Abstract: In order to investigate the factors controlling reservoir porosity in the Kela-2 gas field of the Kuqa Depression,Tarim Basin,the sandstone reservoir characteristics,the origin of overpressure,as well as the evolution of the reservoir charging history were studied by using quantitative grain fluorescence and fluid inclusion data.The research results indicate that horizontal tectonic compression played an important role in the overpressure generation in the Kela-2 gas field.The overpressured presalt sandstone reservoirs with the maximum paleoburial depth over 6 000 m have anomalously high primary porosities.The reason is that the cementation of the sandstone was influenced and even undercompaction occurred as the oil charged into the sandstone reservoirs was not expelled under the efective sealing of salt and gypsum cap rocks in the Kela-2 gas field.This is evidenced by that sandstone reservoirs with high intensities of Quantitative Grain Fluorescence (QGF) and QGF on extract (QGF-E) are associated with high porosity and permeability intervals,and sandstone units below the ancient oil-water contact have low porosity and permeability.Late oil charging occurred at the early period of the Kuqa Formation deposition and the corresponding sandstone reservoirs in the Kela-2 gas field had shallower burial depth and high primary porosities.This research suggests that the oil charging and overpressure played important roles in the development of reservoirs porosity.

Key words: hydrocarbon charging, ancient oil-water contact, reservoir porosity, Kela-2 gas field, Tarim Basin