Ultra-Deep electromagnetic (EM) azimuthal measurements provide critical data for well placement operations, allowing real-time assessment of resistivity boundaries over 100ft from the well. Historically, 1D and 2D inversions displayed vertical boundary changes, however they do not resolve azimuthal changes. Other 3D approaches lacked real-time aspect or endured costly deployment. This paper describes integration of real-time 3D EM Inversions for both inclination and azimuth trajectory corrections, to optimize well path and increase efficiency while drilling HA/HZ wells.
Triaxial ultra-deep electromagnetic borehole logging tools provide 9 component multi-frequency data from multiple receiver assemblies, logging the 3D EM field around the wellbore. Although the raw component data shows observable signal changes representing the 3D EM field, evaluating this raw data in real-time is challenging. Therefore, a 3D EM inversion was implemented to provide real-time 3D representation of the geological structure and fluid distribution around the well. The 3D EM Inversion algorithm has been optimized to return model updates within a few minutes. The near real-time process allows well placement decisions to be made very quickly to help maintain the well path within the target reservoir.
Real-time monitoring of the 3D EM inversion revealed a lateral disparity in the resistivity distribution for the target reservoir. In a particular interval, the presence of higher resistivity to the right-hand side of the well bore was revealed. The increase in resistivity was identified as improved reservoir properties. The trajectory of the well was adjusted to the right, interactively adjusting the plan. As with all deviations from the plan the impact of the azimuthal turn was assessed both in terms of safety and the potential impact on running the completion, no risks were identified, and a successful turn was conducted. Using the same methodology, a turn to the left of the well bore was conducted towards the toe of the well. Optimizing a wells TVD with inclination is common, but azimuthal changes based on LWD readings are much less so.
The 3D Inversion and azimuthal resistivity measurements helped to minimize the loss of the effective length of the wellbore during the drilling in a complex geological structure. The effectiveness of the azimuthal turn can be assessed by comparing the resistivity of the actual and planned trajectories, estimated to have a 24-foot separation. The actual trajectory was placed in a zone with optimum quality reservoir without loss of the effective length (100% NTG).
Real-time 3D Inversion has enabled for the first time the ability to steer azimuthally based on Ultra-deep EM data, changing the hole azimuth in real-time to target improved reservoir properties. The method of correcting the well path with azimuth as well as inclination in real-time based on 3D Inversion data ensures maximum efficiency for the well placement process in complex geology which can show vertical and azimuthal variations in resistivity.
The depths of detection possible with Ultra-Deep EM tools allows these decisions to be made early reducing tortuosity of the well path while revealing the position of resistivity boundaries in all directions.
