公山庙地区沙一段低渗砂岩储层成岩作用及其对储层的影响

Diagenesis of the low-permeability sandstone reservoir of the first member of Shahejie formation in Gongshanmiao area and its influence on the reservoir property

公山庙地区沙一段储层属于特低渗透砂岩储层,但储层低渗的成因仍不明确.通过对该区沙一段储层成岩作用的系统研究,认为主要的成岩作用类型有压实作用、胶结作用、交代作用和溶蚀作用等.总体上经历了早成岩阶段A期—中成岩阶段B期的主要成岩阶段,现今主要处于中成岩阶段B期,呈现"颗粒表面的绿泥石膜出现→钙十字沸石或方沸石胶结、充填→石英次生加大明显和自生石英出现→铁方解石胶结、交代常见及溶蚀作用较明显"的典型成岩序列.主要识别出(铁)方解石胶结相、沸石胶结相、绿泥石-方解石胶结相和岩屑-长石溶蚀相等优势成岩相.从成岩角度分析该区沙一段储层低渗的成因,定量研究认为持续的压实作用和强烈的胶结作用是造成研究区沙一段储层低渗的关键成岩因素,第三期溶蚀作用是改善储层储集性的主要成岩因素,通常中砂岩比细砂岩表现更明显.

Through the systematic study on the diagenesis of the studied reservoir,it is held that compaction,cementation,metasomasis and dissolution are its main diagenesis types,and that 'A phase of early diagenesis stage to B phase of middle diagenetic stage' is its main diagenesis stage,and while B phase of middle diagenetsis stage is present diagenesis stage.The diagenesis series is 'emergence of chlorite membrane on the surface of grain' to 'cementation and filling action of phyllipsite or analcidite' to 'evident overgrowth of quartz and emergence of authigenic quartz' to 'frequent cementation,evident metasomasis and fairly obvious dissolution of ferrocalcite'.Four dominant diagenetic facies (calcite or ferrocalcite cementation facies,zeolite cementation facies,chlorite-calcite cementation facies,rock debris-feldspar resolution facies) can be recognized in the reservoir.According to quantitative study on the diageneses of the reservoir,it is held that continuous compaction and intensive cementation are the main diagenetic factors of forming the low permeability reservoir.The dissolution of the third stage is main diagenetic factor of improving the property of the extra-low permeability reservoir,which appears more obvious in medium-size sandstone than in fine-size sandstone.