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Assessing borehole geophysical data by simulating borehole flow in fractured bedrock aquifers Andrew S. Reeve and Joseph Sawdey University of Maine, Dept. of Earth Sciences asreeve@maine.edu Andrew S. Reeve and Joseph Sawdey Simulating

SLIDE 1

Assessing borehole geophysical data by simulating borehole flow in fractured bedrock aquifers

Andrew S. Reeve and Joseph Sawdey

University of Maine, Dept. of Earth Sciences asreeve@maine.edu

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 2

What is a fractured bedrock aquifer?

Aquifer Subsurface unit that yields a significant amount of water to a well. Fractures Breaks in rock that groundwater flows through

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 3

Assess fractured bedrock aquifer with: rock core surface geophysics borehole geophysics

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 4

Assess fractured bedrock aquifer with: rock core surface geophysics borehole geophysics

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 5

Caliper

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 6

Heat-Pulse Flow Meter

Model Flow Data: Results:

Transmissivity Far-field Head

Purpose:

Water Supply Contaminant Transport

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 7

Borehole Data (Jonesboro, Maine)

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 8

Borehole Flow Model

Presented in Paillet (1998)

Maximize value of data Quantify hydraulic parameters for discrete zones Model not widely available Trail and error methodology

Based on superposed sequence of slug tests

Integral equation for recovery Cooper, Bredehoeft, Papadopulos (1967)

Soil/Sediment Bedrock

Far-Field Head 1 Far-Field Head 2 Level after removing 'slug' Equilibrium level Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 9

Borehole Flow Model

Time

S l u g T e s t R e s p

s e Slug 2 Slug 3 Slug 1

Recovery (length)

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 10

Borehole Flow Model

Time

S l u g T e s t R e s p

s e Slug 2 Slug 3 Slug 1

Recovery (length)

Fracture Response to Slug 1 Fracture Response to Slug 3

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 11

Borehole Flow Model

Time

S l u g T e s t R e s p

s e Slug 2 Slug 3 Slug 1

Recovery (length)

Fracture Response to Slug 1 Fracture Response to Slug 3 Fracture Response to Response to Slug 1

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 12

Simplified Program Structure

Numerically Integrate (scipy.integrate.quadpack.quad) Interpolate Recovery vs. Time (scipy.interpolate.UnivariateSpline) Loop over time Update well water level Loop over fractures Sum fracture responses to slugs using Interpolation Return flow in well between fractures Compare with measured Data (scipy.optimize.leastsq) Borehole Flow Data Assign Hydraulic Data to Borehole

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 13

Validation

Q(Analytic)=0.5000 gpm Q(Dt=0.5)=0.4999 gpm Q(Dt=2.0)=0.4999 gpm

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow

SLIDE 14

Borehole Flow Model Fit

Head Diff.=0.096 m Head Diff.=-0.038 m Head Diff.=-0.047 m

Andrew S. Reeve and Joseph Sawdey Simulating borehole flow