Downhole oil–water separation technology

Downhole oil–water separation (DOWS) technology is an emerging technology that separates oil and gas from produced water at the bottom of the well, and re-injects most of the produced water into another formation which is usually deeper than the producing formation, while the oil and gas rich stream is pumped to the surface. DOWS effectively removes solids from the disposal fluid and thus avoids injectivity impairment caused by solids plugging. Simultaneous injection using DOWS minimizes the opportunity for the contamination of underground sources of drinking water (USDWs) through leaks in tubing and casing during the injection process.

Overview

A DOWS system is installed at the bottom of an oil well, it separates oil and water in the wellbore. The oil rich stream is brought to the surface while the water rich stream is pumped into an injection formation without ever coming to the surface. A DOWS system includes many components but the two primary components are an oil/water separation system and a pumping/injection system used to lift oil to the surface and inject the water into a deeper formation. Two basic types of DOWS systems have been developed, one type uses hydrocyclones to mechanically separate oil and water and the other relies on gravity separation that takes place in the wellbore. Three basic types of pumping/injection systems are used with the DOWS technology. These include electrical submersible pumps, progressive cavity pumps and sucker rod pumps. Hydrocyclone separators are usually used with the electrical submersible pumps because of higher drawdown created with effective injection of water into the lower zone.

Advantages

1. Lower cost of oil production: DOWS technology reduces more than 70% of the water that was supposed to be produced thereby reducing the total cost of lifting, treating, re-injecting and disposal of produced water, the cost of production of oil is greatly reduced.
2. Reduction of environmental impact of oil and gas operations: Standard injection well operations pose a significant but manageable risk of environmental pollution. The highest risks occur due to surface spills during re-injection of the separated brine. By reducing the amount of brine brought to the surface and re-injected the environmental risks associated with re-injection wells can be reduced.
3. Pollution of underground sources of drinking water: produced water in most cases contains brines. With DOWS technology, dissolved impurities are not allowed to get to the surface hence they do not pass through intervals containing underground sources of drinking water (USDW). Also, since the water does not require re-injection from the surface, it will not pass through intervals of USDWs then, either. Therefore, the risks posed by large volumes of these fluids passing USDWs both exiting and re-entering the well upon injection are minimized.
4. Because DOWS technology uses underground equipment, surface brine disposal operations, which may involve pumps, pipes, tank batteries, and other storage facilities may also be reduced in size and extent if not altogether eliminated.
5. The DOWS system is used for re-injection thereby beefing up the drawdown pressure which can result in increased production rate.^[1][2][3]

References

1. Research by Aburime Conrad on Downhole Oil Water Separation Technology As A Means Of Downhole Water Control
2. Argonne and ALL-LLC (Argonne National Laboratory and Arthur Langhus Layne-LLC), 2001, Analysis of Data from a Downhole Oil/water Separator Field Trial in East Texas, prepared by Argonne National Laboratory and Arthur Langhus Layne-LLC for U.S. Department of Energy, National Petroleum Technology Office, Feb. Available at
3. Bowers, B., D.D. Lloyd, P. Schrenkel, and C. Matthews, 1996, “Downhole Application of Liquid- Liquid Hydrocyclones,” presented at Hydrocyclones ‘96, England, April