Combined Polymer and Emulsion Flooding Methods for Oil Reservoirs With a Water Leg

Abstract

Abstract Many light and medium gravity oil reservoirs have an underlying contiguous water zone, in communication with the oil zone. As a result, a conventional waterflood is often unsuccessful because the injected water tends to channel into the more conductive bottom water layer. The research results discussed here show that modified waterfloods of such reservoirs may still be economically viable. Experiments were carried out in a three-dimensional model, employing a number of techniques, including horizontal wells. The flooding fluids consisted of polymer solutions and emulsions. The most successful strategy was to use a 10% quality oilin- water emulsion as a blocking agent, and a polymer solution as the mobility control fluid. Such a combination yielded oil recoveries approaching 70%, as compared to 50% for a conventional waterflood, for equally thick oil and water layers. The experimental results were correlated by means of a threezone analytical model allowing for crossflow between oil and water layers, which is useful for predicting the performance of such floods. Experiments utilizing horizontal injector-producer pairs for conventional waterfloods in the presence of a water leg, as well as floods utilizing polymers and emulsions showed only limited gains over vertical well pairs. Guidelines are offered for the choice of well and fluid combinations for successful floods. Introduction Waterflooding is a relatively inexpensive secondary recovery method that is used widely in the petroleum industry. In the provinces of Alberta and Saskatchewan a number of light and moderately heavy oil reservoirs contain a high water saturation zone in communication with the oil zone. Under conventional waterflood such reservoirs have been observed to show poor performance. The major reason for this is an insufficient and incomplete sweep of the reservoir by the injected water, which tends to move to the producing wells through the more permeable portions of the reservoir. This results in low recovery. Several laboratory model studies have been undertaken to investigate the effect of various parameters on oil recovery in bottom water reservoirs(1–8). High water cuts and rapidly decreasing oil rates early in the production life of such reservoirs have, in many instances, prompted their suspension or abandonment at very low levels of recovery(2). Mobility ratio is perhaps the single most important parameter in waterflooding bottom water reservoirs. A number of flooding fluids have been used to control mobility ratio. This paper examines effective techniques to waterflood bottom water reservoirs using polymer and emulsion as mobility control and/or blocking agents. The effect of vertical and horizontal injectors and different combinations were also investigated. Experimental Set-up and Procedure A diagram of the experimental apparatus is shown in Figure 1. The apparatus is made up of two constant rate pumps and a specially- designed aluminum core holder with a rectangular crosssection. The inside dimensions of the core holder were 5.08 cm (2.0 in.) wide, 7.62 cm (3.0 in.) deep and 122 cm (48 in.) long. Two pumps were used for simultaneous injection of two different fluids to simulate a vertical displacement front. The injection well was specially designed to allow the simultaneous injection of two different fluids.