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Geometric Quantification of Dolomitized Clinoforms Using Digital Outcrop Models and Surface-Based Modeling: Insights for Geobody Connectivity From Outcrop Analogues


Carbonate clinoforms have a proven track record as successful hydrocarbon targets, such as those in the Wasson and Means fields of the Permian Basin. However, reservoir characterization of these lucrative plays is often difficult due to their complex geometries and additional heterogeneity arising from diagenetic processes such as dolomitization. This leads to difficulties in predicting and quantifying static and dynamic behavior within these reservoirs. Our study aims to answer these questions by quantifying and characterizing an outcrop analogue of dolomitized carbonate clinoforms using digital outcrop model studies; and subsequently testing the impact of different interpretations (degree of dolomitization, facies boundary positioning, porosity and permeability distributions) on flow behavior within these clinoforms. Our flow simulations use a novel surface-based modelling (SBM) approach coupled with an unstructured mesh flow simulator (IC-FERST). In contrast with conventional geomodelling techniques, SBM can more accurately preserve complex geometries realistically, such as those found in clinoforms and dolomite geobodies without the resolution and geometry limitations related to traditional cornerpoint grids. Our outcrop analogue in Seru Grandi in Bonaire consists of a series of heterogeneous shallow marine red algae rich clinoforms partially replaced by tongues of Late-Miocene dolomite that extend down from an erosional unconformity marking the transition to overlying undolomitized limestone. Detailed geometrical measurements taken on the digital outcrop model form the input for subsequent modelling. Clinoforms are on average 33 m long and 9 m high, with dolomite bodies ranging from 10 - 30 m long and porosity values ranging from 3 % to 28 %. This database of outcrop geometry quantifications (and variations thereof) is sampled to produce multiple stochastic realizations of surface-based reservoir models at a similar scale to the outcrops (interwell scale). Flow simulation results combined with these geological scenarios can provide a better understanding of the spatial distribution of reservoir properties and provide insights for development planning. This study has direct applications on improving quantification and characterization of complex carbonate subsurface geometries. These improvements allow for better capturing of carbonate geometries and better predictions of flow behavior and connectivity in these systems and will thus be valuable for exploration, production, and development of analogous existing and future carbonate prospects.