Uses of Stable Isotopes in Petroleum.
Isotopes in Petroleum Isotope- atoms with the same atomic number but different mass number In the past the use of stable isotopes in petroleum was not common. With high demand and prices it is now feasible to use isotopic analysis in petroleum.
Isotopes in Petroleum Isotope fractionation of C-12 C C-13C In order for petroleum hydrocarbons to form the Carbon bonds must break Can indicate whether the gas comes from a heavier bituminous or carbonaceous residue.
Common Uses In Petroleum Determining gas maturity Correlating reservoired gas to its source Correlating one reservoir to another Recognizing gas mixtures
(Prinzhofer 2000) Maturation
Determining Maturation Two ways to determine maturation using isotopes 1. Isotopic composition of methane 2. Separation of carbon isotopes between hydrocarbon components.
Methane Isotopic Analysis Methane alone is a poor method of isotopic analysis Does not take into account the other hydrocarbons present such as butane or ethane Gases are mobile so the original source may not be know and does not take into account the possibility of multiple sources
Carbon Isotope Separation Thermal degradation of carbon isotopes that correspond to the main zone of primary cracking of kerogen and secondary cracking of heavy oils. (Prinzhofer 2000)
Carbon Isotope Separation Maturity Diagram LOM (level of organic Metamorphism) indicator of maturity Thermal alteration index Partial functions of carbon isotope separation can be calculated using force field matrices (Galimov and Ivlev) (James 1983)
Carbon Isotope Separation Plotting the LOM, TAI, and Isotopic data on a maturity diagram shows the type of gas as well as the maturity. (James 1983)
Isotope Correlation to Source Calculating source isotopes and hydrocarbon isotopes allows for genetic tracing of source The isotope calculations for the potential source and the hydrocarbons should be plotted on a maturity diagram
Cyanosa Field, Delaware Basin, West Texas Bulk of value were at LOM 11, which compared to the Permian Wolfcampian shales (James 1983) (James 1983)
Correlating Two Reservoirs Marlin Field, Gippsland Basin, Australia Tertiary source LOM, TAI, Isotope analysis was compared to the entire sequence. Correlated to the Cretaceous interval (James 1983) (James 1983)
Gas Mixtures Can indicate whether the source is mature, wet, or if production is being driven by bacteria. Southeastern Alberta (James 1983)
Gas Mixtures Mixture of mature and immature gases Through C12-C13 C13 separation it was concluded the reservoir was a mixture of local gases as well as a component that migrated a substantial distance. Possible Devonian source Later determined to be from Thermal cracking. (James 1983)
Gas Mixtures Bacteriaogenic methane Light methane Plot Isotope ratio on Natural Gas Plot Gulf of Mexico 40 % of the methane was bacteria driven (Chung 1988)
Conclusions With growing demand for petroleum products methods such as isotopic analysis is becoming more common. Stable Isotopes can enhance prospecting as well as production in a petroleum company
References Arthur, Michael A., Anderson, Thomas F., Kaplan, Isaac R., and Land, L Lynton S. Stable Isotopes in Sedimentary Geology: SEPM Short Course No. 10 Dallas 1983. Tulsa, Ok; SEPM Pub. 1983 Chung, H. M., Gormly, J.R., and Squires, R. M. Origin of Gaseous s Hydrocarbons In Subsurface Environments: Theoretical Considerations of Carbon Isotope Distribution. Chemical Geology Vol 71 (1988). 97-103. Faure, Gunter, and Mensing, Teresa M. Isotopes Principles and Applications Third Edition.. Hoboken, New Jersey. John Wiley and Sons Inc.2005 James, Alan T. Correlation of Natural Gas by Use of Carbon Isotopic opic Distribution Between Hydrocarbon Components. AAPG Geologist Bulletin Vol 67 No. 7 (July 1983). 1176-1191. 1191. Prinzhofer, Alain, Mello, Macio R., and Takaki, Tikae. Geochemical cal Characterization of Natural Gas: A Physical Multivariable Approach and its Applications in Maturity and Migrations Estimates. AAPG Bulletin Vol. 84 No. 8.( August 2000). 1152-1172. 1172. Schoell, Martin. Recent advances in Petroleum Isotope Geochemistry Org. Geochemistry Vol. 6 (1984). 645-663. 663.