Gas Well Deliquification: Foam Assisted Lift (FAL) - Part-I
Recently we started on a journey to discuss gas well deliquification technologies currently being used by operators around the globe to handle their water production problems. This blog is targeted towards introduction of the first technology, called Foam Assisted Lift. Foam Assisted lift has many forms and has been around for more than couple decades in the industry. The technology is based on simple theory, that foam has a lower density than liquid water, and if by any means we can transform the reservoir produced water into foam, we will be able to lower its hydro static head and allow the reservoir energy to lift the water column out of well. Most commonly, foaming in wellbore is achieved through two of the following methods:
Capillary Soap Injection Strings or Capillary Foam Assisted Lift (CFAL)
Soap Sticks
Capillary Foam Assisted Lift (CFAL)
CFAL is a very simple method in which soap is injected downhole against the perfs via 1/4” or 3/8” capillary string. This injected soap reduces the liquid column weight make it lighter and helps it to flow upward thus reducing the flowing bottom hole pressure (FBHP).
Equipment & Working
Typical CFAL setup has 1/4 inch or 3/8 inch OD stainless steel capillary string, chemical injection or foot valve, capillary hanger, fluid pump(s) and a tank for soap/chemical storage. For different wellbore environments and fluids different metallurgy of capillary strings should be used, if wellbore has corrosive fluids alloy capillary string would be recommended, based on durability and right metallurgy the capillary string can be a very economical method.
Schematic of components of Capillary Foam Assisted Lift Setup
Working of CFAL is also very simple; Foam which is basically a surfactant in nature is pumped via capillary string at a specified rate; surface pump is used for this purpose, injection valve controls the foam output. This foam reacts with formation fluids and lowers gas slippage, reduces density, minimizes the surface tension and unloads the wellbore liquid to initiate gas flow from reservoir.
With foam injection ON and capillary string inside the hole, rigless well intervention is not possible. CFAL is also not appropriate for significantly depleted reservoirs, as foam creation requires agitation and foam lift is provided by reservoir energy.
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