During the production life of oil reservoir, the water cut gradually increases to high percentage. According to the recent analysis, average worldwide water cut reached 75%. Particularly, water cut in USA is higher than 90%. Most of the produced water is re-injected back into the reservoir as an environmental protection solution as well as to maintain reservoir pressure.
Promising new technologies are being advanced to reshape development strategies in petroleum production. Therefore, it is no longer necessary to dedicate wells to only production or injection; now, both functions can be performed within one multipurpose wellbore.
Downhole oil-water separation (DOWS) is a propitious solution regarding the largest–volume waste stream associated with oil and gas production using the multipurpose well concept. After the production of the hydrocarbon from the pay zone, the separation takes place either above the producing zone in the well bore or at the well head. Furthermore, the lighter phase flows to the surface facility and the heavier phase (water) is reinjected below the oil-water contact in the same pay zone. Technologies exist to reduce water-handling volumes at the surface by keeping the water downhole. These include Hydrocyclone separation, Centrifugal & Phase separator, combined gravity and coalescence, Rotary separator, vane-type separators, etc.
Although the technology was introduced in 1990's, limited number of trail application is so far installed. Different installations provide critical information on the feasibility and development of DOWS technology. This paper presents the state of the art issues of different separation techniques and designs like Hydrocyclone design, ESP design as well as issues related to verifying separation quality etc. The review summarizes the various papers and reports related to the DOWS technology. Particularly, previous review was written quiet some years earlier and therefore do not include the recent development of different components of the system.
The general adoption of the technology is dependent on the understanding of the process and the critical issue solving capacity in the oil and gas industry. As a way forward to the development of the technology, different in-situ options will be suggested considering limitations of the existing systems. Additionally, separation directly in the wellhead has been investigated and dual completion concept is proposed to maximize the efficiency of the system.