Integrating Diagenesis into Reservoir Models for Carbonate Platforms

Megan Murphy-Bishop¹, Jean Hsieh¹, Paul (Mitch) Harris¹, Sebastien Strebelle¹, Marjorie Levy¹, Jeff Carvalho¹, and Jeroen Kenter^2
1Chevron Energy Technology Company, San Ramon, CA
²Chevron Energy Technology Company, Voorburg, Netherlands

Reservoir models are, in part, based on combinations of petrophysical measurements from logs and rock description from core studies. However, reservoir quality in carbonates is commonly a function of both depositional rock type and diagenetic overprint. Diagenesis can significantly modify porosity and permeability in carbonate reservoirs, and the overprint can cross rock type and stratigraphic boundaries. Thus diagenetic trends are often difficult to interpret between wells and to include in models.

To address this issue, we developed a novel workflow to use multiple point statistics (MPS) to model diagenetic “facies” distributions in a carbonate reservoir. In this case study dolomite was the diagenetic parameter. Four models for the formation of dolomite were chosen based on literature review: seawater, reflux, transgressive, and fracture. Generally, the shape of dolomite bodies in a reservoir is unknown. However, these different dolomite models produce unique dolomite geobody shapes. Four training images that represent potential dolomite geobodies were created. Six hypothetical paragenetic sequences for dolomitization were then simulated with MPS using various combinations of the training images. Even if the dolomite in the reservoir represents dolomite produced from different models, a comparison of the various MPS models shows the potential range and character of dolomite distribution. Similarly, other diagenetic parameters such as karstification, calcite cementation or bitumen emplacement, can be integrated into reservoir models to more accurately distribute porosity and permeability resulting from diagenetic overprint throughout carbonate platform reservoirs.

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