Page 478 - Air and Gas Drilling Manual

Chapter 10: Stable Foam drilling 10-3
and formation crude oil) from the annulus. These borehole drilling fluid theft rock
formations are called lost circulation sections. The use of foam creating mixtures
has been considered an important technological tool in countering the detrimental
effects of lost circulation sections. The stable foam creates bubbles with surface
tension properties that tend to fill in the fracture or pore openings in the borehole
wall as the foam attempts to flow to the thief fractures and pores. Foam bubble
blockage restricts or stops the flow of foam into these lost circulation sections and
thereby allows the drilling operations to safely progress. Stable foam drilling fluids
can also be effective in countering the flow of formation water into the annulus.
Sufficient surfactant can be added to the injected fluid stream at the top of the drill
string that will allow the formation water to be foamed as the water enters the
annulus. Stable foams 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. Stable foam drilling operations are nearly always direct
circulation operations.
Since the late 1980s another important application for stable foam drilling
operations has emerged. This is underbalanced drilling applied to oil and natural gas
recovery operations. Over the past two decades practical field research has
demonstrated that most oil and natural gas bearing rock formations can be more
efficiently produced if they are drilled with drilling fluids that have hydrostatic
flowing bottomhole pressures that are slightly less than the pore pressures of the
potential producing rock formations being drilled. Underbalanced drilling operations
allow the oil or natural gas to be produced into the annulus as the drilling operation
progresses. The underbalanced drilling operation allows the natural fracture and pore
systems to be kept clear of rock cutting fines and drilling mud filter cake, thereby,
avoiding formation damage. Formation damage has been a problem in oil and
natural gas recovery operations nearly since the discovery of oil and natural gas
mineral deposits. Underbalanced drilling operations are often carried out using a
variety of incompressible fluids (e.g., crude oil, formation water, or clear water) and
a variety compressible gases (e.g., air, inert atmosphere, or natural gas). Inert
atmosphere is created by a filter system (placed downstream of the primary
compressor) that strips most of the oxygen from the intake air [6]. This filter
process results in a nearly inert atmospheric gas. The filter process can be designed
to yield an atmospheric gas with an oxygen content that will not support
combustion. Field units typically produce and inert atmospheric gas with about 5
percent oxygen content. The success of stable foam drilling fluid based
underbalanced drilling operations in the oil and natural gas recovery industry have
prompted other industrial uses of this technology. In particular, stable foam
underbalanced drilling technology is being experimented with in deep water well and
environmental monitoring well drilling operations.
This chapter outlines the steps and methods used to plan a successful stable
foam drilling operation. This chapter also illustrates the application of these steps
and methods to typical deep drilling operations. The objective of these steps and
methods is to allow engineers and scientists to cost effectively plan their drilling
operations and ultimately select their drilling rig, compressor, and other auxiliary air
and gas equipment. The additional benefit of this planning process, is that the data