Structural and Geomechanical Analysis of Fractured Cambrian-Ordovician Reservoirs in the Northern Appalachian Basin

Abstract

The Cambrian-Ordovician Conasauga and Knox Groups constitute a regional succession of carbonates punctuated by brief periods of clastic deposition. Diagenesis and a history of multiple orogenic events resulted in the development of a complex fracture system. Understanding the orientation and distribution of the natural fracture sets within the Conasauga and Knox Groups is of significance in seeking potential CO₂ storage zones and building reservoir models with fracture networks.

Preliminary fracture studies were carried out to determine natural fracture orientation and distribution within the Conasauga and Knox Groups on the western flank of northern Appalachian Basin. Over 700 observations of fractures were interpreted on newly acquired resistivity and acoustic image logs collected at multiple well locations ranging in depth from 730 to 4150 meters. We evaluated structural parameters of the fractures using statistical analysis. Additionally, we evaluated the likelihood of observed fractures to slip under current stress conditions using 3D Mohr diagram for critically-stressed fracture analysis.

Analysis and interpretation of fracture orientation clusters shows the regional fracture systems are highly complex with possibly systematic and non-systematic fractures within the evaluated lithologic units. Fracture density is observed to increase up-dip within the studied area. Overall, a high percentage of fractures with varying dip direction were observed to strike sub-parallel to the contemporary maximum horizontal stress direction (SHmax) determined from wellbore failure, while a lower percentage strikes perpendicular to the SHmax direction. Critically-stressed fracture analysis shows the natural fractures are not critically stressed in the current state.

‘This project was supported by U.S. Department of Energy's National Energy Technology Laboratory (Award DE-FE0023330) and Ohio Development Services Agency (Grant OER-CDO/D-14-16).’

AAPG Datapages/Search and Discovery Article #90218 © 2015 Eastern Section Meeting, Indianapolis, Indiana, September 20-22, 2015