How In-Place Volumes of Subsurface Reservoir Models are Impacted by Using 3d High-Resolution Outcrop Analogue Data. A Case Study Using Depositional Architectural Heterogeneity of Stromatoporoid/Coral Buildups of the Hanifa Fm, Saudi Arabia

Abstract

High porosity-high permeability stromatoporoid/coral facies are important components of the Late Jurassic carbonate reservoirs in the Middle East. This facies exhibits sub-seismic depositional heterogeneities that subsurface models often overlook due to the limited interwell resolution of subsurface data. Understanding the effect of this facies on the 3D distribution of static reservoir properties and uncertainty in volumetric calculations of hydrocarbons in-place will improve estimates of the ultimate recovery and hence reservoir development decisions. A 3D high-fidelity outcrop-based geocellular depositional model that honors the spatial and petrophysical heterogeneity of the stromatoporoid/coral facies was constructed based on the Hanifa reservoir outcrop analog in central Saudi Arabia. The model was constructed from a 1.2 km × 1 km drone photogrammetry survey, measured sections (total length 150m) and spectral gamma-ray data, >200 thin sections, a 50 m-long core, a 19 km-long network of 2D and 3D Ground Penetrating Radar, and 600 m-long 2D seismic profiles. The facies model was populated with porosity and permeability equivalent to subsurface reservoir facies and utilized as the baseline petrophysical model for the comparison study. A set of pseudo wells at ~1 km spacing were simulated from the model capturing the model's 1D facies stacking and properties around the wellbore. The pseudo wells were utilized to stochastically build facies and static reservoir models scenarios to replicate the baseline model from limited well data. The volumetric calculation of each realization is compared with the baseline to investigate the range of volumetric uncertainty that would be introduced by the lateral distribution of stromatoporoid/coral facies. Early results show that depending upon the modeling methodology, the volumetric discrepancy between stochastic simulations and the deterministic outcrop baseline model is ~10-15%. Using a high-fidelity outcrop-based reservoir model, we have demonstrated the strong influence of 3D depositional heterogeneity of the stromatoporoid/coral facies on the uncertainty associated with hydrocarbon in-place volumes. We conclude that a static reservoir model can be significantly improved by using data-driven geological models that reflect the 3D heterogeneity of depositional facies.