Azimuthal Geosteering: New Opportunities Revealed by Advances in Ultra-Deep Resistivity Technologies

Abstract

Ultra-deep electromagnetic (EM) technology has been used for over a decade for well placement operations. As the measurement primarily responds to resistivity variations around the wellbore, it has been used to map lithological boundaries and fluids enabling geosteering the well path in real time to the desired formations. Traditionally a multi-layer 1D geological model is constructed by inversion algorithms utilizing five measurement components of the EM signal. Recent advances in tool designs and computational capabilities enabled the utilization of the full nine EM measurement components to construct a full 3D model around the wellbore, hence enabling new opportunities in reservoir visualization, well placement decisions and fluid mapping in real time. This paper presents some real-life opportunities of azimuthal geosteering revealed by the ultra-deep resistivity 3D inversion. Advancements in logging-while-drilling (LWD) tool designs including tilted EM transmitter and receiver antennas enabled the acquisition of all nine components of the EM field around an EM tool. Advanced algorithms and real-time transmission systems have been introduced allowing the visualization of the 3D resistivity volume around the wellbore in real time, providing insight into formation and fluid changes in all directions. Well placement decisions can now target optimal zones as defined by their resistivity in any direction around the wellbore and not only in the vertical plane as defined by 1D inversions. New operational workflows including intensive pre-well planning and collision avoidance monitoring have also been enhanced, accounting for any additional risks that could result from real-time azimuthal well path adjustments. Ultra-deep resistivity 3D inversion was successfully used on several geosteering wells crossing multiple formations. Advanced computational methods were utilized in real time, which enabled several real time decisions to be made. The visualization of the resistivity volume around the wellbore revealed variations in all directions around the wellbore, uncovering more complex structures of the subsurface geology. New opportunities were enabled to include "turning" instructions into well placement decisions to maximize reservoir contact and improve petrophysical properties of the drilled interval. In addition, enhanced operational workflows ensured drilling and well collision risks were avoided. This paper presents an integrated approach to utilize a newly developed 3D ultra-deep resistivity inversion technique to adjust well paths in all directions placing wells in the best reservoir properties.