Challenge: Improve oil recovery and reduce water production and coning for a well completed near the oil/water contact (OWC) in a naturally flowing well
Solution: Install downhole water sink (DWS) technology below the OWC to divert water from oil zone and inject it into a lower aquifer
Results:
For naturally flowing oil wells with strong aquifer support, one of the most significant challenges for extending productive life is high water production caused by coning. Producing the water too soon reduces net oil production from the naturally flowing well in the long term and increases surface water handling requirements in the short term. Increasing surface water handling capacity incurs additional costs; therefore, production must be limited to sustain production within the limited capacity of surface water facilities.
For Kuwait Oil Company (KOC), the conventional solution to early water production is to partially perforate across the oil column above the OWC and install tubing sized to maximize the natural flow life cycle. However, water cut still tends to increase.
In Well A, only 55% of the oil column was perforated, but production still reached 53% water cut within 6 months and 74% water cut after 4 years. To extend the natural flow of the well, KOC investigated an alternative technical solution.
DWS technology improves oil production in vertical or moderately deviated wellbores (<60°) by creating a pressure differential to draw water away from the perforated interval. The fundamental principle of the technology is to create an equivalent pressure drawdown or pressure sink ΔP at or just below the OWC, within the water layer, that is equal to or marginally less than the ΔP across the perforated interval within the oil layer. This drawdown reduces the progression of the water cone into the oil column and is achieved with a high-volume ESP.
The pressure sink creates a preferential flow of bottom water or edge water, parallel to the bedding plane, just under the OWC. The water can then be injected directly into an underlying aquifer or produced to surface for processing and reinjection in a disposal well.
Designing the first DWS using an ESP for a naturally flowing well in Kuwait added some engineering complexity. The main challenge was that the well already produced more water than the standard DWS technology was designed to handle. A specialized inverted ESP could handle the additional water, but as a proof-of-concept installation, the completion string for Well A had to be designed with equipment available in country and with standard ESP technology. As a result, the reinjected water flow rate had to be limited to 4,000 bbl/d to minimize the risk of erosion damage to ESP equipment inside the shroud.
Before the DWS system was installed, new perforations were shot just below the OWC (to enable water flow into the pressure sink) and in the lower aquifer (to enable water reinjection). After installation, the ESP was operated for 2 weeks for water reinjection to start water cone reversal before restarting oil production. After full production started, oil production increased by 15% while water cut consistently decreased to stabilize at 70% water cut.
For additional details, see IPTC-18754.
