Maximizing recovery from strong water drive, permeable reservoirs in North Kuwait usually require a combination of approaches. Implementing partial perforating techniques across the oil column above the oil/water contact and installing tubing sizes that secure maximum natural flow life cycle are presently utilized to extend the natural flow life cycle in strong bottom- and edge-water drive reservoirs. Limiting production rate at or below critical coning rate, and conversion to Artificial Lift when the water cut increase forces cessation of natural flow, further improve the ultimate recovery of oil from these reservoirs.
In pilot Well-A, approximately 55% of the oil column above the Oil/Water contact was perforated on initial completion. Within 6 months from initial completion, the Watercut increased from 0% to 53%, then gradually increased to 74% over the next four years of natural flow life. Before the natural flow ceased completely, the well was worked over to install the innovative Downhole Water Sink completion. This completion design comprised of a very short perforated interval at the original depth of the Oil/Water contact and with another perforated interval across a highly permeable aquifer below the layer of interest. A shrouded ESP with Y-tool assembly was then installed, able to generate a drawdown just below the original OWC that is greater than the drawdown across the originally perforated interval.
This pressure sink created at the OWC controls the further development of the water cone around the wellbore thereby increasing the maximum coning rate, in addition to accelerating and increasing the ultimate recovery from this water-drive completion. The excessive water that is usually produced to surface, and processed along with the oil, is now significantly reduced since most of it is now re-directed to a deeper non-oil-producing aquifer. Though the watercut is never eliminated at the oil perforations, the natural flow life cycle is extended, and thereby the ultimate recovery considerably improved. Actual % improvement is yet to be determined since the watercut of the produced fluid at surface has not yet risen to the level that causes cessation of natural flow.
This pilot application of the Downhole Water Sink technology to this North Kuwait water-drive reservoir opened up immense opportunities for comparable recovery improvements in similar and even larger water-drive reservoirs in other Assets within the company. Where reservoir pressures are insufficient to maintain natural flow, a dual ESP system is already designed to lift the oil column using the same Downhole Water Sink principle.