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TRANSIENT CHANGES in FRACTURE APERTURE DURING HYDRAULIC WELL TESTS in FRACTURED GNEISS

TRANSIENT CHANGES in FRACTURE APERTURE DURING HYDRAULIC WELL TESTS in FRACTURED GNEISS. Erik Svenson Leonid Germanovich. Todd Schweisinger Larry Murdoch. (GT). LAR-4 26.5 m. Supported by NSF EAR 0001146. Fracture signifance geometry response. FRACTURED BEDROCK. Wells.

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TRANSIENT CHANGES in FRACTURE APERTURE DURING HYDRAULIC WELL TESTS in FRACTURED GNEISS

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  1. TRANSIENT CHANGES in FRACTURE APERTURE DURING HYDRAULIC WELL TESTS in FRACTURED GNEISS Erik Svenson Leonid Germanovich Todd Schweisinger Larry Murdoch (GT) LAR-4 26.5 m Supported byNSF EAR 0001146

  2. Fracture • signifance • geometry • response FRACTURED BEDROCK Wells Hydraulically active sheet fractures Sweet City Quarry Elberton, GA

  3. Single Well Pressure & Displacement OBJECTIVE/MOTIVATION • Motivation: • Predict movement of fluids in low transmissivity rock • Transmissivity • Fracture Storativity • Heterogeneities • (Leakage and Blockage) • Approach: • Develop Field Scale Test • Interpret Data with (HM) Model

  4. Injection Withdrawal Pumping: (-) (+) Fracture Aperture: Closing Dilating Opening Propagating Asperities in contact HYDROMECHANICAL REGIMES Pressure and Displacement

  5. CONCEPTUAL MODEL

  6. THEORETICAL MODEL d P s P s P s P P p s P P P P d P P s P P P P P,P:Continuity in finite difference s:Estress-displacement d:Sneddon integral, semi-analytical

  7. MODEL RESULTS (SLUG TESTS) Transient Responses During Slug Test Transmissivity, T T = dwell2/t0.37 Similar to Hvorslev Method Slug Injection T = 0.1 cm2/sec t0.37

  8. FRACTURE COMPLIANCE Late-time derivative (slope) of displacement vs. head curve Fracture Compliance During Slug cf ~2.5x10-6m/mH20 cf Storage: Fracture Storativity: time Depth: 25 meters Sf = gwcf Specific Storage of interval: Ss= cf /length Fracture Compliance, cf Inversely proportional to fracture normal stiffness Hysteresis

  9. INFLUENCE OF HETER0GENEITIES Blockage away from well Leakage away from well Hysteresis becomes more pronounced for blockage Hysteresis becomes less pronounced as leakage is placed closer to well

  10. EXTENSOMETER Packer Exploded View of Retractable Anchor Anchor Displacement Transducer Anchor Packer

  11. BASIC FIELD RESULTS (25m deep) Fracture Compliance Plot Slug-In Test (13 Liter Slug) Transmissivity: 0.5 cm2/s

  12. DEPTH VARIATIONS WELL-(LAR-4) FRX. LOCATION NORMALIZED COMPLIANCE PLOTS Repeatable Results 25.5m δmax : 3μm • Variable: • Compliance • Shape 27.0m δmax : 2μm

  13. K & S DISTRIBUTIONS • Three conductive zones (Blue Highlight) • Most of water released from storage in upper 2 zones • Leakage within 8m of borehole (Yellow Highlight) • Well located ~ 6m away Leakage Blockage

  14. CONCLUSIONS • Feasible to measure in-situ displacements • Displacements during slug tests: up to 20 mm • Useheadanddisplacements • to characterize subsurface • Fracture Compliance (cf):0.1 mm/(m of drawdown) -- 5 mm/m • Specific Storage (Single Well): • Ss Proportional cf, estimates ~ 10-6 to 10-5 m-1 • Estimate leakage and blockage away from borehole

  15. TRANSIENT CHANGES in FRACTURE APERTURE DURING HYDRAULIC WELL TESTS in FRACTURED GNEISS Erik Svenson Leonid Germanovich Todd Schweisinger Larry Murdoch (GT) LAR-4 26.5 m Supported byNSF EAR 0001146

  16. Comparison to Hvorslev Hvorslev’s Eqn. T = [0.5 ln(Re/rw)] rc2/t0.37 This work T = [C ] rc2/t0.37 3.7 < C < 6, from graph So, for Hvorslev in frx’d rock Re > 1600rw Most applications of Hvorslev would underestimate K in this system tT/rc2

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