四川盆地长兴组生物礁气藏及天然气勘探

四川盆地上二叠统长兴组主要发育了平原河流相、海陆交互相、碳酸盐岩台地浅缓坡相、台地边缘礁相、开梁海槽相和蜀北-鄂西海盆相,具有形成生物礁气藏的有利生、储、盖条件.为提高地震预测生物礁异常的可靠性,根据已知礁体地质特征及相应的地震反射特征,经过反复研究,于20世纪末成功建立了生物礁地震异常识别模式,在川东发现生物礁异常182个.据沉积相研究,发现开梁海槽两侧至鄂西存在一台地边缘礁相,其上已发现36个边缘礁地震异常,这些边缘礁面积大,钻探证实储量、产量高,是很有价值的勘探领域,预测该相带向北西很可能延伸至盆地西缘.台地浅缓坡相发育大量点礁,仅盆地东部即已发现146个点礁地震异常,预测盆地中部广大地区都很可能是点礁发育区.图6表2参18

Changxing Formation biohermal gas pools and natural gas exploration, Sichuan Basin

Plain fluvial facies, paralic facies, shallow gentle slope facies on carbonate platforms, platform marginal reef facies, Kailiang trench facies, and northern Sichuan-western Hubei ocean basin facies are developed in the Permian Changxing Formation and have favorable source-reservoir-seal conditions. To improve the seismic prediction reliability of biohermal anomalies, an identifying model of biohermal seismic anomalies was established in late 1990s based on the geological features of known reefs and the corresponding seismic reflection features, and 182 biohermal anomalies were found in eastern Sichuan. Researches on sedimentary facies reveal a platform marginal reef facies from both sides of the Kailiang trench to west Hubei, and the seismic anomalies of 36 marginal reefs have been found there. These marginal reefs have large areas and high drill proved reserves. The facies belt is likely to extend to the western margin of the basin. Many point reefs are developed on the slope platform facies, and 146 seismic anomalies of point reefs are found in eastern basin. Point reefs are possibly developed widely in central basin.