拉张槽对四川盆地海相油气分布的控制作用

Control of intracratonic sags on the hydrocarbon accumulations in the marine strata across the Sichuan Basin,China

四川盆地现今为挤压性的沉积盆地,地表所见构造也均为压性构造;但四川盆地沉积盖层在形成、演化过程中发生了拉张运动(地裂运动)并形成了张性构造(拉张槽等)。现今盆地内已发现的主要拉张槽有开江-梁平海槽(拉张槽)和绵阳-长宁拉张槽。开江-梁平海槽(拉张槽)是四川盆地内深埋地下的二叠纪-三叠纪之间的一个北西-南东向展布的深水碳酸盐岩沉积区,是在峨眉地裂运动理论启示下因生物礁油气藏勘探而发现的。绵阳-长宁拉张槽是四川盆地内发育于早寒武世的一个南北向的下寒武统巨厚碎屑岩沉积(降)区,是在兴凯地裂运动理论指导下通过构造-沉积综合研究而发现的。2个拉张槽的发现和特征研究均经历了漫长过程。拉张槽的形成演化不仅控制了优质泥质烃源岩和优质碳酸盐岩储集岩的发育,而且为优质泥质烃源岩-优质碳酸盐岩储集岩组合的形成和油气成藏效应及规模的提高创造了条件,致使环拉张槽周缘地区是克拉通盆地内油气分布最丰富的地区。

As one of the major oil and gas basins in China, the Sichuan Basin is characterized by compressive geomorphic and tectonic basin dominated by contracted structures. However, the sedimentary cover across the basin underwent extensional tectonic movement （taphrogenesis）, and formed extensional structures, such as Kaijiang-Liangping and Mianyang-Changning intracratonic sags etc.. The Kaijiang-Liangping sag occurred during late Permian to early Triassic, characterized by NW-SE striking deposits of deep-water carbonate facies. The discovery of Kaijiang-Liangping sag is based on the theory of the Emeishan taphrogenesis and the organic reefs exploration in the basin. The Mianyang-Changning sag occurred during early Cambrian period, dominated with N-S striking deposits of abundant Lower Cambrian clastic rocks. The discovery of the early Cambrian intracratonic sag is based on the theory of the Xinkai taphrogenesis and the sedimentary-tectonic comprehensive study. The intracratonic sags have significant influence on the oil and gas occurrences along the margin of the sags in the interior of the Sichuan basin, chiefly through its influence on the distribution of high-quality carbonate reservoir rocks and mudstone source-rocks. In particular, the intracratonic sags provide favorable conditions for the formation of assemblage of high-quality carbonate reservoir rock and mudstone source-rock and raise the efficiency and scale of the hydrocarbon accumulations. Therefore, the margin areas of the intracratonic sags are the most favorable areas of the hydrocarbon accumulations in the marine strata of the Sichuan Basin.