Development of secondary porosity in the Fairholme carbonate complex (southwest Alberta, Canada)

Abstract

Because of their economic importance as hydrocarbon reservoirs, the Upper Devonian dolomitized carbonate reefs in southwest Alberta have been the subject of several studies. Still, there is no consensus on the process of matrix dolomitization and furthermore, the process of vug development is not often addressed. The studied outcrops show features of an early diagenetic matrix-selective dolomitization by a Late Devonian seawater-derived fluid. Seepage reflux dolomitization combined with latent reflux is proposed, which best explains most chemical characteristics. The cements in the vugs are precipitated from warm saline, 87Sr-enriched fluids and testify to thermogenic sulphate reduction based on the presence of sulphur, CO 2 and H 2S in inclusions, relatively high homogenization temperatures and depleted δ 13C values, which sets constraints on the timing of vug formation. Secondary porosity may be created by the mixing of formation water with a tectonically and topographically driven fluid and by the dissolution of anhydrite nodules.