Abstract: In a well logging sonde having a sonde body and wall engaging pad, the sonde body comprises two conductive sections spaced from one another by an insulating section. The pad and sonde are maintained in a relative longitudinal position such that the focussing effect from the upper sonde section is relatively weak or negligible for current emitted from the lower pad face and relatively strong for current emitted from the upper pad face. The current is returned through the lower sonde section. Additionally, the current electrodes are provided with particular individual characteristics that are defined to optimize the signal-to-noise ratio of the respective measurements. The pad may be provided with voltage electrodes on a lower insulating region of its face to allow for correction of the measurements for the resistivity of the borehole mud. The pad may be provided with additional current electrodes by which the application of the pad to the borehole wall may be monitored.

Abstract: An apparatus is described for urging the measuring pad of a well logging sonde into engagement with the wall of a borehole. A relatively long primary arm on which the pad is mounted includes an actuator, and is pivotally connected to the body of the well logging sonde by a member extending therefrom. A backup arm is pivotally mounted on the extension member and biased outward from the logging sonde by suitable resilient means. The backup arm also is positively connected to a displacement member associated with the actuator. The primary and backup arms are cooperatively withdrawn into the body of the logging sonde by operation of the actuator. Moreover, the logging sonde is made eccentric in the borehole by suitable resilient means connected between the extension member and the sonde body.

Abstract: Methods and apparatuses for electrically investigating a borehole are described. Tool mounted pads are provided, each with a plurality of small measure electrodes from which individually measurable survey currents are injected toward the wall of the borehole. The measure electrodes are arranged in an array in which the measure electrodes are so placed at intervals along at least a circumferential direction (about the borehole axis) as to inject survey currents into the borehole wall segments which overlap with each other to a predetermined extent as the tool is moved along the borehole. The measure electrodes are made small to enable a detailed electrical investigation over a circumferentially contiguous segment of the borehole so as to obtain indications of the stratigraphy of the formation near the borehole wall as well as fractures and their orientations.

Abstract: Method and apparatus are disclosed for investigating lateral characteristics of an earth formation penetrated by a borehole. Substantially identical measurement transducers are mounted in a fixed separation, side-by-side relationship on a pad adapted for sidewall application. As a pad traverses the borehole, measurement signals are produced corresponding to the same formation investigation conducted along two side-by-side paths on the borehole wall. The signals are recorded and provide an indication of lateral changes between the side-by-side paths. By comparing the signals with varying depth displacements, the best likeness and corresponding displacement are determined and provided as an indication of lateral inclination of the formation. The best likeness indicates a lateral formation homogeneity characteristic and the displacement the inclination of the lateral characteristic between the side-by-side paths.

Abstract: A borehole investigating apparatus includes, an elongated support member, a first pair of wall-engaging pad members individually disposed on opposite sides of the support member along a given line and a second pair of wall-engaging pad members individually disposed on opposite sides of the support member along a given line at right angles to the given line for the first pair. The apparatus further includes first and second pad extending means for respectively moving the pad members of the first and second pairs away from the support member and against the borehole wall. The apparatus further includes primary driving means and a force dividing mechanism coupling this primary driving means to the first and second pad extending means for enabling unequal lateral extension of the pad members of the different pairs..Iaddend.