Dolomitization of Wabamun Limestones at Tangent Field, Northwestern Alberta

Abstract

<p>Tangent oil field in northwestern Alberta has been formed by a structural trap, created by the downthrown block of a Graben, combined with porosity created by the dolomitization of Wabamun limestone.</p> <p>The dolomitization fluids have migrated from the underlying Winterburn formation, via fractures, up into the Wabamun. Well 6-32-80-23W5 is the focus of this study as it contains a complete sequence from dolomite at the base of the Wabamun up through a transition to limestones at the top of the Wabamun. Cathodoluminescence and petrographic analyses of the dolomites and the transition from dolomite to limestone has revealed 5 dolomite types; diffuse microcrystalline dolomite, mosaic dolomite with associated porosity, and without associated porosity, dolomite which replaces calcite fracture fill and dolomite related to pressure solution. These analyses have also revealed the following paragentic sequence for the five dolomite types 1) microcrystalline dolomite 2) dolomite related to pressure solution 3) dolomite replacement of calcite fracture fill 4) mosaic dolomite with and without associated porosity.</p>