库车前陆盆地超深层大油气田形成的地质认识

Geological understanding on the formation of large-scale ultra-deep oil-gas field in Kuqa foreland basin

库车前陆盆地是近年来中国乃至全球超深层油气勘探的热点区域，在盐下6500m至8000m埋深的碎屑岩储层内发现了一批高产、稳产的大型天然气田。地质认识的进步至关重要，为超深层勘探指明了方向。（1）在顶蓬构造的减压作用下，盐下超深层仍发育规模有效储层，储层孔隙度达到3％～9％；构造强挤压应力在盐下断背斜内形成“应力中和面”效应，控制储层垂向分层特征，构造顶部发育高产储层。（2）前陆冲断带强烈挤压作用在盐下形成多排冲断带，断背斜圈闭规模发育，成排成带展布。（3）古近系一新近系巨厚膏盐岩盖层因构造挤压呈塑性流动加厚，叠置于断背斜圈闭之上，具有效封挡作用。库车前陆盆地超深层具有优越的石油地质条件及广阔的勘探前景，南部秋里塔格构造带有望成为超深层油气勘探接替领域。

Kuqa foreland basin is one of the hot spots for ultra-deep hydrocarbon exploration in China and even around the world, where a number of large-scale gas fields of high and steady production have been discovered in the subsalt clastic fromation 6500m to 8000m deep. The progress in geological understanding is crucial in finding out the direction for the exploration of ultra-deep reservoirs. （1） As a result of the depressuring effect of roof structure, there are large-scale effective reservoirs with a porosity of 3% to 9% existing in the subsalt. ＂Stress neutral plane＂ effect formed in the subsalt fault anticlines under the strong extrusion stress, controls the vertical zonation of the reservoirs, making high productivity reservoirs occur on the top. （2） A series of thrust belts are formed in the subsalt under the intense squeezing action of the foreland thrust belt, where abundant fault anticline traps are in rows and belts. （3） The Paleogene gypsum-salt caprocks in plastic flow state covering on the fault anticline traps, providing effective sealing. The ultra-deep reservoirs in Kuqa foreland basin have favorable petroleum geological conditions and bright exploration prospect, and Qiulitage structural belt, in the southern Kuqa foreland basin, is expected to be a relay exploration domain of ultra-deep hydrocarbon.