The Changxing Formation reservoirs of Yuanba gas field are dominated by ultra-deep bioherm developed at ramp-type platform margin.Development appraisal of the gas reservoir is challenged by the diversity of reef development model,unclear reservoir distribution and great difficulty of precise prediction in ultra-deep and thin reservoir rocks.In order to solve these problems,we studied the relationship between sea-level changes and bioherm development model,analyzed the main controlling factors of reefal dolomite reservoirs development,proposed the ideas and methods of reefal reservoir prediction,and predicted the bioherm reservoir distribution.The results show that there are four-stage bioherms in the Changxing Formation of Yuanba area.For single bioherm,there are two reef development models which are controlled by paleo-geomorphology and changes of sea-level.One is single-stage and the other is double-stage(multi-stage).For reef groups,there are five development models including vertical progradation,vertical retrogradation,horizontal migration,horizontal paralleling as well as composite and superimposed model.The major factors controlling the development of favorable bioherm reservoirs in Yuanba area are sedimentary background,eustacy,constructive diagenesis and tectonic fracture.Vertically,the reservoirs mainly occur in the reef cap,while laterally,the reservoirs mostly occur in the reef crest,followed by reef back and reef front.%元坝气田长兴组气藏主体为埋藏超深的缓坡型台缘生物礁气藏,为解决气藏开发评价面临的生物礁发育模式复杂多样、储层分布规律不清、超深薄储层精确预测难度大等问题,本文探讨了海平面升降变化与生物礁发育模式的关系,分析了礁相白云岩储层发育主控因素,提出了生物礁储层预测的思路与方法,明确了生物礁储层平面展布特征.研究表明:元坝地区长兴组地层中共发育4期生物礁,受古地貌和海平面升降变化控制,单礁体可分为单期礁和双期(多期)礁两种模式.礁群可分为纵向进积式、纵向退积式、横向迁移式、横向并列式、复合叠加式5种模式;元坝地区生物礁储层发育主要受沉积背景、海平面升降变化、建设性成岩作用及构造破裂作用控制,垂向上储层主要发育于礁盖,横向上主要发育于礁顶,礁后次之,礁前较差.
展开▼
