Resolving Predictable Reservoir Behavior in Heterogenous Carbonates using Integrated Rock Typing Methods: A Field Scale Case Study of a Michigan Basin Silurian-aged Niagaran Brown Reef
The Silurian-aged pinnacle reef complex of the Michigan basin is a prolific hydrocarbon play and valued for its potential for carbon storage and CO2 driven enhanced oil recovery. Recent work has aided in resolving reefal structure and facies relationships, however, prediction of rock properties remains difficult. This study strives to optimize existing field scale workflows by implementing rock typing techniques that integrate geological, diagenetic and petrophysical attributes across scales into predictable profiles for static model population. The study area is limited to a single field along the northern reef trend in Otsego County, Michigan. The field is currently undergoing CO2-EOR and features a characterization well cored through the leeward profiles of the lower A1 carbonate and Niagaran Brown formations. This characterization well served as the type well of the field to generate rock types and features 230 feet of whole core, 117 core plugs, 16 mercury capillary curves, and 21 thin sections. Conventional and specialized well logs, including borehole image logs were collected. Intervals were picked for mercury injection and thin section analysis post-core description such that each curve and thin section was matched to core plug intervals that best represented geologic and petrophysical characters of each lithofacies encountered and served as control points for normalization of data. The study workflow consisted of four stages: geological and diagenetic characterization, petrophysical and pore-typing characterization, rock type definition, and geophysical facies definition and correlation. Upon completion of characterization stages, data was pooled and normalized beyond control points to the remainder of the core plug database. Data was segmented by depositional environment and subjected to multivariate ordination techniques to identify rock types. Core-calibrated geophysical log data was subjected to descriptive and multivariate analytical techniques to resolve profiles of defined rock types. Preliminary results include: (1) successions of lithofacies observed along the proximal reef apron are consistent with tempestite facies models, (2) trends in diagenetic modifications and controls on the development of microporosity were observed, (3) lithofacies-specific characterization of pore systems revealed heterogeneities and trends that account for distinctly different pressure-saturation profiles, and (4) rock types segmenting major depositional zones yielded enhanced petrophysical predictability and provided insight on how best to populate static models of the field. The project was funded by the Midwest Carbon Sequestration Partnership under DOE/NETL Cooperative Agreement #DE-FC26-0NT42589, Battelle Memorial Institute, the American Association of Petroleum Geologists, the Geological Society of America, and Bowling Green State University.
AAPG Datapages/Search and Discovery Article #90335 © 2018 AAPG 47th Annual AAPG-SPE Eastern Section Joint Meeting, Pittsburgh, Pennsylvania, October 7-11, 2018