眼球状灰岩成因及其油气地质意义

Origin of eyeball-shaped limestone and its significance for petroleum geology

眼球状灰岩是一种形态类似眼球与眼皮结构的碳酸盐岩,在我国南方地区广泛发育。通过对国内外关于眼球状灰岩特征及成因等研究成果的大量调研与梳理,分析并论述了眼球状灰岩的岩石学特征、古沉积环境、成因及油气地质意义等。眼球状灰岩由泥晶—粉晶生屑灰岩的"眼球"与泥质灰岩或灰质泥岩的"眼皮"组成,其成因主要包括沉积作用与成岩作用2个方面。眼球状灰岩的"眼皮"为滞留深水环境下沉积的中等有机质丰度的高—过成熟烃源岩,具有良好的生烃能力。该类灰岩为一套低孔低渗的油气储层,且"眼皮"的储集性能明显优于"眼球"。裂缝可以改善眼球状灰岩的储集物性,裂缝发育的储层具有良好的油气显示。总体来看,眼球状灰岩气藏为自生自储的碳酸盐岩气藏。

Eyeball-shaped limestone is a kind of carbonate rock with a structure shaped as eyeball and eyelid,which is widely developed in south China.The petrological characteristics,paleo-sedimentary environment,origin and hydrocarbon geological significance of eyeball-shaped limestone were analyzed and discussed through a great deal of review and investigation on the characteristics and origin of domestic and abroad eyeball-shaped limestone.The eyeball-shaped limestone is composed of the“eyeball”of micrite-silty bioclastic limestone and the“eyelid”of argillaceous limestone or calcareous mudstone.Its origin mainly includes sedimentation and diagenesis.The“eyelid”of eyeball-shaped limestone is high-maturity to over-mature source rock with medium organic matter content deposited in deep water environment,which has good hydrocarbon generation potential.The eyeball-shaped limestone is also a set of low-porosity and low-permeability reservoir,and the storage performance of“eyelid”is obviously better than that of“eyeball”.Fractures can improve the reservoir physical properties of eyeball-shaped limestone,and the reservoir with fractures has good oil and gas display.On the whole,the eyeball-shaped limestone gas reservoir is a self-generating and self-storing carbonate gas reservoir.