松辽盆地南部乾安油田青山口组含片钠铝石砂岩的成岩作用

Lithification of Dawsonite-Bearing Sandstone in the Qingshankou Formation in the Qian'an Oil Field of the South Songliao Basin

松辽盆地南部乾安油田青山口组发育大量含片钠铝石砂岩。通过偏光显微镜、扫描电镜、茜素红-S染色和X-射线衍射分析等,对含片钠铝石砂岩的骨架碎屑成分、胶结物与自生矿物、成岩共生序列和流体演化等进行了系统研究。结果表明:松辽盆地南部乾安油田含片钠铝石砂岩的粒度为粉砂、微粒—细粒,分选中—好,岩石类型为微粒含片钠铝石长石砂岩、微粒含片钠铝石岩屑长石砂岩。胶结物与自生矿物主要为片钠铝石、铁白云石、方解石、次生加大石英、自生粘土矿物(高岭石及伊利石)。片钠铝石一部分以放射状、束状和板状等产出,另一部分呈凝块状大面积地连片出现,尤为特殊。成岩共生序列依次为方解石-自生高岭石、次生加大石英-伊利石-片钠铝石、铁白云石。CO2注入前形成的自生矿物组合主要为多期方解石组合,高岭石、次生加大石英组合;CO2注入之后形成了片钠铝石和铁白云石组合。流体演化过程为碱性流体环境—酸性流体环境—酸性流体向碱性流体过渡或偏碱性流体环境—碱性流体环境。

The Qingshankou Formation in the Qian＇an oil field of the south Songliao basin contains abundant dawsonite-bearing sandstone. The clastic composition, cements, authigenic minerals, diagenetic paragenesis succession and fluid evolution are investigated through polarizer microscope, scanning electron microscope, alizarin red staining, X-ray diffraction etc. The results shows that the sandstone is fine-grained and micro-grained, poorly to moderately sorted silt dawsonite-bearing arkoses and silty dawsonite-bearing lithic arkoses. The dominant cements and authigenic minerals include dawsonite, ankerite, calcite, secondary quartz oergrowths and authigenic clay mineral （kaolinite and illite ）. Part of dawsonite occurs as radial, bundle and plate, and some are very special as large massive condensates. The paragenetic sequence are in the order of calcite - kaolinite, secondary quartz overgrowths - illite -dawsonite and ankerite. The authigenic minerals formed before CO2 charging include multi-stages of calcite assemblages, kaolinite and secondary quartz overgrowths assemblages. While the main cements formed after CO2 charging are dawsonite and ankerite. Fluid evolution are in a sequence of alkaline - acidic - the transition from acid to alkaline fluids and/or transition from meta alkalescence - alkaline fluids.