Genetic Mechanism Of Siliclastic Reservoirs Beneath The Unconformity In Changdi Area At Zhanhua Depression

Changdi area is an important oil and gas exploration potential.It experienced a complex multistage tectonic movement since the Cretaceous.Under this background,the process of reservoir reconstruction is complex,which shows strong heterogeneity in space.It often has the characteristics of fracture development and distribution are not clear.It is also difficult to identify effective reservoir and predict the rules of reservoir development.This paper takes the Mesozoic and Cenozoic unconformity zone of clastic reservoir in Changdi area of Zhanhua depression as the research object.By Comprehensive utilization of seismic data,logging data,core data,thin section data,fluid inclusion analysis and carbon oxygen isotope analysis data and methods,the fine study is made on unconformity zone of clastic rock reservoirs sedimentary characteristics,reservoir characteristics and diagenesis of characteristics and a geological development model for continental clastic rocks under unconformity is established.The system study about transformation of the physical properties of the reservoir has been carried out in the aspects of the unconformity type,the petrological mechanism,and the diagenesis.Research shows that the formation of Changdi area stratigraphic super peeling frequently,identified two regional unconformity are the parallel unconformity between the first member of Shahejie Formation and the third member of Shahejie Formation(Es1/Es3),and the angle unconformity between the third member of Shahejie Formation and Mesozoic(Es3/K).The former is mainly composed of siltstone and gravelly sandstone,followed by fine sandstone and coarse sandstone.The latter is mainly composed of coarse sandstone,secondary to medium sandstone,gravel bearing sandstone,fine sandstone and siltstone.The rock types are mainly lithic feldspar sandstone and long lithic lithic sandstone.The sedimentary facies are delta facies.Based on the unconformity sedimentary type and distribution of reservoir on the establishment of geological development model under the control of different types of unconformities in the Mesozoic and Cenozoic Changdi area of Zhanhua depression.Diagenesis is complex in the study area,such as compaction,cementation,filling and other destructive diagenesis,as well as atmospheric water leaching and formation fluid dissolution.There are various types of reservoir space in the reservoir,which mainly develop secondary pores,such as intergranular dissolution pores,intragranular dissolving holes and mould holes,as well as some cracks.The reservoir calcite cementation and feldspar particles dissolve strongly under the control of parallel unconformity,and the pore types are mainly intragranular dissolving holes,intergranular dissolving holes and mold holes.The weathering cracks in the high part of the structure are more developed.Under the control of angle unconformity,the carbonate cements in reservoirs are most strongly corroded,and feldspar particles dissolving is relatively weak.The pores are mostly intergranular dissolved pores and the fractures are less developed.The reservoirs under the control of the parallel unconformity experienced compaction ? quartz overgrowth ? carbonate cementation,(early siderite / calcite cementation)/ matrix recrystallization / Quartz particles and their increased side dissolution?the dissolution of feldspar/ authigenic kaolinite ? carbonate cementing / pyrite cementation diagenetic environment evolution.The reservoir under the control of the angle unconformity the mainly experienced compaction ? quartz overgrowth ? crystal calcite cementation / early pyrite cementation ? carbonate cementation dissolution / feldspar lithic dissolution / kaolinite cementation ? granular calcite cementation ? pyrite cementation diagenetic evolution.Based on the evolution of diagenetic environment and sequence of diagenesis in the unconformity zone,the model of parallel unconformity and angle unconformity reservoir transformation is established.The favorable reservoirs are mainly distributed in the Coarse lithology which is easy to be modified by atmospheric fresh water and are far away from the unconformity of a certain depth.The quality of the reservoir is obviously zonal with the increase of distance from the unconformity.