Oil Production by Spontaneous Imbibition from Sandstone and Chalk Cylindrical Cores with Two Ends Open

Abstract

During spontaneous counter-current imbibition of brine into oil-filled porous rock, it is generally assumed that the flow rates of the brine and oil are equal and in opposite directions. However, significant scatter and inconsistent dimensionless times were observed in experiments using matched-viscosity fluids in two ends open (TEO) sandstone cores using an established correlation factor. In further TEO experiments, the oil production at each end face was measured separately and ranged from being equal and symmetrical to highly asymmetrical, with almost all of the mobile oil being produced from one end in nominally duplicate tests. The dimensionless time for scaled imbibition increased with increasing asymmetry in oil production. Thus, for imbibition into cores with the TEO boundary condition, although the overall flows of brine and oil have to be equal, the individual flows at each end face are not necessarily equal and opposite. The asymmetry in oil production during imbibition with the TEO boundary condition was further investigated by imaging the in situ fluid saturations during imbibition, this time using homogeneous chalk and fluids with differing viscosities. In all cases, the amount of brine imbibed at each end face was almost equal even though there was sometimes significant asymmetry in the oil production. This behavior was probably caused by most of the capillary pressure driving imbibition being dissipated in the brine. With only small pressure differences required to produce the oil, any inhomogeneities in the rock which change the production capillary back pressure at the open faces can have a disproportionate effect on the symmetry of oil production.