Abstract: In order to better understand the accumulation mechanism of deep tight sandstone gas in Kelasu structural belt, a study was conducted on the history of hydrocarbon charging and porosity evolution. Taking the Dabei 1 gas reservoir in the Kuqa Depression as an example, the history of hydrocarbon charging was determined by fluid inclusion petrography and micro-temperature measurement technology, and the pore evolution history of the reservoir was restored by quantitative back-stripping method. The accumulation mechanism of Dabei1 gas reservoir was clarified according to the coupling relationship between them. The study results showed that there were three stages in hydrocarbon charging process in Dabei 1 gas reservoir. The first stage was the mature crude oil charging from Neogene Kangcun period to Kuqa period, forming a conventional reservoir, with the reservoir porosity from 12% to 14%. The second stage was highly mature hydrocarbon charging in Neogene Kuqa period, with the reservoir porosity from 8% and 10% and coexistence of conventional gas reservoir and deep-basin tight gas reservoir. The third stage was dry gas filling from Late Neogene Kuqa period to Quaternary western region period, forming tight conventional and deep-basin tight composite gas reservoirs, with reservoir porosity of about 5%. Since the western region period, a large number of fractures have been developed in the reservoir due to the late tectonic movement, and the gas reservoir has been relocated, that is, the natural gas migrated along the fractures under the action of buoyancy and accumulated in the high part of the structure. The study results further prove the prospects of tight gas exploration and development in the Kelasu structural belt in the Kuqa Depression, and provide a theoretical basis for the prediction of favorable areas in the study area.

Key words: tight sandstone gas, deep gas reservoir, accumulation mechanism, porosity evolution, Dabei 1 gas reservoir, Kuqa Depression