碳酸盐岩-膏盐岩共生体系白云岩成因及储盖组合

Dolomite genesis and reservoir-cap rock assemblage in carbonate-evaporite paragenesis system

针对碳酸盐岩-膏盐岩共生体系中储集层发育规律和储盖组合类型不清的问题,开展该体系岩性组合特征、白云岩与储集层成因和储盖组合类型研究。在全球碳酸盐岩油气藏调研的基础上,解剖分析国内外4个碳酸盐岩-膏盐岩组合剖面,综合应用地质和实验分析工作,取得以下3个方面的地质认识:①潮湿气候到干旱气候的变迁决定了碳酸盐岩-膏盐岩共生体系岩性组合序列,正常情况下形成微生物灰岩/生屑灰岩→微生物白云岩→膏云岩→膏盐岩系列,反之亦然,气候的突变会导致某种岩性的缺失。②碳酸盐岩-膏盐岩共生体系中主要发育3类储集层,包括微生物灰岩/生屑灰岩、微生物白云岩和膏云岩储集层,存在沉淀和交代2种成因的白云岩。微生物早期降解和微生物岩晚期热解释放的CO2气体和有机酸,以及早期白云石化作用是微生物白云岩能够成为优质储集层的主控因素。③碳酸盐岩-膏盐岩共生体系理论上存在6类14种储盖组合类型,目前的油气发现主要集中在4种组合中,包括微生物灰岩/生屑灰岩→微生物白云岩→膏云岩→膏盐岩组合、微生物灰岩/生屑灰岩→膏盐岩组合、微生物白云岩→膏云岩→膏盐岩组合和膏云岩→微生物白云岩→致密碳酸盐岩或碎屑岩组合,这显然与地质历史时期古气候变迁的内在规律有关。通过解剖已发现的油气藏,揭示在碳酸盐岩-膏盐岩体系中以上4种储盖组合最为现实,勘探前景较好。

Regarding to the problem on the reservoir-cap rock assemblage evaluation in the carbonate-evaporite paragenesis system,this study examined the dolomite and reservoirs genesis and the characteristics of reservoir-cap rock assemblage.Based on the literature research of the global carbonate reservoirs and the case study on four profiles of carbonate-evaporite succession,together with geological and experimental work,three aspects of understandings are achieved.(1)Lithology of carbonate-evaporite paragenesis system is mainly composed of microbial limestone/bioclastic limestone,microbial dolomite,gypsum dolomite and gypsum salt rock deposited sequentially under the climatic conditions from humid climate to arid climate,and vice versa,and an abrupt climate change event would lead to the lack of one or more rock types.(2)There developed two kinds of dolomite(precipitation and metasomatism)and three kinds of reservoirs in the carbonate-evaporite system;and the carbon dioxide and organic acid generated during early microorganism degradation and late microbial dolomite pyrolysis process,and early dolomitization are the main factors affecting the development of microbial dolomite reservoirs with good quality.(3)In theory,there are 14 types of reservoir-cap rock assemblages of six categories in the carbonate-evaporite system,but oil and gas discoveries are mainly in four types of reservoir-cap rock assemblages,namely'microbial limestone/bioclastic limestone–microbial dolomite–gypsum dolomite–gypsum salt rock','microbial limestone/bioclastic limestone–gypsum salt rock','microbial dolomite–gypsum dolomite–gypsum salt rock'and'gypsum dolomite–microbial dolomite–tight carbonate or clastic rock'.These four kinds of reservoir-cap rock assemblages should be related with the climate change rules in the geologic history,and have good exploration prospects.