In the last 8 years, coiled-tubing–deployed ESP (CTDESP) systems have developed into a proven technology marrying the cost-effectiveness of coiled-tubing conveyance with the benefits of electrical submersible pumping (ESP) systems.
Simultaneously, great strides have been made in the form of real-time measurement of reservoir and production data such as pressure, temperature, and flow rate, by means of permanent gauges placed in the completion string and the use of fiber-optic distributed temperature systems.
CTDESP technology with real-time monitoring and control results in an alternative deployed intelligent completion that is able to optimize pump performance and run life, control injection rates, and maximize ultimate recovery.
Such a system was developed specifically for a Shell Sabah Berhad (SSB) medium oilfield, offshore Sabah- Borneo, East Malaysia. This particular reservoir is a mature depleting field, requiring pressure maintenance to extract more of the reserves. After 2 years of production, the oil rate of the primary reservoir had declined by about half. Studies showed that pressure maintenance by water injection (WI) was feasible and beneficial. However, high capital cost and long lead times prevented the implementation of a conventional WI scheme because the existing, unmanned platform was too small to accommodate a WI facility. The lithology of the area is conducive to pressure maintenance with a large natural aquifer dumping from an upper zone into the lower producing zones (i.e., dumpflood). Two horizontal wells were drilled and completed, allowing natural dumpflooding of an estimated 3,000 bbl/d/well. It was clear that augmenting the natural dumping ability of the upper zone aquifer with an inverted ESP would boost production (up to 10,000 bbl/day per well), accelerate the reservoir pressure maintenance, and increase the sweep in the main producing reservoir.
With anticipated tubing-deployed ESP run lives of 1 to 3 years, the ESP dumpflood strategy would not be a cost-effective solution because of the cost of rig mobilizations required for ESP workovers. Therefore, a CTDESP system was selected to allow installation and subsequent change-out without rig assistance. Such a system was evaluated to be USD 25 million more cost-effective than a conventional surface injection system over the life of the project. In the past 3 years, the assisted intelligent dumpflood strategy has shown its value. By boosting the reservoir pressure, the ultimate recovery factor is believed to have increased from 24 to 48%, adding approximately 10 million bbl of additional reserves. Additionally, one of the nearby production wells has shown a net increase of 600 bbl/d of oil since the start of assisted dumpflooding operations.