四川盆地大气田分布、主控因素与勘探方向

Distribution rules, main controlling factors and exploration directions of giant gas fields in the Sichuan Basin

近10年来,四川盆地天然气勘探取得了多项重大进展,发现了安岳等多个大气田,随着资料的增加和勘探工作的深入,地质理论上有了新认识,有必要进一步分析大气田的分布特征和主控因素,提出新的大气田勘探方向。为此,从统计该盆地已发现的20个大气田的地质参数出发,对大气田的分布、形成的地质条件和发育的主控因素等进行了分析,提出了下一步大气田勘探的方向。研究结果表明:①四川盆地的不同构造区域都有大气田发育,其中以川中低缓构造带为最多,纵向上发育在7个层系,其中以上二叠统长兴组下三叠统飞仙关组礁滩大气田为最多;②形成大气田的烃源岩有4套,其中以烃源岩形成的须家河组大气田为最多;③大气田的储层主要为孔隙型碳酸盐岩和致密砂岩,以构造岩性大气田和常压大气田为最多;④海相大气田的发育主要受克拉通内裂陷和古隆起的控制,克拉通内裂陷主要从烃源岩生烃中心、台缘高能相带和侧向封堵成藏等3个方面加以控制,古隆起主要从台内高能相带、岩溶白云岩储层和长期油气聚集等3方面加以控制,而前陆盆地结构则从构造背景、源储组合、圈闭类型和裂缝分布等4个方面控制了陆相大气田的发育。结论认为,四川盆地下一步大气田勘探方向为5个领域共计12个有利区。

Over the past decade, great progresses have been made in natural gas exploration in the Sichuan Basin, where several large gas fields (such as Anyue) have been discovered. With the increase of data and the deepening of exploration, new knowledges have been gained in geological theory, thus it is necessary to further analyze the distribution characteristics and main controlling factors of large gas fields, thus to put forward new exploration directions for large gas fields. Therefore, based on the statistics on the geological parameters of 20 large gas fields discovered in this basin, the distribution rules, formation conditions and main controlling factors of large gas fields were analyzed, and the follow-up exploration directions were proposed. The following results were achieved.(1) Large gas fields are de- veloped in different tectonic regions in the Sichuan Basin, mostly in the low and gentle tectonic belts in the central Sichuan Basin. Large gas fields are developed in seven series of strata in longitudinal stratigraphic sequences, which are dominated by the reef-shoal large gas fields formed in the Upper Permian Changxing Lower Triassic Feixianguan Fms.(2) There are four sets of source rocks contributing to the formation of large gas fields, mostly from the assemblage of Xujiahe Fm source rocks.(3) Reservoirs in the large gas fields are dominated by porous carbonates and tight sandstones;large gas fields are mostly structural lithological ones and normal pressure ones.(4) The development of marine large gas fields are mainly controlled by intracratonic rifts and paleo-uplifts. The controlling effect of intracratonic rifts is mainly from three aspects, namely the hydrocarbon generation center of source rocks, high-energy facies belts on the platform edges, and lateral sealing for hydrocarbon accumulation. The controlling effect of the paleo-uplifts mainly acts from another three aspects: intra-platform high-energy facies belts, karstic dolomite reservoirs and long-term hydrocarbon accumulation. The structures of foreland basins controlled the development of the continental large gas fields from four aspects: tectonic setting, source and reservoir assemblage, trap type and fracture distribution. In conclusion, a total of 5 domains with 14 favorable zones are the follow-up exploration directions of large gas fields in the Sichuan Basin.