川西坳陷须五段储层微观孔隙结构特征及其控制因素

Characteristics and controlling factors of micro-pore structure of Xu 5 reservoir in western Sichuan depression

非常规气藏储层的微观孔隙结构是影响气藏储集性能和开发效果的重要因素。以须五段砂岩、泥岩储层为研究对象,综合应用扫描电镜、低温氮气吸附法、激光扫描共聚焦显微镜以及微米—纳米CT扫描等技术手段,对川西坳陷须五段储层微观孔隙结构展开深入研究。研究结果表明:(1)须五段砂岩孔隙类型主要有溶蚀孔、晶间孔、微裂缝,溶蚀孔最为发育;泥质岩孔隙类型有矿物基质孔(粒间孔、粒内孔、晶间孔)、有机质孔、微裂缝,粒间孔、晶间孔最为发育。(2)须五段储层孔隙结构复杂,以中孔、大孔为主,多呈广体细颈型和平板狭长缝型,其比表面积介于1.44~11.7m^2/g之间,平均孔径介于5.75~15.6nm之间,砂岩比表面积比泥岩小,但孔径反而较大。(3)考虑到研究区非常规气藏储层的复杂性,单一技术手段表征孔隙结构都存在片面性,那么有机整合多种现代高精度技术手段进行非常规气藏储层微观孔隙分析显得尤为重要。在此基础上,分析了须五段非常规气藏储层微观孔隙结构的控制因素及产能与不同类型孔隙的关系,为后续"甜点"预测提供地质依据。

Micro-pore structure is an important factor controlling the preservation properties and development results of unconventional gas reservoir. In this paper, the micro-pore structure of the Xu 5 reservoir in the western Sichuan depression was studied using SEM （scanning electron microscopy）, low-temperature nitrogen adsorption, laser scanning eonfocal microscopy and micro-nano CT scanning techniques. The following results were obtained. First, the pore space in the Xu 5 sandstone reservoir is composed of solution pores, intercrystal pores and micro fractures, with the solution pores in dominance, and the pore space in the shale reservoir is composed of mineral matrix pores （e.g. intergranular, intragranular and intercrystal pores）, organic pores, and micro fractures, of which the most developed types are intergranular and intercrystal pores. Second, the pore structure of the Xu 5 reservoir is complex, primarily consisting of mesopores and macropores which show in the shapes of wide body and narrow neck, and fiat and narrow seam, with a specific surface area between 1.44 m2/g and 11.7 m2/g, and an average pore diameter ranging from 5.75 nm to 15.6 nm; the specific surface area of the sandstone is smaller than that of the mudstone, but the pore size of the sandstone is larger. Third, since the unconventional gas reservoir is very complex, single technique may only provide incomplete results, and several modern high-precision techniques can be combined together for characterizing the micro-pore structure. On this basis, the factors that control the micro-pore structure and the relationship between the production and pore types in the Xu 5 unconventional gas reservoir were analyzed, in order to provide the geological base for subsequent ＂sweet spot＂ prediction.