鄂西宜昌地区页岩气成藏地质特征

通过分析鄂西宜昌地区页岩气的地质特征,探讨了页岩气成藏的控制因素。结合黄陵隆起的构造演化特征将鄂西宜昌地区的演化划分为刚性基底形成、盖层沉积、隆升改造3个阶段。鄂西宜昌地区受构造演化的控制,其震旦系陡山沱组、寒武系牛蹄塘组和上奥陶统五峰组-下志留统龙马溪组3套页岩在沉积期主体处于相对深水的沉积环境,与四川盆地内部陡山沱组、筇竹寺组和龙马溪组3套页岩具有相同的沉积背景和组成特征,具备形成页岩气的物质条件。基于已发现气藏的解剖,从保存条件和热演化过程2个方面分析了黄陵隆起在鄂西宜昌地区3套页岩气成藏过程中的关键控制作用。鄂西宜昌地区古老刚性隐伏隆升基底的形成时间早、分布广、抗挤压能力强、隆升时间晚且持续时间长,其上覆寒武系、震旦系和上奥陶统-下志留统古老页岩层系的深埋时间短、热演化程度相对较低、构造稳定、保存条件好,为页岩气的成藏提供了良好的地质条件。

Geological characteristics of shale gas reservoir in Yichang area,western Hubei

Through analyzing the geological characteristics of shale gas, this paper discussed the controlling factors of shale gas accumulation in Yichang area of western Hubei. Based on the tectonic evolution characteristics of Huangling uplift, the evolution of Yichang area could be divided into three stages:formation of rigid basement, sedimentation of overlying strata and transformation by uplifting. Under the control of tectonic evolution, three sets of shale, i.e., Sinian Doushantuo Formation, Cambrian Niutitang Formation and Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Yichang area, mainly developed in relatively deep water sedimentary environment and had the same depositional setting and composition characteristics with Doushantuo Formation, Qiongzhusi Formation and Longmaxi Formation in Sichuan Basin and material conditions for shale gas formation. Further, based on analyzing the discovered shale gas reservoir, this paper investigated the key control role of Huangling uplift in shale gas accumulation in Yichang area of western Hubei from the aspects of preservation conditions and thermal evolution process. In Yichang area of western Hubei, the ancient blind rigid basement had the characteristics of early formation, wide distribution, strong compression resistance, late and long-duration uplifting, and the ancient shale in the overlying Cambrian, Sinian and Upper Ordovician-Lower Silurian strata had short buried time, relatively low degree of thermal evolution, stable tectonic structure and good preservation condition, which provided favorable geological conditions for shale gas accumulation.