柴达木盆地煤型气成藏条件及勘探领域

柴达木盆地烃源岩、古今构造、输导条件等关键成藏条件及其时空配置关系研究表明,盆地煤型气具备四大有利成藏条件:侏罗系烃源岩呈现多凹共存、广泛分布特征,重新评价资源潜力达13100×108m3,具备煤型气大型化成藏物质基础;关键成藏期盆地呈现"盆缘古斜坡及鼻隆带和盆内凹陷带"的二级结构,盆缘区是油气运移的长期指向,形成良好的成藏背景;具有"裂缝+孔隙"双重介质储集空间的基岩风化壳大范围分布且不受埋深影响;具备"控源断裂纵向运聚,不整合面横向输导"的油气面状运聚模式,利于天然气规模聚集。油气成藏条件和富集规律的认识为煤型气勘探提供了理论支撑,形成了盆缘大型古斜坡构造—岩性控藏新认识,提出盆缘不整合面上下为重点勘探新领域,阿尔金山前古鼻隆及斜坡为重点勘探新区带,并在油气勘探中取得了明显的效果,近年来新增控制+探明天然气储量1104×108m3,实现了柴达木盆地煤型气勘探的新突破和新进展。

Accumulation Conditions and Exploration Domain of Coal-Type Gas in Qaidam Basin

Based on the key accumulation conditions, such as hydrocarbon source rock, the palaeo-temporary structures and gas migration, as well as the spatial-temporal relationship, there are four important favorable accumulation conditions for coal-type gas in Qaidam Basin. The Jurassic source rock is widely distributed with co-existence of a multiple of depressions. The potential reserve is re-evaluated at 13100×108m3, providing a material basis for large-scale accumulation of coal-type gas. The secondary structures developed in the basin during the key accumulation period, such as ＂basin peripheral palaeo-slope, nose uplift and depression belt＂. The basin peripheral zone is the directive zone for long-term hydrocarbon migration, forming a good background for accumulation. The basement weathering ernst, whose reservoir space is based on dual media - fractures an pores, is extensively distributed, free from of influence of buried depth. The hydrocarbon migration and accumulation are in the pattern of ＂vertical migration and accumulation from source-controlled faults and lateral transportation on unconformity surface＂ helpful to a large-scale accumulation of natural gas. The study of hydrocarbon accumulation conditions and abundance law provides a theoretical basis for coal-type gas exploration and develops the new theories on the reservoirs controlled by large-scale basin peripheral palaeo-slope structures. It is proposed that the new important exploration areas should be located above and below the basin peripheral unconformity surface. The Altyn Tagh foothill palaeo-nose uplift and slope should be highlighted as the new belt and zone for exploration. This theory leads to remarkable results in oil and gas exploration. The newly additional controlled and proven natural gas reserves have reached 1104×108m3 in recent years, making new breakthroughs in coal-type gas exploration in Qaidam Basin.