Blog Series: Gas Well Deliquification - a lifeline for water producing gas wells
Like humans and living beings, oil and gas wells also age and depict signs of falling reservoir pressure, lower hydrocarbon rates and often water production et cetera. This phenomenon is predominant in gas reservoirs with water support or active aquifer. With every pound of drop in reservoir energy & increasing proportion of water with gas, well becomes prone to liquid loading. This phenomenon is not only detrimental to production, but severely impacts the total recovery and economics of a field. Luckily, there is a key to every lock in this world, a solution to every problem. For this one, the answer lies in optimizing vertical lift performance (or outflow performance) by installing appropriate artificial lift systems.
Different artificial lift techniques in one graphic - Source: Dover Energy
The ultimate purpose of any lift system is to reduce the Flowing Bottom-hole Pressure (FBP) and remove the static liquid column that is held up in wellbore causing excess hydrostatic head. If we observe the generic wellhead pressure equation:
Pwhp = Pfbp – Phyd
Pwhp = Wellhead pressure
Pfbp = Flowing bottom-hole pressure
Phyd = Hydrostatic pressure
Generally speaking, higher FBP will cause greater production from reservoir (ignoring skin & assuming constant drawdown). As observed above, hydrostatic pressure (or the pressure due to weight of fluid in the wellbore) is subtracted from FBP. Therefore if this value is comparable to Pfbp, it will severely impact & control the flow from reservoir. Moreover, if this value is greater than Pfbp, well will not be able to flow entirely, or in other words, the energy of reservoir will not be sufficient to “lift” the column of fluid in the wellbore. This condition is known as “liquid loading” in petroleum engineering.
Gas well deliquification techniques or deliq technique for short is industry slang given to sets of artificial lift systems that are commonly used to dewater gas wells. From the wide range of lift techniques available, these systems are known for their handling of high gas-liquid ratios (obviously as they have to operate in gas wells), low reservoir energy & corrosive environment. Following are some of the commonly used deliq methods:
Conventional Gas lift
Progressive cavity pumps
Plunger Lift
Foaming/ Soap
Foam Assisted Gas Lift (FAGL)
Velocity Strings
Schematic of surface & sub-surface components of Foam Assisted Lift technology
All deliq systems have operating windows and could not be applied to every well. The catch is to learn & understand the principle of each technology, identify its applicability in every case, and then select the most appropriate and cost effective lift system for a particular well. Often engineers and companies fail at this stage and blame the technology!
The idea behind this blog series is to introduce gas well deliquification as a subject and take up each artificial lift system in detail per blog. We are not only explaining the working of an artificial lift system, but putting it in perspective for its use in dewatering gas well. So stay tuned!
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