Development of engineering tools to evaluate deliquification measures for gas wells

David List

Research output: ThesisMaster's Thesis

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Most of the produced natural gas is accompanied by small amounts of free liquids which originate from either the reservoir or condensation in the production tubing. At the beginning of a gas well’s lifecycle, these are lifted out of the well by the gas stream itself. However, when the productivity of a well declines, the in-situ gas velocity drops, the liquids are no longer transported by the gas stream and start to collect in the well. This phenomenon, which is called liquid loading, results in a liquid column exerting hydrostatic pressure on the perforations and thus drastically reducing the productivity of the well or killing it all together. Subsequently, it renders these horizons uneconomical and hence also deteriorates the achievable recovery factor. Although there exist numerous technical approaches to remedy this problem, only a few of them are operational sustainable and economically viable, considering that the wells near the end of their lifecycle. A few years ago, four selected deliquification methods were piloted in OMV Austria with results reaching from successful to unsatisfactory for the different pilot wells. This thesis aims to establish not only the theoretical knowledge but also an understanding of the underlying principles or governing mechanisms, to develop a set of engineering tools to evaluate and troubleshoot these selected deliquification methods. The thesis starts with a detailed literature review describing popular liquid loading criteria, like for example Turner’s or Coleman’s critical velocity criterion as well as their limitations and shortcomings. This is followed by elaborating on the four selected methods, velocity string, surface compression, foam lift and plunger lift. In the practical part, three different computer-based engineering tools are created. The first one has the purpose of basic unit conversion of the critical liquid loading related input parameter, for PROSPER, a nodal analysis program which is widely used for tubing size and velocity string design. The default value is considered too conservative by experts, which is also indicated by data evaluated in this thesis. Therefore, it is advisable to use values provided by the literature which make this particularly error-prone unit conversion inevitable. Secondly, a separate tool was built, dedicated to evaluating the feasibility of plunger lift and subsequently analyzing the disappointing performance of the pilot. Using this tool, the root cause can be identified and hopefully avoided in the future. The third is a much larger, more sophisticated Excel-based Visual Basic program with the aim to compare said, selected deliquification measures by their performance. This is especially valuable because liquid loading is usually a problem of low producing wells and thus the selection of deliquification measures should be based on their economics rather than just feasibility. Finally, all the results are interpreted, several recommendations for the application of these developed tools are made, PROSPER and implementation of the discussed models from the literature are stated. Different design choices from the pilots are investigated, discussed, and ideas, as well as advice for the future, is given. Ultimately the tools proofed valuable by yielding results consistent with e. g. PROSPER as well as measurements while offering additional transparency, flexibility, and adaptability to a great extent.
Translated title of the contributionEntwicklung eines Engineering-Tools zur Evaluierung von Maßnahmen zum Flüssigkeitsaustrag für Gassonden
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Langbauer, Clemens, Supervisor (internal)
  • Kometer, Bernd, Supervisor (external)
Award date19 Oct 2018
Publication statusPublished - 2018

Bibliographical note

embargoed until 30-08-2023


  • gas well deliquification
  • liquid loading
  • critical velocity
  • Turner
  • Coleman
  • Nosseir
  • deliquification measures
  • wellhead compressor
  • velocity string
  • coiled tubing
  • plunger lift
  • foam lift
  • capillary string
  • soap sticks
  • liquid loading modelling
  • entrained droplet model
  • continuous film model
  • droplet flow reversal model
  • multiphase flow
  • Gray
  • Gray’s vertical flow correlation for gas wells
  • vertical foam flow correlation
  • plunger lift model
  • plunger lift feasibility
  • systems analysis
  • nodal analysis

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