WGR & water rate

• A sudden increase in the water rate could indicate future productivity problems.
• The data following a rapid increase in WGR should be treated with caution, especially if the pressure measurements are at the wellhead.
• If pressure data is measured at the midpoint of perforations (MPP), then liquid loading or any other wellbore issues will not affect the production data analysis.

Reasons for inconsistencies:

• A sudden increase in the water rate could be due to coning, or a reservoir water influx. Either way, operating problems due to wellbore effects are likely to result in reduced productivity.
• The conversion of wellhead pressure to sandface pressure changes if water production is present (because of liquid hold-up in the wellbore).
• If the water rate is not reported, the quiet-side pressure data can be used instead, as it is not affected by an incorrect liquid rate at the end of tubing (EOT).

• For gas wells with low WGR, the assumption of single-phase gas flow may still be valid.
• For high WGR, the assumption of single-phase flow may not be valid. Data exceeding an approximate threshold value of 100 bbl / MMScf should be used with caution, as typecurves and analytical models assume single-phase flow.

Reasons for inconsistencies:

• Water coning results in a changing skin, which can invalidate the reservoir models in use.
• Saturation changes in the reservoir result in varying effective permeability.

• A sudden decrease in WGR coupled with an unstable water rate could indicate liquid loading.

Reasons for Inconsistencies:

• When the gas rate decreases below a certain value known as the critical rate, the gas can no longer lift the liquids in the wellbore, and liquids start to accumulate. This is known as liquid loading and can result in a decrease in apparent water production. For more information, see the Turner rate plot.
• If sandface pressures are being calculated from wellhead measurements, an additional pressure drop may need to be added to represent the “stagnant” column of liquid.

• Fluctuations in WGR are an indication of slug flow.

Reasons for inconsistencies:

• If slug flow is indicated, yet no water rate is reported, then the quality of the calculated sandface pressures may be questionable, even if the wellhead pressures are of good quality.