Fault-Controlled Porosity Within a Trenton-Black River Hydrothermal Dolomite Reservoir

Osareni Christopher Ogiesoba and Bruce Hart
McGill University, Montreal, QC

Hydrocarbon reservoirs in the Trenton-Black River formation in the Appalachian Basin is known to be associated with porous hydrothermal dolomites formed within fault-controlled grabens. However, not all grabens are porous; and some dry holes have been drilled in some of these grabens. A 3-D seismic study that integrates wireline log-based porosity measurements, seismic attributes and neural network was undertaken to determine the influence of basement-related faults on porosity distribution in the Rochester field area located in southern Ontario.

A poststack frequency (F-X) deconvolution performed on the 3-D datasets has improved the signal to noise ratio and allowed for continuity of events and better fault definitions. We observed two main graben trends: the E-W and N-S trends. The recognition of these orthogonal sets of graben implies two periods of extensional tectonic event. There are two N-S trending grabens, the Western and Eastern grabens. The Western graben is bordered by basement-related flowered-faults and is broken into different compartments by faults. It trends for a distance of about 1.5 km. The Eastern graben is composed of two different grabens bounded by basement-related faults, but lacks the flower structure. It covers a combined distance of about 1.0 km. These faults serve as conduits for migrating hydrothermal fluids and enhanced the dolomitization of the host rock.

Our results show that the best porosity is developed within and along the Western graben that is associated with the flowered-fault structure. The interpretation method adopted in this project, can be used as a model for other Trenton-Black River reservoirs.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005