In Situ Stress Analysis of Wellbore Breakouts from the Oklahoma and the Texas Pandhandle

Abstract: Orientations of crustal stresses are inferred from stressinduced
breakouts (well bore enlargements) in the eastern
part of the Anadarko basin in central Oklahoma, the Marietta
basin in south-central Oklahoma, and the Bravo dome area
of the central Texas Panhandle. Inferred directions of maximum
horizontal principal stress (SHmax) are east-northeast
for the eastern Anadarko basin and northeast for the Marietta
basin and the Bravo dome area.
The relative magnitudes of the three principal stresses
(S,, S2, S3) are known for the Bravo dome area from existing
hydraulic-fracturing measurements, and a normal-faulting
stress regime (Sv>SHmax >SHmIn) is implied. For the eastern
Anadarko basin and the Marietta basin, the magnitudes
of the principal stresses are not known. Possible left-lateral
oblique slip on the Meers fault during the Quaternary implies
that strike-slip (SHmax >Sv>SHmln) and reverse (SHmax
>SHmln >Sv) faulting has occurred in south-central Oklahoma.
Thus, the study region may be a transition zone
between extensional stress in the Texas Panhandle and
compressional stress in Oklahoma.
Breakout data from the eastern Anadarko basin yield a
single consistent SHmax orientation, whereas data from the
Marietta basin and the Bravo dome area yield bimodalorthogonal
distributions believed to consist of northwestoriented
breakouts and northeast-oriented fracture-related
wellbore enlargements. This northeast (orthogonal) trend in
data from the Marietta basin and the Bravo Dome area is
probably related to drilling-induced hydraulic fracturing of the
wellbore or to preexisting natural fractures or joint sets
intersecting the wellbore. On dipmeter log records, breakouts
and fracture-related enlargements have similar elliptical
cross sections. Orthogonally oriented breakout and fracturerelated
wellbore enlargements are therefore differentiated by
comparing their long-axis orientations with directions of
known or inferred horizontal stress.
The mean orientations of either the breakout or fracturerelated
orthogonal trends in the Marietta basin and the Bravo
dome area data sets are not as well constrained as the mean
orientation of breakout data for the eastern Anadarko basin.
Poorly constrained mean orientations give the appearance of
data scatter or dispersion among wellbore enlargement
orientations within the northwest and northeast bimodalorthogonal
trends. Drill holes in the Marietta basin and Bravo
dome area are located primarily between northwest-striking
subparallel faults. Mean data orientations calculated for
either orthogonal trend for individual well data sets appear to
rotate counterclockwise across these two fault-bounded
study areas. Stress trajectory rotation between suparallel
faults within the Marietta basin and the Bravo dome study
areas may account for the data scatter.
Although breakouts and fracture-related enlargements
formed in all parts of the thick sequences of sedimentary
rocks logged, they are primarily in limestone, shale, and
dolomitic rock, p

Tags: anadarko, borehole, bravo dome, breakout, marietta, oklahoma, stress analysis, texas, wellbore