David S. Epps, Perry A. Harris
The search for new oil and gas resources has increased the drilling of reservoirs that are more difficult to evaluate with conventional well logs. These difficult reservoirs include interbedded sandstone-shale sequences, thin beds, low-resistivity pay sequences, as well as others. The industry has needed methods to improve detection and evaluation of these reservoirs using improved devices that are widely available and well understood, and which exceed the capabilities of existing tools, particularly induction devices.
High Resolution Induction (HRI) is a dual induction device that represents an entirely new approach to coil arrangement and windings, and optimizes vertical and radial responses independently. Both in-phase and quadrature signals are digitized simultaneously to correct for adjacent bed effects. Quadrature measurements improve skin effect corrections for beds with varying conductivities. Symmetrical coil arrays and nearly identical vertical geometric factors for both the High Resolution Deep and Medium tools enhance vertical resolution in thin beds, and eliminate the false invasion profiles common to conventional inductions in thin beds.
A pilot series of High Resolution Induction Tools has been built and a field testing program has been carried out in the United States over the past year. The tools have been tested in wells with varying borehole environments, formation thicknesses, and resistivity ranges.
AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.