Mechanical and Hydraulic Properties of Shales

1. Mechanical and Hydraulic Properties of Shales Andreas Reinicke Brian Horsfield, Hans-Martin Schulz, Tobias Meier, Masline Makasi, Erik Rybacki, & Georg Dresen GFZ German Research CentreforGeoscience

2. OUTLINE • key factors for economic production • geomechanical characterization • hydraulical characterization • hydraulical-mechanical coupled processes • conclusions

3. Unconventional Shale Fracturing: Narrow but Long Fractures enhancement of reservoir productivity creation of a high permeable pathway and maximization of inflow area usage of low viscous fluids and small proppant concentrations long but narrow fractures creation of a partially propped fracture Reinicke et al., 2010, Chem Erde

4. Key FactorsforEconomicProductionfrom Gas Shales • Mineralogy • clayrocksareveryheteroginous – an understandingofthevariationsisimportantfor an effectivecompletion • bestproductivity in the Barnett isarchievedfromzonewithabout 45% quartzandonly 27% clay • Geomechanics • the „“brittlenes“ oftheshale rock controlsthefracability. • understandingcreep in shalesgiveinsightstofracturehealingandformationdamageprocesses • Hydraulics • a sufficientporosityandpermeabilityisneccesarrytogueranteeeconomicproductionfromshales

5. Geomechanical Characterisation

6. Brittle and Ductile Behaviour of Rocks brittle shale frac geometry ductile shale frac geometry Grieser and Bray., 2007, SPE

7. Triaxial Testing: Influence ofTemperature and Confinement Rock testing at in-situ conditions is important

8. Triaxial Testing: Influence ofTemperature and Confinement Young‘s Modulus high clay content small calcite content high porosity high TOC small clay content high calcite content low porosity lower TOC

9. Dominant Processes InducingDuctile Deformation • Influence of • pore space • mineralogy • kerogen / fluid phase • Dominant Mechanisms • grain sliding, grain crushing • rearrangement of pore space

10. Brittleness from Log-Data Young‘s modulus Minimum requirement Young’ modulus > 4 GPa Poisson ratio < 0.25 Poisson ratio Rickman et al., 2008, SPE

11. Borehole Breakout: Shale – Transverse Isotropic Material Meier, 2011, pers. com.

12. Borehole Breakout: Shale – Transverse Isotropic Material Meier, 2011, pers. com.

13. Borehole Breakout: Shale – Transverse Isotropic Material CT Scan Meier, 2011, pers. com.

14. Hydraulical Characterisation

15. Pore Space and Permeability of Sandstone and Shale Permeability: Darcy - milliDarcy Sandstone Gas Shale Permeability: nanoDarcy

16. Long-Term EffectsInfluence of Time and Temperature • Importance of in-situ Tests • significant permeability reduction • strong influence of temperature • Strong influence of meas. time const. conditions 210 MPa 40150°C 0.75 6 7 8 25-34 35 36 Zimmermann and Reinicke, 2010, Geothermics

17. Benefit of Using Proppants small proppant concentration + shearing maximizes conductivity Fredd et al., 2000, SPE

18. Mechanical – Hydraulic Coupled Effects Leading to Formation Damage

19. wellbore 3 proppant filled fracture 2 1 Fracture Face Skin (FFS)A Potential Damage Mechanism FFS reservoir sh sH

20. Extend of Embedment LayerCalculation of Fracture Face Skin Permeability Reinicke, 2010, PhD thesis

21. Proppant EmbedmentStress Distribution rock grain matrix proppant Reinicke, 2010, PhD thesis

22. Proppant EmbedmentStress Distribution rock grain matrix proppant Reinicke, 2010, PhD thesis CT Scan

23. Implications for Proppants analytical solution for 3D stress distribution of diametral loaded spheres s = f { Θ, n, F, E, r } increase of contact angle: reduction of fines production stabilization of proppants reduction of proppant embedment material parameters: ceramics / sand / other ??? Penny, 1987, SPE plastically deformable coating: resin coated proppants

24. Conclusions • Tests at in-situ conditions are very important. • Microscale processes influences macroscopic behaviour (damage). • Understanding “brittleness” of the rock is a multiparameter study. • unsolved problems: • What controls the “brittleness” of a shale? • How to reduce fracture closure? • What are the dominant damage mechanisms? • How to transport proppants deep into the fracture network?

25. Thank you for your attention !

26. Fracture Growth in Conventional and Unconventional Reservoirs • in reality propagation of a fracture with several off-branches in a conventional reservoir is observed • In contrast, multiplanar fracture growth in shale gas reservoir stimulation • activation of a perpendicular oriented natural fractures • importance for large underground footprint • rock brittleness influences fracture propagation conventional reservoir real fracture with off-branches shale gas reservoir complex fracture network

27. Formation Damage Mechanisms in a Propped Fracture generation of a Fracture Face Skin - FFS proppant crushing reduction of fracture width filtration of frac fluids filter cake buildup relative perm. changes gas condensation gel residues and chemical precipitation proppant embedment due to mechanical interaction of rock and proppant sedimentation of fines Reinicke et al., 2010, Chem Erde