早成岩期岩溶特征及其对古老深层碳酸盐岩储层的成因启示——以川中地区磨溪8井区灯影组四段为例

为进一步丰富和深化古老深层白云岩储层的成因理论,以四川盆地中部磨溪8井区灯影组四段(灯四段)为例,基于岩心、岩石薄片、测井、储集物性等资料,分析灯四段岩溶特征及演化规律,并探讨了其对储层发育和保存的意义。结果表明,灯四段发育孔洞型储层,储集岩性以微生物白云岩类、岩溶角砾岩和颗粒白云岩为主,岩溶作用具有组构选择性溶蚀、花斑状溶蚀和半离解带等典型早期溶蚀特征。灯四段储层主要集中在向上变浅序列的中—上部,纵向上呈多套薄层状储层频繁叠置、韵律性分布。灯四段优质储层的发育与相对海平面频繁升降驱动的早成岩期岩溶作用密切相关,储层品质与暴露时间和溶蚀强度有关。灯四段储层主要经历了3期岩溶演化阶段:选择性溶蚀阶段、岩溶分带阶段和整体角砾化阶段。适宜的暴露改造有利于原生残余孔隙的溶蚀扩大,对储层改造具有重要的建设性作用;暴露时间过长或溶蚀强度过大导致早期相对孤立的孔洞彼此连接,但大多垮塌或被充填破坏,表现为整体角砾化。整体上,灯四段有效储层具有"小孔(洞)保存,大孔(洞)充填"的特征,随着岩溶阶段的演化,储集性能先优化后变差。

Karst characteristics at early diagenetic stage and their enlightenment for the origin of ancient deep carbonate reservoirs: a case study of the Member 4 of Dengying Formation in Moxi 8 well area,central Sichuan

To further enrich and deepen the generation theory of ancient and deep dolomite reservoirs,a case study of the Member 4 of Dengying Formation in Moxi 8 well rea,central Sichuan Basin was conducted.Based on the data of cores,rock slices,logging and physical properties of reservoir,this paper analyzes the karst characteristics and evolution law of the Member 4 of Dengying Formation and discusses its significance for reservoir development and preservation.The results show that the Member 4 of Dengying Formation is dominated by a porous-type reservoir,the reservoir lithology is dominated by microbial dolomite,karst breccia and granular dolomite,and the karstification shows typical early corrosion characteristics such as fabric-selective corrosion,graniphyric corrosion and semi-discrete zone.The reservoirs of the Member 4 of Dengying Formation are mainly found in the middle and upper part of the upward shallowing sequence,and multiple sets of thin-layered reservoirs are frequently overlapped and rhythmically distributed in the longitudinal direction.The development of high-quality reservoirs in the Member 4 of Dengying Formation is closely related to early diagenetic karstification driven by frequent rising and falling of the relative sea level,and the reservoir quality is related to exposure time and corrosion intensity.The reservoir of the Member 4 of Dengying Formation experienced three stages of karst evolution:selective corrosion,karst zoning and overall brecciation.Appropriate exposure reformation is beneficial to the corrosion expansion of primary residual pores and plays an important and constructive role in reservoir reformation.If the exposure time is too long or the corrosion strength is too high,the early relatively isolated holes connect with each other.Most of them collapse or are damaged by filling,shown as the overall brecciation.On the whole,the effective reservoirs of the Member 4 of Dengying Formation are characterized by "preservation in small pore (hole) and filling in large pore (hole)".With the evolution of reservoirs in the karst stage,the reservoiring performance is first optimized and then getting worse.