Custom-Engineered Solutions
for Underbalanced Drilling

Foam Drilling


Drilling with stable foam is the most versatile of all
the reduced-pressure drilling systems. Stable foam
is a mixture of water, surfactant, chemical additives,
and compressed gases (nitrogen, carbon dioxide, natural gas, and air). Stiff foam is defined as a multiphase, metastable, compressible, non-Newtonian fluid that has a consistency similar to that of shaving cream.

Advantages of foam drilling include:

• Up to 10x the carrying capacity of many common
   liquid-based circulating systems
• Annular velocities as low as 70 ft/hr have proven
   effective
• Stiff foam can handle over 500 bbl/hr of downhole
   fluid influx

The effective fluid density of stiff foam ranges from 0.2 to 0.78 sg. The density ranges are adjusted within the make-up of the stiff foam by adjusting the Liquid Volume Fraction (LVF) via injection of liquid foaming solution and the gas injection by adjusting the annular back pressure valve on the well return line. This valve restricts the flow down the return line and therefore slows the velocities in the annulus, creating additional bottom hole pressure. The term "foam quality" is the gas volume percentage used to define mist and foam. Mist is defined in the range 99.99 to 96+ percent foam quality. Foam is from 96 percent to 55 percent (quality). At qualities below 55 percent, the mixture is called aerated fluid.

Guidelines for foam drilling:

• Water injection volumes: 1000-5000 Gal/Hr
• Soap injection volumes: 3-25 Gal/Hr (0.3-1.0% by weight)
• Air volumes for foam tend to be 30- 40% lower than for mist drilling
• Insufficient air/soap/foam leads to cuttings carrying inefficiencies and slugging,
   with attendant pressure increases


Underbalanced Drilling

Air-Gas Drilling Techniques

Dry Air-Gas Drilling

Mist Drilling

Foam Drilling

Aerated-Fluid Drilling