Successful Design, Execution, and Validation of a Tight-Tolerance Production Liner Cement Operation in Deepwater Namibia: A Case History

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Abstract A successful primary cement operation within a narrow pore-fracture pressure window presents a significant challenge in the industry. Equivalent circulating density (ECD) during cement operations can cause losses or gains, which can add significant risk to zonal isolation objectives and increase potential nonproductive time (NPT). Detailed engineering analysis remains critical to tailor an optimal cement design that helps prevent cement slurry loss to the formation, maintains well balance, and ensures a dependable barrier. Cement operations under these conditions require the resolution of several technical challenges. Key tasks include determination of the optimal top of cement (TOC) to isolate target formations, control of high ECDs caused by tight annular clearances within the 11.75-in. liner, and optimization of centralizer placement and fluid properties to achieve effective cement placement along the extended 9 5/8-in. liner. Additional tasks include verification of effective mud removal and execution of torque-and-drag simulations to confirm safe deployment of the liner to the well bottom. Mitigation of ECD sensitivity and reduction of loss risk required a specially tailored, high-pressure, lightweight 14.0-lbm/gal cement slurry design with properties that mitigate risk of fluid influx, combined with a 13.2-lbm/gal new-generation lost circulation material (LCM) spacer to achieve the required TOC. Underreamed bow-spring centralizers enabled optimal centralizer distribution within the tight-tolerance well and ensured efficient cement placement along the extended 9 5/8-in. liner. Advanced modeling using 3D fluid-displacement cement simulation software validated that the selected operational design would meet all objectives, which included zonal isolation and TOC. The cement operation proceeded without losses or wellbore ballooning. TOC estimation from preoperation 3D simulations indicated 4219 m MD. Post-operation cement bond log (CBL) results confirmed a TOC of 4190 m MD, a variance of only 29 m, which demonstrates both successful operation design and precise software prediction. Results validated the effectiveness of the 3D simulation software and indicated potential elimination of post-operation CBLs in similar wells, which could provide a cost-effective and reliable solution for cement placement and zonal isolation verification

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