Reservoir Characteristics And Factors Controlling The Physical Properties Of The Calcarenaceous Sandstone In The Third Member Of Xujiahe Formation In The Yuanba Area,Northeastern Sichuan Basin

Based on the core data,common thin sections,cast thin sections,cathode luminescent thin sections,scanning electron photomicrograph,X-ray diffraction data,mercury intrusion data and physical property data,a systematic study is conducted on petrologic characteristics,diagenesis characteristics and physical characteristics of the calcarenaceous sandstone in the 3rd Member of the Xujiahe Formation in Yuanba area,northeastern Sichuan.Then the main controlling factors of physical properties were analyzed.The study suggests that the rock type of the 3rd Member of Xujiahe Formation in Yuanba area is calcarenaceous sandstone,which is characterized by high calciums,high calcium cements and low materials.The diagenetic sequence is strong cementation and moderately weak compaction in the early stage,weak dissolution and strong recrystallization in the middle stage.There are few primary pores in calcareous sandstone,and three secondary pore types: recrystallized pores,fractured pores and dissolved pores.The main pores are recrystallized(intercrystal micropores)and fractured pores.The physical properties of calcareous sandstone are generally poor,with an average porosity of 1.95% and an average permeability of 3.34 m D,which is tight sandstone reservoirs.The dissolved pores only improve the local reservoir's physical properties,but the influence on the entire area is small.On the whole,calcareous sandstone is a fracturemicroporous reservoir.Finally,the main controlling factors of the physical properties in calcareous sandstone reservoirs are summarized: the special rock types and sedimentary microfacies are the basis of high-quality reservoirs;dissolution forms some local “sweet spots” in the reservoirs;recrystallization provides a large number of intercrystal micropores that improve the porosity of reservoirs;fractures communicate pores and further improve reservoir quality.In summary,the areas with high content of calcareous and calcareous cements(such as distributary channels)are potential high-quality reservoir and are the key areas for exploration and development.