Hole Shape from Ultrasonic Calipers and Density While Drilling – A Tool for Drillers

Abstract

Abstract A number of calipers and hole size indicators (be they by direct measurement or derived) have been introduced with the logging while drilling (LWD) suite of measurements. These include ultrasonic calipers, derived density calipers, and electrical calipers from resistivity tools. Qualitative indications of borehole shape can also be derived from Pe and density measurements which can be affected by tool standoff. The traditional uses of borehole shape measurements have been principally aimed at petrophysicists, reservoir engineers, and geologists for completion strategy, hole volume determination, correction of electrical logs, borehole stability, and borehole size for images. In this paper we summarize additional applications for drillers: To assess the borehole quality related to the drilling process and borehole assembly being used.To diagnose wellbore stability problems while drillingTo identify hole quality which may affect running the completion or wireline tools Hole shape analysis is carried out by processing azimuthal ultrasonic caliper, Pe, and density data into 1D, 2D, or 3D images to illustrate the borehole shape. Processing of images or caliper curve data in real time enables decisions to be made about modification of the BHA or reconsider drilling practice for the remainder of the well. An obvious application of the images is to visualise the severity and nature of any borehole breakout occurring and to take necessary steps to resolve the problem, for example by increasing mud weight. Our results of processing a number of wells highlight that in many cases the shape of the borehole can be directly related to the drilling process. Examples are shown of boreholes drilled by rotary steerable assemblies and mud motors (with different stabilizer configurations and different drilling modes). Timely feedback of this information to the driller allows changes in the style of drilling or BHA to improve the borehole shape and therefore drilling efficiency. This in turn should lead to an improved shaped borehole and better petrophysical data. Understanding the effects of the drilling process can also allow differentiation of drilling induced shape artefacts and geological reasons for borehole shape changes (e.g. zones of instability or breakout). Information on the shape of the borehole also improves the decisions made for completion strategies where mechanical calipers are not being run. Applications include understanding borehole shape for expandable screens and cement volumes.