The Role of Geomechanics in Hydrocarbon Column Height Estimation. A Southeast Abu Dhabi Case Study
Authors: Fadipe O. A. , Vantala A. , Saleh M. H. , Hassan H. M. , Tameemi K. Al , Hammadi M. K. Al , Ujetz B. 
Published: November 2024

The capacity of any seal to retain hydrocarbons in a trap depends on various factors, including the geometry, rock stress and deformation history of the seal. Geomechanical modelling can help to further understand, derisk and confirm seal integrity. Core is rarely cut in seals, which poses evaluation challenges, especially with the increasing need to focus on complex traps in mature basins. This paper presents the integrated results of using Lower Cretaceous seal elastic properties in estimating column height.

The workflow involves throw estimation and fault trend classification from seismic and well log interpretation to establish any juxtaposition of seal against reservoir(s). Prediction of top seal and fault-seal cross flow was performed through characterization of available cored intervals and associated petrophysical properties from logs. The outcome is calibrated against derivatives from elastic rock properties (Uniaxial Compressive Strength, Poisson Ratio, Youngs Modulus and Friction Angle) to predict expected column height from the identified traps. We use the model to perform a probabilistic seal capacity analysis based on Mohr coulomb's analytical principles.

Fault trend interpretation illuminates the tectonic evolution where different aged faults have different strike orientations; Pre-Cambrian to Cambrian faults strike WNW (S85°W-N75°W) and WNW (N75°W-N60°W), Jurassic faults WNW (N60°W-N45°W) and NNW (N40°W-N25°W) and Upper Cretaceous NE (N40°E-N20°E). Petrophysical properties within the seal unit are poro-perm &lt; 2% and 0.1 mD while core description depicts well-defined argillaceous wisps with very rare porosity in carbonate-rich patches, thus indicating a largely effective top seal. Core characterization along faulted zones could not be performed due to lack of core data. However, integration with elastic properties and critical pore pressure shows some key derivatives, confirming good top seal while predicting variations in fault-seal. The classification of the integrity of the carbonate-rich seal units reflects a minimum UCS threshold &gt; 5000 psi, PR of 0.33, YM of 5 Mpsi and Fang of 25°.

This was validated by analogy with published work (Yan Yusupov et al., 2024), in a carbonate setting where rock strength is known to increase with increasing UCS. Results show that geomechanical modelling can be used to bridge gaps in areas without core data by using key logs and pre-stack seismic data to provide valuable results that can assist in derisking prospects. The case studies illustrate how geomechanical modelling can help to reduce uncertainty in seal integrity and hydrocarbon column height estimation, and to quantify the impact of different scenarios and assumptions on prospect value. It is essential to pay attention to data acquisition within the sealing formations. This paper presents an integrated result where geomechanical modelling was applied to derisk prospect maturation to provide insights for exploration and development decisions.