Experimental investigation of wettability effect and drainage rate on tertiary oil recovery from fractured media

Vertical displacement of oil by gas is one of the most efficient methods for oil recovery from naturally fractured reservoirs. Unlike the homogeneous media, the ultimate oil recovery by gravity drainage in fractured media is more dependent on the production rate. Hence finding the optimum production rate for more oil recovery with respect to the properties of media seems to be essential. In this work, unconsolidated packed models of cylindrical geometry surrounded by fractures were utilized to perform a series of flow visualization experiments during which the contribution of different parameters such as the extent of matrix wettability and the withdrawal rate were studied. In addition, mutual effects of wettability and production rate on tertiary oil recovery efficiency through controlled and free fall gravity drainage processes were also investigated. Experimental results obtained from tertiary gravity drainage experiments demonstrated that just before gas breakthrough, lower withdrawal rates facilitate the tertiary oil recovery under the film flow mechanism, which leads to a higher ultimate recovery factor. However, after gas breakthrough, monitoring oil recovery by gravity drainage showed that higher production rates recovered more oil. Furthermore, under tertiary recovery processes in low-production cases, oil-wet systems achieved higher recovery factors, while at high withdrawal rates, more oil was recovered for 50% oil-wet media.