Slide 1

The Importance of Bedding [and Borehole] Orientation When Looking for Fractures by Charles R. Berg and Andrew C. Newson Bedding OrientationJoints Bedding OrientationJoints The Relationship between Joints and BeddingThe Relationship between Joints and Bedding Removal of Structural TiltRemoval of Structural Tilt Borehole Orientationthe Shadow Zone Borehole Orientationthe Shadow Zone Basic Relationship (Terzaghi, 1965)Basic Relationship (Terzaghi, 1965) ApproximationApproximation 2D Plots of Angle Between the Borehole and Fracture planes2D Plots of Angle Between the Borehole and Fracture planes Relative Amplitude Relative Amplitude Introducing Attenuation (1 minus Relative Amplitude) Introducing Attenuation (1 minus Relative Amplitude) Correcting for Bias (Priest, 1993) Correcting for Bias (Priest, 1993) Examples Examples Horizontal Well Across AnticlineHorizontal Well Across Anticline Highly Deviated Well with Borehole Perpendicular to DipHighly Deviated Well with Borehole Perpendicular to Dip Cardium Fractured SandCardium Fractured Sand Slide 2 Definitions of the term joints Definitions of the term joints 1.Fractures sub-perpendicular to bedding 2.Fractures that terminate at bed boundaries 3.Fractures in which no appreciable movement has occurred 4.Tensional fractures In this study, since the last three criteria are usually unknown, the only workable definition is the first. In this study, since the last three criteria are usually unknown, the only workable definition is the first.Joints Slide 3 Bedding Slide 4 F Slide 5 a a Joint Slide 6 Removal of Structural Tilt by Rotation True DipsResidual Dips Slide 7 Fractures Borehole Case 1Borehole at 90 to Fractures Slide 8 Fractures Borehole Case 2Borehole at 30 to Fractures Slide 9 Fractures Borehole Case 3Borehole at 0 to Fractures Slide 10 Fracture Scan Line (Terzaghi, 1965) Borehole (Approximation) The Scan Line Equation and What is it Missing? Slide 11 Slide 12 Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Not Joints? All Fractures Slide 18 Joints! All Fractures-Residual Dips Slide 19 Contours OnlyPoles Only All Fractures-Residual Dips Fractures are Highly Clustered Perpendicular to Bedding Slide 20 Slide 21 Contours OnlyPoles With Shadow Zone Shadow Zone10% Contour Interval Slide 22 Contours OnlyPoles With Shadow Zone25% Contour Interval Shadow Zone Slide 23 Slide 24 Slide 25 Contours OnlyPoles With All Data-3365m to 4534m Shadow Zone Slide 26 Contours OnlyPoles With Upper Segment-3365m to 4100m Shadow Zone Slide 27 Contours OnlyPoles With Lower Segment 4100m to 4534m Shadow Zone Slide 28 Contours Only Poles With Cardium Example Shadow Zone Slide 29 Be aware of the dips likely to be encountered in the fractured zones Be aware of the dips likely to be encountered in the fractured zones Know likely fracture orientations when planning borehole trajectory Know likely fracture orientations when planning borehole trajectory Try not to let drilling or other considerations override orientation issues. Try not to let drilling or other considerations override orientation issues. A typical example would be that it is easier to drill a well perpendicular to bedding. Because of typical joint/bedding relationships, this may not always be a good ideaA typical example would be that it is easier to drill a well perpendicular to bedding. Because of typical joint/bedding relationships, this may not always be a good idea In low-dip shale gas plays, fractures in nearby vertical wells may be attenuated relative to subsequent horizontal holes. In low-dip shale gas plays, fractures in nearby vertical wells may be attenuated relative to subsequent horizontal holes. We didnt see any fractures in the vertical well, therefore the frac job must have created the fractures.We didnt see any fractures in the vertical well, therefore the frac job must have created the fractures.Conclusions