Page 32 - Well Control for Completions and Interventions

26 Well Control for Completions and Interventions

Figure 1.12 True vertical depth (TVD) and Measured Depth (MD).

o
Example: Determine the fluid density of 36 API gravity oil:
141:5
SG 5 5 0:8447 ðSGÞ
36 1 131:5

Density in ppg 5 0.8447 3 8.33 5 7.04 ppg.
Fluid gradient (psi/ft) 5 0.8447 3 0.433 5 0.3657 psi/ft.
Fluid gradient (kPa/m) 5 844.7/102 5 8.28 kPa/m

1.1.6.1.3 True vertical depth and measured depth
Unless a well is drilled with absolutely no deviation from the vertical, mea-
sured depth will be greater than the vertical depth (Fig. 1.12).

1.1.6.2 Calculating bottom-hole pressure
When a wellbore is filled with a single fluid of the same density, calculat-
ing the hydrostatic pressure is straightforward. Where a wellbore contains
fluids of different densities, the hydrostatic pressure of each fluid must be
calculated, and the result for all the fluids added. The depth of each fluid
interface is required to accurately determine bottom-hole pressure.
Example: Oilfield units:
Consider the well shown here.
Full column of (mixed) fluids to surface
Pressure at surface 0 psi