Constraints from Reactive Transport Numerical Modeling for Porosity Distribution as a Result of Hydrothermal Dolomitization

C. Taberner¹, J. Salas², M. Esteban³, and C. Ayora^4
1 Shell International Exploration and Production B.V, Rijswijk (ZH), Netherlands
² Aluvial S.L., Barcelona, Spain
³ Carbonates International Iberia, Mallorca, Spain
⁴ Institute of Earth Sciences, Barcelona, Spain

Understanding the impact of deep burial diagenesis in the improvement of carbonate reservoir properties has recently become a major theme in exploration and production. Burial and hydrothermal fluids may play a major role in the redistribution and enlargement of porosity, as well as in the generation of new porosity in many carbonate reservoirs, before and /or during oil charge. Nevertheless, the prediction of reservoir porosity in burial / hydrothermal diagenesis scenarios is difficult because different types of controlling factors are involved. These potential controls are not only stratigraphic in nature (i.e. by primary and secondary porosity in specific stratigraphic units that may favor the fluid flow of burial / hydrothermal solutions), but also textural, mineralogical, structural, burial history, flow regimes and rates, amongst others. 1D and 2D reactive transport models of deep burial / hydrothermal solutions attempt to (i) understand the major constraints for porosity generation and / or redistribution, (ii) evaluate the distribution of tight vs. porous hydrothermal dolomite, as well as (iii) predict the most favorable zones where highly corroded / leached limestones and dolomites may occur. Cooling vs. mixing of basinal brines has been evaluated in different hydrogeochemical scenarios (e.g. Darcian fluid flow rates, temperatures and salinities). The discussion will be centered in evaluating the more favorable scenarios that may account for a net increase of porosity due to calcite and / or dolomite dissolution, as well as the resulting porosity distribution patterns in time and space.