Inherent uncertainty in geological data acquisition leads to the generation of large ensembles of equiprobable 3D reservoir models. Running computationally costly numerical flow simulations across such a vast solution space is infeasible. A more suitable approach is to carefully select a small number of geological models that reasonably capture the overall variability of the ensemble. Identifying these representative models is a critical task that enables the oil and gas industry to generate cost-effective production forecasts. Our work leverages virtual reality (VR) to provide engineers with a system for conducting geological uncertainty analysis, enabling them to perform inherently spatial tasks using an associative 3D interaction space. We present our VR system through the lens of the reality-based interaction paradigm, designing 3D interfaces that enable familiar physical interactions inspired by real-world analogies-such as gesture-based operations and view-dependent lenses. We also report an evaluation conducted with 12 reservoir engineers from an industry partner. Our findings offer insights into the benefits, pitfalls, and opportunities for refining our system design. We catalog our results into a set of design recommendations intended to guide researchers and developers of immersive interfaces-in reservoir engineering and broader application domains.