Abstract
Over 30 years ago Poupon proposed using several simple induction arrays, each measured separately, and combining them to produce an induction log with improved characteristics. The response of each simple array becomes a "basis function" that can be combined with the others without introducing unwanted interactions. This approach has been used in the Array Induction Imager Tool (AIT*). The AIT tool consists of eight three-coil arrays, six of which are operated simultaneously at two frequencies.
By treating the response of each measurement as a basis function, an optimization technique has been developed to combine all the raw measurements into logs with vertical, radial, and two-dimensional (2-D) response properties that are not achievable with conventional fixed-focus induction arrays. Using this approach, a set of logs has been developed with a 90% vertical resolution width of 1 ft and a reasonable rejection of borehole rugosity effects. Additional log sets are available that have different resolution-cave effect tradeoffs. A log set with a vertical resolution of 2 ft has less cave effect than conventional induction logs with 8-ft resolution, and a 4-ft resolution set has virtually no cave effect. The effectiveness of this response shaping technique has been demonstrated in case studies with both computed and field logs over a wide range of environmental conditions.
