四川盆地东北部中二叠统层序地层特征

Sequence Stratigraphy of the Middle Permian strata in northeastern Sichuan Basin

关键词:  四川盆地  中二叠统  层序地层  储层

Key words:  Sichuan Basin  Middle Permian  sequence stratigraphy  reservoirs

摘要:

本文以野外露头观察及录井、测井、地震、古生物等资料为基础,通过岩石地层、测井地层及生物地层等的综合分析,在四川盆地东北部中二叠统地层中识别出4种类型的层序界面:隆升侵蚀不整合面、暴露层序不整合面、海侵上超不整合面及岩性岩相转换面。划分了3个三级层序:SQ1对应梁山组和栖霞组,时限约7Ma;SQ2对应茅口组一段,时限约3Ma;SQ3对应茅口组二段-三段,时限约5Ma。三级层序的平均时限约5Ma。同时,分析了层序对储层的控制作用,其主要体现在两个方面:层序控制了沉积相,影响了储层原生孔隙的发育;碳酸盐岩的发育受三级层序海平面升降控制,优质储层明显受控于海退半旋回。

Abstract:

Four sequence boundaries in the Middle Permian strata in northeastern Sichuan Basin are identified:uplift erosion unconformity, subaerial sequence unconformity, transgressive (coastal) onlap unconformity and lithologic-lithofacies unconformity on the basis of outcrops, well logs, seismic and palaeontological data. Three third-order sequences encompass SQ1 corresponding to the Liangshan and Qixia Formations with a time duration of ca. 7 Ma; SQ2 corresponding to the first member of the Maokou Formation with a time duration of ca. 3 Ma, and SQ3 corresponding to the second and third members of the Maokou Formation with a time duration of ca. 5 Ma. The controlling factors include:(1) the controls of the sequences on sedimentary facies, which exert an important influence on the development of primary porosity in the reservoirs, and (2) the controls of carbonate rocks development by the eustatic fluctuations in the third-order sequences. The excellent reservoirs are apparently constrained by the transgressive semi-cycles.