普光地区须家河组致密砂岩储层成岩作用及孔隙演化

Diagenesis and pore evolution of tight sandstone reservoirs of Xujiahe Formation in Puguang area

利用岩石薄片、铸体图像、全岩X衍射、扫描电镜、阴极发光、包裹体测试等分析实验技术,对四川盆地普光地区须家河组致密砂岩储层的成岩作用类型及成岩孔隙演化过程进行系统研究。研究结果表明:1)普光地区须家河组储层岩性以长石岩屑砂岩和岩屑砂岩为主,储集空间类型主要为粒间溶孔、粒内溶孔和黏土矿物晶间微孔;2)强压实作用和多期次多类型强胶结作用是储层致密化的主要因素,烃源岩生排烃期的有机酸溶蚀作用为主要的建设性成岩作用;3)须家河组历经碱性—酸性—碱性—酸性—碱性等5期成岩流体演化阶段,“三碱两酸”5期酸碱交替的流体变化决定了成岩孔隙演化,控制了溶蚀孔隙型有效储层的形成,近烃源岩和烃源岩内砂岩段具有酸性流体充注优势,更利于溶蚀孔隙形成,是有效储层发育的主力层段。研究成果对川东北地区须家河组致密砂岩气的进一步勘探具有重要指导意义。

The diagenetic types and diagenetic pore evolution process of tight sandstone reservoirs of Xujiahe Formation in Puguang area of Sichuan Basin are systematically studied by means of rock thin section,casting image,whole-rock X-ray diffraction,scanning electron microscope,cathodoluminescence,inclusion testing and other analytical and experimental techniques.The research results show that:(1)the reservoir lithology of Xujiahe Formation in Puguang area is mainly feldspathic lithic sandstone and lithic sandstone,and the reservoir space types are mainly intergranular dissolved pores,intragranular dissolved pores and intercrystalline micropores of clay minerals;(2)strong compaction and multi-period and multi-type strong cementation are the main factors of reservoir densification,and organic acid dissolution during hydrocarbon generation and expulsion of source rock is the main constructive diagenesis;(3)the Xujiahe Formation has gone through five stages of diagenetic evolution including alkali-acid-alkali-acid-alkali.The fluid evolution of"three alkalis and two acids"in five stages of acid-base alternation determines the pore evolution and controls the formation of effective reservoirs of dissolution pore type.The sandstone section near the source rock and in the source rock has the advantage of acid fluid filling,which is more conducive to the formation of dissolution pores,and is the main section of effective reservoir development.The research results have guiding significance for exploration of tight sandstone gas of Xujiahe Formation in northeastern Sichuan.