Composite rock types as part of a workflow for the integration of mm-to cm-scale lithological heterogeneity in static reservoir models

Abstract

Abstract Lithological heterogeneity in the form of sedimentary structures such as cross and planar and as interfaces between massive beddings is known to impact fluid flow and fluid-rock reactions in the subsurface. Such heterogeneity exists at mm-to cm-scale and is typically not accounted for in conventional geological models due to technical restrictions posed by the wireline log resolution and the inefficiency of reservoir modelling softwares to handle such fine scale information. Hence, multiphase flow and reactive transport simulations based on conventional models fail to appropriately account for the impact of sedimentary heterogeneity. We present a new workflow which allows building reservoir models where such fine-scale lithological heterogeneity can be integrated, thereby overcoming the limitations associated with log resolution and modelling softwares. First, the rock types are coupled as composites in a systematic manner at a discretization level that can be handled by the modelling softwares. The mm-scale rock properties quantified from core samples are accounted for in the composite rock type characterization. Lithotype logs of the composites are derived by modifying the color-coded depth record based on a combination of different wireline logs. The lithotype logs form the basis for property population in the reservoir models. The coupling of core and wireline data allows to account for the mm-to cm-scale heterogeneity in coarsely discretised reservoir models. The application of the new workflow is demonstrated for the development of a 2-D reservoir model at the CO2CRC's Otway Research site with a vertical resolution of 5 cm while incorporating sedimentary heterogeneity at 5 mm scale. The composite rock type method would allow for the impact of fine scale heterogeneity to be directly accounted for in static reservoir models.