Environmentally Compliant Flexible Cement System Achieves Customer Zonal Isolation Objectives: A Case History from the Norwegian Continental Shelf

Abstract

An operator had a need to cement a 13⅜-in. casing to act as a secondary barrier against a reservoir with the top of cement 100 m above a sand formation. In a subsequent section, the operator required installing and cementing a 9⅝-in. liner as the primary barrier element prior to drilling into the reservoir and placing the top of cement up to the 13 ⅜-in. casing shoe. The operation required placing a minimum 30 m of isolating cement in the cemented interval, where verification of the barrier was to be obtained by using logging tools. To comprehend the operating environment the cement would experience, it was necessary to determine an optimal cement system for the anticipated pressure and temperature cycles in the well. The service company performed a cement integrity evaluation using specialized cement sheath stress analysis software. The simulation software determined which cement system was best suited for exposure to the anticipated pressure and temperature cycles during injection and production. Based on the simulation results, the operator decided to use an environmentally compliant flexible (ECF) cement system. This novel system also significantly reduced the CO2 emissions (CO2e) footprint vs. conventional cement. The operator drilled the 17½-in. open hole to 1888 m measured depth (MD) without any issues using a proprietary flat rheology drilling fluid system. A total of 18.9 m3 of 1.60 specific gravity (SG) ECF cement slurry was pumped. During displacement, no losses were observed as the spacer entered the annulus, and consistent lift pressure was observed as the cement entered the annulus. The job signature pressure match conducted using proprietary zonal isolation software indicated that the openhole size was near gauge hole. The 12¼-in. open hole was drilled, and the 9⅝-in. liner was successfully run to total depth without incident. A total of 16.1 m3 of 1.60 SG ECF cement slurry was pumped. No losses were observed during the cementing operation, and consistent lift pressure was recorded during displacement. The liner was logged using ultrasonic imaging tools, with the top-of-cement bond identified at the 13⅜-in. casing shoe with a total 248 m of isolating cement. The operation achieved the required isolation to install the cemented liner as the primary barrier element prior to drilling into the reservoir, in addition to the exceptional logging results. The ECF cement system provided outstanding bond quality from 1882 to 2130 m. Remarkably, as an energy transition technology when compared with a conventional foamed cement system, the ECF cement system reduced CO2 emissions by 44% and simplified the operation by eliminating the use of foamed cement. Furthermore, the ECF cement is environmentally rated as PLONOR (poses little or no risk) and eliminates the use of polymeric materials to impart flexibility.