This paper analyzes the problem of heel coning under a variety of drive mechanisms and studies how deployment of downhole flow control devices along the length of the horizontal well affects this phenomenon. To reproduce the heel coning effect for homogeneous permeability fields, wellbore hydraulics must be taken into account. The control approach adopted in this work aims to achieve equal inflow from the heel and toe halves of the completion by adjusting the choke position in accordance with the in-situ flow rate. This strategy likens the behavior of the instrumented well to an infinite conductivity well, as far as inflow is concerned. The control strategy, however, has an outflow/lift cost, as it requires running stinger tubing inside the liner. For water-drive, this scheme results in delay of water breakthrough and extension of the pure oil production plateau. Alternatively, plateau production could be increased. For gas cap-drive, analogous conclusions hold except that the gas/oil ratio constraint necessitates a cycled production scheme with rate cutbacks for successive cycles. For the combined aquifer- and gas cap-drive, control mitigates gas coning more than water coning, because the well is positioned nearer the water-oil contact to satisfy the maximum recovery criterion within the operational constraints adopted in this study. Active control by downhole valves, therefore, is an effective means of overcoming the problem of heel coning where the displacing phase is water, gas, or both. Drainage becomes isotropically more uniform. In practice, realization of this scheme requires a fully coupled flow monitoring and control system.
Examination of the applicability of intelligent completions to the problem of heel coning is of importance in at least two respects. First, it introduces an active strategy to overcome a problem whose resolution has hitherto been attempted by passive means, i.e., tapered drainholes, labyrinth screens, nonuniformly slotted liners, and stinger completions.1 It is an evolution from passive to active control. Second, it broadens the scope of intelligent completions from productivity enhancement by commingling production, to productivity enhancement by controlling sweep. It is a shift in focus from production to recovery.
This paper examines the problem of coning in its various forms for homogeneous permeability fields to provide a basis for the resolution of the more important problem of sweep control in heterogeneous formations, which requires a strong coupling of monitoring and control. It examines the single-well behavior; the multiwell problem is examined in a parallel work.2
Statement of the Problem
It is to be determined whether the deployment of downhole flow control can improve the performance of a horizontal well draining a water-, gas cap-, or dual-drive reservoir subject to realistic operational constraints. This problem reduces to determining whether the phenomenon of coning can be overcome by utilizing downhole flow control.