四川盆地震旦系油气地质条件及勘探前景分析

THE PETROLEUM GEOLOGICAL CONDITION AND EXPLORATION PROSPECT ANALYSIS IN SINIAN,SICHUAN BASIN

通过对四川盆地震旦系40多年的钻探情况分析后认为,震旦系勘探程度低,对四川盆地加里东古隆起和盆地周边一些高陡构造的钻探均未获得气藏。四川盆地震旦系烃源条件优越、封盖条件好,储层好,分布广泛,具备形成大气田的地质条件。四川盆地震旦系第一个成油期是加里东期,海西期油气被破坏;印支期烃源二次生烃并形成古油藏,古隆起对油气捕集有着重要的意义。喜马拉雅期前由于持续埋深、温度增高、油裂解气的影响形成异常高压,天然气溶于水中形成水溶气;挤压隆升过程中,造成的油气再分配和水溶气的脱溶,最终形成现今的气藏和含气区。该文通过对四川盆地震旦系的油气成藏条件分析,提出川东华蓥山地区和川西北天井山古隆起是除乐山─龙女寺古隆起外未来震旦系勘探的有利地区。

The exploration degree of Sinian in the Sichuan Basin is low according to drilled information analysis. The drilled wells distriboute on Leshan--Longnusi paleo-uplift area and orogenic belt which is around the basin, but they almost failed. The source rock and caprock are good and have good geological conditions to form large gas field. The first oil generation period was in Caledonian and the oil was destroyed to bitumen in Hercynian. The second oil generation was in Indosinian. The Leshan--Longnvsi paleo-uplift was important to oil accumulation in this period. The oil was thermal cracked to gas by deep buried before Himalayan. It also formed abnormal high pressure and induced gas dissolving into water. During the uplift processes, due to the redistribution of gas and gas released from formation water, the gas field and gas-bearing areas were finally formed. Through analyzing the reservoir forming conditions of Sinian in the Sichuan Basin, this paper points out that the paleo-structures before Himalayan and Tianjingshan paleo-uplift in Caledonian should be the favorable exploration areas in the future.