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Case Study: Woodford Shale Source Rock Characterization By Geochemical And Sem Evaluation In A Horizontal Well

Abstract

The benefits to hydrocarbon exploration from geochemical and petrologic analysis have been known for many years. Yet 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. This greatly reduces the time it takes to obtain results that may take weeks or even months. When this data is coupled with standard surface logging techniques of gas and formation analysis, they provide valuable information about the hydrocarbon source rock to the reservoir. This will aid with production of the subject well and future development planning. For this case study, several instruments were used in a mobile laboratory during the drilling of a Woodford horizontal well on cutting samples taken at regular intervals: Rock Eval®, GCIR II for Gas Isotopes, Niton® XRF, Hitachi TM-3000 SEM. The Rock Eval pyrolysis provided data on producible hydrocarbons, thermal maturity and total organic content in each sample. The GCIR II analyzed the gas isotopes from both isotubes and isojars yielding data on c1, c2, c3 and c4 isotopes. This data provided insight into permeability, porosity and provided information on hydrocarbon compartmentalization. In addition, GCIR data analysis composed regional stable isotope mapping (DNA) of the target formation. XRF analysis was able to quantify the elemental composition of the cutting samples. This provided an understanding of the best locations to frac based on silica and aluminum content, changes in mineral composition due to alterations of depositional environment, better regional understanding of the reservoir and an indication of Total Organic Carbon assisting with, “sweet spot” identification. Petrologic analysis was done using the SEM. This instrument gave direct observation of both microstructures and available pore space. In turn this data gave corroboration to the previous geochemical and elemental analysis. As a control to the measurements made during the drilling of the well, two Woodford outcrops from the Arbuckle Mountains of Oklahoma were examined from samples taken at specified intervals through the formation using the standard practices of Stratigraphy. These samples were subjected to analysis using the XRF and SEM. Not only did this provide a bench mark for the test well, it provided information to assist with regional variations within the Woodford source rock.