Back to the Source: A Chronicle of Ideas and Techniques on Petroleum Source Rocks

Abstract

Our knowledge of the petroleum source rocks is relatively of recent origin for three reasons: (1) Source rocks are deeper than the accumulations, and are not easily accessible; (2) the main objective of exploration has been to drill into reservoirs; information about the origin of petroleum and characteristics of the source rocks were long considered as pure science; and (3) methodologies and instruments to study the source rocks were developed much later, compared to the reservoir technologies. In the first century of oil (1860-1940s), exploration strategy was dominated by locating traps and seepages, and ideas about the source rock was seldom based on concrete data. In the 1930s, Parker Trask investigated depositional environments for petroleum source rocks. In the 1950s, John Hunt reported the first crude-source rock correlations from the Uintah Basin of Utah. By 1960, it was established that kerogen in carbon-rich, clayey rocks was the origin of oil. In the 1960s, gas chromatography was widely applied to oil and sediments, and the role of burial heat in thermal cracking of kerogen was developed. The 1970s witnessed a revolution in source-rock geochemistry as techniques such as pyrolysis, vitrinite reflectance, and kerogen typology were advanced. This trend was culminated in the 1980s-90s when the petroleum system approach became popular, and numerical models were constructed to quantify the source rock thermal maturity and oil and gas generation. This required integration of sedimentological and tectonic studies, which were previously decoupled from petroleum geochemistry. The shale revolution of the 2010s has transformed the source rock to a target reservoir, and has thus initiated new research pathways such as source-rock geomechanics. North American petroleum geology that started with locating traps has made a full circle after 150 years; at the source rock level both conventional and unconventional plays have converged.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018