Depogrid: Next Generation Unstructured Grids for Accurate Reservoir Modeling and Simulation

Abstract As the oil and gas industry is moving toward tapping reserves in more complex structural environments, there comes the challenge for the reservoir modeling platform to accurately and robustly build and simulate a model to aid in making more trustworthy reserve estimates and field development plans. The 3D geocellular model sits at the core of an integrated seismic-to-simulation workflow, within which one can characterize and predict the behavior of reservoirs and can make confident quantitative decisions about one's assets. In structurally complex areas, the construction of accurate 3D models is often impeded by fundamental limitations of standard geocellular modeling technologies. With these limitations in mind, a new cut-cell unstructured grid has been developed that honors the geological structure precisely, enables accurate property modeling in a flattened, un-faulted, pseudo-depositional space, and can be simulated directly in a next-generation simulator; we call this unstructured grid built in depositional space a ‘depogrid’. The polyhedral, cut-cell nature of the depogrid arises when the regularly gridded volume in depositional space is cut by the structural model features (faults and unconformities) before being forward-deformed into geological space. By construction, the grid cell columns are orthogonal to the local stratigraphy, yet they can accurately represent complex structures and volumes, independent of the grid resolution. A next-generation high resolution reservoir seamlessly consumes the globally unstructured grid topology, with the structural complexity and non-neighbor connections, and honors the flow dynamics accurately. This ensures a more geologically consistent simulation model, realistic parameters to tune for history matching workflows and the ability to make reliable predictions. We present some particular reservoir modeling and simulation considerations where the depogrid approach improves on typical gridding technologies. The seismic-to-simulation workflow is then applied to several structural examples to demonstrate how the depogrid is best suited to model the geological structure and properties in a variety of reservoirs and subsequently improves the accuracy and efficiency of field development planning and risk mitigation.