Clay Mineralogy and Cation Exchange in the Marcellus Shale
Staub, Patrick; Benelli, Paolo; Bank, Tracy; Giese, Rossman
The mineral composition of Marcellus Shale was determined using powder X-ray diffraction scans of 14 core and outcrop samples collected throughout the unit's geographic and stratigraphic extent. Each of the 10 outcrop and 4 core samples was separated into coarse and fine components which were analyzed separately. Samples were prepared using high-purity corundum as an internal standard and X-ray diffraction data were analyzed using RockJock11 software. Illite is present in all examined samples at concentrations ranging from approximately 20 wt% to greater than 60 wt%. Preliminary examination of the illite diffraction suggests that there are few if any smectite layers present. On the other hand, chlorite is present in some samples and absent in others. Calcite also varies widely from below the detection limit to greater than 50 wt%. Dolomite is present at trace concentrations. Quartz varies from roughly 20 wt% to more than 35 wt%. As an independent check on the presence of expandable layers in the clay-fraction of the samples, cation exchange capacity (CEC) was measured using UV-VIS spectrophotometry of a copper complex (Cu-ethylenediamine) which adsorbs strongly to the exchange sites present in the sample. CEC values from the Marcellus shale are within the typical ranges of kaolinite and illite and are consistent with the absence of smectite.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013