Abstract

The benefits to hydrocarbon exploration from geochemical and SEM analysis have been known for many years. The advent of smaller, cheaper and more specialized equipment is now providing the ability to make highly precise and critical measurements during the drilling process rather than having to wait for weeks or even months to obtain results. When these data are coupled with standard surface-logging techniques of gas and formation analysis, they provide valuable information about the reservoir that helps with current production of subject wells and future development planning.

For this case study, several instruments were used on cutting samples taken at 30-ft intervals in a mobile laboratory during the drilling of a Woodford Shale horizontal well, including Rock-Eval, gas chromatography infra-red (GCIR II) for gas isotopes (proprietary), Niton X-ray fluorescence (XRF), and Hitachi TM-3030 scanning electron microscopy (SEM).

The Rock-Eval pyrolysis provided data on producible hydrocarbons, thermal maturity and total organic carbon (TOC) content of each sample. The GCIR II analyzed the gas isotopes from isotubes and isojars yielding data on c1, c2 and c3 isotopes. These data provided insight into permeability and porosity and provided information on hydrocarbon compartmentalization and differentiation from oil-based mud (OBM). XRF analysis was able to quantify the inorganic elemental composition of the cutting samples, providing an understanding of the best locations to frac based on silica content, changes in mineral composition and an indication of TOC. Petrographic analysis was done using the SEM. This instrument gave direct observation of both microstructures and available pore space. These data gave corroboration to previous geochemical and elemental analyses.