Temperature Dependent Diffusion of Noble Gases in Unconventional Shale Formations: A Comparison of the Appalachian and Permian Basins
Accurate estimations of recoverable hydrocarbons from unconventional formations require a better understanding of fluid transport phenomena along natural fractures and induced pathways but predictions of fluids-in-place within tight shales are complicated by a lack of knowledge regarding the history of geologic fluid migration in the crust. To improve our understanding of paleo-fluid flow and enhance these predictions, we measure the temperature dependent release of noble gases (e.g., 4He, 21Ne*, and 40Ar*) from shale samples collected from the Marcellus and Permian formations. By conducting step heating experiments on bulk shale samples as well as chemically separated mineral species, we calculate the diffusion coefficients for 4He and 21Ne from quartz and carbonate grains over a temperature range of 25-400ºC. In situ factors such as deformation structures (e.g., faults, fractures) and lithologic characteristics (e.g., porosity) will affect noble gas concentrations within the grain and allow us to utilize these techniques as a proxy for thermal and structural history of the sedimentary basin. Because the rate of crustal production of 4He and 21Ne* is fixed at a nearly constant ratio (4He21Ne* ~ 22x106), the divergence from this ratio of the measured values taken from shale material allows us to make inferences as to temperature and fracture network history of the formation. The noble gas signatures of rock samples from petroleum basins will allow us to better constrain the source, migration pathways, residence time, permeability, and porosity of deposited sediments at oil/gas relevant conditions. These noble gas analyses will further allow us to evaluate the similarities and differences between the Northern Appalachian Basin and the Permian Basin that result from their unique geologic and thermal conditions during deposition and burial.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019