Page 195 - Air and gas Drilling Field Guide 3rd Edition

186 CHAPTER 8 Air, Gas, and Unstable Foam Drilling

water or formation oil to be carried from the well during the drilling
operation.
11. Determinethe approximatevolumetric flowrateof formation water
or formation oil that can be carried from the well during the drilling
operation (assuming the injected air is saturated for bottom hole
conditions).
Chapter 6 derived and summarized the basic direct circulation drilling
planning governing equations. In Chapter 7 the basic reverse circulation dril-
ling planning governing equations were derived and summarized. This chapter
discusses only direct circulation illustrative examples.

8.2 MINIMUM VOLUMETRIC FLOW RATE
AND COMPRESSOR SELECTION
Over the past three decades, various research and commercial organizations have
developed mathematical and empirical models used to predict the performance
of air and gas drilling operations. Each of the models is based on a variety of engi-
neering assumptions concerning the interaction of the gas flow in the annulus
and its rock cuttings and liquid carrying capacities.

8.2.1 Discussion of Theories
In 1957, R. R. Angel developed the first field useful mathematical and empirical
model for air and gas drilling operations [1, 2]. This initial work by Angel was sup-
ported by industry (i.e., Phillips Petroleum Company) and continues to be useful
to drilling supervisors and drilling engineers even today. This modeling effort
drew heavily from the large body of engineering knowledge related to industrial
pneumatic conveying (the transport of solids by flowing atmospheric air). Thus,
from the outset, Angel’s model was developed to be an engineering tool. The
major air and rock cuttings mixture assumption made in this model was that
the rock cutting particles move together from the bottom of the borehole to
the surface with the velocity of the local annulus air flow. Through the decades,
other researchers have expanded this modeling effort to include other engineer-
ing aspects of the drilling operation [3]. This simple hole cleaning theory was
demonstrated in Chapter 2 [see Equation (2-1)].
In 1981, interest in air and gas drilling technology found its way into an aca-
demic research effort [4, 5]. This research was carried out at the University of
Tulsa and later at Pennsylvania State University and was supported by the U.S.
Department of Energy. The effort sought to detail the interaction between the
gas flow in the annulus and the transport of the rock cuttings. Figures 8-2 and
8-3 illustrate typical slug and nonslug (cluster) motion of particles in industrial
pneumatic conveying [6]. This recent experimental work found that in the