Research On Reservoir Characteristics And Formation Mechanism Of Xiaoheba Formation In Southeastern Sichuan Basin

Southeast Sichuan area is the key area for oil and gas exploration,the petroleum exploration potential of marine clastic rocks has been strongly confirmed recently.The Silurian Xiaoheba Formation in this area is an important sandstone reservoir,the study of reservoir characteristics and genesis has important guiding significance for the deployment of the next step.Based on this,on the basis of geology,sedimentology and petrology,thesis is is supported by the measured data of the field profile,the method is physical testing,thin section identification,casting thin section identification and SEM.The reservoir characteristics,type of diagenesis and evolution sequence of the Xiaoheba Formation in the study area are analyzed in depth.The formation mechanism of reservoirs in the Xiaoheba Formation is comprehensively analyzed from the angle of sedimentation and diagenesis.Combined with macroscopic outcrop,the reservoir rocks were classified from microcosmic perspective.By testing and analyzing the data,the related characteristics of pore structure are revealed,and the types of reservoir space are divided.The pore throat of the reservoir in the Xiaoheba group is small,low to ultra low porosity is the primary feature of its storage space.Microscopic observation shows that feldspar quartz sandstone and lithic quartz sandstone account for a large proportion,in addition,the clay content in the interstitial material is significantly higher than that of other cements(siliceous,carbonate,etc.).Secondary pores are the main components in the reservoir pores,and the micro-sized intergranular dissolution pores are occupied by a large proportion.In general,there is a positive correlation between porosity and permeability.The Xiaoheba group mainly developed mechanical compaction,cementation and dissolution diagenesis.Compaction,carbonate cementation,and siliceous cementation are destructive diagenesis.A large amount of dissolution pores and intergranular pores are developed inside the clay matrix,the retentive diagenesis is the main contribution to the reservoir space.The dissolution of carbonate cements,feldspar and some cuttings has transformed the reservoir space,resulting in a large number of secondary dissolution pores.,this major enhanced diagenesis further improves the reservoir property.The development of relatively high-quality reservoirs in Xiaoheba Formation is controlled by several factors: First of all,sedimentary environment is the most important controlling factor,which determines rock type and distribution characteristics of sand bodies.The high quality reservoirs in this area are mostly developed in the underwater distributary channel and the transitional zone between the sand bar and the distributary bay.Secondly,diagenesis is the most critical controlling factor,which determines the degree of reservoir secondary porosity alteration.In particular,dissolution plays a positive role in secondary pore transformation and reservoir physical property improvement.In addition,the overall mudstone content of the sandstone in the study area is high,and a large number of intergranular micropores and Intercrystalline micropores are developed in the clays,which provide an important reservoir space for relatively high quality reservoir.