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

C. Taberner1, M. Esteban2, G. Warrlich3, W. Asyee1, M. Boya Ferrero3, and P. Cassidy1
1 Shell International Exploration and Production B.V, Rijswijk (ZH), Netherlands
2 Carbonates International Iberia, Mallorca, Spain
3 Petroleum Development Oman, Muscat, Oman

Reservoir properties in the Malampaya Buildup were previously interpreted as related to early diagenesis. Poor reservoirs were related to intense submarine cementation along the ocean side of the buildup. Better reservoir properties in the platform interior were considered to be related to early meteoric dissolution. The integration of diagenetic studies with extensive petrophysical characterization and newly acquired high-resolution 3D seismics provides new perspectives in the interpretation of the porosity in Malampaya buildup. Worst reservoir properties are constrained to the southernmost sector of the reservoir where any early meteoric / coastal karst porosity was mostly destroyed by the precipitation of late burial fracture-fed calcite and dolomite cements. Late burial corrosion resulted in high porosity – high permeability layers and super K layers near the fault-related late-cemented zone at the southern part of the Malampaya buildup. The porosity distribution can be better explained by the inflow of deep-seated fluids along faults located in the southern sector of the Malampaya buildup, causing cementation at the fault zone and a corrosion front of high K and enhanced permeability zones along high porosity layers away from the fault zone. The integrated approach and the results obtained from this study may provide new insights in the interpretation of the origin and distribution of porosity in other carbonate reservoirs of similar age and structural setting. PNOC and CHEVRON are thanked for their support.