Page 197 - Air and gas Drilling Field Guide 3rd Edition

188 CHAPTER 8 Air, Gas, and Unstable Foam Drilling

G

FIxed Bed

H
F

Log Δp/L G 3 G 2 C

G 1 B
G=0
D
E

A

Log v

FIGURE 8-4. Solids flow characteristics in vertical pneumatic conveying. Note that the unit of
_
G is lb/sec [6].

vertical annulus geometry the upward flow of air will choke with the rock cut-
tings in much the same manner as industrial vertical pneumatic conveying. This
choking effect is shown in Figure 8-4 [6]. This experimental work did verify the
original Angel assumption for a limited range of volumetric flow rates with
entrained small diameter rock cutting particles. This research effort resulted in
future improvements in the predictive models.
In 1983, another predictive model was proposed that took into account a rock
cutting particle velocity that was different from that of the air flow [7]. This
model gives air and rock mixture values, which can improve the accuracy
of the predictions. The problem with this model is that the individual average
velocities of the particles are difficult to determine analytically for inclusion in
this model.
In 1992, additional theoretical work was carried out to further refine the inclu-
sion of the effect of rock cutting particle velocities [8]. This model also suffered
from the difficulty involved in determining average particle velocities.