柴北缘深层气藏形成的地质条件及有利勘探区带

柴北缘具备深层气藏形成的地质条件.柴北缘广泛存在埋深>4 500 m,R_0>1.3%的中下侏罗统气源岩.发育中下侏罗统三角洲、扇三角洲、水下扇、滨湖相砂体和第三系冲积扇、河泛平原、辫状河三角洲和滨浅湖相砂体.存在路乐河组(E_(1+2))和下干柴沟组上段(E_3~2)2套区域性盖层.深层存在潜伏构造、大型背斜和背斜两翼或古隆起周缘构造岩性圈闭,其中对潜伏构造和大型背斜构造比较落实.柴北缘生气期较晚,与圈闭形成史、储盖层发育史和断层发育史有较好的匹配关系,有利于深层气成藏和保存.柴北缘深层气藏勘探的风险主要包括气源岩的生气潜力和分布范围难以落实,深部储层的储集能力难以预测.深层潜伏构造带、冷湖构造带和鄂博梁-伊克雅吾汝构造带可作为近期深层气藏勘探优先考虑的目标,而冷湖构造带两翼和南八仙古隆起周边的构造岩性圈闭可列入深层气藏中长期勘探规划.

Geological Conditions of Deep Gas Pools and Their Favorable Prospects

The northern margin of the Qaidam basin has the geological conditions for forming deep gas pools. The Lower and Middle Jurassic source rocks are extensive in the margin, with buried depth >4 500 m and R_0>1. 3%. There developed the Lower and Middle Jurassic delta, fan delta, underwater fan, lake shore sand bodies and Terti-ary fluvial fan, river plain, braid river delta and lake shore to shallow lake sand bodies. There are two regional seals, the Lulehe formation (E_(1+2)) and Xiaganchaigou formation (E_3~2). Buried structures, giant anticlines, structur-al and lithological traps around ancient uplifts are found. The gas generation of the Northern margin of the Qaidam basin was late, and it matched the histories of trap formation, reservoir-cap development and fault development and was favorable for pool formation and preservation. The risk of the deep gas exploration in the Qaidam basin is that it is difficult to determine the gas generation potential and distribution area as well as the preserved ability of deep reservoirs. The deep buried structures, the Lenghu structural belt and the Erboliang-Yikeyawuru structural belt can be considered as the most favorable targets of deep gas exploration. On a long view, the two wings of the Lenghu structural belt and the structural lithological traps around the Nanbaxian ancient uplift are exploratory targets.