--> Abstract: Hydrothermal Dolomite and Leached Limestone Reservoirs: Representative Core Fabrics and Facies, by Graham R. Davies, Tom Boreen, and Langhorne Smith; #90039 (2005)

Datapages, Inc.Print this page

Hydrothermal Dolomite and Leached Limestone Reservoirs: Representative Core Fabrics and Facies

Graham R. Davies1, Tom Boreen2, and Langhorne Smith3
1 Graham Davies Geological Consultansts Ltd, Calgary, AB
2 Suncor Energy, Calgary, AB
3 New York State Museum, Albany, NY

In the last 10 years or so, there has been a strong upsurge in the number of dolomite reservoirs interpreted to have formed or to have been influenced by alteration of host limestones by saline fluids of hydrothermal origin. Extensional but particularly transtensional locations on strike slip faults appear to be the favored sites for focused hydrothermal fluid flow and more massive dolomitization. However, there are many examples of dolomite reservoirs in which characteristics of hydrothermal dolomite (HTD) fabrics and facies extend for 45 to more than 200 kms – that is, they appear to be regional hydrothermal dolomite trends. Although high resolution aeromagmatic mapping and 3D seismic interpretation across parts of these trends typically show structural complexity and arrays of faults, questions remain concerning emplacement mechanisms and fluid source/volumetrics for these more extensive dolomite bodies.

Texture, fabric, pore type and pore volume in HTD reservoirs are controlled mainly by the facies of the original limestone host. Porosity and permeability of the host at time of dolomite emplacement strongly influence the size of the dolomite reservoir and its lateral distribution away from fault conduits. In relatively tight or low permeability limestones, such as the Ordovician Trenton-Black River formations of the Michigan and Appalachian Basins, structurally-controlled HTD reservoir trends may be sublinear and narrow. In contrast, originally more permeable grainstones and amphiporid-stromatoporoid floatstones-rudstones in the Devonian of the Western Canada Sedimentary Basin (WCSB) may lead to more ‘regional' reservoir development. Dilational breccias, zebra fabric, arrays of shear microfactures (rimmed microfractures) and related fabrics may be formed preferentially proximal to periodically-active faults (fault proximity indicators). Leached limestones with high volumes of microporosity may form peripheral to HTD and contribute to hydrocarbon storage and production.

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