Enhancing Reservoir Understanding with New Ultra-HD Inversion of Deep Azimuthal Resistivity

Abstract Strategic reservoir navigation and geological uncertainty mitigation are some of the most desired objectives for horizontal production wells. With standard formation evaluation suites, there are limitations in the ability to optimize the well placement in the sweet spot of the reservoir, especially in an area with high lateral variation in reservoir properties. In order to minimize the risks, reservoir navigation services with dedicated tool and data processing workflows are required. Deep Azimuthal Resistivity (DAR) tool and Multi-Component-While-Drilling (MCWD) inversion software have been widely used in many different types of reservoirs around the world. DAR tool measures short- to mid-range EM response from formation: with compensated 8-coil resistivity providing low noise readings, and pure orthogonal azimuthal signals giving direction and distance to conductive structures around the tool. MCWD is the established resistivity inversion algorithm for reservoir navigation services. The purpose of inversion is to identify a resistivity model (also known as an earth model), in which the modeled resistivity tool response matches with the actual resistivity logs with as low a misfit as possible. The new Ultra High-Definition (UHD) inversion workflow is built on the MCWD software and is highly flexible, allowing for faster inversion results and multiple interpretation scenarios with the ability to directly correlate seismic architecture and offset well data. An important component of the UHD workflow is a dynamic regularization step to improve feature resolution and lateral continuity. A post-well evaluation of a challenging well drilled in the Marlin Sul field in Brazil has been done to validate this new UHD workflow. The Marlim Sul Field was discovered in November 1987 and is located approximately 120 kilometers offshore in the north of the state of Rio de Janeiro, in water depths ranging from 850 to 2,400 meters and covering an area of about 600 km². The field consists of a single Oligocene producing horizon of sandstone turbidites. By applying the UHD inversion workflow, the reservoir architecture was accurately mapped with thickness ranging from 4 to 10m TVT along with identification of possible internal channels crossed. Dips seen on the UHD inversions show a close correlation to the dips seen on the high-resolution resistivity image supporting the robustness of this innovative approach, considering the different resolution of both technologies. In this paper, we will discuss the importance of utilizing UHD inversions in overall complex geological scenarios to optimize well placement, delineate remote layers through high-definition mapping and, therefore, increasing inversions calculation confidence and reducing geological uncertainty.