State-of-the-art Review of Liquid Loading in Gas Wells

Falcone, G. and Barbosa, J.R. (2013) State-of-the-art Review of Liquid Loading in Gas Wells. DGMK/ÖGEW-Frühjahrstagung, Fachbereich Aufsuchung und Gewinnung, Celle, Germany, 18-19 Apr 2013.

Abstract

Gas wells suffering from liquid loading are incapable of removing the liquid associated with produced gas from the wellbore. This phenomenon is initiated when the upward gas velocity in the well falls below a critical value at which point the liquid, that was initially flowing upwards, begins to fall back. This liquid accumulates downhole, where it increases the hydrostatic back-pressure on the reservoir, destabilises the multiphase flow in the well (following flow regime changes), decreases production rate and, in severe cases, kills the well. The typical liquid loading sequence begins with a gas flow rate that is high enough to transport all liquids to surface and there is no liquid fall-back in the well. However, as the gas velocity slows or the liquid content in the well rises, there is insufficient energy in the well to carry all liquids to surface and some begins to flow backwards. As the hydrostatic head downhole increases, the liquid column that has accumulated in the well can re-enter the near-wellbore region of the reservoir. This results in the well becoming “unloaded” so that it can flow once more, with the gas carrying all liquids to surface. However, the reinjection of liquids into the reservoir may cause formation damage, which will impair the well productivity. This cycle continues, providing the typical intermittent response of liquid-loaded gas wells, until the reservoir potential starts to fall or the liquid yield rises. Diagnosing liquid loading is often difficult as the affected well(s) may continue production without any substantial performance impairment for a long period of time. Typical symptoms of liquid loading include sharp drops in the cumulative production decline curve, the onset of liquid slugs in the surface facilities, abrupt changes in the flowing pressure gradient, low temperature spikes at the wellhead and declining water production or condensate-gas-ratio. Many remedial lifting options have been devel oped for use in the field; some unloading solutions (e.g. velocity strings) rely on the existing natural energy of the system, while others (e.g. downhole pumps) provide extra energy to bring the water to surface, so reducing the liquid loading problem. As each of the remedial options have their own technical characteristics, their applicability varies depend ing on the characteristics and the status of the well. Although a number of established techniques are used to alleviate the effects of liquid loading, the industry still lacks reliable predictive models to help select the best remedial option for a particular loading occurrence. In this paper, an up-to-date critical review of current methods to forecast the onset of liquid loading and model the subsequent wellbore performance is presented. The review also includes recent attempts to understand the dynamic interactions between reservoir and wellbore during liquid loading.

• Item Type: Conference or Workshop Item
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Falcone, Professor Gioia
• Authors: Falcone, G., and Barbosa, J.R.
• College/School: College of Science and Engineering > School of Engineering > Systems Power and Energy