龙女寺东端须家河组致密砂岩成岩作用及储层形成机理

Diagenesis of Tight Sandstones and Formation Mechanism of the Reservoir in the Xujiahe Formation,the Eastern Margin of Longnvsi

致密砂岩作为非常规油气的重要载体,对其致密化成因及储层形成机理研究具有重要意义。利用钻井岩心、薄片观察、阴极发光和流体包裹体等手段,对川中地区龙女寺东端须家河组致密砂岩的成岩作用及储层形成机理进行研究。结果表明:龙女寺东端须家河组遭受了机械压实-压溶作用、胶结作用、交代作用、溶蚀作用和构造破裂作用,机械压实作用和胶结作用是导致砂岩致密化的主要因素,溶蚀作用和破裂作用是储层形成的主要因素;须家河组目前处于中成岩A-B期,经历的流体活动主要有同生成岩期地表水沉淀早期方解石胶结和绿泥石薄膜,早成岩B期压溶作用控制石英Ⅰ期次生加大形成与孔隙流体溶解黏土矿物、长石和易溶岩屑等,中成岩A期大量油气充注促进石英Ⅱ、Ⅲ期次生加大与少量方解石溶解,中成岩B期燕山/喜山运动促进储层形成;储层形成机理主要涵盖残余原生孔的保存和次生孔的形成,有利的沉积环境、溶蚀作用、异常高压和构造破裂作用共同控制储层形成,有利的沉积环境、溶蚀作用和异常高压主要是保护残余原生孔和形成次生孔,构造破裂作用产生大量微裂缝,提高储层渗流能力,并为形成溶蚀扩大孔提供条件。

Tight sandstones as an important carrier of unconventional oil and gas is great significance to study its densifying cause and formation of the reservoir. Through using drilling core,thin section observation,cathode luminescence and fluid inclusion,this article has researched diagenesis and the reservoir＇s formation mechanism of tight sandstones in the Xujiahe Formation,the eastern margin of Longnvsi,Sichuan. The results show that the Xujiahe Formation of the eastern margin of Longnvsi suffered mechanical compaction,pressure solution,cementation,replacement,dissolution and fracture. Mechanical compaction and cementation are the main factors that lead to densification of sandstones. Dissolution and fracture are the main factors that lead to formation of the reservoir. At present,the Xujiahe Formation is in the middle diagenetic stage A-B. Main experienced fluid activities are early calcite cementation and chlorite film of surface water precipitation in syndiageneticstage. Pressolution controls the formation of secondary quartz increase and pore fluid dissolution of clay minerals,feldspars,easily dissolved cuttings etc. in the early diagenetic stage B. A large number of oil and gas injecting promote secondary increase of quartz and dissolute a small amount of calcites in the middle diagenetic stage A. The formation of the Yanshan and Himalayan movement promote the formation of the reservoir in the middle diagenetic stage B. The formation mechanism of the reservoir is mainly covered by the preservation of the residual primary hole and the formation of the secondary pores. Formation of the reservoir is jointly controlled by favorable sedimentary environment,dissolution,abnormal high pressure and tectonic rupture. Favorable sedimentary environment,dissolution and abnormal high pressure are mainly to protect the primary hole and to form secondary pores. A large number of micro cracks are produced by tectonic disruption,not only improving seepage ability of the reservoir,also providing the conditions for forming the dissolution pores.