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