Applications of the Continuous Dipmeter in Western Canada

This paper discusses the application of the continuous dip meter, an instrument which not only determines dips and tops of formations but alsoyields basic information on sedimentology and stratigraphy. After a brief description of the apparatus and the methods of plotting its readings, theauthor explains the interpretation of information for various geologic features- reefs, sands and unconformities. All of the examples are from oil wells in Western Canada, and the influence of the continuous dipmeter on petroleum exploration is stressed. Introduction It is a basic physical fact that oil tends to migrate to a position abovewater, and that gas tends to migrate above both oil and water. It seems, therefore, that nothing is more fundamental in oil exploration than determining which way is up. Essentially, this is the purpose of the continuous dipmeter. However, interspersed with the basic information as to which way is up is awealth of other information related to deposition. So the dipmeter becomes, inaddition, a basic tool for studies of sedimentology and stratigraphy. The down hole equipment of the continuous dipmeter, illustrated in Figure1, features three identical sets of electrodes mounted on spring-actuated wall-contact arms. The arms are spaced 120 degrees from each other. The electrodes lie in a common plane perpendicular to the axis of the tool. As this system of electrodes passes a bed boundary, similar resistivity signals fromeach electrode are sent to the surface and recorded on film. If an anomaly onthe curves is caused by a bedding plane crossing the borehole at other than a 90-degree angle, the anomalies on the individual curves occur at slightly different depths. Figure 2 illustrates the behaviour of the three curvesat a steeply dipping bedding plane. The relative displacements of the three curves, in inches of borehole, arecombined with hole caliper and hole deviation data to compute the amount and direction of formation dip. This process is performed for many correlatable anomalies on the three resistivity curves.