Fracture Characterization and Prediction in Unconventional Carbonates — “Mississippian Limestone”, Northeastern Oklahoma

Abstract

Unconventional Mississippian oil and gas reservoirs in central and northern Oklahoma and southern Kansas are characterized by porosities of 1–2 percent or less, and permeability values measured in fractions of millidarcies. As such, natural fractures are an important part of reservoir performance in the “Mississippi Lime”. Understanding the types and distribution of fractures in these carbonate rocks and how they may be related to facies and sequence stratigraphic architecture, may increase the predictability of fracture-enhanced permeability in the subsurface. The study area is located in northeastern Oklahoma in Logan, Payne, and Osage counties. Four cores were used for the study: Adkisson 1–33, Winney 1–8, Elinore 1–18, and Orion Blackbird 3–44. Fractures in the core were analyzed on a morphological basis (i.e. fracture type) and various fracture properties were measured (i.e. aperture, spacing, continuity, length, and density of fractures). This data was used in conjunction with facies analysis, wireline logs, and the established high-resolution sequence stratigraphic framework. Six facies types were defined in core. Of these six facies, the skeletal-peloidal wackestone had the highest density of fractures per foot, averaging 5.1 fractures per foot. The skeletal-peloidal packstone to grainstone facies had the lowest fracture density, averaging 1.6 fractures per foot. The natural fractures seen in core include: ptygmatic, stylolite-related, extensional, and shear fractures. The preliminary data from the Orion Blackbird core suggests that intensity of fracturing is facies dependent. Therefore, an understanding of the high resolution sequence stratigraphic architecture and facies distribution both vertically and laterally can greatly increase the predictability of fracturing and subsequent trends in permeability in the subsurface.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015