PERMFILE43377

• Permit No: M1999002
• IBM Index Class Name: Permit File
• Doc Date: 6/18/1999
• Doc Name: SONIC LOG DATA HELP DETERMINE FORMATION STRENGTH
• Section_Exhibit Name: OBJECTORS EXHIBITS
• Media Type: D
• Archive: No

.:
TECHNOLOGY
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formation strength
Nathan Stein Sans Co. Boston
set of equations helps
improve the reliability
of using acoustical
wave velocity (dynamic)
data to obtain quick, accept-
able estimates for the Mohr-
Coulomb (static) strengths of
different types of rock.
Good estimates of forma-
tion strength from offset
well sonic log data tan help
in the planning of bit pro-
grams and well stimulation
procedures.
Dynamic shear modulus
values were calculated from
Mohr-Coulomb strength
plots for five limestone sam-
ples.
Care must be exercised in
applying this method with
log data. The terminal stress
decreases as rock strength
increases. The true vertical
stress should be used in the
calculations until the ternil-
na] vertical stress is exceed-
ed.
If the field-measured
stress conditions exceed
6,300 psi for friable sands,
1,500 psi for well-cemented
sands, and 500 psi for Ifine-
stones, then the calculations
should be based on the ter-
minal stress values rather
than true stress.
The use of sonic Log data
to estimate rock strength has
hvo pluses:
•The measurements re-
late to the in situ strength of
undamaged rock.
• Strength sun~eys can be
Fig I
made quickl}' and inexpen-
sively rf the measurements
can be properly converted to
standard strength values.
Preciously available meth-
ods for using sonic data to
predict the standard-
strength values of rock may
be unreliable.
The calculation procedure
presented in this article uses
the results of theoretical ana-
lyses of laboratory rock
strength tests and acoustical
wave velocin• data to im-
prove the reliability of using
sonic log data.
The traditional Mohr-Cou-
lonabstrength plots for rocks
can be related to sonic data
obtained either in the labora-
tor}~ or from sonic logs.
Acoustical wave velocity
6Vyllie, et al., measured
compressional acoustic wave
velocity values for different
rock samples over a wride
range of applied stresses.[
One of the objectives was to
determine how to use acous-
tical wave velodty log data
to calculate the porosity of
formations penetrated by a
N'e Q.
1V}'Ilie developed atime- ;
average equation which
seemed to be most accurate
rchen there was sufficient
stress applied to the rock
sample to reach anear-con-
stant velocity value, called
the terminal velodh~ (Fig. 1).
[n Fig. 1, note the initial ~
Fig. 2
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