SPE-CSGM_Workshop_Mundle_May2015

© 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

© 2015
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

© 2015
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

© 2015
Geochemical characterizations & forensics
o  Gases/fluids for different zones can
be ‘fingerprinted’
o  But why do you keep getting
burned with this approach?

© 2015
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

© 2015
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

© 2015
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

© 2015
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)

© 2015
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:

© 2015
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

© 2015
No insight from water isotopes
o  Water isotopes implicated groundwater sources that
conflicted with other indicators (chlorides, TDS, etc.)

© 2015
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

© 2015
Identifying source zones
o  Fluids provide a line of evidence for potential sources, but
they do not provide a refined interpretation

© 2015
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

© 2015
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

© 2015
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

© 2015
Simpler case study: High gas flows
•  SCV had high gas flow
•  No fluids
•  Commercial isotope
interpretations were
consistently picking the
wrong depth/zone

© 2015
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

© 2015
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-CSGM_Workshop_Mundle_May2015

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