Erik Svenson Leonid Germanovich

Todd SchweisingerLarry Murdoch

Supported by NSF EAR 0001146

TRANSIENT CHANGES in FRACTURE

APERTURE DURING HYDRAULIC WELL

TESTS in FRACTURED GNEISS

LAR-4 26.5 m

(GT)

FRACTURED BEDROCK

Hydraulically active sheet fractures

Wells

Sweet City QuarryElberton, GA

• Fracture •signifance•geometry•response

OBJECTIVE/MOTIVATION

•Single Well •Pressure & Displacement

Approach:

• Develop Field Scale Test

• Interpret Data with (HM) Model

•Motivation:Predict movement of fluids in low transmissivity

rock•Transmissivity

•Fracture Storativity

•Heterogeneities (Leakage and Blockage)

HYDROMECHANICAL REGIMES

Pressure and Displacement

Pumping:

Fracture Aperture:

(-)Withdrawal Injection

(+)

Closing Dilating Opening Propagating

Asperities in contact

CONCEPTUAL MODEL

THEORETICAL MODEL

P P P p

P PP P

P P

P PP PP P

P,P: Continuity in finite difference

: Estress-displacement

Sneddon integral, semi-analytical

Time (seconds)0.1 1 10 100 1000 10000

Hea

d(m

eter

s)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Dis

pla

cem

ent

(m

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2HeadDisplacement

Transient Responses During Slug Test

t0.37

MODEL RESULTS (SLUG TESTS)

T = dwell2/t0.37

Similar to Hvorslev Method

Transmissivity, T

T = 0.1 cm2/sec

Slug

Inj

ectio

n

FRACTURE COMPLIANCE

~2.5x10-6m/mH20

Head (m)

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Dis

pla

cem

ent

(m

)

0.0

0.2

0.4

0.6

0.8

1.0

Late-time derivative (slope) of displacement vs. head curve

f

Fracture Compliance, f

Inversely proportional to fracture normal

stiffness

Fracture Compliance During Slug

f

time

Hysteresis

Sf = wf

Storage:

Depth: 25 meters

Fracture Storativity:

Specific Storage of interval:

Ss = f /length

INFLUENCE OF HETER0GENEITIES

Head (m)0.0 0.2 0.4 0.6 0.8 1.0 1.2

Dis

pla

cem

ent

(m

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2Baseline1m3m14m38m76m

Leakage away from well

Head (m)0.0 0.2 0.4 0.6 0.8 1.0 1.2

Dis

plac

emen

t (

m)

0.0

0.5

1.0

1.5

2.0Baseline1m3m14m38m76m

Blockage away from well

Hysteresis becomes less pronounced as leakage is

placed closer to well

Hysteresis becomes more pronounced for blockage

EXTENSOMETER

Displacement Transducer

Packer

Exploded View of

Retractable AnchorAnchor

Anchor

Packer

BASIC FIELD RESULTS (25m deep)

Time(seconds)1 10 100 1000

Hea

d(m

)

0

1

2

3

4

5

6

7

Dis

pla

cem

ent( m

)0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5HeadDisp.

Slug-In Test (13 Liter Slug)

Head(m)0 2 4 6 8

Dis

pla

cem

ent

(m

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Head vs Disp.

Fracture Compliance Plot

Δ Head: 6.4 mH20 Fracture Compliance, f: 1.75 x10-6 m/mH20

Δ Displacement: 3.3 µm Specific Storage, Ss: ~ 10-6mH20-1

Transmissivity: 0.5 cm2/s

DEPTH VARIATIONSD

ep

th(m

ete

rs)

10

20

30

40

50

60

Ca

sin

gF

ra

ctu

red

Bio

tite

Gn

eis

s

WELL-(LAR-4) FRX. LOCATION

h/hmax

0.0 0.2 0.4 0.6 0.8 1.0 1.2

m

ax

0.0

0.2

0.4

0.6

0.8

1.0

1.2 T1-11/04

T2-11/04

T3-11/04

T1-1/21/05

T2-1/21/05

T3-1/21/05

25.5m

27.0m

NORMALIZED COMPLIANCE PLOTS

Repeatable Results

Variable:•Compliance• Shape

h/hmax

0.0 0.2 0.4 0.6 0.8 1.0 1.2

m

ax

0.0

0.2

0.4

0.6

0.8

1.0

1.2 T1-5.5LT2-5.5L

δmax : 2μm

δmax : 3μm

K & S DISTRIBUTIONS

Leakage

Blockage

• 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

CONCLUSIONS

Feasible to measure in-situ displacementsdisplacements

• DisplacementsDisplacements during slug tests:

up to 20 m

• UseUse head andand displacementsdisplacements to to characterize

subsurfacesubsurface

• Fracture Compliance (f ):

0.1 m/(m of drawdown) -- 5 m/m

• Specific Storage (Single Well): Ss Proportional f, estimates ~ 10~ 10-6-6 to 10 to 10-5-5

mm-1-1

• Estimate leakage Estimate leakage and blockage blockage away from borehole away from borehole

Erik Svenson Leonid Germanovich

Todd SchweisingerLarry Murdoch

Supported by NSF EAR 0001146

TRANSIENT CHANGES in FRACTURE

APERTURE DURING HYDRAULIC WELL

TESTS in FRACTURED GNEISS

LAR-4 26.5 m

(GT)

Comparison to Hvorslev

T = [C ] rc2/t0.37

T = [0.5 ln(Re/rw)] rc2/t0.37

Hvorslev’s Eqn.

This work

td

0.01 0.1 1 10 100

h/h o

0.0

0.2

0.4

0.6

0.8

1.0

Kni 1.11E12

Kni 1.11E11

Kni 1.06 E10

Kni 0.75 E9

Kni 0.26 E8

3.7 < C < 6, from graph

So, for Hvorslev in frx’d rock

Re > 1600rw

Most applications of Hvorslev would underestimate K in this systemtT/rc2