Following the Gulf of Mexico Deepwater drilling moratorium in 2010, the industry focus towards well integrity assurance has significantly increased. Several new and updated regulations and best practices have been published in the last two years, including API Standard 65 – Part 2 and API RP 96. These two industry accepted standards highlighted that determining the hole volume to confirm the cement slurry volume, to fill-up the annulus to the designed top of cement, is one of the many factors impacting cement placement success during well construction process.

A new solution for riserless section was developed based on existing Logging While Drilling (LWD) electromagnetic propagation resistivity measurements, which meets the requirement to understand hole volume drilled with water based mud in deepwater environment.

Historically, deriving an accurate caliper from LWD electromagnetic propagation resistivity measurements has never been easy due to big uncertainty of mud resistivity (Li et al, 2003). The implementation of a novel simultaneous inversion model and forward modeling database from standard 2-Mhz propagation resistivity, for water-based mud (WBM) and large boreholes, provided the solution to overcome that uncertainty (Whyte et al, 2012).

This novel solution was specifically developed to address the needs for the riserless top-hole sections of high cost deepwater wells: from cement volume calculations, identification of borehole degradation through time, and new opportunities for identification of shallow water flows using the full capacity from the inversion process.

The extensive validation of this innovative approach with wireline mechanical calipers in numerous hole sections resulted in far better results than initially anticipated (Whyte et al, 2012). The information obtained provided significant insights into the reliability and limitations of the current algorithm. The ability to monitor the borehole size while drilling, as well as analyzing the reaming and trip out passes from recorded data, makes this measurement a valuable source of time-lapse information. The next validation process consisted in the comparison between cement volumes computed using these measurements against identification of cement returns during riserless cementing operations in deepwater wells.

The LWD caliper derived from propagation resistivity measurement was analyzed in more than a dozen of wells in Gulf of Mexico. Specific case studies covering the drilling and cementing operations are presented in this paper.