Borehole Stress Orientation  MIN  MAX Top View Drilling Induced Fracture Borehole Breakout Courtesy of Steve Hansen, Schlumberger

Types of Directional Drilling for Fractures Courtesy of CSPE Nelson & Serra (1995)

PotentialDrillingDirections on Folds Courtesy of CSPE Nelson et.al. (1987a)

After Nolen-Hoeksema & Howard (1987) Fracture Spacing & Drilling Direction Courtesy of AAPG

Nolen-Hoeksema & Howard (1987) Drilling Direction Nomograph Courtesy of AAPG

High Intensity Fold-Related Fractures

Bedding/Fracture/Well Rotation unrotated rotated Joubert & Rice (1997)

UBIFMI UBI vs. FMI Courtesy of Steve Hansen, Schlumberger UBI Shows Topography FMI Shows Resistivity

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.

Rotated Fracture Poles NN before bedding rotation after bedding rotation equal area, lower hemisphere, stereonets. fracture poles for all 9 wells ~ 1700 poles Joubert & Rice (1997)

Equation - Fracture Intercept Rate i th fracture - occurrence of i th fracture, The fracture frequency in any arbitrary direction is the sum of: - the cosine of the angle between the normal intercept rate direction of the i th fracture, over all fractures.

Occurrence Weighting (Lacazette 1990) Drill Hole Fracture 2 Fracture 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 < W2 Joubert & Rice (1997)

Occurrence Corrected Rose Diagrams occurrence weighted fracture planes rotated raw fracture planes Joubert & Rice (1997)

Intercept Rate NORTH EAST SOUTH WEST horizontal 15 deg. 30 deg. 45 deg. 60 deg. 75 deg. vertical Polar chart showing number of fractures intercepted per meter for different drilling directions - (bedding rotated flat). Well #1 Joubert & Rice (1997)

Aperture Variation on Rose Diagram N maximum aperture minimum aperture Joubert & Rice (1997)

Fracture Aperture Courtesy of Steve Hansen, Schlumberger

Equation - Flow Intercept Rate - fracture aperture of the i th fracture Joubert & Rice (1997)

Flow Intercept Rate HORZ. 15 DEG Joubert & Rice (1997)

Calculated Horizontal vs Vertical Drilling horz Vert. inclination angle relative to bedding % of maximum flow well # Triassic Carbonate Reservoirs, Northern British Columbia, Canada From Joubert & Rice (1997) Drilling at low angles to bedding makes a good well

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

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