Effects of precursor wetting films in immiscible displacement through porous media

A computer-aided simulator of immiscible displacement in strongly water-wet consolidated porous media that takes into account the effects of the wetti ng films is developed. The porous medium is modeled as a three-dimensional network of randomly sized unit cells of the constricted-tube type. Precurso r wetting films are assumed to advance through the microroughness of the po re walls. Two types of pore wall microroughness are considered. In the firs t type of microroughness, the film advances quickly, driven by capillary pr essure. In the second type, the meniscus moves relatively slowly, driven by local bulk pressure differences. In the latter case, the wetting film ofte n forms a collar that squeezes the thread of oil causing oil disconnection. Each pore is assumed to have either one of the aforementioned microroughne ss types, or both. The type of microroughness in each pore is assigned rand omly. The simulator is used to predict the residual oil saturation as a fun ction of the pertinent parameters (capillary number, viscosity ratio, fract ion of pores with each type of wall microroughness). These results are comp ared with those obtained in the absence of wetting films. It is found that wetting films cause substantial increase of the residual oil saturation. Fu rthermore, the action of the wetting films causes an increase of the mean v olume of the residual oil ganglia.