Geochemical Parameters for Unraveling Mixtures. Examples from the South Atlantic Continental Margins, the U.S. Gulf of Mexico and the Giant North-Central West Siberian Gas Fields
Moldowan, John M.1; Zinniker, David 1; Dahl,
Jeremy 1; Rovenskaya-Nemchenko, Alla 2; Liu, Zhaoqian 1;
Nemchenko, Tatyana 3
(1)Department of Geological & Environmental
Sciences, Stanford University, Stanford, CA. (2) The Foundation for East-West
Cooperation, Moscow, 119234, Russian Federation. (3) Vernadsky Institute of
Geochemistry and Analytical Chemistry, Moscow, Russian Federation.
The recognition, correlation and quantification of oil mixtures
remain challenging in many petroleum system studies. Most prolific basins or
regions have multiple source rocks generating at wide ranges of maturity.
Mixtures present themselves in many forms, including any proportions of black
oil, light oil and condensate, which can be single-sourced or co-sourced.
Knowledge of all active sources and the maturities of their generated
hydrocarbons is the critical starting point to develop correct basin models.
Selection of the best parameters
to de-convolute oil-source mixtures can best be determined from singly sourced
end-member oil and source rock samples. The ideal parameters show very large
differences in magnitude between the candidate sources and are independent of
maturity difference.
In the south Atlantic margins, we are faced with oil mixtures that may include oil generated in the lacustrine rift sections of Barremian-Aptian age, transitional to marine post-rift sources of late Aptian into the late Cretaceous and Tertiary marine-deltaic oil from the latest Cretaceous through the Tertiary. Mixtures from this region can be recognized, unraveled and quantified by using compound specific isotope analysis of biomarkers (CSIA-B) and diamondoids (CSIA-D) and a special C30-sterane biomarker analysis.
The source(s) of thermal gas in the giant gas fields of north central Western Siberia (e.g., Urengoi, Yamburg), which have often been speculated from various sources were determined to be derived from the Lower to Middle Jurassic (Tyumen)by using our special isotope methods, CSIA-D and CSIA-B. The ultrastable diamondoid compounds in CSIA-D provide a unique advantage for source correlation of thermally altered liquids or condensates and for condensate mixtures with black oil.
Affinities and mixtures of oil and gas sourced from the Smackover, Tuscaloosa and other sources in the Gulf of Mexico can be determined and unraveled by using CSIA-D and ratios of the extended diamondoids up to pentamantane in scope.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.