INTEGRATION OF NUCLEAR MAGNETIC RESONANCE, PETROPHYSICAL LOGS, ROUTINE CORE ANALYSIS, MICP, XRD AND PETROGRAPHY TO CHARACTERIZE MIDDLE BAKKEN ROCK QUALITY IN THE WILLISTON BASIN, NORTH DAKOTA, USA

The Middle Bakken Member of the Devonian-Mississippian Bakken Formation is the primary reservoir zone and lateral drilling target in the Williston Basin Bakken play. Rock quality attributes including grain size, pore structure, mineralogy, and diagenetic cements or dissolution have been recognized to change stratigraphically and laterally within this reservoir. Characterization of key reservoir parameters is necessary to build accurate geological and engineering model simulations that guide field development decisions including completion design and spacing. To better understand the reservoir differences between future development areas a variety of core and petrophysical data was acquired and integrated.

Nuclear magnetic resonance (NMR) wireline logs from 106 wells were used to identify lateral variation of pore sizes in the Middle Bakken within the Williston Basin in northwestern North Dakota, U.S.A. Mercury injection capillary pressure (MICP) measurements were used to identify pore-throat sizes. Thin-section petrography and X-ray diffraction (XRD) were used to identify the mineralogy, grain size, and diagenetic components associated with the pore systems, and calculated mineralogy logs were used to link the plug-scale information to the log-scale NMR. Changes in grain composition and diagenetic components were observed between the study areas and corresponded with changes in the pore system and permeability. These changes in key reservoir characteristics suggest that reservoir performance across these areas may vary.