Characterizing the Dissolved Gas Component
of Deep Groundwater Systems
Kevin Krogstad
Golder Associates Ltd.
Calgary, Alberta
WaterTech 2015, Kananaskis, Alberta
Why Would I Sample for Dissolved Gas?

Dissolved Gases Provide Valuable Information
Noble gases can be used to “fingerprint” sources of groundwater
 Gas isotope ratios can be used to determine origin of hydrocarbons
 Dissolved gases can be effective tracers in many cases


Dissolved Gases may Impact Processes and Procedures
Dropping pressure below “bubble point” may form bubbles within the aquifer
matrix
 Dissolved gases may be toxic and/or explosive
 Changes in dissolved gas content can significantly affect chemistry


Dissolved Gases may be the Primary Goal

Fracking litigation
 Geologic sequestration of carbon dioxide
 Coalbed methane
Where Does the Dissolved Gas Come From?






Atmosphere
Water/Rock Interactions
Phase Interactions
Chemical Processes
Microbiological Processes
Thermal Processes
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Potential Challenges

Changing Solubility
𝐶𝑣 = 𝐾ℎ 𝐶𝑤
ℎ𝑏 − ℎ 𝑛𝑉𝑎
𝑉𝑣 =
ℎ − 𝑧 + ℎ𝑎𝑡𝑚 𝐾ℎ
𝐷𝑐0
𝐷
𝛾 𝑡 = 𝛾0 − 𝑅𝑇
𝑡−
𝑟0
𝑟0
𝑑 ln 𝐾𝑒𝑞 ∆𝐻𝜃
=
𝑑𝑇
𝑅𝑇 2
𝑡
0
𝐷
∅ 𝑢 𝑑𝑢 + 2
𝑐 𝑡−
𝜋 0
𝑡
0
∅ 𝑢
2 𝑡−𝑢
𝑑𝑢
𝑚𝐶𝐻4
𝜇𝐶𝐻4
ln 𝑥𝐶𝐻4 ∅𝐶𝐻4 𝑃 −
− 2𝐶𝐻4,𝑁𝑎 𝑚𝑁𝑎 + 𝑚𝐾 + 2𝑚𝐶𝑎 + 2𝑚𝑀𝑔 − 0.06𝑚𝑆𝑂4 + 0.00624𝑚𝑁𝑎 𝑚𝐶𝑙
𝑅𝑇
𝑛
3𝑛−6
𝑢1
𝑢1 − 𝑢′1 1 − 𝑒𝑥𝑝 −𝑢′1
𝑃𝑡𝑜𝑡𝑎𝑙 =
𝑝𝑖
𝑓𝑔𝑎𝑠 =
𝑒𝑥𝑝
𝑥𝑓𝑛𝑐𝑟𝑜𝑡
𝑢′1
2
1 − 𝑒𝑥𝑝 −𝑢1
𝑖=1
April 30, 2015
𝑖
4
Methane Solubility vs. Pressure
Methane Solubility in Water (mg/L)
2500
Methane Solubility (mg/L)
2000
1500
1000
500
0
0
10
Adapted from Edwards, 1991
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20
30
40
50
Pressure (atm)
5
60
70
80
90
100
Potential Challenges


Changing Solubility
Changing Chemistry
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Changing Chemistry



+
𝐶𝑂2(g)+H2O  H2CO3(aq)HCO3−(aq)+𝐻 (aq)
+
−
𝐻2𝑆(g)H2S(aq)𝐻 (aq) + 𝐻𝑆 (aq)
Injection systems designed for surface chemistry may be encountering
a very different environment in the aquifer.
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Potential Challenges



Changing Solubility
Changing Chemistry
Aquifer Parameter Effects
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Aquifer Parameter Effects



“Bubble Point”- spontaneous
formation of bubbles within the
aquifer framework.
Bubbles “bridge” flow pathways,
reducing the effective hydraulic
conductivity.
Specific Storage is defined as
𝑆𝑠 = 𝜌𝑔(𝛼 + 𝑛𝛽), where
𝜌𝑔 is the specific weight of
water,
𝛼 is the compressibility of
aquifer material,
𝛽 is fluid compressibility, and
𝑛 is porosity
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Aquifer Parameter Effects
300.00
290.00
280.00
270.00
OWOBS
PWSIM
260.00
PWOBS
OWSIM
250.00
240.00
230.00
220.00
-0.05
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0.15
0.35
0.55
10
0.75
0.95
Potential Challenges




Changing Solubility
Changing Chemistry
Aquifer Parameter Effects
Health and Safety Issues
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Health and Safety Issues

Hydrocarbon gases

Methane
 Ethane
 Propane, etc.

Toxic gases

Hydrogen Sulfide
 Radon
 Carbon Dioxide, Nitrogen, etc. (suffocants)
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Sampling for Dissolved Gases




Goal of the program
Access and conditions
Budget
Schedule
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Free Gas Sampling

Free gas is the “excess gas” given off by water, either under changing
conditions or during equilibrium exchanges, and does not include gas
normally in solution.

Each gas in the solution has its own equilibrium, and its own exsolution
rate.

Gases may have been exposed to plastic tubing, which may adsorb or
even transmit some gases.

Bubbles in the discharge line may travel faster than water, potentially
resulting in misleading calculations.
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Wellhead Gas Sampling
• No water pumping
required
• Good sample volumes
• Wellhead gas is not
necessarily at equilibrium
with groundwater.
• Extremely vulnerable to
atmospheric
contamination.
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Inverted Bottle Method
• Very simple
• No complicated equipment
Water In
Water Displaced
by Gas
• Difficult to use in harsh
weather
• Quantitatively vague
Water Out
Adapted from Hirsche & Mayer, 2007
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Flow-Through Separator
• Relatively easy collection
process
• No moving parts
• Vulnerable to operator
error
• Uncertain pressures
• Atmospheric
contamination
Dissolved Gas Sampling



Dissolved gas is included in a water sample and remains in solution, or
contained with the original volume of water, until analyzed.
Dissolved gas is in equilibrium with its surroundings, so it is important to
isolate a sample from the atmosphere to prevent contamination.
Equilibrium changes with temperature, chemistry, pressure, and other
factors, and each gas species has its own equilibrium levels.
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Wireline Tools
• Capable of
sampling at great
depths
• Widely accepted
• Requires service rig
• Complicated
equipment
• Expensive
• Limited volume
Photo From PetroWiki
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Copper Tube Samplers
• Accurate and stable
• Good for noble gas
isotopes
• Very limited volume
• Complicated
support equipment
• Limited analysis
options
Photo From University of Utah Dissolved Gas Lab
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Diffusion Samplers
• Collects only gas
• No freezing issues
• Very limited volume
• Complicated
equipment
• Limited analysis
options
Photos From University of Utah Dissolved Gas Lab
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Equilibrated Grab Samplers
• Minimal Sample
Handling After
Collection
• Depth-Specific
Sample Collection
• No Power Source
Required
• No Positive Pressure
Seal
• Advance Deployment
Recommended
Photo from ProHydro, Inc.
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Discrete Interval Samplers
• Holds a sample
under pressure
• Can be targeted on
a specific interval of
the well
• Does not isolate
sample from
atmosphere, good
for water samples
but less so for
multiphase samples
Photo from Solinst Canada, Ltd.
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Golder’s Isobaric In Situ (IBIS) Sampler



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Large sample volume
Maintains sample at reservoir pressure
Completely isolated from atmosphere
No complicated controllers or machinery
Rather heavy
Prone to freezing at extreme temperatures
Check
Valve
Ball
valve
Hex
Nut
Ball
Valve
Hex
Nut
So….





Dissolved gases can provide important information
Dissolved gases can alter formation conductivity and chemistry
Health and safety hazards- H2S, explosive gases, etc.
Need true gas composition to really understand the equilibrium at depth
Baseline monitoring for CCS, SAGD, and others
Thank You for Your Attention!
Kevin Krogstad
Golder Associates Ltd.
102, 2535 3rd Avenue SE
Calgary AB T2A 7W5
Selected References
Edwards, J.S., 1991. Potential Hazards Resulting from the Presence of Methane Dissolved in Groundwater.
4th International Mine Water Congress, Ljubljana, Yugoslavia, September, 1991.
Harvey, O.R., Qafoku, N.P., Cantrell, K.J., Lee, G., Amonette, J.E., and C.F. Brown, 2013. Geochemical
Implications of Gas Leakage Associated with Geologic CO2 Storage- A Qualitative Review. Environmental
Science Technology, vol. 47, pp. 23-36.
Hirsche, T. and B. Mayer, 2007. A Comprehensive Literature Review on the Applicability of Free and
Dissolved Gas Sampling for Baseline Water Well Testing. Alberta Environment, Edmonton, Alberta, 56 p.
Marinas, M., Roy, J.W., and J.E. Smith, 2013. Changes in Entrapped Gas Content and Hydraulic
Conductivity with Pressure. Ground Water, vol. 51, no. 1, pp. 41-50.
Pyne, R.D.G., 2005. Aquifer Storage Recovery: A Guide to Groundwater Recharge Through Wells, 2nd
Edition. ASR Systems, Gainesville, FL. 608 p.
Ward, P.D., 2006. Impact from the Deep. Scientific American, October 1, 2006.
Yager, R.M and J.C. Fountain, 2005. Effect of Natural Gas Exsolution on Specific Storage in a Confined
Aquifer Undergoing Water Level Decline. Ground Water, vol. 39, no. 4, pp. 517-525.
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