Abstract: Origin of Subpressure and Hydrocarbon Exploration in Shiwu Fault Depression, Songliao Basin, China

Guojun Zhou

In the Shiwu fault depression, evolutionary history of formation pressure can be deduced on the basis of structural evolutionary history. Uplifting and denudation caused high pressure to evolve into low pressure. The main factors controlling the evolution are (1) generation of fractures and release of high pressure, (2) temperature reduction and water-cooling pressure reduction, (3) desaturation and gas dissociation, and (4) diffusion and dissipation of gas.

According to the pressure evolutionary history, the study area has had two pool-forming stages. During uplifting and denudation, fracture generation, and the transformation from high pressure to low pressure, the protogenic high-pressure oil and gas pools were transformed into low-pressure relic pools, and secondary pools with normal pressure formed above them. A predictor equation of the low pressure has been proposed on the basis of the balanced depth in the undercompaction zone, as well as the eroded thickness of the overlying strata. According to this equation, measured pressure data, well logs, and seismic interval velocity data, pressure prediction has been made in the study area by drawing on experience gained at key points.

In the light of pressure evolutionary history and pool-forming history, it is regarded that the exploration potential of the low-pressure zone is not as good as that of the hydrostatic-pressure zone. This has been verified by petroleum exploration activities.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994