Multi-Component While Drilling MCWD Resistivity Inversion for Thin Carbonate Reservoirs

Abstract

Abstract To maximize reservoir contact during well placement in layered carbonate reservoirs, reentry and newly drilled wells often target a specific layer. In this case, traditional well placement techniques of horizontal wells using a reactive or semi-proactive approach result in repeated exits of the reservoir target into the cap rock or potentially dip out of the target zone. This environment may result in losing reservoir footage, a lower net-to-gross, prolonged drilling time and wellbore challenges. All these items increase wellbore delivery time and cost. Existing logging-while-drilling (LWD) technology for well placement and formation evaluation has been extensively used in different environments. For example, borehole resistivity image logs to acquire real-time formation dips and provide at-bit resistivity measurements to help identify local features that may correlate with the structural dip. However, in many cases, especially for wells drilled close to the flank, carbonate layers are not as "flat" as seen in the seismic sections. Conventional deep-azimuthal resistivity technology was designed and introduced mainly for a clastics environment, where a clear resistivity contrast between shale and sand zones exists. The technology can help in mapping the target sand beyond the well trajectory. This is not the case with carbonate reservoirs, where the contrast is not obvious and the signal saturates due to proximity to anhydrite layers, masking the different reservoir layer boundaries. To overcome this challenge and enable bed boundary mapping tools to focus on a shallow depth of investigation, a new resistivity inversion called multi-component while drilling (MCWD) is introduced. The MCWD inversion technique utilizes the deep-azimuthal resistivity data to map the thickness and boundaries of different resistivity layers focused within the required depth of investigation. Consequently, conventional deep-azimuthal resistivity technology is adapted for proactive geosteering in relatively conductive medium by mapping the high-resistivity layer boundary (anhydrite) and the low-resistivity contrast base layer to maintain the wellbore optimally in the target zone. Results of this new inversion are demonstrated to show the combination of deep-azimuthal resistivity technology along with MCWD inversion to successfully place horizontal laterals within carbonate sublayer. Another added value is the mapped structural features that can help to improve the structure model and assist with real-time geosteering decisions. In addition, qualitative petrophysical evaluation could help to map the water front and the oil/water contact in some cases. The deployment of this technology has helped to improve drastically the Net-to-Gross (N/G) in these challenging environments, and more applications are currently being studied to develop further the use of the real-time azimuthal directional resistivity logging data.