| According to the analysis of chemical properties of Triassic-Jurassic formation water samples from more than 40 wells in the west of Sichuan Basin, it is shown that the metamorphic grade of formation water figures a increasing tend in longitudinal with increasing depth and the mineralization degree gets gradually high in regional from the basin margin (Longmenshan Thrust) into the basin center (Chuanxi Depression), and meanwhile the water types take a change from NaHCO3 (indicating an open environment) to CaCl2 (an enclosed environment). The preservation condition is commonly good (closed) in marine Middle Triassic Leikoupo Formation although the hydrodynamic environment are various in it. It is poor in the upper part of continental Jurassic formation because of frequent hydrodynamic alternation but it is good in the middle and lower parts of the Jurassic formation. The preservation condition is generally good in continental Upper Triassic Xujiahe Formation. It is suggested that the "favorable zone" for hydrocarbon preservation mainly is in Chuanxi Depression, the "secondary favorable zone" is in the Longmenshan Forward Thrust, and the "unfavorable zone" is in the Longmenshan Front Thrust. |
