川东下三叠统嘉陵江组层序—岩相古地理特征

Sequence-lithofacies Paleogeographic Characteristics of Lower Triassic Jialingjiang Formation in Eastern Sichuan Basin

通过沉积相和高频层序地层分析,确定川东地区下三叠统嘉陵江组主要为蒸发台地和局限台地沉积环境,可划分出SQ1、SQ2二个三级层序及SSQ1-SSQ5五个四级层序,经历了从局限台地→蒸发台地→局限台地→蒸发台地的沉积演化过程,主力储、产层发育于SSQ1和SSQ2层序,此五个四级层序主要由TST和HST两个体系域组成。以四级层序为编图单元,编制了SSQ1-SSQ5各四级层序的岩相古地理图和探讨了有利储集相带展布规律,认为SSQ1和SSQ2二个四级层序叠置发育的局限台地—台内浅滩为最有利的储层发育相带,应成为今后的勘探重点。

Studies of the sedimentary facies and sequence stratigraphy have indicated that the main depositional environments of the Lower Triassic Jialingjiang Formation in the eastern Sichuan Basin were a restricted platforms and evaporite platforms.Two third-order sequences(SQ1,SQ2)and five fourth-order sequences(SSQ1SSQ5)were recognized.Sediments in the Jialingjiang strata evolved from a restricted platform to an evaporite platform,then to restricted platform again,and finally to an evaporite platform.The main hydrocarbon reservoirs and producing layers appear in the SSQ1-SSQ2 sequence.Sequences SSQ1SSQ5 are further subdivided into transgressive systems tracts(TST)and highstand systems tracts(HST).Taking these sequences as mapping units,lithofacies paleogeographic maps were prepared for each of the fourth-order tracts.Evidence from the study of the distribution of favorable reservoirs indicates that the restricted platform-to-platform shoal in the SSQ1 and SSQ2 sequences are key areas for future exploration.