Origin and Distribution of Favorable Reservoir in Upper Triassic Feixianguan Formation of Northeastern Sichuan Basin, China

Yang, Xiaoping¹, Wenzhi Zhao², Hong Cao³ (1) Geology Department of RIPED, Petrochina, Beijing, China (2) PetroChina, Beijing, China (3) Geophysics Department of RIPED, Petrochina, Beijing, China

In northeastern Sichuan basin, a great achievement of petroleum exploration is to find a giant gas field in upper Triassic Feixianguan formation in past few years, which includes Luojiazhai, Dukouhe, Tieshanpo pools. Moreover, in early 2005 it is found another giant gas pool: Puguang gas pool with an estimated reserve exceeding 3500×108m3. Therefore it is quite significant to Study on origin and distribution of favorable reservoir for them.

In the upper Triassic Feixianguan formation of northeastern Sichuan Basin, it is mainly developed three types of sedimentary facie, which are lagoon-tidal flat, oolitic bank of platform margin and slope. The favorable reservoir mainly distributes in oolitic bank of platform margin and consists of oolitic dolomite, residual oolitic dolomite and sugary grained residual oolitic mid-macro crystalline dolomite. With studying on petrography, cathodoluminescence, scanning electron microscopy, X-ray diffractometry, minor element, and liquid inclusion for the reservoir, it is found that mixing dolomitization and dissolution are two key factors to form effective reservoir. When the reservoir experienced post-sediment diageneses, it is happened four periods of dissolution which are meteoric water dissolution, organic acid water dissolution during shallow-buried, sulfuric acid water dissolution during deep-buried period and meteoric water dissolution during the basin rising up. Moreover, it is also found that the effective reservoir vertically interbeds with sparry oolitic limestone and literally distributes in oolitic banks nearby lagoon-tidal flat.