Reservoir formation conditions and key exploration & development technoloiges in the Yingdong Oilfield in western Qaidam Basin

Located in east part of Yingxiongling structural belt in the Qaidam Basin, the Yingdong oilfield has a extremely complicated ground condition. Due to no significant discovery, this oilfield was considered to have no favorable geologic conditions for formation of oil or gas reservoir. In the past few years, with continuous improvement in the mountain 3D seismic surveys and logging data interpretation, some breakthroughs were obtained in 2010, and the Yingdong oilfield, the largest-scale reserves of a single reservoir with highest organic matter abundance, most favorable physical property and optimal development efficiencies in the Qaidam Basin, had been discovered, the production capacity was up to 0.55 × 106 t. Through detailed analyses of the Yingdong oilfield, some studies, such as hydrocarbon accumulation conditions and technical challenges, are carried out, and following conclusions can be achieved. The Yingxiongling area is located in Mangya hydrocarbon-generation sag in the west part of the Qaidam Basin, its oil sources are rich; the Neogene Xiayoushashan Formation and Shangyoushashan Formation are dominated by wide and gentle delta front—shore-shallow lacustrine sediments with interbeds of sandstone and mudstone, the sandbodies are widely distributed with favorable physical condition, and the mudstone is the key caprock, combined with high-quality Paleogene hydrocarbon source rocks, a complete source-reservoir-cap assemblage can be formed. Large-scale detachment faults of the Yingdong area connect high-quality Paleogene hydrocarbon source rocks with middle-shallow buried structural traps, thus, reservoirs formed in the early stage are modified, and at the same time, hydrocarbons formed in the later stage continue to migrate and accumulate; in this way, the deep and shallow faults form a relay-style hydrocarbon transport system, and hydrocarbons are accumulated in the shallow structural traps in the later stage; in this area, the middle-shallow faults have good lateral plugging performance which is favorable for preservation of oil and gas. For complex landforms and reservoir features in the Yingdong area, the integral 3D seismic acquisition, processing and interpretation technology is developed for complex mountain areas to provide a reliable foundation for hydrocarbon exploration. For some problems in the Yingdong oilfield like long oil/gas-bearing intervals, great difficulty in identification of fluids, the development mode of multiple oil/gas/water systems in the long intervals is established, and the geologic modeling technology with constraint of multiple conditions on complex fault blocks is also developed. Thus, hydrocarbon accumulation mechanism in the Yingdong oilfield is clear, and some complex key technology of engineering are well solved, providing necessary geologic theories and technical supports for high-efficiency development and rapid production construction in the Yingdong oilfield. Keywords: Neotectonic movement, Structural traps, Faulted block, Complex mountain areas, High-efficiency development, Xiayoushashan Formation and Shangyoushashan Formation, Yingdong oilfield, Qaidam basin