Network analogues of wettability at the pore scale

This paper is part of the special publication Developments in petrophysics (eds M.A. Lovell and P.K. Harvey). This paper examines the macroscopic consequences of wettability variations at the pore scale. Important theoretical issues relating to distributed contact angles are examined and a process simulator capable of simulating the full flooding cycle characteristic of laboratory wettability tests is described. Simulations predict that final waterflood recoveries from weakly water wet (or even weakly oil wet) systems can often exceed those from strongly water- wet systems (even though initial imbibition rates may lead to the opposite conclusion). The underlying pore level physics has been explored by defining a capillarity surface, which incorporates the combined effects of both contact angle and pore dimension during the imbibition process. Finally, a regime-based framework has been developed which may go some way towards reconciling apparently contradictory wettability experiments.