中国页岩气成藏模式

Shale gas accumulation patterns in China

尽管我国在页岩气地质理论和勘探开发方面已经取得了重大进展,但对于页岩气成藏的地质特殊性和富集规律性方面的研究依然较为薄弱。为此,针对中国页岩气成藏模式开展了研究。研究结果表明:(1)前中生代大陆边缘型海相和海陆过渡相沉积、中新生代盆地型陆相沉积发育了多样性的富有机质页岩;(2)以中新生代陆相沉积为主的盆地叠覆在前中生代海相或海陆过渡相大陆边缘沉积之上,前者在盆地中形成了厚度大、有机质丰度高但时代新、热演化程度低的陆相页岩,盆地构造深部位有利于页岩气富集,后者时代老、热演化程度高、历经构造运动次数多的页岩得到了良好的保存,构造稳定区是页岩气富集的有利区;(3)主要形成于中新元古代、震旦纪—奥陶纪及泥盆纪—三叠纪的裂陷槽,是海相富有机质页岩沉积的有利区域,它们与成藏组合条件好的海陆过渡相页岩、中小型盆地中的煤系页岩及接受岩浆侵入影响的中低热演化程度页岩等一起,共同构架了我国丰富多彩的页岩气成藏模式;(4)基于已有的钻探成果,可以将中国页岩气成藏模式归纳为构造型和地层型两大类,前者主要与构造形态有关,而后者则主要与岩性地层变化有关;(5)页岩发育及含气量变化主要受沉积、成岩及后期构造运动等多方面地质因素的影响和控制,有利的沉积环境、适宜的热演化程度、良好的盖层封闭性和构造保存条件,是页岩气富集的必要前提。

Although significant progress has made in the geological theory and exploration and development of shale gas in China, the research on the geological particularity and enrichment regularity associated with shale gas accumulation remains weak. With this in mind,we analyze the shale gas accumulation pattern in China. The findings show that:(1) A variety of organic-rich shales were deposited in the continental margin-type marine and transitional environments during the Pre-Mesozoic period and the basin-type terrestrial environment during the Mesozoic and Cenozoic eras.(2) The basins dominated by Mesozoic and Cenozoic terrestrial sediments are superimposed on the Pre-Mesozoic continental margin-type marine-or transitional-facies sediments. The former developed the terrestrial shales with large thickness, high organic matter abundance, new age, and low thermal maturity;meanwhile, the deep part of the basin is favorable for shale gas enrichment. However, the latter preserved the shale with old age, high thermal maturity, and undergoing multiphase tectonic movements;and the tectonically stable regions are favorable for shale gas enrichment.(3) The aulacogens mainly formed in the MesoNeoproterozoic, Sinian-Ordovician, and Devon-Triassic periods are favorable for marine organic-rich shale deposition;moreover, this type of shale and other types including transitional facies shales with favorable reservoir-forming assemblages, coal-measure shales in small and medium-sized basins, and low-medium mature shales affected by magma intrusion, have jointly constituted the various shale gas accumulation patterns in China.(4) Based on the drilling discoveries in our country, shale gas accumulation patterns can be categorized into two types: tectonic-controlled and stratigraphic-controlled. The former is mainly related to structural features, whereas the latter is mainly related to the variation of lithology and strata.(5) Shale development and gas content are mainly affected and controlled by geological factors including sedimentation, diagenesis, and later tectonic movements. Favorable sedimentary environments, appropriate thermal maturity, good sealing capacity of caprock, and excellent structural preservation are the necessary conditions for shale gas enrichment.