Characterization and Modeling of Petrofacies and Pore-Volume Distribution within a Gas-Storage Reservoir, Ray Reef Field, Southern Michigan Basin, Michigan
This study establishes petrophysically significant facies ("petrofacies") that relate rock fabric to petrophysical properties within a pinnacle reef reservoir of the Michigan Basin (Ray Reef Field), and examines their application in the creation of petrophysical models and pore-volume estimates for the field. Both deterministic and stochastic modeling methods were used with and without petrofacies conditioning to create several model scenarios for the field. Model results reveal significant differences in the distribution of reservoir-quality rock; however estimated pore volumes vary by less than 0.5% among all models and range from 707-714 million cubic feet (20,025,000-20,225,000 cubic meters).
The Niagaran reef trend of the Michigan Basin was extensively studied in the latter half of the 20th century, yet the relationship between depositional texture and petrophysical properties remained poorly understood. Petrofacies of this study, which are based on pore type and size, relate petrophysical trends to depositional fabric; their distribution influences the distribution of reservoir-quality rock in the field.
Comparisons between models created with and without petrofacies conditioning demonstrate that conditioning to petrofacies introduces spatial heterogeneity and precludes the development of vertically continuous zones of high (and low) porosity and permeability. This effect can be seen in both deterministic and stochastic models. However, the effect of petrofacies conditioning on stochastic models is secondary to the high degree of heterogeneity imposed by variogram ranges of 40 ft (12.2 m) horizontally and 10-45 ft (3.0-13.7 m) vertically; such heterogeneity honors data analysis performed in this study and observations made in outcrop.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009