四川盆地中二叠统沉积相模式及有利储集体分布

近年来四川盆地中二叠统栖霞组和茅口组勘探取得一些突破,显示该区中二叠统巨大的天然气勘探前景。前人对该区中二叠统沉积相和储层等做了大量研究,但对中二叠统栖霞组和茅口组沉积相类型和沉积相模式存在较大分歧,进而制约了有利储集体分布预测研究。文章结合近期一些新钻井和地震资料综合分析基础上,通过岩石学特征、沉积构造和生物化石等相标志分析,认为四川盆地中二叠统栖霞组和茅口组主要发育台地边缘相、开阔台地相和台洼相,其中中二叠统栖霞组早期以碳酸盐岩台地模式为主,栖霞组中晚期和茅口组演变为镶边台地和孤立台凹模式。该区主要发育有台缘滩和台内滩两类主要的储集体,且主要集中在层序高位体系域,台缘滩储集体主要分布在Sq1-HST期雅安-绵竹和剑阁-广元等区带,以及Sq2-HST时期雅安-绵竹-广元区带;台内滩储集体主要分布在Sq1-HST和Sq2-HST期川中高石梯-磨溪区块,以及Sq2-HST时期的威远-自贡区带,Sq2-HST时期高石梯-磨溪区块台内滩储集体受古岩溶和构造热液叠加影响呈条带状展布。四川盆地中二叠统台缘滩和台内滩分布范围较广,具有良好的勘探前景。

Sedimentary facies model and favorable reservoir distribution of the Middle Permian in Sichuan Basin

Some breakthroughs have been made in the exploration of the Middle Permian Qixia and Maokou Formations in the Sichuan Basin in recent years,indicating great prospects for gas explorationin the Middle Permian of this area.Previous studies focused on sedimentary facies and reservoirs of the Middle Permian in this area,but there are many differences in terms of the types and model of sedimentary facies of the Middle Permian Qixia and Maokou Formations.This has restricted the prediction of favorable reservoir distribution.Therefore,we carried out facies marker analysis including petrologic feature,sedimentary structure and biological fossil,based on the comprehensive study of some latest drilling and seismic data.The results show that the major sedimentary facies of the Middle Permian Qixia and Maokou Formations include platform margin,open-platform and intra-platform sag,among which the carbonate platform is dominant in the lower Qixia Formation of the Middle Permian,while rimmed platform and isolated intra-platform sag dominate the middle and upper Qixia Formation as well as in the Maokou Formation.The reservoirs of the study area are mainly marginal-platform and intra-platform shoals,concentrating in highstand system tracts.The marginal-platform shoal reservoirs mainly occur in areas including Ya'an-Mianzhu and Jiange-Guangyuan during the Sq1-HST period,and Ya'an-Mianzhu-Guangyuan area during the Sq2-HST period;the intra-platform shoal reservoirs are mainly distributed in the Gaoshiti-Moxi block in the central Sichuan Basin during the Sq1-HST and Sq2-HST periods,and Weiyuan-Zigong area during the Sq2-HST period.The intra-platform shoal reservoirs in Gaishiti-Moxi block during the Sq2-HST period are distributed in the form of strips due to the joint influences of paleokarst and tectonic hydrothermal fluids.The marginal-platform and intra-platform shoals are widely distributed in the Middle Permian of Sichuan Basin,and have bright prospects for hydrocarbon exploration.