Organic Geochemical Probes of Subsurface Migration in Morrow Formation Crude Oils
BROTHERS, LUCINDA, and R. CAMERON DOREY, Wichita State University, Wichita, KS
Distributions of petroleum compounds in crude oils can be altered during secondary migration by adsorption and other chromatographic processes. Trends in distributions of alkanes and nitrogen-containing compounds among oils may indicate migration pathways when used in conjunction with structural and lithologic maps.
Several crude oils which were produced from reservoir sands of the Morrow Formation in western Kansas and eastern Colorado were analyzed for hydrocarbons and nitrogen-containing organic compounds. Gas chromatographic (GC) traces of crude oils, using a flame-ionization detector, were examined for migration-induced depletion of higher molecular-weight a-alkanes (including compounds in the C50+ range) relative to lower molecular-weight n-alkanes.
Deasphalted oils were fractionated into saturate, aromatic, and polar fractions using column chromatography. Nitrogen-containing compounds, which are more polar than alkanes, are much more susceptible to adsorption onto mineral surfaces than hydrocarbons. The GC traces of the aromatic and polar fractions of crude oils were examined using a thermionic specific detector, which responds specifically to nitrogen-containing organic compounds.
Lithologically Morrow sands and shales contain abundant clay minerals which potentially expose active adsorptive surfaces to petroleum compounds as migration of the crude oil proceeds. The fluvio-deltaic depositional environment of the sands provides clay minerals along probable flow paths in the form of clay drapes or as gradational facies changes in silt and clay content. Differences in both alkane and nitrogenous compound profiles of crude oils from the study area exhibit possible migration-induced alteration of the oils.
AAPG Search and Discovery Article #91008©1991 AAPG Mid-Continent Section Meeting, Kansas Geological Society, Wichita Kansas, September 22-24, 1991 (2009)