四川盆地页岩气与煤层气勘探前景分析

Exploration prospect of shale gas and coal-bed methane in Sichuan Basin

页岩气与煤层气是非常规气勘探的重要领域,国外早已进入实质性商业勘探开发。我国从本世纪初对页岩气关注渐增。页岩气以吸附、溶解、游离状态存在,形成于暗色高炭泥质烃源岩中。该文根据四川盆地烃源岩研究成果,论证了上二叠统龙潭组煤系利于煤层气成藏,有利区块位于华蓥山及其东南侧与南端地带。该地带以烟煤为主,瓦斯含量高、埋藏浅。上三叠统须家河组煤系,煤岩瓦斯含量低,有利页岩气成藏。有利区块有二:一是川西南威远背斜周缘及川南之北段区块;二是米仓山前缘,目的层埋藏较浅。油系泥质烃源岩有利页岩气成藏的层系是下侏罗统,有利区块位于川东北、川北有机质成熟度高的高陡构造翼部及盆地边缘浅埋带。下志留统龙马溪组、下寒武统筇竹寺组暗色泥质烃源岩,在盆地内早期有利页岩气成藏。现今因成熟度剧增,不利页岩气保存,而且目的层埋深大,可在老气田"立体勘探"时关注。但在大巴山靠盆地一侧,江南古陆西北缘,其有机质成熟度有降低的趋势,不失为页岩气成藏的有利地带。

The exploration of shale gas and coal-bed methane is an important field of the non-conventional gas exploration. The shale gas reservoir formed in dark-colored high-carboniferous argillaceous hydrocarbon source rocks with the mechanism of adsorption-dissolution-free existence. Based on the study result of hydrocarbon source rocks of Sichuan Basin, it is demonstrated that Longtan Formation of Upper Permian is favorable to form coal-bed methane reservoir. The favorable areas are located in Huaying Mountains, and its southeastern side and southern side. The strata of this region mainly contain bituminous coal with the superiority of high gas content and shallow burying. For low gas content, the coal measures of Upper Triassic Xujiahe Formation are favorable for the accumulation of shale gas. There are two advantageous areas： the one includes the periphery of Weiyuan Anticline （which is located in southwestern Sichuan Basin） and the north part of southern Sichuan Basin, while another area is frontier area of Micang Mountain with shallow buried target. The argillaceous hydrocarbon source sequence of petroliferous strata, being favorable for the accumulation of shale gas, is Lower Jurassic. The favorable areas are located in the precipitous structural flanks and shallow buried fringe of northeastern and northern parts of Sichuan Basin. The dark-colored argillaceous hydrocarbon source rocks of Lower Silurian Longrnaxi Formation and Lower Cambrian Qiongzhusi Formation are favorable for the accumulation of shale gas in early-middle maturation period. At present, these sequences are unfavorable to preserve shale gas, due to the sharply increased organic maturity and deeply buried target zones. In frontier side of Daba Mountain and northwestern fringe of Jiangnan Ancient Land, organic maturity has a trend of decrease, so these areas are favorable for accumulation of shale gas too.