Diagenetic characteristics and evolution of tight quartz sandstones of Shangshihezi Formation in Gaoqing area

Key words:  Gaoqing area  Shangshihezi Formation  tight quartz sandstone  diagenesis  diagenetic evolution

Abstract:

Gaoqing area is located in Dongying sag of Jiyang Depression. The tight quartz sandstone of Permian Shanghihezi Formation in Gaoqing area is mainly quartz sandstone. On the basis of thin sections, casting thin sections, cathodoluminescence, scanning electron microscopy(SEM), and fluid inclusion observation, burial history and hydrocarbon accumulation history are used to study the diagenesis and diagenetic evolution of diagenetic sequences. The results showed that tight quartz sandstone in the Gaoqing area has experienced a complex set of diagenesis, and compaction, cementation and dissolution are the main diagenesis types, including strong compaction, multi-phase quartz overgrowth cementation, a variety of multiphase kaolinite cementation, illite cementation and calcite cementation which are main factors lead to quartz sandstone tightness. The burial history includes an early deep burial stage, a middle uplift stage, and a late deep burial stage. The quartz sandstone in the B sub-stage of mesogenetic diagenesis has experienced the following evolution sequence:early stage compaction→feldspar dissolution; quartz overgrowth cementation; kaolinite cementation→calcite cementation; quartz dissolution; the slip layer cementation→carbonate-cement dissolution; calcite cement dissolution; quartz overgrowth cementation and microfracture. There have been two hydrocarbon filling events happened in this area from the stage of Dongying Formation, leding to a series of diagenetic changes in the organic acid diagenetic environment.