Page 28 - Well Control for Completions and Interventions

22 Well Control for Completions and Interventions

Density will decrease with increasing temperature. At 100 C the density
of fresh water is 0.95 SG. As pressure increases, density will increase.
However, water has a very low compressibility, so any density increase for
water-based fluid is negligible. If oil-based fluids are used, the density
increase becomes more significant.
Note: Fluid density corrections for temperature and pressure are described in
Chapter 5, Completion, Workover, and Intervention Fluids.
Force: Consider a mass of 1 lb suspended by a length of string. A force
will keep the string in tension. The product of gravitational acceleration
and the mass causes the force. Force can be expressed in unit pound-
force, which can be defined as:
One pound-force is the force which will influence a body with 1 lb mass
2 2
when subjected to gravitational acceleration of 9.80665 m/s (32.147 ft/s ).
Gravitational acceleration varies between the equator and the poles. For exam-
2
ple, gravitational acceleration at the North Pole is equal to 9.831 m/s ,which
gives a force influence on a mass of 1 lb according to the following:

9:831
G 5 1 3 5 1:0025ðlbsÞ
9:80665
The value 9.80665 expressed here is used as standard, and represents
the acceleration of gravity at 45 degree latitude North—midpoint
between the pole and the equator.
When using oilfield units, the variation in gravitational acceleration is
ignored, and a 1-lb mass is considered to exert a 1 lb-force influence. Mass
and weight become synonymous, since a 1 lb-force and 1 lb weight are one
and the same. This may upset pure scientists (especially astrophysicists), but
for practical terrestrial purposes there is no difference and it seems OK.
In SI units, one kilo is, strictly speaking, mass. Force (mass 3 gravita-
tional acceleration) is measured in newtons. The newton is the SI unit for
force, and is equal to the amount of net force required to accelerate a
2
mass of 1 kg at a rate of 1 m/s .
1kg 5 9:81 N: Hence; 1N 5 1=9:81 kg 5 0:102 kg
A newton is approximately equivalent to 0.102 kilo (102 g).

Pressure: Pressure is defined in physics as force per unit area:
Force
P 5 (1.4)
Unit Area