--> Abstract: Geological Constraints on Porosity Evolution and Permeability: A Comparison of Limestone Versus Dolomite Carbonate Reservoirs, by G. Darke, P. H. Nadeau, J. Garland, and S. N. Ehrenberg; #90039 (2005)

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Geological Constraints on Porosity Evolution and Permeability: A Comparison of Limestone Versus Dolomite Carbonate Reservoirs

G. Darke1, P. H. Nadeau1, J. Garland2, and S. N. Ehrenberg1
1 Statoil ASA, N-4035 Stavanger, Norway
2 Cambridge Carbonates Ltd, Durham, DH1 4JR, United Kingdom

Geological processes for the evolution of porosity and permeability in carbonate rocks, as a function of burial and thermal history, are under evaluation. The primary objective of this work is to provide observational constraints for quantitative predictions and risk reduction in the hydrocarbon exploration setting. Recent advancements in understanding of siliciclastic diagenesis have resulted in predictive models as a function of burial and thermal history (Bjørkum et al., 1998). Compilation of global data for carbonate reservoirs has provided an observational framework for the establishment of similar models in carbonates (Darke et al 2004).

Geologic models are under evaluation, to identify controls on petroleum occurrences in carbonate reservoirs. A database representing 6,776 limestone reservoirs and 1,264 dolomite reservoirs provides the basic input for the analysis. The data allow reservoir quality and heterogeneity quantification applicable in the early stages of exploration when little additional data are available. Here we extend the analysis methodology to compare limestone versus dolomite reservoir lithologies.

Globally, 75% of total reserves (and 86% of oil) in carbonate reservoirs occur between 80° and 120°C (Darke et al., 2004), a result which differs from hydrocarbon accumulations in general where the temperature range is typically 60° to 120° C (Bjørkum & Nadeau, 1998). This can be linked to top-seal diagenesis (Nadeau et al., 2005 in press). The data clearly demonstrate an exponential relationship to exploration risks as a function of reservoir temperature. The industry, however, often drills beyond the optimal entrapment zone with corresponding reductions in exploration efficiency.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005