU-GPU平台上计算了高温高压耦合(0℃～400℃, 0～1.4 GPa)下致密砂岩渗透率值及其各向异性随温压变化规律,并讨论了致密砂岩中水在达到超临界状态后对致密岩石内部结构的影响.

STUDY OF TIGHT SANDSTONE PERMEABILITY FROM LATTICE BOLTZMANN & DIGITAL ROCK MODEL

Due to the experimental technology condition, to measure the permeability of the porous rock is still a changeling problem, especially for low or ultralow permeability porous rock. X-ray computed tomography (CT) technology, which can conveniently be used to obtain high-resolution internal structure data of the rock, is more and more widely used to predict and explore the permeability physical properties of the low or ultralow porous rock. How to determine the CT cross-section resolution is one of the key issues in the predict process, even this approach has some incomparable advantages of experimental methods, with high precision, convenient, and the field measurement. In this work, the tight sandstone sample from the Ordos Basin Triassic formation is selected and different tomography resolution data are obtained from Kochi Institute for Core Sample Research (10μm), National Synchrotron Radiation Laboratory of Chinese Academy of Sciences (5μm, 2μm) and National Institute of Metrology of China (2μm), respectively. Then, based on the D3Q27 lattice Boltzmann method & virtual digital physical technology, the permeability under coupled confining pressure (0～200MPa), pore pressure (0～65MPa) and temperature (25℃～180℃) is measured. The results show that when the tomography resolution is located at 2μ, the results are consisted with the experimental results obtained from Inc AUTOLAB 2000C rock system. The permeability anisotropy of tight sandstone under ultra-high temperature and pressure (0℃～400℃, 0～1.4GPa) is explored and this will be helpful to understand the strength decrease of asthenosphere and interaction between lithosphere and asthenosphere.