Page 197 - Applied Petroleum Geomechanics

192 Applied Petroleum Geomechanics

Tingay et al. (2013) developed an average overburden stress equation
for the northern Malay basin:
s V ¼ 0:0064Z 1:1599 (6.9)
ss
where s V is in MPa; Z ss is the true vertical depth below sea level (TVDSS) in
meters. This equationis accurateto 1.35 MPa over all calculatedvertical stress
magnitudes in the studied depth range of 100e3500 m (Tingay et al., 2013).
Using density log data, another overburden stress equation was obtained
in offshore Northern Malay basin:

s V ¼ 0:023Z bml (6.10)
where s V is the overburden stress below the sea floor (MPa); Z bml is the true
vertical depth (TVD) starting from the sea floor (m).
Vertical stress trend for the North Sea was established using data from 10
North Sea wells (Yang and Aplin, 2004). The equation is as follows:
7
s V ¼ 0:01799Z bml þ 9:95 10 Z bml (6.11)
2
where s V is in MPa; Z bml is in meters. They suggested that the equation can
be used to calculate the vertical stress to the depth at which the density log
starts its run.
6.1.2.2 Overburden stress for onshore drilling
For onshore drilling, overburden calculation is simpler than that in offshore.
Dohmen et al. (2013) presented the following equation to calculate
overburden stress in the Bakken play in North Dakota:
s V ¼ 0:0231Z (6.12)
where s V is in MPa; Z is the TVD below the surface in meters. This
expression is similar to Eq. (6.10) for offshore Northern Malay basin.
Zhang and Wieseneck (2011) analyzed reliable density log data and
obtained the following equation to estimate overburden stress in the
Haynesville and Bossier plays:
s V ¼ 0:6186Z 1:061 (6.13)

where s V is in psi; and Z is in feet.
From density log, Warpinski (1989) obtained the following equation for
overburden stress estimate at DOE’s Multiwell Experiment (MWX) site in
the Piceance basin of western Colorado:
s V ¼ 0:0238Z (6.14)

where s V is in MPa; Z is in meters.