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Show COLLEGE OF MINES & EARTH SCIENCES UNDERGRADUATE RESEARCH ABSTRACTS ESTIMATING TOTAL OGANIC CARBON CONTENT IN THE CRETACEOUS MANCOS SHALE Ryan Hillier (Lisa Stright) Department of Geology and Geophysics University of Utah The Cretaceous Mancos Shale is a prospective shale gas reservoir located in the Uinta Basin in Eastern Utah. In order to determine the hydrocarbon potential of the Mancos Shale, the quantity of organic matter, measured by percent of total organic carbon (%TOC) within the shale matrix and pore space, must be determined. The % T O C can be estimated through a petrophysical approach called the AlogR method. The AlogR method employs the use of wireline logs, geochemical data, and thermal-maturity data to calculate in-situ %TOC. O n e known shortfall of the AlogR method is that calculated % T O C values are underpredicted in shale gas systems that have reached thermal maturation values within the dry-gas window. However, the exact degree of thermal maturity is often uncertain due to subjective visual characterization from vitrinite reflectance data. To compensate for the uncertainty associated with thermal-maturity, petrophysicists have incorporated adjustment parameters into the AlogR equations in order to achieve an optimal match between observed and calculated % T O C values. These parameters create an improved match between calculated and observed % T O C values, but they do not address the underlying geologic relationship between thermal-maturity and %TOC. Vitrinite reflectance values within the Uinta Basin indicate portions of the Mancos Shale are within the dry-gas window. Using results from 2-D burial history modeling, a more advanced method of characterizing thermal-maturity via a modified AlogR workflow is presented. This model optimizes input parameters, including the aforementioned adjustment parameters and thermal maturity model results, to obtain the best fit between calculated and measured % T O C values. This optimization reveals that of all of the parameters, thermal-maturity is the most dominant factor in accurately predicting %TOC. These results also suggest that implementing thermal-maturity models into a modified AlogR workflow can achieve a more robust method for calculating % T O C in shale gas systems that are within the dry-gas maturation window. Ryan Hillier Lisa Stright 49 |
