Underutilized advanced geochemical technologies for oil and gas exploration and production-1. The diamondoids

Abstract

Abstract In many regional geochemical studies of prolific basins, thermally-altered fluids generated from deep, post-mature sources mixed with normally-mature black oil from mature sources have gone unrecognized, uncharacterized, and the extent to which those mixtures have occurred has been underestimated. Quantitative diamondoid analysis (QDA) is discussed as a method to reveal such mixtures and examples from the San Joaquin Basin, California, USA, and the offshore Santos Basin, Brazil, are used to illustrate this application. While QDA reveals mixed-source oils, other techniques are necessary to correlate the mature component of the oil to its source, an identification which is necessary for correct input of effective sources into basin models. One of these methods is quantitative extended diamondoid analysis (QEDA). It consists of comparing relative concentrations of large diamondoid isomers and homologs in oils and condensates. Correlations using QEDA are much like biomarkers correlations. However, due to the stability of diamondoids, QEDA can be done on fluids of very high thermal maturity. Compound specific isotope analysis of diamondoids (CSIA-D), the determination of the carbon isotopic signature of a variety of individual diamondoid species, is another novel and complementary method to tie high-maturity fluids back to their source. QEDA and CSIA-D are, in fact, universally applicable to all source-correlation problems. Example correlations using QEDA and CSIA-D from Eastern Venezuela, West Africa (Ghana), Brazil margin, West Siberia and the Williston Basin are discussed.