T53 Unconventional Energy Resources

Sunday, 4 November 2018
1:30 PM - 5:30 PM
Room 145

USING RADIOGENIC NOBLE GASES TO EVALUATE BASIN SCALE CRUSTAL FLUID MIGRATION OF THE APPALACHIAN BASIN

Paper number: T53-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

The generation and migration of crustal fluids within sedimentary basins are a result of tectonic deformation and hydrogeological cycles. Heat, deformation, and compression expel fluids from pore spaces and provide cross-formational migration pathways in the otherwise low permeability rock. However, the mechanism, timing, and extent of regional crustal fluid flow remains poorly constrained. Noble gases may be specifically useful for evaluating regional-scale fluid flow processes because their original gas composition is preserved independent of microbial activity, chemical reactions, or changes in oxygen fugacity and the genesis and composition of each isotope is well known. Herein, we applied noble gas geochemistry to evaluate their utility as a tracer of regional-scale fluid flow within the Northern Appalachian Basin (NAB) .

The production of radiogenic noble gases (e.g., 4He, 21Ne, 40Ar) with distinct isotopic ratios, have great potential to provide information about subsurface fluid flow processes. The 4He/21Ne* ratio is particularly useful as a method of tracing the conditions and extent of fluid migration for multiple reasons: 1) the amount of each isotope can be accurately predicted by knowing the relative abundance of the parent isotopes (U, Th, K); 2) the production ratio is globally uniform in silicate rocks (4He/21Ne = 22 x 106); and 3) the diffusion rates of the isotopes out of quartz grains differ as a function of atomic mass and radii. Thus, the ratio changes as a result of fluid-rock interactions. Through time, 4He and 21Ne produced in the rock matrix diffuse into pore fluids at differing rates below ~80oC (i.e., closure temperature of Ne in quartz). Therefore, we anticipate that the 4He/21Ne* can provide information about the scale and temperature conditions of fluid flow.

In this study, we report 4He, 21Ne, and 40Ar isotopic data from 36 producing natural gas wells in the NAB. Our preliminary results suggest there is a systematic increase in the 4He/21Ne* in samples with a further distance from the Appalachian structural front. To a first order, these data are in line with the dominant direction of regional-scale fluid flow. Further, quantifiable fractionation of 4He/21Ne* suggests that a component of fluid migration must have continued after periods of basin inversion at which point temperatures were below ~80oC.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322303

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.