Foam Drilling | What is Foam Drilling?
Foam Drilling Equipment
Most foam drilling equipment is the same as that used in dry air drilling. Additional items are summarized below.
Compressors and Pumps
Because of lower surface injection pressures, the compressors used in foam drilling can be smaller than those used in dry air drilling. Air (Nitrogen) is the gas most typically used to generate foam. High capacity liquid injection pumps are needed for foam drilling to supply liquid rates in the range of 10 to 20 gpm.
Foam Generators
A foam generator ensures thorough mixing of the gas and liquid phases. It introduces the liquid into the gas stream through a bore tube. The mixture is then directed through a venturi-type flow constriction.
Other types of foam generators are located downstream from the meeting point of air and liquid. Even if the foam is not generated at the surface by a foam generator, the natural flow path of the mixture through a number of valves and the kelly may produce a good quality foam.
Portable Units
Portable foam drilling units are available in some locations. They consist of air compressors, a booster, a divided mixing tank, liquid pumps, foam generators and metering systems. A typical portable unit capacity varies from 650 to 1,500 scfm volumetrically, with 1,000 to 3,000 psi pressure capacity.
Return System
Typically, a choke is installed at the blooie line to pressurize the annulus. If additional back-pressure is needed, then the pressure capacity of the rotating head, blowout preventer and the section of the blooie line between the choke and the rotating head must be sufficient to support the highest likely back-pressure.
The volumes of liquid discharged into the pits are normally greater than those in air and mist drilling. The return pits must be sized accordingly to handle the anticipated volumes of liquid.
