Page 31 - Well Control for Completions and Interventions

Introduction and Well Control Fundamentals 25

1.1.6.1.1 Metric (bar/m)
Pressure gradient ðbar=mÞ 5 Fluid density kg=L 3 0:0981
3
Pressure gradient ðbar=mÞ 5 Fluid density Kg=m 3 0:0000981

Example: What is the gradient of a 10 pgg (1.20 SG) brine.
Oilfield : 10 3 0:052 5 0:52 psi=ft
SI 1200=102 5 11:76 kPa=mor 1200 x 0:00981 5 11:772
Once the fluid gradient is known, hydrostatic pressure at any point in
the well can be determined.
P hy 5 Gradient 3 TVD (1.7)

Where P hy 5 hydrostatic pressure (psi or kPa or bar); TVD 5 True verti-
cal depth (feet or meters).
Example (oilfield units): What is the hydrostatic pressure at 11,500 ft
TVD in a well filled with 10.5 ppg brine?
10:5 3 0:052 3 11; 500 5 6279 psi:

Example (SI): What is the hydrostatic pressure at 3500 m TVD in a
3
well filled with 1250 kg/m brine?
ð1250=102Þ 3 3500 5 42; 892 kPa

When calculating hydrostatic pressure, the vertical depth TVD must
be used. Measured depth must be used for calculating volume and
capacity.

1.1.6.1.2 Crude oil density
Crude oil density is commonly expressed as API gravity ( API). To con-

vert API gravity to SG:
141:5
SG 5 (1.8)
Deg API 1 131:5
To convert SG to oilfield units:

SG 3 8:33 5 ppg 8:33 is fresh water density in ppgÞ
ð
SG 3 0:433 5 psi=ft ð0:433 is the gradient of fresh waterÞ