METHODOLOGY FOR THE RESEARCHES ON OIL/GAS MIGRATION IN FAULTDOWN BASINS

Generally speaking,the generation and migration of oil and gas are essentially controlled by the evolution of a basin and faultings.The tectonic evolutionary cycles of a basin tend to be consistent with those of abnormal pressure of fluids.The period of faulting is most likely to be the main stage of oil/gas migration as the hydrocarbons become mature.The juxtaposition of sandstones and mudstones is resulted by faulting at both sides of a fault.Thereafter,oil/gas could migrate across or along the fault plane,i.e."stair-step" migration pattern.Such a migration pattern indicates that a fault plane can act not only as a migration path,but also as a trap.The data of the effective beds and the depth for hydrocarbon expulsion can be obtained by the interpretation of compact curves using dynamic analysis.Caution shoud be taken on applying geochemical data for oil/source rock correlation,tracing the migration path and calculating the expulsion rate of hydrocarbons because geochemical analysis would be interfered by many factors.The traditonal evaluation of source rocks based on the amount of residual hydrocarbons is not reliable enough.With the concept of "time sequence",the convinced results of the researches on oil/gas migration can be achieved only by the integrated analysis on the various data and informations mentioned above,which would checked by each other.