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66 GEOCHEMICAL ASSESSMENT OF UNCONVENTIONAL SHALE GAS RESOURCE SYSTEMS
This appears to be due to mixing and dilution by organic Barker C. Pyrolysis techniques for source rock evaluation. AAPG
lean sediments overlying organic‐rich shales. The best Bull 1974;58 (11):2349–2361.
shales often have an organic‐lean carbonate overlying them, Barker C, Takach NE. Prediction of natural gas composition in
which functions as a seal and frac barrier. TOC, oil, and ultradeep sandstone reservoirs. AAPG Bull 1992;76:1859–1873.
pyrolysis yields, and T max values are shown to be reduced Baskin DK. Atomic H/C ratio of kerogen as an estimate of thermal
with long‐term storage (20 years or more), whereas car maturity and organic matter conversion. AAPG Bull 1997;81:
bonate contents increase. This suggests weathering‐induced 1437–1450.
oxidation effects. Behar F, Jarvie D. Compositional modeling of gas generation from
Based on both experimental and empirical results, excess two shale gas resource systems: Barnett Shale (United States)
thermal maturity appears to reduce the amount of gas found and Posidonia Shale (Germany). AAPG Memoir 2013;103:
in shale reservoirs. This is hypothesized to be due to 25–44.
oxidation of methane, but may also be due to destruction of Behar F, Vandenbroucke M. Experimental determination of the
the porosity in the rock fabric and the subsequent loss of rate constants of the n‐C thermal cracking at 120, 400, and
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retained gas. 800 bar: implications for high‐pressure/high‐temperature
prospects. Energy Fuels 1996;10:932–940.
The top resource plays in North America are highly vari
able in terms of production due primarily to porosity and Behar F, Lorant F, Lewan MD. Role of NSO compounds during
primary cracking of a Type II kerogen and Type III lignite. Org
pressure. Both porosity and pressure evolve in part from Geochem 2008a;39:1–22.
organic matter decomposition as the kerogen mass is con Behar F, Lorant F, Mazeas L. Elaboration of a new compositional
verted to petroleum creating organoporosity and increased kinetic schema for oil cracking. Org Geochem 2008b;39:
pressure from petroleum cracking or gas generation. The 764–782.
shale gas system showing the lowest decline rate is the Behar F, Roy S, Jarvie D. Artificial maturation of a Type I kerogen
hybrid Montney Shale of the Western Canada Sedimentary in closed system: mass balance and kinetic modelling. Org
Basin. Geochem 2010;41 (11):1235–1247.
Shale drilling has been completed safely and under envi Burnham AK, Braun RL. Development of a detailed model of
ronmentally sound operations in North America. There are petroleum formation, destruction, and expulsion from lacustrine
always concerns for safety and environment in all drilling and marine source rocks, Advances in Organic Geochemistry
operations, but with over 50,000 shale wells drilled over the 1989. Org Geochem 1990;16 (1–3):27–39.
past 10 years a safe and sound track record is evident. In Burnham AK, Gregg HR, Ward RL, Knauss KG, Copenhaver SA,
cases where known geological conditions such as near pre Reynolds JG, Sanborn R. Decomposition kinetics and mecha
13
13
existing intraplate plates, saltwater disposal wells should nism of n‐hexadecane‐1,2‐ C and dodec‐1‐ene‐1,2‐ C doped
2
2
either not be drilled or handled differently. Regulations for in petroleum and n‐hexadecane. Geochim Cosmochim Acta
cementing of casing protecting freshwater aquifers should 1997;61 (17):3725–3737.
always be updated for any changes in known operational or Claypool GE, Mancini EA. Geochemical relationships of petro
geological conditions just as safety measures are taken in leum in Mesozoic reservoirs to carbonate source rocks of
any other industry. Jurassic Smackover formation, Southwestern Alabama. AAPG
Overall, shale gas resource systems provide a remark Bull 1989;73:904–924.
able energy resource that is the best carbon‐based resource Cooles GP, MacKenzie AS, Quigley TM. Calculation of petro
that we have in terms of carbon dioxide and other emissions leum masses generated and expelled from source rocks.
as well as being quite inexpensive over the course of the Advances in Organic Geochemistry 1985. Org Geochem
1986;10 (1–3):235–245.
last 100 years. It represents a solution to reduced energy
dependence, if not near complete independence for North Dahl JEP, Moldowan JM, Moldowan S. Determination of thermal
maturity and extent of oil cracking in tight shales using extract
America. Hopefully, this resource can be adequately and biomarker and diamondoid concentrations and distributions.
safely tapped elsewhere to provide comparable energy Unconventional Resources Technology Conf (URTeC), URTeC
benefit to global energy consumers. paper 1574980; 2013. 5 p.
di Primio R, Horsfield B, Guzman‐Vega MA. Determining the tem
perature of petroleum formation from the kinetic properties of
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