Page 223 - Air and gas Drilling Field Guide 3rd Edition

214 CHAPTER 9 Aerated Fluids Drilling

avoiding formation damage. Formation damage has been a problem in oil and nat-
ural gas recovery operations nearly since the discovery of oil and natural gas min-
eral 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 of compressible gases (e.g., air, inert atmosphere, or natural gas).
An inert atmosphere is created by a filter system (placed downstream of the pri-
mary compressor) that strips most of the oxygen from the intake air [3]. This dril-
ling gas is known as membrane generated nitrogen.
This chapter outlines the steps and methods used to plan a successful aerated
fluids drilling operation. This chapter also discusses 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 plan their drilling
operations cost effectively. The additional benefit of this planning process is that
data created by the process can be used later to control the drilling operations as
the actual operations progress.

9.1 DEEP WELL DRILLING PLANNING
Aerated drilling operations use a variety of incompressible fluids and compressed
gases to develop a gasified drilling fluid. The majority of the operations use stan-
dard fresh water-based drilling mud with injected compressed air or membrane
generated nitrogen. In this chapter, a performance drilling operation will be
assumed and, therefore, standard drilling mud and atmospheric air will be used
as the example aerated drilling fluids.
The basic planning steps for a deep well are as follow:
1. Determine the geometry of the borehole sections to be drilled with aerated
drilling fluids (i.e., open hole diameters, the casing inside diameters, and
section depths).
2. Determine the geometry of the associated drill string for each section to be
drilled with aerated drilling fluids (i.e., drill bit size and type, the drill collar
size, drill pipe size and description, and maximum depth).
3. Determine the type of rock formations to be drilled in each section and
estimate the anticipated drilling rate of penetration (use offset wells).
4. Determine the elevation of the drilling site above sea level, the temperature
of the air during the drilling operation, and the approximate geothermal
temperature gradient.
5. Establish the objective of the aerated drilling fluids operation:
n Performance drilling
n Underbalanced drilling
6. For either of the aforementioned objectives, determine the required approx-
imate volumetric flow rate of the mixture of incompressible fluid and the
compressed air (or other gas) to be used in the aerated fluid drilling