The first fifty years of petroleum geochemistry, and where we go from here

Abstract

Petroleum geochemistry uses the principles of chemistry and geology to understand the origin, migration and alteration of petroleum in and upon the earth at the macro and molecular levels. This presentation will discuss the people, organizations, literature, instrumentation, data, concepts and applications of petroleum geochemistry, and touch on what the future might hold. Petroleum geochemistry is a sub-discipline of organic geochemistry, a field whose seminal textbook of the same name was published by Geoffrey Eglinton and Sister Mary Murphy fifty years ago in 1969. Dr Keith Kvenvolden, the acknowledged “Chronicler of Organic Geochemistry”, has systematically reviewed the history of organic geochemistry and its petroleum sub-discipline, from the earliest work by Parker Trask and Alfred Treibs through the development of distinctive professional societies, presentation venues and technical journals. From a few pioneers in the late 1950s to the many hundreds of professional organic and petroleum geochemists active today, the field has produced over a dozen textbooks and multiple journals. Thousands of new publications enter the literature every year. While early petroleum geochemists were mainly from the United States and Western Europe, recent years have seen a strong surge of geochemists from Asia, South America and Africa, and this trend is expected to continue in coming years. The past fifty years have witnessed remarkable advances in instrumentation, with dramatic increases in speed and selectivity in molecular measurements as well as precision and sensitivity in measurement of stable isotopes. Detection and accurate measurement of non-hydrocarbons, including the determination of organometallics and their speciation, has resulted in new avenues of investigation focused on the ultimate origin of these markers in crude oil. These advances have expanded the use of petroleum geochemistry from just a tool for exploration at one extreme of the value chain to encompass the entire value chain from E&P to transportation to refining to marketing, with additional recognized applications in environmental and remediation efforts. The conceptual underpinning of petroleum geochemistry has undergone radical change in fifty years. A few examples among many: oil-source rock correlation, once a one-to-one exercise, is now widely accepted as a one-to-many problem; certain coal types are now widely accepted as sources for liquid petroleum; in-reservoir biodegradation, considered an aerobic process only a few decades ago, is now widely recognized as a dominantly anaerobic process, and a non-trivial source for methane in the subsurface; accepted mechanisms of petroleum migration have narrowed from a large set of possibilities to a primarily “whole phase” concept. In addition to these conceptual changes, personnel characteristics as well as data generation and handling are dramatically different than they were fifty years ago. Early petroleum “geochemists” were either chemists – often refinery chemists – or geologists whose main concern was understanding the origin of the fluids they seek, and where to find more of them. Today many petroleum geochemists are purpose-trained, with strong multidisciplinary academic and professional backgrounds, and they search for solutions at the integrated petroleum systems level. Data analyses, formerly corporate-based, are now largely acquired commercially, and both samples and data are archived extensively for future use. Despite all these changes, however, it is still the case that geochemical datasets are never as complete as we would like them to be, and success still requires making interpretations from partial (and often very scanty) datasets. Despite the long, colorful and productive history of petroleum geochemistry over the past five decades, past developments will pale in comparison to the excitement of the next fifty years. Whole-sample analytical methods are already replacing the need for LC-separated compound classes prior to analysis, and today’s sophisticated hyphenated techniques for whole-oil and whole-rock analysis are already becoming tomorrow’s routine approaches. Compound-specific stable isotope approaches will become commonplace for all of the ‘organic’ elements (CHONS), and clumped and positional isotopy will open new avenues of investigation into the pressure-temperature origin of natural gases and, eventually, oils. Speciation of metals in crude oil will become routine, and we will unwrap the knowledge encased in their stable isotope ratios. Continued expansion of the use of noble gas isotopes to track the migration of natural gas, applications of nucleic acids as the “ultimate biomarker” for geochemical organic matter, and several additional frontier techniques, once only evident on the horizon, are now being developed and will have a strong role to play for decades to come. Although petroleum geochemistry is now five decades old, petroleum geochemists clearly have an amazing amount of running room in front of them.

AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019