Abstract: 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.

Key words: Kuqa foreland basin, ultra-deep exploration, natural gas, geolo gical understanding, subsalt fault anticline traps