Turner rate

• The critical Turner rate is defined as the minimum rate required to lift liquids in the wellbore. The plot is the ratio of gas rate / critical-Turner rate (q/q_T).
• If the ratio < 1, there is a likelihood of liquid loading.
• The critical Coleman rate is an alternative to the Turner rate. The Turner rate is approximately 20% higher than the Coleman rate, and many operators prefer the Coleman calculation to that of Turner.
• If the ratio is < 1, calculations for sandface pressures from wellhead measurements are likely to be in error, due to not accounting for a “stagnant” liquid column. For additional information, see the WGR & water rate plot.

Reasons for inconsistencies:

• The gas rate below which liquid loading occurs depends on the diameter of the pipe and the pressure of the gas. Liquid loading occurs more often when producing through the casing.
• When liquid loading is indicated (ratio < 1), it is often accompanied by a reduced production of liquids, or a reduced liquid / gas ratio. For additional information, see the WGR & water rate plot.
• Usually following the onset of liquid loading, the tubing is replaced with a smaller diameter tubing to increase the gas rate and lift the liquids. This event may not be recorded.
• If the specified tubing ID is incorrect, the Turner rate calculation may also be incorrect. This affects the value of the critical Turner rate, but has little effect on the calculated sandface flowing pressures.

• Tubing and casing pressures track each other when there are no problems in the wellbore (for example, liquid loading, hydrating).

Reasons for inconsistencies:

• Diverging tubing (p_t)and casing (p_c) pressures are an indication of liquid loading or hydrating in the wellbore.
• To convert from wellhead to sandface pressure, use the quiet-side pressure (usually the casing) and assume the liquid level is at the end of tubing (EOT).
• If sandface pressure is being calculated from wellhead measurements, and the flowing side is being used, multiphase flow calculations must be used, and their accuracy is poor.