Segregated production method for oil wells with active water coning

Abstract

This paper describes a simulation study of a novel method to control water coning in an oil producing well. The method uses a dual-completion configuration that is above and below OWC. In this configuration, the well section above OWC is completed in the oil zone and produces oil, while the well section completed below OWC in the water-saturated zone produces water both independently of and concurrently with oil production. Segregated water production creates a drain (rat hole water sink) to control the rise of the water cone. Coning control results from the effect of water sink on flow potential between the sink and oil-producing perforations. The study investigated simulated production performance of the well both with and without the rat hole water sink. At first, the water sink's position and flow rate were examined to determine the critical production rate of oil (i.e., maximum production rate without the water breakthrough). Next, the various amounts of water produced during oil production at rates greater than critical were compared. The comparison study used both lab data and field data from an actual well/reservoir system of known geometry and reservoir properties. The coning behavior of the production system with the rat hole water sink was mathematically modelled using the flow potential distribution generated by two constant-terminal-rate sinks located between the two linear boundaries and the constant-pressure outer radial boundary. The model was verified by using the existing and simulated data of water coning in conventional wells and by setting the water sink flow rate at zero, with oil being the only produced fluid. Also, verification tests were used to select the type of oil reservoir with the thick oil zone and the small dip angle for the comparison studies. The study demonstrates the existence of an active mechanism to control water coning with the rat hole water sink. It shows that a sink with low water flow rate may prevent the water cone from breaking through the oil zone and into the producing perforations so that the oil with no water cut can be produced above the critical flow rate. A simulation using the new method yielded less produced water and either the same or a higher oil rate than the conventional method. However, potential increase of oil production above its critical value is limited by the stability of the controlled water cone. Also, for high oil production rates, more precision is needed to control the water production rate.