borehole stress orientation min max top view drilling induced fracture borehole breakout courtesy...
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Borehole Stress OrientationBorehole Stress Orientation
MIN
MAX
Top View
Drilling Drilling Induced Induced FractureFracture
Borehole Borehole BreakoutBreakout
Courtesy of Steve Hansen, Schlumberger
Types of Directional Drilling Types of Directional Drilling for Fracturesfor Fractures
Courtesy of CSPE
Nelson & Serra (1995)
Potential Potential Drilling Drilling Directions Directions on Foldson Folds
Courtesy of CSPE
Nelson et.al. (1987a)
After Nolen-Hoeksema & Howard (1987)
Fracture Spacing & Drilling DirectionFracture Spacing & Drilling Direction
Courtesy of AAPG
Nolen-Hoeksema & Howard (1987)
Drilling Direction NomographDrilling Direction Nomograph
Courtesy of AAPG
High Intensity Fold-Related FracturesHigh Intensity Fold-Related Fractures
Bedding/Fracture/Well RotationBedding/Fracture/Well Rotation
unrotated
rotated
Joubert & Rice (1997)
UBI FMI
UBI vs. UBI vs.
FMIFMI
Courtesy of Steve Hansen, Schlumberger
UBI Shows
Topography
FMI Shows
Resistivity
Quantitative Fracture AnalysisQuantitative Fracture Analysis
Polar projections of fold and fault related fractures with dip of 300 deg NW
After removing structural bedding dip, fractures trend clearly NW-SE and to perpendicular to bedding.
Rotated Fracture PolesRotated Fracture Poles
N N
before beddingrotation
after beddingrotation
equal area, lower hemisphere, stereonets.
fracture poles forall 9 wells ~ 1700poles
Joubert & Rice (1997)
Equation - Fracture Intercept RateEquation - Fracture Intercept Rate
freqi
iiW cos i
i th fracture
Wi - occurrence of i th fracture,
The fracture frequency in anyarbitrary direction is the sumof:
- the cosine of the angle between thenormal intercept rate direction of the i th fracture,over all fractures.
cos i
Occurrence Weighting Occurrence Weighting (Lacazette 1990)(Lacazette 1990)
Drill HoleFracture 2
Fracture 1
1
2
Occurrence WL
1
cos Fracture 2 is lesslikely to be intercepted by the drill hole than fracture 1 - as the angle of the normal approaches 90 deg. W increases.
W1 < W2
Joubert & Rice (1997)
Occurrence Corrected Rose Occurrence Corrected Rose DiagramsDiagrams
occurrence weighted fracture planes
rotated raw fracture planes
Joubert & Rice (1997)
Intercept RateIntercept Rate
0
0.2
0.4
0.6
0.8
1
1.2
NORTH
EAST
SOUTH
WESThorizontal
15 deg.
30 deg.
45 deg.
60 deg.
75 deg.
vertical
Polar chart showing number of fracturesintercepted per meterfor different drilling directions - (bedding rotated flat).
Well #1
Joubert & Rice (1997)
Aperture Variation on Rose Aperture Variation on Rose DiagramDiagramN
maximumaperture
minimumaperture
Joubert & Rice (1997)
Fracture Fracture ApertureAperture
Courtesy of Steve Hansen, Schlumberger
Equation - Flow Intercept Equation - Flow Intercept RateRate
- fracture aperture of the i th fracture
ei
flow iWi
i ei ( cos ) 3
Joubert & Rice (1997)
Flow Intercept RateFlow Intercept Rate
NORTH
EAST
SOUTH
WEST
HORZ.15 DEG.
30 456075 90
Joubert & Rice (1997)
Calculated Horizontal vs Vertical DrillingCalculated Horizontal vs Vertical Drilling
0
20
40
60
80
100
120
horz. 15 30 45 60 75 Vert.
inclination angle relative to bedding
% o
f m
axim
um
flo
w 123456789
well #
Triassic Carbonate Reservoirs, Northern British Columbia, Canada
From Joubert & Rice (1997)
Drilling at low angles to bedding makes a good well
Shear AnisotropyShear Anisotropy
• Preferential directional alignment of elastic properties due to regional stress fields
• Horizontal anisotropy - uniform laterally but not vertically (transversely isotropic with a vertical axis of symmetry)
• Vertical anisotropy - uniform vertically but not laterally (transversely isotropic with a horizontal axis of symmetry)
• Shear waves travel faster along axis of symmetry
Shear Wave BirefringenceShear Wave Birefringence
• Fracture-induced elastic anisotropy can be detected through shear-wave splitting, or birefringence
• Shear waves split into fast and slow polarizations
• Data are analyzed for orientation and degree of anisotropy indicated by the amount of birefringence
• Fast shear polarization direction relates to fracture orientation
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