Characteristics Of Reservior In The Second And Fourth Members Of Xujiahe Formation In The Upper Triassic Of Sichuan Central Area

Depending on researches and evaluation of sedimentary facies, petrologic features, diagenesis and factors influencing reservoir of the Xu2 and Xu4 members of Xujiahe formation, the dissertation has showed the distribution features of the reservoirs in plane and predicted the favorable prospect area of the reservoirs.The main depositional system of Xu2 and Xu4 members are lake facies and delta facies, which belong to delta front slope sub-facies. They are distributed mainly in the west and the south part of the studying area, with the development of many micro-facies such as meare bar, underwater distributary channel, mouth bar and faraway sand bar. The lithology of the reservoir is mainly fine-medium lithic feldspathic sandstone and feldspathic detritus sandstone, with lower compositional maturity and preferable textural maturity. The reservoir of Xu2 and Xu4 members is typical hydrocarbon reservoir with low porosity and low permeability. Its accumulative vacuity are pores and fractures. The pores are mainly intergranular pore, intragranular pore and matrix-pore. The type of reservoir mainly belongs to fractured, in which the pore is regarded as the mainly space for the accumulation of oil and gas. The fractures in this type of reservoir holds an important position, which does not only improve the permeability condition greatly, and also make the oil-gas re-accumulation. The diagenesis, which influences the pore development of Xu2 and Xu4 members, is mainly compaction, cementation and dissolution. Among these factors the compaction is the main factor for reducing porosity of the sandstone. However, the dissolution increases the porosity. Combining with the actual production and the porosity of log interpretation, the sand reservoir can be divided into three types:ⅠandⅡ(effective reservoirs) andⅢ(bad reservoir).According to the sedimentary facies zones, sand-body distribution rule and distribution features of reservoir etc, it can be concluded that the favorable prospect area of I reservoir in Xu2 member includes Bajiaochang-jinhua, QiulinPenglai—Suinan, Moxio-Gaokel well and Yingshan area. The favorable prospect area of I reservoir in Xu4 member includes Tongnan-Gaokel well, Bajiao changJinhua-Qiulin. The favorable prospect area ofⅡreservoir includes Siunan-Moxi, Penglai and Yingshan area.