GeoConvention2016_Identifying Surface Casing Vent Flows (SCVF) Using Geoforensics
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Transcript of GeoConvention2016_Identifying Surface Casing Vent Flows (SCVF) Using Geoforensics
©2015ChemistryMa2ersInc. 1GeoConven)on2016–www.chemistry-ma:ers.com
Makingchemistrydatameaningful
Characterizingthesourcezonesforsurfacecasingventleaks
CourtD.Sandau,PhD,P.ChemMarch8,2016–GeoConvenCon2016,Calgary,AB
©2015ChemistryMa2ersInc.
Acknowledgements
2
• Sco:Mundle,PhD,C.Chem,P.Chem
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• Livetweets:#GeoCon2016and#GeoForensics
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SurfaceCasingVentFlowsandGeoforensics
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Geoforensics
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Introducing a new term: Geoforensics • Forensics is derived from latin “forens”, meaning of, belonging
to the forum, public
• Geoforensics is the application of scientific methods used to identify source(s) of chemical constituents (natural or man made) in fluids (gases, groundwater, oil), soil and/or rock from the subsurface of the Earth for use in potential litigious issues or for public debate or discussion.
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SurfaceCasingVentFlows(SCVFs)
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SCVFs come in many shapes and sizes - High pressure and intensity are generally easy to
identify (e.g. EOR fields) - Low flows/pressures provide difficult sampling
opportunities (Houdini wells – “no you see them, now you don’t” - L.F. 2012 – “Flow’ers and Show’ers”
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WhatdoSCVFslooklike?
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Steam
Oily Bubbles Intermittent Flow Constant Fizz
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o Surface casing used to protect shallow (potable) aquifers
o Fluids(gas and/or liquid) migrate from deeper zones through SCV
o Gas migration occurs outside the SCV
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 and gas migration
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o Geochemical characterization of sources to identify ‘fugitive’ gas migration in the oil/gas sector
Geochemical ‘fingerprinting’
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GeochemicalcharacterizaJons&forensics
o Gases/fluids for different zones can be ‘fingerprinted’
o But why does this approach sometimes fail?
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Thegeochemistryisneverwrong,buttheinterpretaJonisoPenincorrect
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 Misinterpretation of the data (e.g. not noticing altered fingerprints, or using wrong data)
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Don’tmakeassumpJonsbasedonregionalgeochemistry
o Where do the ‘fingerprints’ originate?
o Commercial isotope “databases” often use regional values rather than local values that can mislead interpretations
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SamplingandDataAcquisiJon–Step1
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Need high quality SCV samples o Can separate and collect gas, liquid and
steam o AER is considering requirement for
monitoring SCV flow in SAGD wells, what about steam?
o Need low atmospheric content in gas samples for compositional and isotopic characterization
Steam
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Samplemediacanaffect‘fingerprints’
• Over time isotopic composition of methane and CO2 changes • Methane artificially appears more ‘thermogenic’ • Shift in CO2 is not predictable
• Manufacturer recommendations = analyze in 48 hours
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GoalforGasSampling
• Maximizegasconcentra)on– Leastamountofairaspossible– Purgeairfrom“system”,allowgastoaccumulateifnecessary
• Eliminatemoisture– Breakoutwaterorsteam
• Preservesampletopreventdegrada)on
• Analyzesamplewithinhold)me– 48hoursforbags
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LiquidsSampling
• Slow/lowvolumeliquidventflowsproblema)csampling
• Requirespassivesamplingtopreservechemistryoftheliquid
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0.0001$
0.001$
0.01$
0.1$
1$
10$
100$
1000$
10000$
100000$
Lithium
$Sodium
$Po
tassium$
Rubidium
$Ce
sium$
Beryllium
$Magne
sium$
Calcium
$Stron=
um$
Bariu
m$
Boron$
Alum
inum
$Ga
llium
$Indium
$Thallium$
Silicon
$Ge
rmanium$
Tin$
Lead$
Phosph
orus$
Arsenic$
An=m
ony$
Bism
uth$
Sulphu
r$Selenium
$Telluriu
m$
Chlorin
e$Brom
ine$
Iodine
$
Scandium
$YD
rium$
Titanium
$Zircon
ium$
Vanadium
$Niob
ium$
Tantalum
$Ch
romium$
Molybde
num$
Tungsten
$Mangane
se$
Iron$
Cobalt$
Nickel$
Palladium
$Pla=
num$
Copp
er$
Silver$
Gold$
Zinc$
Cadm
ium$
Mercury$
Lanthanu
m$
Ceriu
m$
Praseo
dymium$
Neod
ymium$
Samarium$
Europium
$Ga
dolinium$
Terbium$
Dysprosiu
m$
Holm
ium$
Erbium
$YD
erbium
$
Thorium$
Uranium$
BleedNbarrel$FlowNthrough$Cell$
1 2 3 4 5 6 7 d-block f-block
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BestPracJcesRequiredforSCVFSampling
• Bantheterm“Grabasample”• Samplinggasesissamplingtheinvisible
– Needgoodconnec)ons/seals– Leaktests(checkconnec)ons)– Ensuresampleintegritymaintained
• Samplingliquids– Easiertosample,some)meshardertocollect– Passivecollec)onsystems,butprotectedfromenvironmental
degrada)on
• Higherqualitydata=Higherchanceforsuccess!
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IdenJficaJonandCharacterizaJonofSourceZones
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HowcanyougetitrighteveryJme?
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: Identify matrix 1.) Fluid 2.) Gas
GEOCHEMISTRY:
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CaseStudies–UsingEnd-MemberstoIdenJfySCVFs
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CaseStudy• Collectedfoursamplesfromeachloca)on:
– SCVgassample– SCVliquidsample– Produc)oncasinggassample– Produc)oncasingliquidsample
• Usedlocalgroundwateranddeepaquiferwellsinregionforcomparison
• Targetedsourcezones(end-members)weresampledandcharacterized
• FullMGILforregion
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Conservative Chemistry
o Characterization of SCV fluids focused on both routine and ‘conservative’ analytes:
• pH, alkalinity • Concentrations of dissolved cations and anions • Extended metals (65 in total) • Stable isotopes (18O, 2H, 11B, 13C, 34S, 37Cl, 81Br, 87/86Sr)
• Conservative isotopes were required for the following cases to elucidate fluid source due to pH alteration of all susceptible analytes
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SCVF Analysis o Specific conservative isotopes and their analyte
concentrations were discovered to be characteristic of specific formations.
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SCVF – Example 1
Conclusion: o SCV leak is from production zone
o Gas is entirely production formation o Water is production zone mixed with
intermediate GW
C1 C2 C3 CO2
SCV -51.9 -45.4 -35.9 bdl Casinggas -50.0 -43.1 -35.9 -2.5
Isot
ope
valu
e
Concentration value
Gas Results
Liquid Results
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Mississippian Cretaceous
Mississippian
Cretaceous
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SCVF – Example 2
o Gas/liquid origin not from production zone o Based on MGIL, 300-400 m origin
Conclusion: o SCV leak is from shallow zone
C1 C2 C3 CO2
SCV -61.7 -48.0 bdl bdl Casinggas -48.6 -39.9 -36.6 -18.8
Isot
ope
valu
e
Concentration value
Gas Results
Liquid Results
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Mississippian Cretaceous
Mississippian
Cretaceous
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Best Practices for SCVF Sampling • Collecthighqualitysamples–protectedfromdegrada)on,purgegaspriortosampling,etc.
• Preservesamplesinthefield• Collectpoten)alsourcesamplesandfromtheproduc)oncasing(ifpossible)
• Usebasicchemistrybutifnotuseful,mayneedconserva)veanalytes
• Conserva)veanalytescanprovideclarityfordifficultSCVfluidsamples
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Best Practices for Identifying SCVF • Propersamplingandcharacteriza)onofpoten)alsourcezones(gasandliquids)
• SolidMGILforthearea• Gooddatabasefortheareaofsuccessfulinterven)ons
• Geochemistrydataisalwaystellingyousomething,interpre)ngthemessageiskey!
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