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Hydrologic Characterization of Fractured Rocks for DFN Models

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

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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 (L 2 /T) –Controls speed of propagation of pressure effect of a disturbance –Very (!!!) important for scaling results

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Overview Useful Concepts Steady Flow Methods –Packer Tests –Flow Logs Transient Flow Methods –Boundary effects –Dimension effects

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

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

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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

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P n - # of no flows/# of tests L - length of test zone

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Oxfilet (Osnes Extraction of Fixed Interval Length Evaluation of Transmissivity) Guess T and P 10 of Fractures Oxfiet generated fracture along hole Oxfilet calculates packer test transmissivities Oxfilet compares measured and simulated pacer test transmissivities

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

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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

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Flow Log Types Spinner Heat pulse Hydrophysical Induced electromagnetic

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

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UCM (Electromagnetic Log) Flow Fluid Resistivity Temp

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

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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

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

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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

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Transient Well Tests

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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

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Radial Diffusion Equation (Radial Cylindrical Flow)

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Exponential Integral:

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Semilog Approximation of the Exponential Integral (MKS units)

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Exponential Integral Function SemilogLog-Log

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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

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Exponential Integral and Derivative

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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

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Dimensionless Variables (Radial Cylindrical Flow)

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Useful Definitions

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Generalized Radial Flow

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Dimension Information from Well Tests

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Integer Flow Dimensions

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Linear (1-D), x-section area r 0 Cylindrical (2-D) x-section area r 1 Spherical (3-D) x-section area r 2 Generalized Flow, x-section area r n-1

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

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

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

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Geometric Information From Well Tests

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1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+001.00E+011.00E+021.00E+031.00E+041.00E+051.00E+061.00E+071.00E+08 Dimensionless Time Dimensionless Pressure Linear Flow Composite Boundary Spherical Flow Composite Dimension

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

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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

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

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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

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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

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