Carlos Silva
Halliburton Logging Services, Houston
David Spooner
Halliburton Logging Services, Corpus Christi
ABSTRACT
The intrinsic resistivity (Rt) of a formation in thin, interbedded reservoirs, commonly found along the Texas Gulf Coast, has been a difficult parameter to obtain with conventional induction devices. Since the introduction of an induction tool designed to measure resistivities in beds less than 5 feet thick, this problem has been reduced significantly.
The High Resolution Induction tool is the first deep induction-resistivity device that can resolve formations as thin as 2 feet. The HRI tool incorporates a new coil-array design that optimizes both the vertical and horizontal responses. As a result of this new coil array, both the deep and medium resistivity measurements have identical vertical resolution. The tool has a depth of investigation 40% deeper than the conventional 6FF4 0 induction tool. The HRI tool greatly improves thin-bed definition and significantly reduces shoulder-bed effects. The skin-effect correction is trade in real time by utilizing the quadrature signal, or X-signal, which is measured directly.
In the case study presented, HRI tool response is compared to 6FF40 tool response in the Yegua formation located in Duval County of South Texas. The Yegua formation in this region is typically comprised of thin, sand-shale sequences that conventional induction tools cannot fully resolve. The HRI tool accurately defined these sands and supplied the log analyst with highly reliable data which were used to calculate water saturations that were considerably lower than those determined from the 6FF40 measurements. Production data one year after the well was completed corroborated the interpretation made with HRI data.
Similar comparisons were subsequently made in several wells in the Texas Gulf Coast region. The superiority of the HRI response was clearly demonstrated by these examples.