Thermal Maturity of Gas Shales in the Appalachian Plateau of Pennsylvania

Open Access
Author:
Modlich, Mitchell Andrew
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 14, 2014
Committee Members:
  • Rudy Slingerland, Thesis Advisor
Keywords:
  • Appalachian Basin
  • Thermal Maturity
  • Gas Shale
  • Thermal Modeling
  • Devonian
Abstract:
Ongoing shale gas exploration and production in the western Appalachian Basin of Pennsylvania (WPAB) necessitates a better understanding of the thermal evolution of the basin to constrain uncertainty in risk assessments. Anomalies of thermal maturity in southwestern and west-central Pennsylvania along the Allegheny Front are hypothesized to be associated with hot brines driven through Upper Devonian aquifers from the foreland to the east. To test this hypothesis, a total of 402 1-D vertical heat diffusion experiments are conducted in 9 locations to investigate the effects of heating by fluid flow on organic-rich shales in the WPAB. Model simulations are constrained by compiled datasets of maximum reflectance of coal vitrinite, random reflectance of dispersed marine vitrinite in shales, and apatite fission-track ages. Modeling results indicate that the salient or promontory in maturity in Carboniferous and Devonian strata in northern Somerset and southern Cambria Counties is reproduced by an increase in temperatures of 40 – 50 °C above those expected solely by heat conduction for at least one myr. from 260 – 259 Ma following the end of the Alleghanian Orogeny. These results show that an increase in the thermal gradient caused by hot fluids for a geologically plausible amount of time can explain the anomalous variations in thermal maturity in western Pennsylvania.