Origin of abnormal high pressure and its relationship with hydrocarbon accumulation in the Dina 2 Gas Field, Kuqa Depression

Abstract

Abstract: Based on distribution of formation pressure by indirect estimation and formation testing, this study investigates origin of abnormal high pressure in the Dina 2 Gas Field in the Kuqa Depression in combination with the latest research findings. Contribution of major overpressure mechanisms to this gas field is estimated, and generation of the abnormal high pressure as well as its relationship with natural gas accumulation is explored. Disequilibrium compaction, tectonic stress, and overpressure transfer are the major overpressure mechanisms. Overpressure transfer resulted from vertical opening of faults and folding is the most important cause for the overpressure. Gas accumulation and abnormal high pressure generation in the reservoirs of the Dina 2 Gas Field show synchroneity. During the early oil-gas charge in the Kangcun stage, the reservoirs were generally normal pressure systems. In the Kuqa deposition stage, rapid deposition caused disequilibrium compaction and led to generation of excess pressure (approximately 5–10 MPa) in the reservoirs. During the Kuqa Formation denudation stage to the Quaternary, reservoir overpressure was greatly increased to approximately 40–50 MPa as a result of vertical pressure transfer by episodic fault activation, lateral overpressure transfer by folding and horizontal tectonic stress due to intense tectonic compression. The last stage was the major period of ultra-high pressure generation and gas accumulation in the Dina 2 Gas Field. Key words: abnormal high pressure, overpressure transfer, tectonic compression, Dina 2 Gas Field, Kuqa Depression