Nature, Origins and Evolution of Porosity in Dolomites
- Bruce Purser,
- Maurice Tucker and
- Donald Zenger
Published Online: 14 APR 2009
Copyright © 1994 The International Association of Sedimentologists
Dolomites: A Volume in Honour of Dolomieu
How to Cite
Purser, B. H., Brown, A. and Aissaoui, D. M. (2009) Nature, Origins and Evolution of Porosity in Dolomites, in Dolomites: A Volume in Honour of Dolomieu (eds B. Purser, M. Tucker and D. Zenger), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304077.ch16
- Published Online: 14 APR 2009
- Published Print: 25 MAY 1994
Print ISBN: 9780632037872
Online ISBN: 9781444304077
- dolomite reservoirs;
- nature, origins and evolution of porosity in dolomites;
- varied fabrics in Palaeozoic dolomites of North America;
- pore types in dolomites and their relation to dolomitization;
- fabric-replacive porosity in dolomites;
- Mururoa Atoll, French Polynesia;
- predolomite vugs and moulds;
- porosity evolution and dolomitization;
- porosity destroyed by dolomitization;
- syndolomite voids
Porosity in dolomites is not necessarily related to dolomitization. Many interparticle and dissolutional voids are inherited from precursor limestones. Voids related to dolomitization, such as intercrystalline pores in sucrosic dolomites, may result from the transfer of porosity due to dissolution at one site and incomplete cementation at another. Still other pores clearly postdate dolomitization, such as fractures, dolomite crystal moulds and evaporite dissolution moulds.
During the processes of dolomitization, the rock may gain, lose or conserve its initial porosity, even in the same dolomite body. The actual gain or loss depends upon the scale of observation and the position of investigated samples in the dolomite body. The Plio-Quaternary dolomite lens at Mururoa Atoll demonstrates this principle. In the areas on the downflow side of the hydrological regime, interparticle porosity is preserved and intraparticle porosity is created, whereas in areas in the upflow part porosity is occluded by excess dolomite cementation.
As with all other rock types, the average porosity of dolomite decreases with burial, probably owing to the generation of dolomite cements by pressure-dissolution. However, dolomite loses porosity at a slower rate than limestone and, in many deeply buried or tectonically active areas, dolomite porosity is selectively preserved. Fractures are both beneficial and detrimental for dolomites. They enhance permeability, especially in dolomites with poorly connected pore systems. However, fractures may also provide pathways for fluids, which may precipitate cement selectively occluding nearby porosity. In general, fracturing occurs more readily in dolomites than in limestones.
Because porosity in dolomites has multiple origins, exploration strategy should be adapted to the type of pore system in question. Prediction of dolomite reservoirs whose porosity is inherited from that of the precursor sediment clearly requires an understanding of the sedimentary framework. Inter-crystalline pore systems formed during dolomitization require the application of a hydrodynamic dolomitization model for predicting porosity within the dolomite body. Given our limited understanding of ancient hydrodynamics, this could be difficult. Finally, porosities preserved or created under burial or tectonic conditions can best be understood by studying the geodynamic history of the basin.