四川复合型前陆盆地单井埋藏史分析

Burial history analysis of the Sichuan Foreland Basin based on single well data

地层埋藏史研究是分析地热史、生烃史、排烃史和油气运聚史的基础,是盆地构造分析的有效方法。通过对四川复合型前陆盆地地层接触关系、构造运动期次、钻井取得的地层厚度和岩性资料的分析,利用地层分段回剥技术,编制了33口探井单井埋藏史图件。研究结果表明:①埋藏史曲线可划分出5种沉降类型,不同类型沉降曲线代表了不同的地质意义;②前陆盆地靠造山带一侧的沉降较靠稳定陆块一侧的沉降大,但也有例外;③从沉降量来看,自晚三叠世以来,川西中部都江堰附近的沉降量达9 500m,川北通江附近则为7 200m,分析认为这是造山带载荷与沉积载荷不同所致;④四川复合型前陆盆地的沉降机制应是挠曲负载。

The strata burial history is the basis of studies on geothermal history as well as the history of hydrocarbon generation,expulsion,migration,and accumulation.It is also an effective method of basin structural analysis.Based on the analysis of stratigraphic contacts,phases of tectonic activities,and thickness and lithology data from drilling in the Sichuan Foreland Basin,the stepwise stratigraphic back-stripping technique is used to map the strata burial history from the data of 33exploratory wells.The following conclusions are drawn.The burial history curve can be divided into 5subsidence curve types,each with unique geologic significance.The subsidence in the orogenic-belt-side is stronger than that in the stable-massif-side of the foreland basin.However,there is also an exception sometimes.Subsidence amplitude since the Late Triassic is 9500mnear Dujiangyan in the central West Sichuan Basin,while it is 7200mnear Tongjiang in North Sichuan Basin.This phenomenon is believed to be caused by the differences between orogenic belt load and sediment load.The subsidence mechanism of this foreland basin is flexural load.This study is of great significance to further investigation into the Sichuan Foreland Basin.