伊拉克X油田巨厚生物碎屑灰岩储层强非均质性及主控因素

Reservoir intense heterogeneity and main controlling factors of thick bioclastic limestone in X Oilfield,Iraq

伊拉克X油田Mishrif组为巨厚强非均质生物碎屑灰岩,开发难度大。基于岩心、铸体薄片、压汞实验、孔渗、核磁共振实验、测井曲线和开发动态等资料,通过数理统计和储层特征对比,刻画Mishrif储层垂向和平面非均质性;根据层序地层学和沉积学理论,明确储层非均质性成因。结果表明:X油田Mishrif组发育三套稳定隔层、多套夹层和三种成因的超高渗层,隔夹层、超高渗层与围岩存在巨大渗透率级差。Mishrif组垂向上储层特征呈三段式,即MB2段层内均质且孔、渗相关关系好,超高渗层分布在MB2段顶部,夹层发育程度低;MB1段层内非均质性强,物性变化快且幅度大,超高渗层分布规律弱,夹层发育程度高;MA段层内非均质性强,孔、渗相关关系差,超高渗层沿断层带分布,夹层较发育。平面上,储层展布具有“北厚南薄、核厚翼薄、网络状、点厚面薄”4种样式。研究区浅水缓坡沉积背景下发育多期层序旋回是巨厚强非均质生物碎屑灰岩的主要成因。碳酸盐岩缓坡相带分异显著,储层渗透率随沉积水动力增加而增高。开阔水体环境中沉积作用稳定,地层厚度大,储层非均质性弱;高能沉积环境是超高渗层的发育基础;局限沉积环境中夹层发育程度高,非均质性强。层序旋回控制储层垂向叠置关系和平面展布样式,层序界面处成岩改造强烈,发育超高渗层或稳定隔层。构造作用导致岩石遭受埋藏溶蚀,进一步提高储层物性。该结果可深化生物碎屑灰岩储层地质认识,为巨厚碳酸盐岩油藏高效开发提供参考。

The carbonate reservoir of Mishrif Formation in X Oilfield in Iraq is greatly heterogeneous and is difficult to be developed.Based on data such as core,cast thin sections,mercury injection,physical property and nuclear magnetic resonance,logging and development performance,the reservoir heterogeneity in the Mishrif Formation is fine described by statistics and analogy.The main controlling factors of the reservoir are clarified according to sequence stratigraphy and sedimentary.The results show that there are three stable baffles,multiple barriers and three kinds of ultra-high flow zone,whose permeability are greatly different from that of surround rock.The Mishrif Formation was divided into three intervals vertically.MB2 zone was relatively less heterogenetic with better correlation of porosity and permeability.The ultra-high flow zone is only developed in the upper of MB2 zone and the barriers is much less developed.MB1 zone was greatly heterogeneity and the physical property change greatly.The ultra-high flow zone is developed randomly and the barrier is widely developed.MA zone was pretty heterogeneity with poor correlation of porosity and permeability.The ultra-high flow zone is developed along the faults and the barrier is less developed.The reservoir is displayed in four pattern in plane which were the north thick and south thin,the center thick and side thin,the network,the point thick and plane thin.The shallow carbonate ramp with multi-sequence cycle was the main cause for the heterogeneity of thick bioclastic limestone.The facies in carbonate ramp was different from each other.The higher depositional energy,the higher reservoir permeability.The deposition in open environment is stable and the reservoir is relatively homogeneous.The high energy environment was the foundation of ultra-high flow zone and the barriers were mainly developed in restricted environment.The sequence controlled the reservoir vertical configuration and plane variation.The diagenesis in the sequence boundary is extensive,where ultra-high flow zone and stable baffles were displayed.Tectonism may lead to burial dissolution and improve reservoir property.The research results can deepen the geological understanding of bioclastic limestone and support thick carbonate rock intense waterflood development.