Francis P. Miknis1,
Ronald C. Surdam2
(1) Western Research Institute, Laramie, WY
(2) University of Wyoming, Laramie, WY
Abstract: Solid-state NMR Analysis of Sedimentary Rocks From Different Laramide Basins of North America
Solid-state carbon-13 nuclear magnetic resonance (NMR) techniques of cross polarization (CP) with magic-angle spinning (MAS) were used to measure changes in the aliphatic and aromatic carbon distributions in sedimentary rocks and coals from different Laramide basins in North America. The NMR measurements were made on sets of shales and coals taken from different formations and from different burial depths in the Alberta, Bighorn, Denver, San Juan, Piceance Creek, Washakie, Powder River and Wind River basins. The objectives of this work were to relate changes that occur in the carbon structure of sedimentary organic matter during maturation to mechanisms of hydrocarbon generation and to delineate pressure chambers and seals in sedimentary basins.
With increasing burial depth and maturation, the NMR data show a progressive loss of aliphatic carbons relative to the aromatic carbons due to hydrocarbon generation and to aromatization of some of the aliphatic carbons. At some limiting depth, the remaining aliphatic carbon fraction is not sufficient to generate significant additional hydrocarbons. The vitrinite reflectance value at this limiting depth is typically near 1.3%. This observation suggests that significant quantities of gas are generated in Laramide Basins as a result of the cracking of previously generated liquid hydrocarbons to gas. This information significantly reduces the uncertainty in the search for gas accumulations in Rocky Mountain Laramide Basins.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana