塔里木盆地西部一间房露头区奥陶系台缘储层沉积体系分析

Reservoir depositional system analysis of Ordovician carbonate platform margin in Yijianfang outcrops of western Tarim Basin

碳酸盐岩台地边缘优质储层相带预测一直是石油勘探家关注的焦点,露头沉积体系精细结构分析及其储集性能研究是总结预测模型的一把关键钥匙。在塔里木盆地西部一间房露头区,通过详细的野外地质调查、沉积体横向追踪与对比、典型沉积体系剖面写实、系统取样和室内测试分析等方法,对中奥陶统一间房组台缘生物礁-滩沉积体系、上奥陶统良里塔格组底部的台缘斜坡-斜坡扇沉积体系进行了系统的沉积体系内部成因相构成及其储集性能研究。研究认为台缘沉积体系具有复杂的内部构成,其成因相具有相对固定的空间配置格架和品质迥异的储集性能。在台缘靠近台地一侧往往发育生物礁-滩沉积体系,由生物礁、生物碎屑滩和台缘背景沉积等3种成因相组合构成。生物碎屑滩产出于生物礁周围,礁前则具有特征的砾质滩。由内侧滩向外侧滩沉积物颗粒变细、分选性变差、生屑含量和亮晶胶结物减少。而在台缘靠近盆地一侧,则往往台缘斜坡-斜坡扇沉积体系,主要由斜坡、斜坡扇、扇面水道和滑塌体等4种成因相组合构成。扇面水道通常切割斜坡扇,滑塌体周围往往伴生有小型斜坡扇体。由斜坡扇或者扇面水道的近端向远端,沉积物由砾质逐渐转变为砂质。在上述两种台缘沉积体系中,礁前内侧砂质滩和礁后内侧砂质滩、远端砂质斜坡扇具有良好的储层品质。比较而言,台缘生物礁-滩沉积体系的潜在储集性能总体上优于台缘斜坡-斜坡扇沉积体系。

High-quality reservoir phase belts prediction of carbonate platform margin is the focus that petroleum explorationists have always been concerning.Fine structure analysis and reservoir property study of outcrop depositional system is the key to summarizing prediction models.Based on detailed field geological investigation,lateral tracing and correlation of lithosomic bodies,profile survey about typical depositional systems and systematic sampling and lab analysis,the composition of genetic facies and reservoir property have been studied about platform margin reef-shoal depositional system of Yijianfang Formation in the Middle Ordovician and platform margin slope-slope fan depositional system of Lianglitake Formation in the Upper Ordovician in Yijianfang outcrop area of western Tarim Basin.The study suggested that platform margin depositional system had complex internal structure,whose genetic facies have relatively fixed space framework and different reservoir properties.Reef-shoal depositional system always developed on the platform margin near the carbonate platform,which consists of reef,bioclastic beach and background deposit of platform margin.The bioclastic beach developed around reefs,in front of which was special gravel beach.From inside to outside of bioclastic beach,the sediment size becomes finer,sorting gets worse,bioclast content decreases and calcsparite cement reduces.But on the platform margin near the basin,slope-slope fan depositional system often developed,which mainly consists of slope,slope fan,fan channel and slip block.Slope fans were usually cut by fan channels and small slope fans develop around the slip block.From proximal part to distal part of the slope fans and fan channels,sediments gradually changed from rudaceous to arenaceous.In the above-mentioned two kinds of platform margin depositional systems,the reef-front interior arenaceous beaches,reef-back interior arenaceous beaches,and distal arenaceous slope fans have good reservoir quality.In comparison,the potential reservoir quality of reef-shoal depositional system is better than slope-slope fan depositional system on the platform margin overall.