Return to the Source: Mapping the Microstructure of Organic Matter and Pores in the Utica Shale

Murphy, Michael; Cole, David R.; Daniels, Jeffrey; Sheets, Julie; Welch, Sue; Swift, Alexander M.; Huber, Dan; Sosa, John

The mineralogy and pore structure of the Utica shale in Ohio was characterized at the micro- to nano-scale by scanning electron microscopy (SEM), Quantitative Evaluation of Minerals by SEM (QEMSCAN), energy-dispersive X-ray spectroscopy (EDX), and focused ion beam-SEM (FIB-SEM). Electron and x-ray imaging, image processing, and image analysis methods were used to produce 2-D and 3-D maps of the pores, organic matter, and other mineral phases.

Image analysis was augmented and validated with petrophysical lab techniques. Cores were scanned with x-ray computed tomography (CT) to create 3-D maps at the centimeter to millimeter scale, and to determine regions of interest for smaller-scale sampling. An elemental analyzer was used to quantify total organic content. Pore features were explored using mercury injection porosimetry to analyze pores down to around 4 nm, and gas adsorption (BET) to analyze pores down to several Angstroms.

Initial results indicate that most of the connected pores in the Utica are smaller than 10s of nm in diameter, and are found primarily in organic matter. Other types of pores are larger than organic matter pores, but are not well connected. Organic matter pore size and total porosity appear to increase with thermal maturity. Images of the microstructure show evidence of pore structure variation between different types of organic matter. Some of the organic matter types appear to relate to different organisms, but other types seem to be associated with thermal maturation. The micro-maps show what appears to have been primary porosity is now largely filled with amorphous organic matter phases that might have been mobile in the subsurface.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013