四川盆地西部三叠系—侏罗系地层水化学特征与油气保存关系

Chemical Characteristics of Triassic-Jurassic Formation Water and Relationship of it to Hydrocarbon Preservation in the West of Sichuan Basin

对四川盆地西部40余口钻井的三叠系—侏罗系地层水化学特征的分析表明:地层水的变质程度在纵向上随着地层埋深而增大;区域上从盆地边缘龙门山区向盆地坳陷中心,矿化度逐渐变高,水型由开启环境的Na HCO3型过渡到封闭环境的Ca Cl2型。海相中三叠统雷口坡组的水动力环境以多样性为特征,但整体保存条件良好;陆相侏罗系上部,地层水的水动力交替较强,保存条件偏差,中下部整体进入区域性的"保存区";陆相上三叠统须家河组总体保存条件良好,大多数位于"保存区"。地层水化学性质与油气保存的关系分析表明,油气保存的"有利区"主要位于川西坳陷带,"较有利区"位于龙门山前锋推覆带,"不利区"位于龙门山前山推覆带。

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 NaHCO_3 （indicating an open environment） to CaCl_2 （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.