Inflow Performance and Pressure Interference in Dual-Completed Wells With Water Coning Control

Abstract

Dual-completed wells with Downhole Water Sink (DWS) are used for water coning control in oil reservoirs with bottom water drive. In DWS wells, the second (bottom) completion—placed in the water column—is used for draining water. This prevents the water cone invasion and allows free oil inflow in the top completion. The decision on using DWS or a conventional (single-completed) well is based upon deliverability comparison of the two wells. This paper shows how to describe DWS well deliverability in terms of the top and bottom production rates, water cut, and pressure drawdown. Also, the effect of pressure interference between two well completions on deliverability limits has been studied and qualified experimentally. DWS well deliverability depends on two variables, pressure drawdown and water drainage rate, and is described by a three-dimensional Inflow Performance Domain (IPD). Visual-Basic software based on a new analytical model of IPD has been developed to calculate critical (fluid breakthrough) rates for oil and water. The critical rates identify inflow conditions to the well’s completions—single or two-phase inflow. Also calculated are the values of water cut and maximum pressure drawdown at the well. An example demonstrates the procedure and a complete IPD plot. The experimental study, using a Hele-Shaw physical model of DWS well, demonstrates the reduction of well’s deliverability caused by pressure interference from the second (bottom) completion. The experiments have shown, however, that the deliverability decrease is small and over-compensated by the increase of oil rate due to simultaneous reduction of water cut.