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SPE-CSGM_Workshop_Mundle_May2015
- 1. © 2015
Chemistry Matters Inc.
Making chemistry data meaningful
Characterizing the source zones
for surface casing vent leaks
Scott Mundle* and Court Sandau
Presented at:
SPE/CSGM Gas Migration Challenges – Identification and Treatment Workshop
May 13-14, 2015
SPE Gas Migration Workshop May 13-14, 2015
- 2. © 2015
Chemistry Matters Inc.
o Geochemical characterization of sources to identify ‘fugitive’
gas/fluid migration in the oil/gas sector
Geochemical ‘fingerprinting
2SPE Gas Migration Workshop May 13-14, 2015
- 3. © 2015
Chemistry Matters Inc.
o Surface casing used to protect
shallow (potable) aquifers
o Gas (and fluids) in SCVs migrate
from deeper zones
o Irregular and low flow rates (can be
difficult to sample/monitor)
o How can you determine the
source(s) of the leaks?
Surface casing vent flow
SPE Gas Migration Workshop May 13-14, 2015 3
- 4. © 2015
Chemistry Matters Inc.
Geochemical characterizations & forensics
o Gases/fluids for different zones can
be ‘fingerprinted’
o But why do you keep getting
burned with this approach?
SPE Gas Migration Workshop May 13-14, 2015 4
- 5. © 2015
Chemistry Matters Inc.
The geochemistry is never wrong, but the
interpretation is often incorrect
o Common problems:
o Sample degraded prior to
analysis
o Either the wrong ‘end-
members’, or no ‘end-
members are used to
identify sources
o Numbers are reported that
are at or below the
detection limits of the
instrument
SPE Gas Migration Workshop May 13-14, 2015 5
- 6. © 2015
Chemistry Matters Inc.
Don’t make assumptions based on regional
geochemistry
o Where do the ‘fingerprints’
originate?
o Isotope “databases” often
use regional values rather
than local values that can
mislead interpretations
SPE Gas Migration Workshop May 13-14, 2015 6
- 7. © 2015
Chemistry Matters Inc.
Need high quality SCV samples
o Can separate and collect gas and liquid
o Gas can be purged to remove “breathing”
gas from well
o Need low atmospheric content in gas
samples for compositional and isotopic
characterization
SPE Gas Migration Workshop May 13-14, 2015 7
- 8. © 2015
Chemistry Matters Inc.
Sampling can affect water chemistry
0.0001$
0.001$
0.01$
0.1$
1$
10$
100$
1000$
10000$
100000$
Lithium$
Sodium$
Potassium$
Rubidium$
Cesium$
Beryllium$
Magnesium$
Calcium$
Stron=um$
Barium$
Boron$
Aluminum$
Gallium$
Indium$
Thallium$
Silicon$
Germanium$
Tin$
Lead$
Phosphorus$
Arsenic$
An=mony$
Bismuth$
Sulphur$
Selenium$
Tellurium$
Chlorine$
Bromine$
Iodine$
Scandium$
YDrium$
Titanium$
Zirconium$
Vanadium$
Niobium$
Tantalum$
Chromium$
Molybdenum$
Tungsten$
Manganese$
Iron$
Cobalt$
Nickel$
Palladium$
Pla=num$
Copper$
Silver$
Gold$
Zinc$
Cadmium$
Mercury$
Lanthanum$
Cerium$
Praseodymium$
Neodymium$
Samarium$
Europium$
Gadolinium$
Terbium$
Dysprosium$
Holmium$
Erbium$
YDerbium$
Thorium$
Uranium$
BleedNbarrel$
FlowNthrough$Cell$
1 2 3 4 5 6 7 d-block f-block
Group 2 metals and f-block metals lower in bleed barrels
- suspended solids settle out in bleed barrel (low energy environment)
SPE Gas Migration Workshop May 13-14, 2015 8
- 9. © 2015
Chemistry Matters Inc.
How can you get it right every time?
Mudgas Geochemical Profile
Characterized stratigraphy
Prod./Source Zones:
1.) Fluids
2.) Gases
Characterized end-members
Shallow Fluids
1.) Surface water
2.) Groundwater
Characterized inputs
SCVs:
What are the Source(s)?
1.) Fluid
2.) Gas
GEOCHEMISTRY:
SPE Gas Migration Workshop May 13-14, 2015 9
- 10. © 2015
Chemistry Matters Inc.
Complex case study: Fluid and gas flows
• Collected four samples from each location:
– SCV gas sample
– SCV liquid sample
– Production casing gas sample
– Production casing liquid sample
• Used local groundwater and deep aquifer wells in region for
comparison
• Used perforated wells with DST samples to acquire ‘end-
members’ for other potential source zones
SPE Gas Migration Workshop May 13-14, 2015 10
- 11. © 2015
Chemistry Matters Inc.
No insight from water isotopes
o Water isotopes implicated groundwater sources that
conflicted with other indicators (chlorides, TDS, etc.)
SPE Gas Migration Workshop May 13-14, 2015 11
- 12. © 2015
Chemistry Matters Inc.
A clearer picture with advanced analyses
o Different sources had characteristic ranges of concentrations
and isotope values. This provided first line of evidence to
indicate that different source zones can be identified
SPE Gas Migration Workshop May 13-14, 2015 12
- 13. © 2015
Chemistry Matters Inc.
Identifying source zones
o Fluids provide a line of evidence for potential sources, but
they do not provide a refined interpretation
SPE Gas Migration Workshop May 13-14, 2015 13
- 14. © 2015
Chemistry Matters Inc.
Combined fluid and gas characterization
*Exact values property of client, shift in isotope values indicated
δ13C Values
GASES C1 C2 C3
SCV A - 1.9 B - 2.3 C
Casing A* B* C*
o Gases provide a second line of evidence for potential sources
and help confirm a production zone leak
SPE Gas Migration Workshop May 13-14, 2015 14
- 15. © 2015
Chemistry Matters Inc.
Complete geochemistry = complete picture
δ13C Values
GASES C1 C2 C3
SCV A - 1.9 B - 2.3 C
Casing A* B* C*
*Exact values property of client, shift in isotope values indicated
δ13C Values
GASES C1 C2 C3
SCV A - 13.1 B - 8.1 bdl
Casing A* B* C*o Gases provide a second line of
evidence to confirm a cretaceous
zone leak
SPE Gas Migration Workshop May 13-14, 2015 15
- 16. © 2015
Chemistry Matters Inc.
δ13C Values
GASES C1 C2 C3
SCV A - 13.1 B - 8.1 bdl
Casing A* B* C*
Resolving the depth of source zone
o Mudgas log can refine cretaceous
leak to within 200-300m range
SPE Gas Migration Workshop May 13-14, 2015 16
- 17. © 2015
Chemistry Matters Inc.
Simpler case study: High gas flows
• SCV had high gas flow
• No fluids
• Commercial isotope
interpretations were
consistently picking the
wrong depth/zone
SPE Gas Migration Workshop May 13-14, 2015 17
- 18. © 2015
Chemistry Matters Inc.
Bulk gas compositions gave little insight
o Data equally implicates different zones and/or mixtures
18SPE Gas Migration Workshop May 13-14, 2015
- 19. © 2015
Chemistry Matters Inc.
Carbon isotopes suggest different zones
o Data could implicate two different zones
19SPE Gas Migration Workshop May 13-14, 2015
- 20. © 2015
Chemistry Matters Inc.
Advanced models implicate same zone
o All leaks actually from similar zone!
20SPE Gas Migration Workshop May 13-14, 2015
- 21. © 2015
Chemistry Matters Inc.
Did it work?
• Similar zone
implicated for all
SCV in area
• Gas zone overlying
production zone
implicated
• Cement squeezes
successful at
predicted depth for
all interventions
undertaken in 2014
SPE Gas Migration Workshop May 13-14, 2015 21
- 22. © 2015
Chemistry Matters Inc.
Where can it all go wrong?
• Similar altered
isotope ‘fingerprints
can be expected from
different sources
SPE Gas Migration Workshop May 13-14, 2015 22
- 23. © 2015
Chemistry Matters Inc.
Best practices for SCV ‘geoforensics’
• Collect high quality samples
• Collect samples for potential source(s) and from the
production casing (if possible)
• Start with basic chemistry but may need more conservative
analytes and advanced interpretations
• Ask the right questions and get it right !
– What source zone characterizations were used in the interpretation?
– Where were these source zones characterized (geographically)?
– What are the reliable detection limits for your instrumentation?
High quality samples, isotope analysis and accurate
interpretation of microbial effects provide more
conclusive source determination.
SPE Gas Migration Workshop May 13-14, 2015 23