Water-oil ratio
- Abbreviation
- WOR
- Also known as
- WOR
The water-oil ratio (WOR) is the volume of water a well or field produces divided by the volume of oil it produces over the same period. A WOR of 5 means five barrels of water for every barrel of oil. It rises as fields mature and strongly affects operating costs.
What is the water-oil ratio?
Most oil wells produce water along with oil, and the proportion of water usually grows over time as reservoir water moves toward the well or injected water breaks through. The water-oil ratio expresses that relationship directly:
WOR = water produced / oil produced
WOR and water cut
Water cut expresses the same information as a fraction of total liquid. The two convert directly:
- Water cut = WOR / (1 + WOR)
- A WOR of 1 equals a 50 percent water cut. A WOR of 9 equals a 90 percent water cut.
WOR emphasizes how many barrels of water must be handled per barrel of oil, which ties it directly to costs.
Why WOR matters
- Operating costs. Every barrel of produced water must be lifted, separated, treated and disposed of or reinjected, raising lease operating expense.
- Economic limit. As WOR rises, a well eventually reaches the point where oil revenue no longer covers water handling costs.
- Diagnostics. Engineers plot WOR and its rate of change over time to identify the cause of excess water, such as coning, channeling or normal displacement, and to choose water control measures.
- Forecasting. WOR trends are used to estimate remaining recoverable oil.
What affects WOR
Reservoir drive mechanism, waterflooding performance, mobility ratio, completion quality, and mechanical problems such as casing leaks can all influence how quickly WOR rises.
Frequently asked questions
It depends on economics, but mature fields commonly operate at WORs of 10 or higher, meaning more than 90 percent of produced liquid is water.
Sometimes, through water shutoff treatments, repairing mechanical problems or changing injection patterns.
Sources
- water-oil ratio; water cut, SLB Energy Glossary
- Water control diagnostic plots, K. S. Chan, SPE Annual Technical Conference, 1995