Page 397 - Air and Gas Drilling Manual

Chapter
Nine

Aerated Fluids Drilling

The term aerated fluids describes the broad category of drilling fluids that are
basically incompressible fluids injected with compressed air or other gases. Aerated
drilling fluids have been used to drill both shallow and deep boreholes since the
advent of air and gas drilling technology in the mid-1930’s. The first engineering
discussion of an aerated drilling mud project was given in 1953 [1]. Aerated drilling
fluids were initially used to drill through rock formations that had fracture and/or
pore systems that could drain the incompressible drilling fluids (e.g., fresh water,
water and oil based drilling muds, formation water, and formation crude oil) from
the annulus. These borehole drilling fluid theft rock formations are called lost
circulation sections. The injection of air into drilling muds has been considered an
important technological tool in countering the detrimental effects of lost circulation
sections. The injection of air into drilling mud creates bubbles in the mud and
because of the surface tension properties of the bubbles relative to the properties of
rock and drilling mud, the bubbles tend to fill in the fracture or pore openings in the
borehole wall as the aerated mud attempts to flow to the thief fractures and pores [2].
This bubble blockage restricts the flow of the drilling mud into these lost circulation
sections and thereby allows the drilling operations to safely progress. Aerated fluids
have been used to avoid lost circulation in shallow water well drilling, geotechnical
drilling, mining drilling, and in deep oil and natural gas recovery drilling
operations. Aerated fluids drilling operations are nearly always direct circulation
operations.
Since the late 1980s another important application for aerated fluids drilling
operations has emerged. This is underbalanced drilling applied to oil and natural gas

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