Summary
This paper introduces a new systematic way to evaluate gas well
deliquification options throughout the life of a well by using power as the
most general measure of cost.
As a gas well depletes, the gas velocity declines to the point that liquid
droplets are not removed from the wellbore. Liquids accumulate and impose
increased pressure on the sandface. To maintain production, we apply artificial
lift. In some cases, such as plungers or foamers, we make better use of the
remaining reservoir energy. In other cases, we apply external energy using
methods such as gas lift or pumps.
Improving gas well recovery by removing wellbore liquids accumulation is of
interest to industry in two general ways. First, there is the perennial
question of how to select deliquification techniques for the entire life of the
well. This paper provides a framework to compare the relative merits of various
artificial lift systems through final depletion. Furthermore, stakeholders are
demanding more substantial bases for booked reserves, and with more development
this method offers a defensible estimation of the economic limit with respect
to liquids accumulation that honors the depth, productivity, and completion
characteristics of a particular well.
To understand the appropriate application of artificial lift power, we
proceeded in two stages. First, we modeled a synthetic two-phase gas well
including the liquid-loading behavior. The model produced the familiar result
of natural flow in early production followed by lower production as the well
declines and liquids accumulate. Next, we compared using the well’s energy
(i.e., siphon or velocity tubing strings) to the addition of external energy
(i.e., gas-lift injection and downhole pumps) to optimize production at every
stage of the depletion. We used the theoretical external power as a proxy for
well operating cost to calculate the economic limit.
Ultimate recovery was improved by the addition of external energy. In
particular, pumping was found to be favored over gas lift, because it provided
lower bottomhole pressures and required less power, thereby yielding higher
production at any point in time along with a lower economic limit rate.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
2 August 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
5 November 2008
- Manuscript approved:
24 January 2009
- Published online:
23 July 2009
- Version of record:
16 May 2011
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