Formation mechanism of underpressured reservoir in Huatugou oilfield of Qaidam basin

Abstract

Underpressured reservoirs are widespread in the Huatugou (花土沟) oilfield of the western uplift in Qaidam basin, western China. At depths between 462 and 1 248 m, the pressure of Neogene reservoirs in the Huatugou oilfield is only about 40% to 80% of hydrostatic pressure. Based on a study of the geological characteristics of these underpressured reservoirs, this work used fluid inclusion analysis and numerical simulation to investigate the mechanism creating these abnormal pressures and to evaluate the characteristics of the hydrocarbon distribution. The results show that the underpressured reservoirs are all well-sealed by undercompacted and thick mudrocks. The large-scale tectonic uplift in the late Himalayan plays an important role in the generation of underpressure in the Huatugou oilfield. At the beginning of this movement, the field was overpressured due to episodic petroleum accumulation. Later, structural uplift and erosion led to porous rebound and a temperature decrease, which produced the underpressure.

Keywords

underpressure / formation mechanism / structural uplift / Huatugou oilfield / Qaidam basin

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