Diagraphy tool and survey process for examining geological formations comprises use of individual and paired emitters from emitter array and two receiver assemblies to measure attenuation and phase shift

摘要

A diagraphy tool has an array of emitter coils, first and second arrays of receiver coils, separated from the emitter coils by a first and second distance respectively, and a controller which actively selects the emitter coils from the emitter assembly and which is designed to determine differences between signals received by the two receiver coil arrays. The controller is configured to take measurements at a number of intervals to give a series of results showing phase shifts and attenuation from which can be determined a virtually orientated phase shift and attenuation at any angle from the emitter or receiver coils. A second emitter coil array is placed at the second distance from the first receiver array and the first distance from the second receiver array and the controller can determine the measurements in response to emitter coils selected from the first and second emitter arrays at each point in a series of intervals and combine them. Each receiver array has three receiver coils aligned orthogonally, parallel to the corresponding coil in the other array. The emitter array has two or three emitter coils arranged orthogonally, parallel to the corresponding coil in the receiver arrays. The diagraphy tool has a major axis along which one bobbin from each array is aligned (Tz, R1z, R2z) and the others are perpendicular (Tx, Ty, R1x, R1y, R2x, R2y). The controller activates each emitter bobbin separately to obtain the following ratios: C2xx/C1xx, C2xy/C1xy, C2xz/C1xz, C2yx/C1yx, C2yy/C1yy, C2yz/C1yz, C2zy/C1zy, C2zz/C1zz, where Cjuv designates the electromagnetic coupling between the emitter Tv where v=x, y or z and the receiver Rju where j=1 or 2 and u=x,y or z. The controller also calculates various other ratios.