Abstract

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Title:: Geological Conditions of Tight Oil Reservoirs in Wudun Sag of Dunhuang Basin, Gansu, China

Author(s):: ZHANG Xue-cai; LI Jia-gui; LIU Quan-wen; 1. Oil and Gas Exploration Management Center, Shengli Oilfield Company, SINOPEC, Dongying 257000, Shandong, China; 2. Geological Logging Company, Shengli Oilfield Company, SINOPEC, Dongying 257000, Shandong, China; 3. Guangdong Research Center for Unconventional Energy Engineering Technology, Maoming 525000, Guangdong, China

Keywords:: tight oil; source rock; hydrocarbon accumulation; Jurassic; geological condition; exploration potential; Wudun sag; Dunhuang Basin

Abstract:: The exploration in Wudun sag of Dunhuang Basin, Gansu is poor. The basement is buried deeply; the thickness of Middle and Lower Jurassic is large; the potential for generating hydrocarbon is better; the reservoir is tight. The accumulation model of Wudun sag is self-generating and self-bearing, so that it is a new oil-gas exploration area. The accumulation geological conditions of Jurassic tight oil reservoirs in Wudun sag were analyzed, and the exploration potential was evaluated. The results show that the lacustrine mudstone and glutenite clastic reservoir are very favorable for forming the tight oil reservoirs in Middle Jurassic Zhongjiankou Formation-Lower Jurassic Dashankou Formation in Wudun sag; the average of total organic carbon is 3.26%, and the organic matter is mainly type Ⅱ in mature stage with better potential for generating hydrocarbon; for the clastic reservoir, there is mainly primary pore with ultra-low to low porosity and ultra-low permeability; the traps include structural, lithologic, stratigraphic and structural-lithologic in Wudun sag; hydrocarbon accumulation is both controlled by source rocks and structural settings; the further advantageous exploration targets are the traps with abundant reservoir growth and beneficial structural condition in the central sub-sag belts and reservoir nearby.