Conceptual and numerical modeling of fracture-related high temperature dolomite: Implications for reservoir characterization. 9th Middle East Geosciences Conference, GEO 2010.

Abstract

Classical diagenesis studies make use of a wide range of analytical techniques in order to suggest conceptual models that explain specific, relatively time-framed, diagenetic processes and their impacts on reservoirs. Still, these models are qualitative and do not yield “real” data for direct use by reservoir engineers for rock-typing and geo-modeling. This contribution provides new insights into numerical modeling of dolomitization following two approaches (geostatistical and geochemical transport reactive), and attempts to express the conceptual models of hydrothermal dolomitization which is known to have affected reservoirs in the Middle East, in more quantitative terms. A 3-D geostatistical model representing the Ranero dolomitized Cretaceous platform carbonates was constructed, covering an area of 5x2 km and a depth of 2 km. It is based on interpretation of aerial photographs, geological and topographic maps, as well as field observations. The resulting 3-D block included the stratigraphical units, fractures and the dolomite bodies. Geostatistical simulations succeeded in reproducing the dolomitized pattern. A relationship was set to restrict the presence of dolostones to the fractures at depth. A 2-D geochemical transport reactive model was built to represent a high temperature dolomite (HTD) front (ca. 350 m long; cells: 5x1 m) in the Marjaba Jurassic platform carbonates. The nature of the dolomitizing fluid was constrained based on results of fluid inclusions and crush-leach analyses. Two aquifer analogues for the end-members of the mixed dolomitized fluids were chosen according to their similar sedimentological character, mineralogical compositions and ambient temperatures to the expected sources of evaporative marine-related waters and hydrothermal fluids. The geostatistical model helped in illustrating the relationships between the hydrothermal dolomite distribution and the fracture pattern. Numerical reactive transport simulations are valuable not only for predicting hydrothermal dolomite texture (porosity/permeability) distribution but also for validating the prescribed dolomitization model. This study provides means to predict fracture-related HTD distribution and related evolved reservoir properties, thereby achieving better reservoir characterization.