IN-SITU FLUORESCENCE SPECTROSCOPY FOR SARA MODELING

Basin and petroleum system modeling and understanding oil migration are important when determining the potential of a hydrocarbon reservoir. Gas Chromatography (GC) and Saturate-Aromatic-Resin-Asphaltene (SARA) analysis are essential when analyzing the chemical composition and predicting content of source rock hydrocarbon fluids. These measurements require sample preparation, are destructive and cannot be performed inside a producing well. Nondestructive in-situ fluorescence measurements can be performed using a miniaturized fluorescence sensor integrated in a downhole logging tool. This tool can be used to map the fluid properties and help with exploration and reservoir potential assessment. In addition, measurements from this tool can potentially be used to accurately predict API gravity and condensate zones in a reservoir, thus provide information for well completion and perforation, and ultimately increase oil recovery with significant economic implications.

We have also developed methods for estimating from measurements obtained with such sensor the amount of saturates and aromatic components in the hydrocarbon fluids, as well as API gravity. Fluorescence spectra of several oil samples ranging from 45° to 29° API gravity have been collected. Based on these measurements, the analysis characterizes the influence of chemical composition of hydrocarbon fluids on fluorescence emission spectra as related to Urbach absorption, and establishes multivariate regression models between fluorescence spectra and SARA components for a given set of samples. The results suggest that, for lighter crude oils the width of fluorescence emission spectra can be used to determine the activation energy during the maturation process. This maturity trend is compatible with the results observed from the SARA/GC analysis. In addition, the contribution of the fluorescence spectra to each one of the SARA components in the estimated regression model appears to behave differently yet with certain level of cross correlation. These results are true for fluorescence obtained from different laser channels. We will also present data for spectrometer operation suitable in borehole conditions and the integration of this measurement into a downhole logging tool.