A new logging-while-drilling (LWD) device provides laterolog resistivity logs and borehole images in 6-in. holes drilled with water-based mud. On a single drill collar, the tool combines classical laterolog measurements and azimuthal imaging capabilities. The tool uses two monitored button electrodes and five toroidal antennas to produce focused laterolog resistivity measurements with azimuthal sensitivity. The measurements are made at four different depths of investigation but with similar vertical resolution. In addition, two deeper (non-azimuthal) and a bit resistivity measurements can be acquired by the toroidal array. A parametric inversion combines the data, delivering an estimation of true formation resistivity in invaded formations. A new measurement configuration within the button electrodes provides the downhole mud resistivity, which can be used to detect salinity changes in the borehole and to improve the correction of measurements influenced by salinity. A high-resolution imager, consisting of an array of button electrodes on a removable stabilizer, will provide the high resolution of a wireline imager with the full borehole coverage of an LWD device. A dedicated data-compression algorithm allows real-time transmission of the resistivity images, enabling applications such as well placement and fracture evaluation while drilling. Several field examples illustrate the application of this slim-hole device in horizontal wells for formation evaluation, fracture system characterization, and structural analysis.
Highly deviated wells have become an essential aspect of the energy industry. A successful horizontal well is an extremely valuable asset for any operator. Accurate placement of the borehole within the reservoir, correct evaluation of formation fluids, and identification of features impacting producibility are key elements for success. LWD technology has been used to steer and evaluate deviated wells for several years. Yet, it is only recently that the measurements offered in 6-in. boreholes have become comparable to those available in larger diameters.
