川东冯家湾构造石炭系的沉积特征及有利储集微相

Sedimentary Characteristics and Favorable Reservoir Microfacies of Carboniferous in the Fengjiawan Structure of Eastern Sichuan Basin

川东地区石炭纪由于受到海西早期强烈构造隆升和侵蚀作用影响,仅残存不完整的上石炭统黄龙组,但经过强烈的白云石化作用和古岩溶作用下形成了川东地区主要的天然气产层。本文以川东地区冯家湾构造石炭系为研究对象,基于系统的岩心观察描述、薄片鉴定和物性分析,以及最新的钻井资料,在精细小层划分和对比的基础上,对黄龙组沉积微相和有利储集微相进行了详细研究。研究区石炭系黄龙组残存黄龙组一段和二段,通过旋回对比原则,将黄龙组二段进一步细分为三个亚段,区内地层残存厚度变化不大。通过岩相、古生物等沉积相识别标志,确定该区黄龙组主要发育碳酸盐潮坪相,细分为潮上坪、潮间坪和潮下坪亚相及若干微相,并建立了碳酸盐潮坪沉积模式。其中,黄龙组一段主要处于潮上坪沉积环境,黄龙组二段主要发育潮间–潮下带旋回性沉积环境。结合物性分析资料,确定研究区有利储集微相主要为潮间坪的砂屑滩和藻砂坪微相。

Due to the strong tectonic uplift and erosion in the early Hercynian period, only the incomplete Upper Carboniferous Huanglong Formation remained in the Carboniferous Period of Eastern Si-chuan, but the main natural gas producing layers in Eastern Sichuan were formed under the strong dolomitization and paleokarst action. Taking the Carboniferous system of Fengjiawan structure in eastern Sichuan as the research object, based on systematic core observation and description, thin section identification and physical analysis, as well as the latest drilling data, the sedimentary microfacies and favorable reservoir microfacies of Huanglong Formation are studied in detail on the basis of fine stratigraphic division and comparison. The first and second members of Huanglong formation remain in Carboniferous in the research area. According to the principle of cyclic correlation, the second member of Huanglong Formation can be further divided into three sub-sections, and the residual thickness of the strata in the study area has little change. Based on lithofacies, paleontology and other sedimentary facies identification indicators, it is determined that the main carbonate tidal flat facies are developed in Huanglong Formation in this area, which is subdivided into supratidal, intertidal and subtidal plateau subfacies and some microfacies, and the carbonate tidal flat sedimentary model is established. Among them, the first member of Huanglong Formation is mainly in the upper tidal flat sedimentary environment, while the second member of Huanglong Formation mainly develops intertidal-subtidal cyclic sedimentary environment. Based on the physical property analysis data, it is determined that the favorable reservoir microfacies in the study area are mainly the intertidal sandy beach and algal sandy flat microfacies.