Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (5): 1095-1105.doi: 10.11743/ogg20190515

• Petroleum Geology • Previous Articles     Next Articles

Accumulation conditions and favorable plays for deep gas exploration at the northern margin of Qaidam Basin

Tian Jixian1, Li Jian1, Zeng Xu1, Kong Hua1, Wang Peng2, Sha Wei2, Wang Mu2, Shi Zhenghao2, Song Dekang2   

  1. 1. Research Institute of Petroleum Exploration and Development, PetroChina, Langfang, Hebei 065007, China;
    2. Exploration and Development Research Institute of Qinghai Oilfield Co., Ltd., PetroChina, Dunhuang, Gansu 736200, China
  • Received:2018-06-13 Revised:2019-05-08 Online:2019-10-28 Published:2019-08-17

Abstract: The potential of deep natural gas resources is great at the northern margin of Qaidam Basin,but it is lower in exploration maturity.The gas accumulation conditions and plays for exploration are still to be revealed,restricting the exploration progress of natural gas.Given studies on seismic,geological,geochemical and drilling data,we analyzed the conditions for gas accumulation in deep strata at the northern margin of Qaidam Basin comprehensively in terms of source rock,reservoir,structure,and carrier system,and pointed out the favorable plays for deep gas exploration based on the existing exploration results and geological conditions.The results show that due to the widespread distribution of the Jurassic,a new Jurassic hydrocarbon generation depression is discovered in the western segment of the piedmont of Altun Mountain,featuring high potential of hydrocarbon generation in the deep high-to-over-mature source rocks.Both the weathering crust of bedrocks and clastic rocks with well-developed secondary pores may serve as the effective reservoirs in deep horizons:the physical properties of the former are not controlled by depth,and the latter were well developed characterized by high quality in deep horizons.The fracture-dominated carrier system of wide distribution is conducive to the vertical and horizontal migration of natural gas generated from ultra-deep source rocks.Multi-stage tectonic activities have led to the formation of multiple types of traps in deep layers at the northern margin of Qaidam Basin; meanwhile the continuous hydrocarbon generation of source rocks have facilitated the earlier,multi-stage hydrocarbon accumulation in these deep traps.In view of the above results,it is concluded that the traps around the hydrocarbon generation sag with well-developed deep large faults are favorable for deep gas accumulation,and the paleo-uplift at the basin margin and the large-scale anticlinal traps in the late tectonic zone are prospective areas for hydrocarbon exploration,with the deep layers in the piedmont of the Altun Mountain being the most prospective one.

Key words: accumulation condition, carrier system, bedrock reservoir, deep gas reservoir, Jurassic, northern margin of the Qaidam Basin

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