碳酸盐岩烃源岩判识与实践——以四川盆地为例

How to Judge Carbonate Rock as Source Rock:A Case of Sichuan Basin

碳酸盐岩可以成为烃源岩,并为油气藏提供丰富的烃源,但不是所有碳酸盐岩都可以视为烃源岩。碳酸盐岩在成藏进程中,往往作为输导层或储集层,并常有外源有机质的干扰。碳酸盐岩烃源岩应该是有机质原生赋存(与矿物结合成为沉积的一部分),具有一定丰度值,在适宜的热成熟阶段,同样可以形成液态烃和气态烃。碳酸盐岩烃源岩发育于低能环境的沉积相——开阔海台地相、局限海台地相、生物泥丘相、斜坡相,等等。泥质泥晶灰岩,生物泥—粒泥岩—泥粒岩微相,应该是碳酸盐岩烃源岩的主要岩类。碳酸盐岩烃源岩与油系泥质烃源岩比较,具有油窗凸显且高峰期前移、气态烃峰期不明显且有后延、液态烃产率高的特点。据对碳酸盐岩烃源潜量的评估,它在四川盆地烃源中占20%～25%,为油气成藏作出了重要贡献。

Carbonate rocks are able to source rocks that supply rich hydrocarbon for reservoir but not all of carbonate rocks can be as source rocks.In the process of hydrocarbon accumulation,carbonate rocks commonly act as carrying beds or reservoirs and are interfered easily by allogenic organic matter.It is considered that carbonate source rock should be a place holding organic matter（combined with minerals as a part of sediments） and is of a certain abundance.Hence as a result,liquid and gaseous hydrocarbon would be generated if the carbonate rock is during a appropriate thermal-mature stage.Carbonate rocks generally develop in low-energy environments of sedimentary facies,such as open sea platform,restricted sea platform,biomudlump and slope facies.Pelitic micritic limestone,biomarl-wackstone and packstone microfacies should be the hosts of carbonate source rocks.Comparing with oil-rich argillaceous source rocks,the carbonate rocks are characterized by evident oil window phases with peak ahead-migrating,unobvious peak phases of gaseous hydrocarbon with peak back-migrating,and high-yield liquid hydrocarbon.According to the assessment of potential hydrocarbon quantity in Sichuan Basin,carbonate rocks contribute 20%～25% of hydrocarbon quantity to source,which play an important act to hydrocarbon accumulation in the basin.