西藏岗巴—定日盆地下白垩统页岩气资源潜力

Exploration potential analysis of shale gas in the Lower Cretaceous,Gamba-Tingri basin of Tibet

西藏岗巴—定日盆地下白垩统泥页岩分布广泛,通过分析其厚度、有机质丰度、有机质演化程度及脆度,评价了页岩气勘探潜力。研究区下白垩统岗巴东山组和察且拉组为一套陆棚—斜坡沉积环境下的含菱铁矿结核或条带的页岩、粉砂质页岩,地层横向分布范围较广,主要分布在定日、定结—岗巴以及江孜—浪卡子地区,厚度一般超过100 m;有机质类型良好,以腐泥型或者偏腐泥的Ⅱ1型为主,总体处于高成熟—过成熟演化阶段,以生成湿气—干气为主;页岩矿物成分以石英、长石为代表的脆性矿物为主,易于形成诱导性裂缝,同时吸附性能较强。通过分析有机地球化学参数及借鉴其他地区页岩气勘探实践,认为岗巴—定日盆地下白垩统泥页岩具有形成页岩气藏的有利条件。

The shale developing in the Lower Cretaceous distributes widely in Gamba-Tingri basin. The shale gas explora-tion potential has been evaluated through the analysis of its thickness,organic abundance,organic evolution and brittleness.Cretaceous Gamba-Dongshan Formation in the study area consists of a set of shale or silty shale having siderite nodules orstrips,which was formed under shelf-slope depositional environment. The formation distributes widely in the horizon direc-tion including Tingri,Tingjie-Bamba and Gyangze-Nagarze areas,where shale thickness is generally over 100 m. Its organ-ic type is good mainly developing sapropelic or partial sapropelicⅡ1 type. And the organic matter is overall high mature orover mature and generates moisture-dry gas mainly. The shale mineral composition mainly consists of brittle quartz andfeldspar,which is favorable for induced fracture formation and has strong adsorption at the same time. It is concluded thatthe shale in the Lower Cretaceous of the Gamba-Tingri basin has favorable conditions for shale gas accumulation based onorganic geochemical parameters analysis and other shale gas exploration practice.