Establishing Critical Gas Velocities for Liquid Loading in Deviated Gas Wells

Abstract

Severe liquid loading in wells producing from some wet gas reservoirs, results in the well being unable to transport fluids to surface. In field applications, liquid loading is known to be more pronounced in deviated wells than in vertical wells. This study highlights a methodology to estimate the critical velocities for liquid loading in inclined gas wells. Knowledge and use of the technique is of importance to production engineers and stakeholders of a gas asset. Test data from a 3-inch diameter line with inclination from vertical to near horizontal was obtained from open literature. For each deviation angle, and based on the test conditions, a correlation for liquid holdup in inclined wells was used to determine the void fraction at the region of interest. The corresponding maximum and average film thicknesses, as well as the interfacial friction factor were determined. The principle of momentum conservation for a deviated tubing was applied and the superficial critical gas velocities for liquid loading were estimated. These estimated velocities were compared to those obtained from the test data. For the different superficial liquid velocities investigated, the estimated critical gas velocities increased with increasing deviation from vertical. The maximum critical velocity was reached when the deviation angle was about 40° to 50° from vertical. Beyond this point, the critical gas velocity decreased with increasing deviation angle from vertical up to the near-horizontal inclination. The results also showed that the gas critical velocity increased with increasing liquid superficial velocity. The overall trend of the critical velocity variation was similar to the trend in the actual test data obtained from open literature. The range of estimated critical gas velocities varied from about 9 m/s to about 35 m/s, with overall Root Mean Square Errors between 3.3 m/s and 6 m/s. In conclusion, results from this methodology was able to give a first-hand estimate of critical superficial velocities for inclined gas wells. This work presents a methodology to estimate critical gas velocities for inclined gas wells. This knowledge is important for field engineers and asset managers in the planning and production phases of gas wells. The benefits include optimizing the gas completion hardware during design, and maximizing gas flow rates during production operation. Overall, this increases the economic bottom-line for the field operator.