Downhole Oil/Water Separation Moves Into High Gear
Authors: Peachey B.R. , Solanki S.C. , Zahacy T.A. , Piers K. 
Published: March 2010

The Centre For Engineering Research Inc., now C-FER Technolgoies Inc. (C-FER), New Paradigm Engineering Ltd., and a consortium of over 39 oil producers and equipment suppliers have spent the last six years developing and testing a Downhole Oil/Water Separation (DHOWS) process which consists of hydrocyclones and conventional pumping equipment. By end 1996, over 18 field trials were completed using electrical submersible pumps (ESP), progressing cavity pumps (PCP) and beam pumping systems in a wide variety of conditions. In the original prototype ESP application, water reductions of up to 97% were achieved. Generally, the water oil ratio (WOR) to surface can be reduced to two or less.

A brief summary is provided of the field trials completed and the key results achieved, including oil production increases, water reduction, predicted increases in reserves recovery and general factors affecting a successful DHOWS application. The challenges which have been overcome are discussed together with an outline of potential future applications and challenges. It is anticipated that DHOWS applications will soon change the current paradigms of the industry in relation to what is possible in the area of water management.

Introduction

As many "oil companies" have begun to recognize, they should really be known as "water companies." The majority of oil wells, especially in the more mature North American fields, produce more water then they do oil. In Western Canada, the average water oil ratio (WOR) for all the conventional production is at nearly six cubic metres of water per cubic metre of oil. The average WOR in Alberta has been rising as more of the production comes from large mature fields. These water production trends have been relatively consistent in Alberta and Saskatchewan for a number of years (Figure 1) with some dips occurring when oil prices dropped. British Columbia has remained at a consistently lower average WOR for the province. As Alberta's production of both oil and water dominates over the smaller volumes from Saskatchewan and B.C., the total western Canadian WOR trend closely follows the Alberta provincial plot(1).

As water production rises, so do the costs and problems associated with it. Artificial lift equipment, gathering lines, surface facilities, and water disposal systems reach operating capacity limits, which in turn forces a reduction in oil rates. As produced water rates continue to grow, capacity additions to handle more water become difficult to justify, due to the continually declining oil rates. Corrosion rates may also increase and cause increased maintenance and corrosion prevention costs in older facilities and increases in the size, frequency and clean-up costs for brine spills from gathering or disposal lines. Adding to the problem is the pressing need for more disposal wells, more injection pipelines and injection pumps while the revenue stream continues to fall and the operating cost per cubic metre of crude increases.

The bottom-line is that with an average WOR of six and an assumed, all costs included, average water handling cost of C$3/m3 of water, then the total water bill for the three main producing provinces is now over C$1.2 billion/yr. vs. an average cost of less than C$0.4 billion/yr. in 1980.