摘要
致密油孔隙结构表征是该类储层评价的核心，直接制约其规模开发。由于传统方法的局限性，文中运用医用CT、场发射扫描电镜、微米CT和纳米CT 4种技术相结合的方法，从毫米级、微米级和纳米级3个尺度综合描述致密油孔隙结构。以川中致密油岩心为例进行研究，结果表明，川中致密油储层具有多尺度多类型孔隙连续分布的特征。基于医用CT扫描分析，储层连通性较差，孔隙空间分布也极度分散，其孔隙度主要分布范围在0.5%以下；在SEM图像上，观察到大量的微米级粒间残余孔道和纳米级粒内溶蚀孔道，但孔隙网络重建表明，基质孔道在微纳尺度的连通性都很差；除基质孔道外，在渗透率较高的岩心SEM图像中观察到粒间缝和方解石颗粒解理缝2类微裂缝，其存在能较好地改善储层连通性。实验分析认为，在孔隙结构表征中，开展微米级孔道和微裂缝的基础研究是致密油规模勘探开发的关键。
Abstract
Pore structure characterization is an essential issue for tight oil evaluation, which holds the key to its efficient development. Due to the limitations of traditional methods, a novel analysis procedure combining medical CT, FESEM, Micro-CT and Nano-CT is proposed to characterize tight oil pore structure in this paper on millimeter scale, micrometer scale and nanometer scale. Taking Chuanzhong tight oil reservoir cores as examples, these cores have multi-type and multi-scale continuous pore distribution. Based on the medical CT analysis, the porosity connectivity is poor and its space is of extremely fragmented distribution with the main range from 0 to 0.5%. The SEM images show two main types of pores, the residual intergranular pore on micrometer scale and the dissolved intra-granular pore on nanometer scale, but poor scale network reconstructions show that the matrix connectivity is very poor both on micrometer scale and nanometer scale. Apart from the matrix pore, two kinds of micro-fractures, the intergranular micro-fracture and the calcite particle cleavage micro-fracture, are identified in some areas of the high permeability core, which can improve the connectivity. It can be summarized from the experimental analysis that tight oil pore structure characterization for micro-pore and micro-fracture needs to be focused further, which is the key to its efficient exploration and development.
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