Evaluating Reservoir Characteristics of the Utica Shale at Varying Levels of Thermal Maturity
Cooney, Michele L.; Carter, Kristin M.
The Utica Shale is attracting considerable attention in Pennsylvania, Ohio, and New York, and was recently estimated by the U.S. Geological Survey to contain a mean undiscovered resource of 940 MMBbl oil, 38.2 Tcf gas, and 208 MMBbl natural gas liquids. Due to the potential importance of this undiscovered resource, the purpose of the current study was to compare and contrast lithostratigraphic facies of the Utica play across Pennsylvania using a combination of publicly available rock cuttings, outcrop samples, and well and geologic data. Six deep wells from six different counties were selected to represent a range of thermal maturities across the state: Crawford County (oil to wet gas area), Mercer County (wet gas area), Warren County (dry gas area), Armstrong County (dry gas to overmature area), and Centre and Sullivan counties (overmature area). Rock cutting samples from these wells were collected to represent the four lithostratigraphic facies of the Utica play: the Reedsville, Utica, Antes, and Point Pleasant. Selected cuttings and outcrop samples were evaluated for mineralogical content using XRD methods, and cuttings were also evaluated for TOC and bitumen reflectance to assess organic richness and thermal maturity.
Lithostratigraphic facies of the Utica play have unique mineralogical compositions. While all four contain tectosilicate minerals, the Reedsville Shale is particularly high in phyllosilicates (8-14% chlorite). The Utica and Point Pleasant shales are the most quartz-rich, ranging from 36-54% and 40-50% quartz, respectively. In addition, the Point Pleasant is abundant in carbonate minerals (11-24% calcite and 1-6% dolomite). Vitrinite reflectance (Ro) values, estimated from bitumen reflectance measurements using the methods of Jacob (1989) and Landis and Castaño (1995), point to the Antes as the most thermally mature (2.0% to 2.8% Ro equivalent (eq.), respectively). High thermal maturity in the Antes is associated with well locations in Centre and Sullivan counties (Pennsylvania's overmature area). Utica and Point Pleasant samples reported Ro eq. values ranging from 1.7 to 2.3%. These values are based on data collected from several well locations across the state and span a wide range of thermal maturities (oil to overmature). Reedsville Shale samples represent the least mature rocks in our dataset, with Ro eq. values averaging 1.5 to 2.0%. TOC results, intended to assess the organic richness of these samples, are pending.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013