Chemical and isotopic tracers ofnatural gas and formation waters innaturalgasandformationwatersinfractured shalesJennifer McIntosh, Melissa Schlegel, Brittney BatesDepartment of Hydrology & Water ResourcesUniversity of Arizona, Tucson AZEPA Technical Workshop Feb 24-25, 2011

# Outline of Presentatio n1)What is the chemical and isotopic signature of formationgwaters and natural gas in fractured shales?2) How does it compare with shallow drift aquifers,coalbeds and other deep geologic formations?coalbeds,andotherdeepgeologicformations?Illinois Basin-Case Study- 3 organic-rich formations: glacial drift,Penn. coal, & Dev. fractured shaleorganicrich Ordov Shale not part of--richOrdov.Shale,notpartofthis study20km

500 mSchlegel et al. (in press, 2011, Geochimica et Cosmochimica Acta)Illinois Basin-Case Study- microbial methane in all 3 unitsthermogenic methane in shale and coal-thermogenicmethaneinshaleandcoal20km

500 mSchlegel et al. (in press, 2011, Geochimica et Cosmochimica Acta)Illinois Basin - water & gas samplesShallowaquifersPenn.CoalsDev.ShaleLimestoneaquifers9New data (white symbols): Schlegel et al. (in press)9Previous data (black symbols): McIntosh et al., 2002; Strąpoćet al., 2007, 2008a,b; Coleman etal, 19881000000Fingerprint of natural gases100000ShallowAquifersHighC1/C2,noC3Coals100001001000Shale10ShallowaquifersPenn.Coals1-80 -75 -70 -65 -60 -55 -50 -45 -40δ13CCH4(ä PDB)Dev.ShaleThermogenic gasδCCH4(äPDB)9In general, 3 organic-rich units have different gas compositions (C1/C2+C3) and 

# δ13C-CH4values.9Cannot distinguish thermogenic from microbial CH4in Dev. Shales using carbon isotopes alone.Differences in C isotopes of gasShallowaquifersPenn.CoalsDev.Shale9Microbial methane from shallow glacial drift, coalbeds and fractured shalesall plot along carbonisotope fractionation line of ~1.05 to 1.09, except for a few coal samples influenced by methaneoxidation/sulfate reduction (Strapoc et al., 2008), and one outlier glacial drift sample.Differences in C isotopes of gasShallowaquifersPenn.CoalsDev.ShaleThermogenic gasThermogenicgas9Thermogenic gas in Penn. coalbeds is distinct from microbial gas, with lower 

# δ13C-CO2and higher



# δ13C-CH4values.9Thermogenic gas in the Dev. fractured shales contains very little CO2(<0.1 mole%) - not shown.Differences in C isotopes of gasShallowaquifersPenn.CoalsDev.ShaleShallowAquifersCoalsShale9Microbial CH4from shallow aquifers, coalbeds, andfractured shales have distinct 

# δ13C-CH4values, which corresponds to increasing fractionation of CO2reservoir during CO2reduction.9C isotopes of CH4and CO2may be used to distinguish sources of methane.Differences in H isotopes of gas/waterShallowaquifersPenn.CoalsDev.ShaleThermogenic gasThermogenicgas9 

# δD-CH4not useful in distinguishing gas sources; Microbial CH4from shallow aquifers, coalbeds,and fractured shales have similar 

# δD-CH4values.9Major difference is in H isotope values of formation waters - related to meteoric water/brine mixingFingerprint of formation waters0CoalsGMWLBasinalbrinemixing line-20mixingline60-40Shale-80-ShallowaquifersPenn.CoalsDev.ShaleShallowAquifers-10 -8 -6 -4 -2 0 2δ18OH2O(ä9In general, formation waters associated withfractured shales are more enriched in18O and2Hthan shallow (drinking water) aquifers9Isotopic composition of coal waters overlap fractured shales and shallow aquifers10000 000Salinity differences in fluids1000.00010000.000Coals100.000h l1.00010.000Shale0.100ShallowaquifersPenn.CoalsDevShale0.0100.0001 0.0010 0.0100 0.1000 1.0000 10.0000Br-(mM)Dev.ShaleShallowAquifersBr(mM)9Formation waters associated with natural gas incoalbeds and fractured shales are enriched in Cland Br (and other solutes) relative to shallow (drinking water) aquifers40Fingerprint of formation waters3020010ShallowAquifers-10ShallowaquifersPenn.CoalsDevShale-200 10 20 30 40Alkalinity (meq/kg).ShaleAlkalinity(meq/kg)9Formation waters associated with microbial CH4in shales or coalbedstypically have high 

# δ13CDIC values (>10 per mil), and variable alkalinities (<5 to 37 meq/kg)9Shallow aquifers have alkalinities <10 meq/kg, and low 

# δ13C-DIC values(<0per mil)40Fingerprint of formation waters3020010-10ShallowaquifersPenn.CoalsDevShaleBasinal brine - no microbial CH4-200 10 20 30 40Alkalinity (meq/kg)Dev.ShaleAlkalinity(meq/kg)9Basinal brines not associated with microbialmethane have low alkalinities (<8 meq/kg) and low



# δ13C-DIC values (most near 0 per mil)Summary9Natural gas (microbial & thermogenic) from shales and coalbeds can bedistinguished from microbial methane in glacial drift aquifers based on gascomposition and 

# δ13C values of CH4and CO2.9Formation waters from Dev. fractured shales can be distinguished fromshallow glacial drift aquifers using major ion chemistry (Cl, Br, other solutes)and stable isotopes (18O2H13C)andstableisotopes(18O,2H,13C).Schlegel, M.E., McIntosh, J.C., Bates, B., Kirk, M., Martini, A.M. (in press, 2011) Comparison of fluidh id i bi lfli liihiidib iFor more informationgeochemistryandmicrobiologyofmultiple organic-richreservoirsin a sedimentarybasin:evidence for controls on methanogenesis and microbial transport.Geochimica et CosmochimicaActa.Martini, A.M., Walter, L.M., McIntosh, J.C. (2008) Identification of microbial and thermogenic gast fUDiblkh lIlli idMi hi B iAicomponensrompperevonanacsae cores,nos anMichiganBasins.mercanAssociation of Petroleum Geologists Bulletin, 92, 327-339.McIntosh, J.C. and Martini, A.M. (2008) Hydrogeochemical indicators for microbial methane in fracturedblack shales: Case studies of the Antrim, New Albany, and Ohio shales.InHill, D., Lillis, P.,Curtis JedsGasShaleintheRocky MountainsandBeyondRockyMountain AssociationofCurtis,J.,,ckyMountains,MountainAssociationGeologists 2008 Guidebook, p. 162-174.McIntosh, J.C., Walter, L.M., and Martini, A.M. (2004) Extensive microbial modification of formationwater geochemistry: Case study from a Midcontinent sedimentary basin, United States . GSABulletin vol 116no5pp743-759Bulletin,vol.116,.,..Martini, A.M., Walter, L.M., Budai, J.M., Ku, T.C.W., McIntosh, J.C., and Schoell, M. (2003) Microbialproduction and modifi cation of gases in sedimentary basins: A geochemical case study from aDevonian Shale gas play, Michigan Basin. AAPG Bulletin, vol. 87, no. 8, pp.1355-1375.McIntosh,J.C.,Walter,L.M.,andMartini,A.M.(2002)Pleistocenerechargeto mid-continent basins:McIntoshartini,Pleistocencontinentbasins:effects on salinity structure and microbial gas generation. Geochimica et Cosmochimica Acta,vol. 66, no. 10, pp. 1681-1700.Martini, A.M., Petsch, S.T., McIntosh, J.C., Schlegel, M., Damashek, J., Miller, S.E., Kirk, M. (2010)Microbial Gas from UnconventionalReservoirs: The New AlbanyShale as a case study. GasResearch Institute, Report-07122-16.Walter, L.M., McIntosh, J.C., Martini A.M., and Budai, J.M. (2001) Hydrogeochemistry of the NewAlbany Shale, Illinois Basin. Gas Research Institute, Report-5094.