4D Radar Imaging of Wellbore Geometry While Drilling

Abstract

Despite advances in Measurement-While-Drilling / Logging-While-Drilling (MWD/LWD) technologies, the oil & gas industry has until recently lacked viable technologies and tools to measure wellbore geometry in large hole sizes (>12-1/4″) while drilling and subsequently the ability to visualize and describe the borehole shape and size in an intuitive way. A direct mechanical measurement solution such as used on wireline, e.g., multi-finger tools, is not feasible to implement on MWD/LWD tools due to the nature of the drilling operation. Conventional technologies and methods, including acoustic- and density-based measurement methods have been used with reasonable results in smaller hole sizes (≤12-1/4″) when combined with low mud weights. However, many commercially available tools within the industry have low vertical and azimuthal resolution due to sparse sampling or sparse storing in its internal downhole memory of such caliper measurements, resulting in limited use of such data for borehole shape and size purposes. Such conventional technologies and methods have not been, or very seldom used in large hole sizes, primarily due to lack of available technologies and tools, resulting from challenges related to the sensor to wellbore interface standoff distance. A novel Logging-While-Drilling Caliper tool based on impulse radar technology has been developed to overcome the challenges related to mud weight, sensor to wellbore standoff in oil-based muds and at the same time addressing challenges related to sparse datasets. This tool enables the oil and gas industry to accurately image borehole shape and size with both high vertical and azimuthal resolution, including within large hole sizes where there has not been any viable solution whilst drilling. The high sampling rate together with a large downhole memory (128 GB) allows the industry to evaluate the borehole shape and size as a function of time (timelapse). An Impulse Radar Caliper tool has been pilot tested in several wells on the Norwegian Continental Shelf (NCS), in borehole sections ranging from 12-1/4″ to 17-1/2″. During the pilot testing, the Impulse Radar Caliper tool acquired wellbore shape and size measurements while drilling, and some intervals while pulling out of hole. Several wellbore features, not previously imaged in such large hole sizes, have been identified and their time-dependent development studied in detail. The results from this pilot campaign are discussed in this paper together with the 3D/4D tunnel-view visualization used to assess the processed caliper measurements.