Research on biogenetic gas reservoir formation of Shizigou FM on Pliocene in Yiliping of the Caidam Basin

The forming history of biogenetic gas reservoir is discussed at Shizigou FM on Pliocene in Yiliping of the Caidam Basin. Firstly,natural gas of Shizigou FM is testified as biogenetic gas by the biogenetic gas simulating experiment. Secondly,producing mechanism of biogenetic gas is different from that of conventional natural gas. Through analyzing sedimentary facies, ancient climate, and temperature, the producing conditions of biogenetic gas are clear and higher salinity and lower temperature make it possible for biogenetic gas to appear on the deeper formation. Next, the reservoir and cap conditions are fine on Shizigou FM of Pliocene in Yiliping. There are two kinds of preserving mechanism,one is reservoirs physical property variation preservation, the other is hydrocarbon density Preservation. In the end, the model of reservoir forming is constructed and biogenetic gas reservoir formation process is divided into four phases, which are free gas escaping phase, water-soluble gas reservoir phase, water-soluble gas containing net gas reservoir phase, and net gas water-containing soluble gas reservoir phase.