Abstract
Petroleum geochemistry applications have evolved and developed during the unconventional boom of the past 10 years as operators have expanded rig rates and grown production numbers. Most unconventional plays primarily target the source rock, and petroleum geochemists have used this decade to further develop their understanding of source rocks and the generation and expulsion of hydrocarbons. One geochemistry application that has been expanded during this period is the process of extracting hydrocarbons from source/reservoir material and comparing this to produced hydrocarbons. This practice has been applied in unconventional plays to discern more discrete relationships with the goal of using extracted hydrocarbons to confirm a correlation to the acting source/reservoir that provides economic production. Combined with other geochemical and multidisciplinary datasets, these types of projects aid in many practical aspects of unconventional development programs, such as confirming landing zones, drainage height of frac zones, and defining effective source rocks. While it is generally acknowledged that the laboratory extraction process is not a perfect replication of naturally generated and expelled hydrocarbons, it is clear that useful correlations can be made. However, there are a variety of different extraction methods, and these different methods can yield variable quality of extracts. While most practitioners have been careful to confirm and report their methods and success with extract work, there are few published studies that show direct comparisons of different extraction methods in a controlled setting (Johnson and Lusas, 1983; Kornacki, 2019). This lack of data makes it difficult for operators who are designing geochemistry studies that involve hydrocarbon extractions, to judge which method is the most appropriate for their immediate purpose. In this paper, we explore a direct comparison of several different extraction methods, carried out in a controlled and consistent environment, under conditions most similar to typical unconventional petroleum geochemistry projects: "warts and all" if you will. The purpose is not to judge which is the ‘best’ method– the authors acknowledge that different methods may be required to meet different experimental goals – but rather, establish how significant the differences are between the methods. We will also discuss which method might be the most appropriate to use when attempting to compare an extract to a produced oil. Because this work is an application to unconventional plays, the analysis will be focused on extract methods that provide the best preservation of light end hydrocarbons (nC4 – nC20). Most unconventional plays produce light hydrocarbons (LHC) that are more mobile in tight reservoirs. Therefore, while C15+ components are often critical for genetic interpretation of oils in any play type, they may not be the focus for operators with smaller scope programs or production focused projects, especially in thermally mature areas.
