In situ permeability testing in boreholes

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IN-SITU HYDRAULIC TESTING OF LOW
PERMEABILITY MATERIALS
Dr Martin Preene, Preene Groundwater Consulting, UK
Stephan Rohs, Golder Associates, Germany

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• Definitions and current UK
practice
• Specialist applications
• Test equipment
• Test interpretation
• Conclusion
SYNOPSIS

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PRACTICE PROFILE
Preene Groundwater Consulting is the Professional Practice
of Dr Martin Preene and provides specialist advice and design
services in the fields of dewatering, groundwater engineering
and hydrogeology to clients worldwide
Dr Martin Preene has more than 25 years’ experience on
projects worldwide in the investigation, design, installation
and operation of groundwater control and dewatering
systems. He is widely published on dewatering and
groundwater control and is the author of the UK industry
guidance on dewatering (CIRIA Report C515 Groundwater
Control Design and Practice) as well as a dewatering text book
(Groundwater Lowering in Construction: A Practical Guide to
Dewatering)

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• Hydraulic conductivity is a measure of how easily water can pass
through soil or rock. Also known as coefficient of permeability or
permeability
• Symbol k
• Units of velocity – metres/sec, metres/day
• Very wide range of values in natural soils and rocks,10-2 to 10-11 m/s
• Hydraulic conductivity depends on the properties of the soil/rock
and the properties of water. The viscosity of water varies with
temperature, so hydraulic conductivity will vary with temperature
DEFINITION OF PERMEABILITY

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• The goal of hydraulic testing is to characterize the hydraulic
properties of the system composed of the borehole and
geological formation
DEFINITION OF HYDRAULIC TESTING
Formation properties:
 Permeability
 Static formation pressure
 Flow model
Borehole properties:
 Wellbore storage coefficient
Near wellbore properties:
 Skin

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• Hydraulic properties (including permeability) cannot be
measured directly
• They are derived from the hydraulic reaction (variation
of pressure and/or flow) of the system:
– Pressure (P) in the test interval as function of time P = f1(t)
– Flow rate (q) of the test interval as function of time q = f2(t)
DEFINITION OF HYDRAULIC TESTING

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DEFINITION OF HYDRAULIC TESTINGFLOWRATE
ZEIT
CONSTANT PRESSURE TESTS
Pressure recovery
CONSTANT RATE TESTS SLUG- AND PULSE-TESTS
Pressure recovery
PRESSURE

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• Current (and historic) UK practice is defined in BS5930:1999 (amended 2010)
CURRENT UK GEOTECHNICAL PRACTICE
Packer injection
tests (sometimes
referred to as
Lugeon tests)
Variable and
constant head tests
in boreholes,
typically analysed
by the methods of
Hvorslev (1951)
Falling
head
Rising
head

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• Analysis methods are based on references from the 1950s and 1960s
CURRENT UK GEOTECHNICAL PRACTICE
 New standards (related to Eurocode 7) have being
developed for permeability testing for geotechnical
purposes
 BS EN ISO 22282 Geohydraulic Tests
Part 1. General rules
Part 2. Water permeability test in borehole without packer
Part 3. Water pressure test in rock
Part 4. Pumping tests
Part 5. Infiltrometer tests
Part 6. Closed packer systems
 The new standards use similar methods of analysis to
BS5930
 More sophisticated methods of testing and analysis have
been developed outside the geotechnical industry

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• The specialist testing and interpretation methods described
in this presentation are derived from methods used in
reservoir engineering in the oil and gas industries
• Potential applications related to construction and
geotechnics include:
– Nuclear repository engineering
– High specification cut-off walls
– Critical consolidation analyses
– Unconventional gas (shale gas) development
– Gas storage caverns
– Deep geothermal systems
APPLICATIONS FOR SPECIALIST TESTING

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• In moderate to high permeability
environments constant rate tests and/or slug
tests are appropriate
• In low permeability environments the choice
of viable test methods is limited:
– Very low flow rates involved
– Large wellbore storage effect
– Time constraints
TEST DESIGN

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• Pulse tests are an appropriate hydraulic test method for very low
permeabilities
• For a pulse test a defined volume of test fluid is injected or extracted from
the test interval, which results in a pressure decrease or increase. The
subsequent pressure recovery is used in the analysis
TEST DESIGN
2250
2500
2750
3000
3250
3500
3750
4000
4250
4500
0 5 10 15 20 25 30 35 40 45 50
Elapsed Time [hrs]
Pressure[kPa]
15
16
17
18
19
20
Temperature[°C]
P2 (Interval)
T2 (Interval)
PW DEF
INF +
COM PSR

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• A typical pulse test consists of the following steps:
1. Packer Inflation (INF) and Packer Compliance
(COM)
2. Pressure Static Recovery (PSR)
3. Pulse Injection (PI) or Pulse Withdrawal (PW)
4. Packer Deflation (DEF)
TEST DESIGN

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TEST EQUIPMENT
Control lines
Pressure gauges
Shut-in tool
Upper Packer
Test interval
Lower Packer
 Main parts of the downhole
equipment
1. Packer to isolate the
section of interest
2. Pressure gauges
3. Shut-in tool (SIT)

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• Volume change of test interval due to:
1. Packer compliance
2. Borehole convergence
• Temperature change
• Borehole history effects
INFLUENCES ON TEST RESPONSE

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• Traditional geotechnical methods of analysis are based on the
analysis of pressure (or head) vs time (e.g. Hvorslev analysis)
• More sophisticated analyses use the ‘first derivative’ (the rate of
change of fluid pressure with time) as well as pressure vs. time
• Furthermore, tests are interpretated against the wider geological
context and conceptual model
– Suitable flow regime (porous media, multiple fissures, single fissure)
– Borehole history
– Strata type and hydrogeological conceptual model
• The desired outcome is to ‘test interpretation’ rather than simply
‘analysing’ the test data
ANALYSIS METHODS

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– Pulse test analysis method is based on a signal processing
technique known as deconvolution, which:
1. Increases the ability to identify an appropiate flow model
2. Improves the sensitivity of the analysis with regard to
permeability
– Analysis is normally done
by numerical modelling
using proprietary software
packages
– Multiple analyses allow
better interpretation of
test results
– The numerical analysis
allows a full test simulation
TEST INTERPRETATION

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• Parameter correlation
– e.g. influence of different borehole
histories on parameters, including
formation permeability and static
formation pressure
• Relationship between
different parameters (e.g.
static formation pressure
and permeability)
TEST INTERPRETATION

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• More sophisticated methods of permeability testing and
analysis have been developed in other industries and may
have applications in geotechnical engineering
• Pulse tests are an appropriate method to measure the
hydraulic properties of very low permeable formations
• The deconvolution method of analysis allows a reliable flow
model identification and permeability estimation and, in
combination with statistical methods, the reliability of the
derived parameters and connected uncertainties can be
quantified
• These methods are likely to be used in any future
investigations for nuclear repository engineering
CONCLUSION

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IN-SITU HYDRAULIC TESTING OF LOW
PERMEABILITY MATERIALS
Dr Martin Preene, Preene Groundwater Consulting, UK
Stephan Rohs, Golder Associates, Germany