川西中段上沙溪庙组层序格架内成岩相展布

Diagenetic Facies Distribution within the Upper Shaximiao Formation Sequence Framework in the Middle Part of Western Sichuan

运用层序地层学、储层地质学理论和方法,利用视压实率、视胶结率和视溶蚀孔隙度开展了川西坳陷中段上沙溪庙组层序格架内成岩相定量研究,并进行了有利储层预测。结果表明:上沙溪庙组为一个三级层序,可进一步划分出低位体系域、湖侵体系域和高位体系域,建立了等时层序地层格架;依据成岩强度标准,划分出中强压实中溶蚀成岩相、强胶结中溶蚀成岩相、强胶结弱溶蚀成岩相、强压实成岩相和强胶结成岩相5种主要成岩相类型,其中,湖侵体系域不发育强胶结中溶蚀成岩相,层序格架内成岩相平面展布受沉积相带和物源控制明显;依据储集潜力大小将储层分为4类,其中Ⅱ类储层为研究区有利的储层类型,主要分布在中强压实中溶蚀成岩相和强胶结中溶蚀成岩相发育区。该研究成果可为研究区下一步油气勘探提供必要的地质依据。

Based on the theories and methods of sequence stratigraphy and reservoir geology,the apparent compaction rate,apparent cementation rate and apparent dissolution-porosity are used to quantitatively model the diagenetic facies distribution within the upper Shaximiao Formation sequence framework in the middle part of western Sichuan and predict favorable reservoirs. Research indicates that the upper Shaximiao Formation is identified as a 3-order sequence,which can be.further divided into low-stand system tract,transgressive system tract and high-stand system tract,and the corresponding isochronous sequence stratigraphy framework is also established. According to the diagenesis intensity criterion,5 major categories of diagenetic facies are classified,including medium-compaction and medium-dissolution diagenetic facies,strong-cementation and medium-dissolution diagenetic facies,strong-cementation and weak- dissolution diagenetic facies,strong- compaction diagenetic facies and strong- cementation diagenetic facies.There is no strong-cementation and medium-dissolution diagenetic facies in transgressive system tract and the lateral diagenetic facies distribution within sequence framework is greatly dependent on sedimentary facies and provenance. The reservoir is classified into 4 categories according to their reservoir potential. Category-II reservoir is considered as a favorable reservoir in this workarea and mainly distributes in the regions with well-developed medium-compaction and medium-dissolution diagenetic facies and well-developed strong-cementation and medium-dissolution diagenetic facies. This research could provide a necessary geological reference for the next hydrocarbon exploration in this workarea.