Characterization of Crude Oil and Condensate by Time-Resolved Laser Fluorescence Microscopy--Preliminary Study

P. K. Mukhopadhyay, S. Gangopadhyay, C. Landis, M. Pheil, W. L. Borst

To determine the type and maturity of normal and biodegraded crude oil and condensates, 13 samples from diverse types of Tertiary and Cretaceous reservoirs from Alabama, California, Texas, and Venezuela were characterized utilizing pulsed laser fluorescence microscopy (developed by Borst for coal characterization). Parameters such as fluorescence lifetime in nanoseconds (ns) for three resolved fluorophores and percent contribution of each fluorophore were correlated with organic geochemical and bulk chemical data on crude oils and condensates. The fluorescence lifetime (ns) of the intermediate component has been correlated with ratios of aromatics to heterocomponents (fluorescence emitters). This relationship, when compared with the ratio of aromatics to asphaltenes (fluo escence quenchers), revealed characteristic distribution of oils derived from two different reservoirs: (1) marine source-derived oil from Lovetts Creek field (Smackover), Alabama, and (2) terrestrial source-derived oil from Charamousca field (Wilcox), south Texas. These data are supported by geochemical fingerprinting. The above-mentioned ratios and the ratios of the fluorescence lifetimes of two individual fluorophores also show characteristic patterns for biodegraded (alteration in reservoir) and nonbiodegraded crude oils from the Wilcox, Duval County, south Texas, and the Oficina reservoir, Venezuela. These ratios also suggest the possible maturity of two biodegraded crude oils from the Wilcox, south Texas, that coincides with the results of a biomarker study. The above parameters in icate the similarity in origin of two crude oils and one condensate from the Travis Peak Formation, Chapel Hill field, east Texas. The maturities of all the analyzed crude oils and condensates were determined by the spectral maximum of the composite, continuous-wave spectrum and the percentage contribution of each fluorophore from laser fluorescence, which can be correlated to API gravity of the nonbiodegraded oils.

Laser fluorescence microscopy may become an important tool for correlating crude oil with condensate and condensate/oil with deasphaltized source rock extracts as well as for determining the maturation of biodegraded crude oil.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.