东海陆架盆地丽水西凹古新统砂岩储层成岩作用及成岩演化

Diagenesis and diagenetic evolution of Paleocene sandstone seservoirs in Lishui West Sag,East China Sea shelf basin

东海陆架盆地丽水西凹古新统发育多种类型储层,通过4口典型井的岩心薄片鉴定、物性测试、碳氧同位素测试等手段,对丽水西凹古新统砂岩储层成岩作用、成岩演化和孔隙演化进行了研究。结果表明:(1)丽水西凹古新统砂岩储层以浅海-三角洲相中细粒岩屑砂岩为主,成分成熟度与结构成熟度较低,矿物组成以岩屑为主,石英、长石次之;(2)砂岩经历了机械压实、碳酸盐岩与黏土矿物胶结、长石溶蚀等成岩作用,灵峰组下段砂岩储层碳酸盐胶结物形成于淡水成岩环境,明月峰组及灵峰组上段砂岩储层碳酸盐胶结物形成于混合水成岩环境,恢复的成岩温度介于76~141℃之间;(3)古新统明月峰组下段及灵峰组上段砂岩处于早成岩B期,灵峰组下段及月桂峰组砂岩处于中成岩A期;(4)砂岩储层经历了压实减孔(-18.3%)、早期胶结减孔(-3.9%)、溶蚀增孔(+4.8%)、晚期胶结减孔(-6.7%)的孔隙演化过程,各套砂岩储层经历了差异化的成岩演化过程,分别发育以机械压实作用、碳酸盐岩与黏土矿物胶结作用、不稳定碎屑溶蚀作用为主要特征的成岩演化类型。明月峰组下段及灵峰组上段砂岩发育优质储层,灵峰组下段和月桂峰组砂岩以更具勘探难度的非常规致密砂岩储层为主,研究成果对深入认识丽水西凹古新统砂岩储层,指导油气勘探具有重要意义。

Many types of reservoirs are developed in Paleocene in Lishui West Sag,East China Sea shelf basin.Diagenesis,diagenetic evolution and pore evolution of Paleocene sandstone reservoirs in Lishui West Sag are studied by means of core slice identification,physical property testing,and carbon and oxygen isotope testing of four typical wells.The results show that:(1)the Paleocene sandstone reservoirs in Lishui West Sag are mainly composed of shallow sea delta facies medium and fine-grained lithic sandstone,with low compositional maturity and structural maturity.The mineral composition is mainly composed of lithic,followed by quartz and feldspar.(2)Sandstone experienced diagenesis such as mechanical compaction,cementation between carbonate rock and clay minerals,feldspar dissolution,etc.The carbonate cement of sandstone reservoir in the lower section of the Lingfeng Formation was formed in a freshwater diagenetic environment,while the carbonate cement of sandstone reservoir in the Mingyuefeng Formation and the upper section of the Lingfeng Formation was formed in a mixed water diagenetic environment,and the restored diagenetic temperature was between 76~141℃.(3)The sandstones in the lower member of Mingyuefeng Formation and the upper member of Lingfeng Formation of Paleocene are in early diagenetic stage B,and the sandstones in the lower member of Lingfeng Formation and Yueguifeng Formation are in middle diagenetic stage A.(4)Sandstone reservoirs have experienced pore evolution processes including compaction porosity reduction(-18.3%),early cementation porosity reduction(-3.9%),dissolution porosity increase(+4.8%)and late cementation porosity reduction(-6.7%).Each set of sandstone reservoirs has experienced differential diagenetic evolution processes,and diagenetic evolution types characterized by mechanical compaction,cementation between carbonate rock and clay minerals,and unstable clastic dissolution are developed respectively.Conventional high-quality reservoirs are developed in the lower member of Mingyuefeng Formation and the upper member of Lingfeng Formation.The sandstones of the lower member of Lingfeng Formation and Yueguifeng Formation are mainly exploring targets of unconventional,tight sandstone reservoirs,which are more difficult to explore.The research results are of great significance for in-depth understanding of Paleocene sandstone reservoirs in Lishui West Sag and guiding oil and gas exploration.