Study on Forming Conditions of Condensate Gas Reservoir in Deep-Seated Formation in Dongying Sag

Abstract By the analysis of the composition, the phase and the carbon isotope characteristics of the natural gas, It reached that the natural gas reservoir of Fengshen 1 of the lower section of the forth strata of Shahejie Formation, buried underground 4300m approximately, is a secondary condensate gas reservoir, as well as an indigenously generating and accumulating gas reservoir which source rock is the dark mudstone within the salt-layer of the lower section of the forth strata of Shahejie Formation. The synchronous conglomerate fan-body and the abnormal high-pressure zone, which occur in their hanging walls of the major faults in the north of Dongying Sag, are the favorable conditions for petroleum accumulation and preservation. The thick rock gypsum deposited on the conglomerate fan-body is the best cap rock. The appropriate pressure and temperature condition determinate the formation and the preservation of the condensate gas reservoir. In Dongying period, the source rock of the lower section of the forth strata of Shahejie Formation stepped into mature stage and a great quantity of petroleum was generated and migrated laterally into the conglomerate fan-body and accumulated as a pool finally. In Quaternary Period, the petroleum in the pool was cracked into condensate gas because of the rising of pressure and temperature. In one word, the deep strata of Dongying Sag, even Jiyang Depression will be the most important domain of condensate gas reservoir exploration of Shengli Oilfield.