四川盆地元坝地区自流井组页岩储层孔隙结构特征

四川盆地元坝地区自流井组页岩是陆相页岩气的主要研究层段之一，目前正处于勘探攻关的重要阶段。页岩孔隙结构是评价页岩储层储集能力的重要指标，是明确页岩气富集机理的关键。采用总有机碳含量、全岩X衍射、N₂吸附-高压压汞孔径联合实验及氩离子抛光-扫描电镜等多种实验测试方法对其孔隙结构进行了定量表征。结果表明：自流井组页岩粘土矿物含量高，介于38.8%~67.3%，平均为52.8%。孔隙类型以矿物基质孔隙为主，有机质孔次之，微裂缝局部发育；N₂吸附滞后环反应主要发育平行板状狭缝型孔隙，同时含有少量墨水瓶型孔；主要孔径分布区间为中孔，大安寨段与东岳庙段相比，由于微孔比例偏低，宏孔比例偏高，所以中值孔径与孔体积较大、比表面积相对较小。自流井组页岩储层孔体积与比表面积主要由粘土矿物决定，孔体积和比表面积与TOC呈负相关或无关，主要由于有机质内镜质体与丝质体不发育孔隙，以及可溶有机质对孔体积和吸附位的占据。研究成果对研究区陆相页岩气的研究与勘探具有重要的借鉴和指导意义。

Pore structure characteristics of shale reservoirs in the Ziliujing Formation in Yuanba area,Sichuan Basin

Shale of the Ziliujing Formation in Yuanba area of Sichuan Basin, currently at a critical stage of exploration, is one of the main research targets of terrestrial shale gas.As a significant index to evaluate the storage capacity of shale reservoirs, shale pore structure is the key to clarify the enrichment mechanism of shale gas.In this study, the pore structure is quantitatively characterized through an integration of total organic carbon (TOC) content tests, whole rock X-ray diffraction, combined experiment of N₂ adsorption and high-pressure mercury intrusion for pore size and scanning electron microscopy (SEM) after argon ion milling.The results show that the Ziliujing Formation shale is dominated by clay minerals, accounting for 38.8% to 67.3% with an average of 52.8%;the pores are mainly matrix pores, followed by organic pores, and with micro-fractures developed locally.The hysteresis loops of N₂ adsorption reflect the well development of parallel plate-like slit pores together with a small amount of ink bottle-shaped pores.The main interval of pore size distribution falls in mesopores.Compared with Dongyuemiao Member, Da'anzhai Member contains fewer micropores and more macropores, leading to a higher median value of pore size and pore volume, while a relatively smaller specific surface area (SSA).The pore volume and SSA of shale reservoirs in the Ziliujing Formation depend on clay minerals.The pore volume and SSA are in a negative correlation or irrelevant with the TOC content, mainly due to the infertility of organic pores in vitrinite and filament and the occupation of pore volume and adsorption sites by soluble organic matters.These will be of referential significance to the exploration of terrestrial shale gas in the study area.