A WORKFLOW FOR QUANTITATIVE SHALE LITHOFACIES MODELING AT MULTIPLE SCALES: CASE STUDY FROM THE BAKKEN FORMATION IN NORTH DAKOTA

Constructing integrated shale lithofacies models is significantly important to analyze multi-scale variation of geologic and petrophysical parameters of shale formations to interpret depositional and diagenetic environments. This study presents the results from upper and lower shale members in the Bakken Formation of the Williston Basin in North Dakota. The major objectives of this study are to better understand various geologic controls on mineralogy and organic matter content, and provide a quantitative framework for shale lithofacies characterization at core, well, and regional scales. Shale lithofacies is defined using quantitative mineralogy, Total Organic Carbon, various petrophysical and geomechanical properties derived from core data, such as XRD, XRF, pyrolysis, and secondary X-ray emission spectroscopy. Next, “statistical learning theory” is used to recognize the pattern of different shale lithofacies and corresponding petrophysical parameters from conventional and advanced well logs. After core and well log-based classification of shale lithofacies, geostatistical algorithm, such as Sequential Indicator Simulation, is used to generate 3D Bakken shale lithofacies models at regional scale. The results show that upper and lower Bakken shale members are vertically and laterally heterogeneous at core, well, and regional scales, but can be classified into five different lithofacies. Organic-rich shale lithofacies are more dominant than organic-lean gray shale lithofacies. Several factors, such as source of elements, paleo-redox conditions, and organic matter productivity appear to have controlled deposition of shale lithofacies. Silica in the Organic Siliceous Shale lithofacies is derived from both biogenic and eolian action. Organic-rich shale lithofacies show positive correlation with hydrocarbon production.