An interative procedure to determine depth and time of primary oil migration and expulsion efficiency of source rocks

This study seeks to propose an iterative procedure for estimating time and depth of primary oil migration and expulsion efficiency of a source rock. The procedure is based on two assumptions: (a) oil moves out of the source rock as a separate phase; and (b) oil migration does not start until residual oil saturation is reached. Oil saturation increases with oil generation and porosity reduction during burial. Changes in total volume, pore and oil volumes by oil generation and compaction are calculated at discrete time steps. Oil expulsion begins when oil saturation reaches residual oil saturation and relative permeability of oil rises above zero. The volume of oil expulsion can also be calculated iteratively after oil migration starts. The difference between oil generation and residual oil gives the volume of oil expulsion at each time step. The mass ratio of oil expelled to total oil that is generated provides the expulsion efficiency of the source rock.