页岩储层微观孔隙结构特征

为了研究页岩储层的微观孔隙结构特征，应用场发射环境扫描电子显微镜观察了页岩表面纳米级孔隙微观形态，并通过低温氮吸附法测定了页岩的氮气吸附等温线，同时结合高压压汞实验对页岩储层孔隙结构进行了深入研究。研究结果表明：页岩储层孔隙处于纳米量级，孔隙类型可分为有机质纳米孔、黏土矿物粒间孔、岩石骨架矿物孔、古生物化石孔和微裂缝5种类型，其中有机质纳米孔和黏土矿物粒间孔发育最为广泛;页岩孔径分布复杂，既含有大量的中孔（2～50nm），又含有一定量的微孔（<2nm）和大孔（>50nm）;孔径小于50nm的微孔和中孔提供了大部分比表面积和孔体积，是气体吸附和存储的主要场所;页岩阈压非常高，孔喉分选性好，连通性差，退汞效率低，中孔对气体渗流起明显贡献作用，微孔则主要起储集作用。

Characterization of microscopic pore structures in shale reservoirs

Nanostructure morphology of shale reservoirs was investigated using a field-emission environmental scanning electron microscope and adsorption-desorption isotherms were measured with low-temperature nitrogen adsorption experiments. Combined with high-pressure mercury injection, further investigation into characterization of pore structures in shale reservoirs was gained. Results show that pores in shale reservoirs are generally in a nanometer grade, it can be classified into five types: organic nanopores, interparticle pores between clay minerals, mineral pores in rock skeletons, apertures in palaeontologic fossils and microfractures, of which the most common ones are organic nanopores and interparticle pores between clay minerals. The pore-size distribution of shales are complex, which includes not only predominant mesopores (2～50nm), but also a certain amount of micropores (<2nm) and macropores (>50nm). Micropores and mesopores with a diameter less than 50nm amount to most of specific surface area and pore volume of shale pores, and mainly are places for gas adsorption and storage. Shale is characterized by high threshold pressure, good-sorting pore throats, poor connectivity and low efficiency of mercury withdrawal. In addition, mesopores in shale apparently contribute a lot to gas percolation, while micropores in shale are mainly for gas storage.