Page 257 - Air and gas Drilling Field Guide 3rd Edition

248 CHAPTER 10 Stable Foam Drilling

where K is the consistency index, n is the power law exponent, V is the average
velocity of the foam inside the pipe (ft/sec, m/sec), D is the inside diameter of the
2
2
pipe (ft, m), g is the acceleration of gravity (32.2 ft/sec , 9.81 m/sec ), and C vis is
a conversion constant (equals 1.0 for USCS, equals 14.5727 for SI).
The power law equation for the effective viscosity for the flow of foam in an
annulus pressure conduit is [9]
n
n 1
KC vis 2n þ 1 12 V
m ¼ ; (10-3)
e
g 3n D 2 D 1
where V an is the average velocity of the foam in the annulus (ft/sec, m/sec), D 1 is
the inner surface diameter of the annulus (ft, m), and D 2 is the outer surface diam-
eter of the annulus (ft, m).
The correlation expression for the consistency index as a function of the foam
quality G is [16]
2 3
K ¼ 0:15626 þ 56:147 G 312:77 G þ 576:65 G
4 5 6 7 (10-4)
þ 63:960 G 960:46 G 154:68 G þ 1670:2 G
8
937:88 G :
Also, the correlation expression for the power law exponent as a function of foam
quality G is [16]
2 3
n ¼ 0:096932 þ 2:3654 G 10:467 G þ 12:955 G (10-5)
4 5 6
þ14:467 G 39:673 G þ 20:625 G
These correlation expressions were developed for the fresh water and surfac-
tant combination used in the experiments by Ikoku and colleagues. The
surfactant foaming agent used in the experiments was a 1.0% solution (with
fresh water) of Adofoam BF-1 (Nalco Chemical Co.)[9–13].
The following is a limited list of the commercial foaming agents available
through various drilling service and chemical companies. These are

DuraFoam Weatherford
SMA-100 Weatherford
DrillFoam PDS Air Drilling Associates
DrillFoam MSDS Air Drilling Associates
Adofoam BF-1 Nalco Chemical Company
AirFoam AP-50 Aqua-Clear
AirFoam B Aqua-Clear
F-52 surfactant Dowell
F-78 surfactant Dowell

10.1.1 Laboratory Stable Foam Screening
The flow performance of a stable foam drilling fluid is very dependent on the
quality of the fresh water (or formation water), the surfactant, and what other
additives would be used to create the foam. In order to assess the performance