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Van Tuyl Lecture: Joe Macquaker, ExxonMobil
February 28 @ 4:00 pm - 5:00 pm
Joe Macquaker, ExxonMobil Exploration Company
Topic: What are “Shales”? How Do We Know and Why Do We Care?
Abstract: More than 70% of the stratigraphic record is composed of fine-grained sediments. They are very important economically as they act as source rocks and seals in conventional hydrocarbon systems, reservoirs in unconventional systems and are important raw materials for the ceramics industry. In spite of their commercial importance and common occurrence they are poorly known compared to other sediment types. This arises because they are very fine grained and difficult to characterize at hand specimen scales. To mitigate these difficulties geologists tend to use proxy methods to discriminate their variability. Such methods, typically using geochemical and petrophysical methods to supplement data obtained from their varying appearance in hand specimen. While these techniques produce large volumes of useful data, they do not generate crucial information about grain origins, grain size, presence of cements, porosity types, and details of bedding / laminae geometries. Existing mudstone characterizations, and indeed the terms used to describe different rock types, are therefore sub-optimal when it comes to interpreting many of their key attributes.
This paper aims to describe how careful analyses of thin sections, at scales ranging from 10-6 to 10-2 m scales can be used to generate additional information that enables crucial gaps in existing fine-grained rock descriptions to be filled. In particular, I will show how, using a combination of light optical and electron optical techniques microfabric, provenance and grain origin, information at sub-hand specimen scales can be used to inform geologists about depositional processes, grains can be distinguished from cements, grain origins determined, and porosity types identified. Such data provide important information about how fine-grained sediments that are source rocks differ from those that are seals and those that are unconventional reservoirs.
These enhanced descriptions have the potential to revolutionize the way we interpret the origin and significance of these largely unknown sediments. The data generated have profound implications about how we interpret the fundamental mechanisms of natural organic carbon sequestration in the ancient record, as well as how we use the data that they contain to predict where the best unconventional reservoir rocks and seals are located.