Dolomite

Dolomite: Perspectives on a
Perplexing Mineral

Dolomite is a metastable carbonate. It forms in a variety of distinctly different settings and can change as conditions change. The mode of formation influences dolomite morphology and thus impacts exploration and production strategies. New approaches to carbonate evaluation are helping geoscientists unearth reservoir-quality dolomite, despite its heterogeneous and often enigmatic nature.

Mishari Al-Awadi
Kuwait Oil Company
East Ahmadi, Kuwait
William J. Clark
William Ray Moore
Denver, Colorado, USA
Michael Herron
Tuanfeng Zhang
Weishu Zhao
Cambridge, Massachusetts, USA
Neil Hurley
Dhahran, Saudi Arabia
Djisan Kho
East Ahmadi, Kuwait
Bernard Montaron
Dubai, UAE
Fadhil Sadooni
Qatar University
Doha, Qatar
Oilfield Review Autumn 2009: 21, no. 3.
Copyright © 2009 Schlumberger.
For help in preparation of this article, thanks to
Tony Smithson, Northport, Alabama, USA.
Carbonate Advisor, CMR, EcoScope, ECS, ELAN,
Litho-Density and MDT are marks of Schlumberger.

“I think you should be more explicit here in step two.”
Modified with permission from Sidney Harris, copyright ScienceCartoonsPlus.com.

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Oilfield Review

Dolomite is a complex mineral. It can precipitate directly from solutions containing magnesium, calcium and carbonate ions to form cement or unlithified sediment. However, most dolomite forms through the chemical alteration of precursor carbonate rock or sediment—primarily limestone or calcareous muds. These carbonates tend to be unstable, composed chiefly of calcite or its more thermodynamically unstable polymorph, aragonite. When these precursor materials are exposed to magnesium-rich fluids, a portion of the calcium ions may be replaced by magnesium ions to form a more stable magnesium calcium carbonate known as dolomite.
Dolomite is found in a wide range of settings including hydrothermal veins, lakes, shallow oceans, lagoons and evaporative basins.