Pore Level Modeling of the Effects of Wettability

Abstract We describe a network model to study the effects of wettability which is based on the pore level scenario of Kovscek et al.1 The network model simulates primary drainage, water injection and oil re-injection. The portions of the rock surface contacted by oil after primary drainage can become oil-wet. Water remains in the corners of the pore space and these sections remain water-wet. During forced water injection, oil layers can become sandwiched between water in the corners and water in the center of the pore space. These layers maintain continuity of the oil phase and allow low oil saturations to be achieved during forced water injection. However, the flow rates through them are very low. We investigate models with different fractions of oil-wet pores, contact angles and initial water saturations. We present relative permeabilities, recovery curves and capillary pressures and interpret the results in terms of the behavior at the pore scale. The residual oil saturation, Sor, shows a non-monotonic dependence on wettability. In many cases weakly water-wet and moderately oil-wet systems have a lower Sor than either strongly water-wet or strongly oil-wet systems. Weakly oil-wet media may have a high Sor, and low relative permeabilities to both oil and water.