Hydrologic Characterization of Fractured Rocks for DFN Models

1. Hydrologic Characterization of Fractured Rocks for DFN Models

2. Useful Definitions and Concepts • Transmissivity -- Properties of a conductor (aquifer, reservoir, single fracture, fracture zone) (L2/T) • Permeability, Hydraulic Conductivity -- Property of material inside conductor (L/T)

3. Definitions, continued • Storativity -- Storage of a conductor or conducting feature (dimensionless) • Specific Storage -- Property of material in a conductor (1/L) • Hydraulic Diffusivity -- Ratio of T/S (L2/T) • Controls speed of propagation of pressure effect of a disturbance • Very (!!!) important for scaling results

4. Overview • Useful Concepts • Steady Flow Methods • Packer Tests • Flow Logs • Transient Flow Methods • Boundary effects • Dimension effects

5. Steady Flow Methods • Packer Testing • Falling Head Test • Constant Pressure/Lugeon Test • Flow Logging • Heat pulse • Spinner • Hydrophysical

6. Steady Radial Flow rw • Pressure and flow constant • Only exists with constant pressure boundary • Generally under-estimates due to skin R

7. Packer Test (Fixed Interval Length) • Used in Civil Engineering • Testing at fixed interval lengths • Some zones have no fractures; some zones have multiple fractures • Efficient testing has some no flows but not too many

8. Pn - # of no flows/# of tests L - length of test zone

9. Oxfilet (Osnes Extraction of Fixed Interval Length Evaluation of Transmissivity) • Guess T and P10 of Fractures • Oxfiet generated fracture along hole • Oxfilet calculates packer test transmissivities • Oxfilet compares measured and simulated pacer test transmissivities

10. Oxfilet Interface Fracture Network Stats Data and Simulated PDF’s Packer Test Stats Data and Simulated CDF’s

11. Oxfilet Challenges • Results non-unique but constrained (range of combinations of distributions of T and frequency that will fit a test • Flow logging preferred method

12. Flow Log Types • Spinner • Heat pulse • Hydrophysical • Induced electromagnetic

13. Hydrophysical Log (1) Replace fluid with deionized water (2) Log fluid resistivity while pumping Spinner

14. UCM (Electromagnetic Log) Fluid Resistivity Flow Temp

15. Posiva (Finland) Heat Pulse Flow Log (Äspö) Heat Pulse Log

16. Thoughts on Flow Logging • Cumulative logging methods fast and easy • Discrete interval logging methods provide better detail and wide range of distribution • Complementary temperature and fluid resistivity can be useful

17. Image Logging Borehole TV (BIPS) FMI (micro-resistivity)

18. Hydro-Testing Work Flow • Steady tests (flow log) to identify conductors • Image log or core analysis to geo-logically characterize conductors • Transient tests to characterize network away from hole

19. Transient Well Tests

20. Overview of Transient Tests • Important source (most important?) of geometric information on fracture plumbing system • Cylindrical flow and beyond • Dimensions, boundaries, and reading derivative curves

21. Radial Diffusion Equation(Radial Cylindrical Flow)

22. Exponential Integral:

23. Semilog Approximation of the Exponential Integral (MKS units)

24. Exponential Integral Function Semilog Log-Log

25. Derivative Methods • Plots P/log(t) • Intent to make semi-line unambiguous • Effect is a very powerful tool to interpret geometry from tests • Derivative is a map of transmissivity versus distance from the well • Shape of derivative constrains network geometry

26. Exponential Integral and Derivative

27. Calculating Pressure Derivative in Spreadsheets Formula in Cell C8: t   p/  t, or approximately =a8*(b9-b7)/(a9-a7) If the derivative is noisy, calculate derivative over a larger spread, for example, at C7 calculate using rows 10 and 4 Note: Averaging deteriorates at beginning and end of data especially if a larger is used

28. Dimensionless Variables(Radial Cylindrical Flow)

29. Useful Definitions

30. Generalized Radial Flow

31. Dimension Information from Well Tests

32. Integer Flow Dimensions

33. Spherical (3-D) x-section area r2 Linear (1-D), x-section area r0 Generalized Flow, x-section area  rn-1 Cylindrical (2-D) x-section area r1

34. Log Slope and Dimension For Log Plots of Pressure or Inverse Flow Verus Time For Log Plots of Pressure or Inverse Flow Derivative

35. Boundary and Dimension Effects 2-D 1-D 3-D Reservoir geometry Network/Flow geometry

36. Fracture Intensity (Fracture Area/Rock Mass Volume) Can Influence Dimension Boundary Effect

37. Geometric Information From Well Tests

38. Composite Dimension 1.00E+03 1.00E+02 Composite Boundary 1.00E+01 Dimensionless Pressure Linear Flow 1.00E+00 Spherical Flow 1.00E-01 1.00E-02 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 Dimensionless Time

39. Comments on Interference Tests • Radius of Investigation (very handy !!!) • Estimate diffusivity from response time • Independent of dimension

40. Important Notes on Tests • Transmissivity can be determined only from pumping wells in fractured or heterogeneous rock without assuming uniform flow over region of influence • Storativity (diffusivity) can only be obtained from observation responses • Observation wells give geometric information for areas farther from pumping source than themselves

41. Composite Dimension • Dimesional Variation Reflect Local Scale versus Larger Scale Effects • May Reflect Borehole Geometry as Well as Conductive Geometry

42. Parts of Composite Dimension Curves • Early Time Effects (Wellbore Storage, Finite Borehole) • Inner Shell (n1) • Transition (changes in area, property) • Outer Shell (n2) • Boundary Effects

43. Composite Interference Response • Response depends on relative distances of transition radius and observation well radius • Inner zone not observed for observation points near or beyond the transition radius