页岩油储层储集空间定量表征及分级评价标准探讨—以江汉盆地为例

Shale oil is the most potential field of hydrocarbon exploration on land, which has been well developed in China. Shale oil reservoir is characterized by ultra-low porosity and low permeability with diverse types of reservoir space, where nanoscale pore throat systems develop. Qualitative analysis method is often used to discuss the shale oil reservoir while the quantitative method is single. There still lacks research on quantitative characterization of reservoir space and grading evaluation of shale oil reservoir. This project selected argillaceous dolomite of Xingou Formation developed in the Jianghan Basin as target area in order to solve the problems mentioned above. The methods of porosity calculation are comprehensively analyzed combining the logging data, and the quantitative evaluation model is built for the argillaceous dolomite in the study area. Combining the principle of material balance, the organic and inorganic porosity can be quantitatively characterized based on the analysis of reservoir porosity, FIB-SEM, high-pressure mercury, X-ray, micro-CT and naro-CT. Through the laboratory test of organic geochemistry of argillaceous dolomite, the relationship between TOC, Ro, diagenesis and organic porosity will be discussed, while the relationship between mineral composition, diagenesis and inorganic porosity. Thus, the main controlling factors of organic and inorganic porosity will be indicated. Additionally, main parameters are selected for grading evaluation of the organic and inorganic porosity, with their relationship with porosity discussed, the grading evaluation criteria of shale oil reservoir will be built.

页岩油是我国陆上发展势头最快且最具潜力的油气勘探领域，页岩油储层具有特低孔、低渗的特征，储集空间类型多样，并广泛发育纳米级孔喉系统。但目前针对页岩油储层的研究多为定性分析，定量研究的技术手段较为单一，并且尚缺乏对页岩油储层储集空间定量表征和分级评价方面的研究。本项选取江汉盆地新沟嘴组泥质白云岩为靶区，拟解决上述问题。结合测井资料，综合分析孔隙度计算方法，建立适合研究区泥质白云岩的孔隙度定量评价模型。在FIB抛光-SEM成像技术、高压压汞、X-衍射、微米和纳米CT等分析基础上，结合物质平衡原理，定量表征储层有机和无机孔隙。根据泥质白云岩有机地球化学分析结果，探讨TOC、Ro、成岩作用与有机孔隙，矿物组分和成岩作用与无机孔隙之间的关系，揭示有机、无机孔隙发育的主要控制因素。优选上述典型参数，探讨其与孔隙度的关系，建立页岩油储层分级评价标准。

鉴于目前页岩油气的研究对象主要为泥页岩，很少有研究关注泥质白云岩。本项通过探讨江汉盆地泥质白云岩储层微观孔隙结构特征研究以期明确页岩油气在泥质白云岩层系的储集机制。区内页岩油储层储集空间类型以无机孔隙（包括晶间孔、粒间孔、溶蚀孔）为主、也存在少量有机孔隙及微裂缝。扫面电镜法定量表征了页岩储层无机孔隙度，其大小主要分布在6.37%～18.58%，平均值为11.62%，与实测孔隙度接近；孔隙三维重构结果表明，孔隙连通性总体较好，但同时存在分布较为孤立的孔隙。矿物组分和溶蚀作用为研究区物性重要影响因素，前者影响机制较为复杂，而后者对储层物性具有明显的改善作用。确定了新沟嘴组页岩油储层孔隙度下限为8%，渗透率下限为0.03mD，并建立了孔隙度和渗透率下限与深度回归方程。探讨了微观孔隙结构参数与物性关系，根据曲线拐点将储层物性分为三类，其中孔隙度界限为8%和14%，渗透率界限为0.03mD和0.1mD。