Jeff S. Lonnee1, Hans G. Machel1
(1) University of Alberta, Edmonton, AB
ABSTRACT: Reservoir Enhancement in the Clarke Lake Field, British Columbia: Facies Control on Diagenesis in the Middle Devonian Slave Point Formation
The Clarke Lake gas field of northeastern British Columbia is hosted in Middle Devonian carbonates of the Slave Point Formation. Since discovery in 1956, Clarke Lake has produced roughly 1.5 Tcf, making it one of the largest gas fields in Canada. Production is associated with the occurrence of dolomite, yet the controls on dolomite distribution are enigmatic.
The initial focus of this study was to identify facies and their relationship to diagenetic modifications (i.e. dolomite). Facies identified in the Slave Point Formation range from basinal to open shelf, but are characterized primarily by stromatoporoid-amphiporid-coral floatstones to rudstones deposited in shelf-margin shoals and restricted to shallow open shelf environments. Facies that contained high primary porosity and permeability appear to have experienced the most significant diagenetic alterations. Pervasive dolomitization of facies occurred near the edge of the platform margin, where in terms of reservoir enhancement, porosity increased by roughly 50%. As a result, the most prolific reservoir rocks are positioned between basinal shales and tight limestones of the platform interior.
The majority of dolomite within the Slave Point Formation varies from white to grey in colour, is coarse crystalline (> 1mm), and displays sweeping extinction. Petrographic and geochemical data are indicative of a hydrothermal origin for the dolomite, similar to other Devonian carbonates in western Canada. With evidence that dolomitization is facies dependent, there now exists a new tool for exploitation of existing fields and exploration of new fields of this type throughout northeastern British Columbia.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado