Borehole Stress Orientation

1
Borehole Stress Orientation
Top View
sMIN
Drilling Induced Fracture
Borehole Breakout
sMAX
Courtesy of Steve Hansen, Schlumberger
2
Types of Directional Drilling for Fractures
Nelson Serra (1995)
Courtesy of CSPE
3
Potential Drilling Directions on Folds
Nelson et.al. (1987a)
Courtesy of CSPE
4
Fracture Spacing Drilling Direction
After Nolen-Hoeksema Howard (1987)
Courtesy of AAPG
5
Drilling Direction Nomograph
Nolen-Hoeksema Howard (1987)
Courtesy of AAPG
6
High Intensity Fold-Related Fractures
7
Bedding/Fracture/Well Rotation
Joubert Rice (1997)
unrotated
rotated
8
UBI
FMI
UBI vs. FMI
UBI Shows Topography FMI Shows Resistivity
Courtesy of Steve Hansen, Schlumberger
9
Quantitative 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.
10
Rotated Fracture Poles
equal area, lower hemisphere, stereonets. fract
ure poles for all 9 wells 1700 poles
Joubert Rice (1997)
11
Equation - Fracture Intercept Rate
The fracture frequency in any arbitrary direction
is the sum of
i th fracture
- occurrence of i th fracture,
- the cosine of the angle between the normal
intercept rate direction of the i th fracture,
over all fractures.
12
Occurrence Weighting (Lacazette 1990)
Joubert Rice (1997)
Fracture 2 is less likely to be intercepted by
the drill hole than fracture 1 - as the angle of
the normal approaches 90 deg. W increases. W1 lt
W2
Drill Hole
13
Occurrence Corrected Rose Diagrams
rotated raw fracture planes
occurrence weighted fracture planes
Joubert Rice (1997)
14
Intercept Rate
Joubert Rice (1997)
NORTH
Polar chart showing number of fractures intercept
ed per meter for different drilling directions -
(bedding rotated flat).
1.2
1
0.8
0.6
0.4
0.2
EAST
WEST
0
horizontal
15 deg.
30 deg.
45 deg.
60 deg.
Well 1
75 deg.
vertical
SOUTH
15
Aperture Variation on Rose Diagram
N
maximum aperture
minimum aperture
Joubert Rice (1997)
16
Fracture Aperture
Courtesy of Steve Hansen, Schlumberger
17
Equation - Flow Intercept Rate
- fracture aperture of the i th fracture
Joubert Rice (1997)
18
Flow Intercept Rate
Joubert Rice (1997)
19
Calculated Horizontal vs Vertical Drilling
Drilling at low angles to bedding makes a good
well
Triassic Carbonate Reservoirs, Northern British
Columbia, Canada
From Joubert Rice (1997)
20
Shear 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

21
Shear 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