Deep overpressure gas accumulation

The Kela-2 gas field in the Kuqa Depression of the Tarim Basin is one of the greatest fields recently discov- ered in the deep overpressure reservoir in the world. The play conditions of Kela-2 field and Ya21-l structure features in the Qiongdongnan Basin on the South China Sea shelf has been studied, and a gas accumulation under deep overpres- sure must have the following two conditions (besides other favourable conditions for gas accumulation): one is that the time of gas charge matches with overpressure occurrence time, and the other is a good quality caprock. If the charge was early and the overpressure occurrence was late, and a fine caprock of the evaporite bed existed, the accumulation of gas is favourable; conversely, it is difficult to form a gas reservoir.