A New Logging-While-Drilling Azimuthal Density Sensor for Large Borehole Applications—Gulf of Mexico Case Studies

Abstract

In the current market, operational geology and geoscience asset teams have clear and aggressive financial reduction targets that need to be met without compromising the formation evaluation (FE) requirements of a well construction project. Advances in drilling and completion technologies and practices for deep-water wells commonly require operators to drill larger borehole sizes throughout the well construction process. For deep-water subsalt wellbores, this often implies exiting a thick salt layer with borehole deviation in borehole sizes ranging from 14.5 to 17.5 in. This paper introduces a unique 9.5-in. nominal collar size logging-while-drilling (LWD) density tool that makes it possible to address the FE challenges encountered in large borehole sizes. Any LWD method that can provide crucial cost-effective and accurate FE data can add value to well drilling and logging programs. The new tool provides density and photoelectric measurements in large-diameter boreholes. It also contains an ultrasonic sensor that can provide accurate borehole geometry information, which is useful for identifying stress-related breakout and providing accurate estimates of borehole volume for later placement of cement for zonal isolation. In such settings, formation density measurements are crucial for determining key evaluation parameters, such as porosity and rock mechanical properties, but acquisition of these measurements can be challenging using existing LWD technologies. In addition, real-time structural dip information for subsalt environments provides insight for the interpretation of the geological structure of the field but is often difficult to obtain in large-diameter boreholes. Several case studies demonstrate the value added by the new tool and its breadth of application, as well as the implications for pre-job analysis, bottom-hole assembly (BHA) modeling, data-acquisition procedures, sensor response analysis, and economic benefits to the operator. The capability of acquiring logging data for interpretation purposes and to fulfill specific regulatory requirements without negatively affecting the drilling program provides a desirable cost-management opportunity. The results presented here provide a reference for appropriate business cases to help justify the use of this unique LWD technology in drilling and logging projects involving large-diameter boreholes.