EFFECTS OF CONNATE WATER ON IMMISCIBLE DISPLACEMENT PROCESSES IN POROUS-MEDIA

Connate water is the name given to the water that occurs naturally in petroleum reservoirs in the form of an invisible dispersion or film wi thin the oil phase. In this study, the effects of connate water on imm iscible water/oil displacement processes in porous media were investig ated. Special attention was directed towards the effects of connate wa ter on viscous fingering instabilities and on oil recovery displacemen t efficiency. Experiments were performed using a two-dimensional, wate r-wet, consolidated porous medium cell of porosity 0.30. The fluid sys tem employed was water displacing a lower-density paraffin oil phase. Three different flow modes were used for the experiments, namely, hori zontal, vertical-upward and vertical-downward. For each flow mode, cor responding pairs of experiments were performed for five different flow rates in the absence and presence of connate water. At low flow rates , the irregularity of the viscous fingering pattern increased signific antly in the presence of connate water and the corresponding oil recov ery decreased. At high flow rates, the fingering pattern and oil recov ery were largely independent of the flow mode and the presence of conn ate water. Depending on the flow mode situation, buoyancy effects can either stabilize or destabilize the displacement process when the dens ities of the two fluids are different. (C) 1997 Elsevier Science S.A.