reservoir · inflow performance
Water Cut
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Inputs
STB/d
STB/d
Description
Computes water cut — the fraction of total liquid production that is water — the most commonly reported production surveillance metric for tracking a well's water-handling trend over its producing life.
Variables
| Symbol | Unit | Description |
|---|---|---|
| WC | fraction | Water Cut |
| qw | STB/d | Produced water rate, measured at the same conditions/time as the oil rate. |
| qo | STB/d | Produced oil rate, measured at the same conditions/time as the water rate. |
Assumptions
- qw and qo are measured (or well-test-derived) rates at the same point in time and the same measurement conditions
- Both rates are surface (stock-tank/standard) rates, not reservoir-condition rates
- No significant water is being lost to the formation (e.g. via cross-flow) between the reservoir and the measurement point
Limitations
- A single-point measurement — does not itself reveal the underlying mechanism (aquifer influx, injection breakthrough, coning, or mechanical failure such as casing/tubing leak) driving the water cut
- Surface rates can be affected by separator or test-facility measurement error, particularly at very high or very low water fractions
- Does not account for produced water from a different source (e.g. condensed water in gas wells) versus formation water — both are counted identically in this ratio
Use Cases
- → Production surveillance: Track water cut over time to identify water breakthrough trends and estimate remaining oil-productive life.
- → Artificial lift / facility sizing: Size separators, pumps, and water-handling/disposal facilities based on current and projected water cut.
- → Workover/shutoff candidate screening: Flag wells with rapidly rising or excessively high water cut as candidates for a water-shutoff workover or economic-limit review.
Related Calculations
Region Notes
Permian Basin
Unconventional Wolfcamp/Bone Spring wells commonly show high initial water cut from flowback and fracturing fluid recovery before declining to a lower baseline formation water cut.
Gulf of Mexico
Strong aquifer-supported reservoirs often show a rapid, sustained water-cut rise once the advancing water contact reaches a well's perforations.
North Sea
Waterflooded Brent Group fields track water cut closely against injection volumes to manage sweep efficiency and identify early breakthrough in high-permeability streaks.
Global
A sudden step-change increase in water cut (rather than a gradual trend) often indicates a mechanical issue (casing/tubing leak) rather than a genuine reservoir water-breakthrough event — investigate before assuming a reservoir cause.
References
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