Quantitative fluorescence techniques for detecting residual oils and reconstructing hydrocarbon charge history

Abstract

Two new fluorescence techniques, quantitative grain fluorescence (QGF) and quantitative grain fluorescence on Extract (QGF-E), can detect palaeo-oil zones and current residual oil zones in petroleum wells, respectively. QGF and QGF-E measure the fluorescence emission spectra of trace fluorescence from reservoir grains and their extracts. QGF is measured on dry, disaggregated reservoir grains after a cleaning procedure involving solvent, hydrogen peroxide and acid; whereas QGF-E is measured on the solvent extract from the QGF cleaned grains. Palaeo-oil zones have distinct QGF spectra with spectral peaks between 375 and 475 nm and elevated fluorescence intensities compared with spectra for rocks that have always been water saturated. Current and residual oil zones have distinct QGF-E spectra with spectral peaks at around 370 nm and elevated QGF-E intensities compared with that for current water zones. Both QGF and QGF-E responses increase upwards from the palaeo-oil–water and residual oil–water contacts, respectively. An oil producing well from Timor Sea, NW Australia was investigated in detail using the QGF and QGF-E techniques to illustrate how they can be used to reconstruct hydrocarbon migration history.