ON THE ORIGIN OF PRESSURE FIELD IN THE FUYANG FORMATION OF THE NE SONGLIAO BASIN

The pressure field in the Fuyang Formation can be obviously divided into 4 areas which are mainly controlled by the origin and evolution of hydrodynamic field.The pressures in centripetal and cross-formational flow areas are normal with the coefficients decreasing from 1.02 to 0.97 along flow direction,while the pressure in centrifugal flow area is dominated by overpressures,with the coefficients decreasing from 1.30 to 1.06 along flow direction,being normal pressures towards its rim,and motionless area is dominated by subpressures with the coefficients of 0.96～0.75.The pressures are related with the recharge-discharge system of pore fluids and pressure field is also influenced by(1)gas escaping,(2)evaporation of water,(3)hydration of unstable debris,such as feldspar and volcanic fragments,(4)unloading caused by bed evasion,and(5)geothermal decrease.