A new logging-while-drilling (LWD technology has been developed and field-tested that introduces directional electromagnetic (EM measurements through the use of tilted and transverse current-loop antennae. The multispacing and multifrequency directional measurements allow monitoring the distance to formation boundaries and orientation of boundaries to facilitate proactive well placement. Also, in combination with conventional LWD resistivity, these directional EM measurements allow accurate structure and formation resistivity interpretation around the wellbore, independent of mud type. Specific antenna combinations furthermore provide the capability to detect and characterize resistivity anisotropy in near-vertical wells while drilling.
A new directional EM tool based on the technology is designed with a symmetric transmitter-receiver configuration that allows optimization of the sensitivity to the desired formation parameters. Adding the symmetrical directional measurements together maximizes sensitivity to bed boundaries while canceling the influence of anisotropy and formation dip, which is optimal for geosteering. Subtracting the measurements allows anisotropy to be determined while boundary effects are minimized. The antennae are mounted on a conductive collar, which significantly reduces the large borehole effects that are normally associated with transverse EM measurements in conductive mud. Besides exploring the physics of the new directional propagation measurements, we will demonstrate their applications with field test examples. By detecting and tracking in real time formation boundaries of up to 15 ft around the wellbore, the directional propagation tool allows sufficient time to make trajectory adjustments and stay in the reservoir. The bedding orientation information also answers the question, in which direction to steer, which is often ambiguous with traditional propagation measurements. Particularly interesting applications are the placement of wells in thin oil rims and in reservoirs with complex, irregular injection structures.
Field test examples will also be shown of the drastically enhanced formation evaluation capabilities offered by directional measurements in high-angle and horizontal wells, where formation resistivities can now be determined while accurately accounting for proximate bed boundaries. The ability to measure resistivity anisotropy in near-vertical wells will be demonstrated by a field test example in which the anisotropy measurement was confirmed by comparing it with a conventional propagation resistivity measurement run in a nearby high-angle well.
