Abnormal formation pressures and oil-gas migration in China

Abnormal formation pressures occur not only in marine strata but also in terrestrialsedimentary basins in China.It develops most in Tertiary,followed by Mesozoic and Palaeozoic.Residualpressure decreases with the age of strata.Abnormal pressure raainly results from imbalanced compaction andhydrocarbon generation,and depends on various geological conditions.The secondary cause is the uplift ofcrust at the late stage and the transformation of clay minerals.Practical data show that the abnormal forma-tion pressure provides the dynamic force and passages for the primary migration of oil-gas,and in reservoirs,itcan affect the distribution of flow potential,which controls the migration direction and the aocumulation placeof oil and gas.