Delivering Zonal Isolation Assurance in Challenging Long Horizontal Dual Lateral 8- ½-in Hole Reservoir Section–A Case Study in UAE Offshore Field

Abstract

AbstractThe concept of zonal isolation has evolved recently by addressing new industry challenges in identifying dependable barriers throughout the life of a well. In a UAE offshore field, the production section zonal isolation is challenging because of wellbore geometry (long horizontal section) and dual-lateral completion. The cement sheath is exposed to downhole stresses during well construction and the production phases, which compromise well integrity.Adhering to cementing design best practices coupled with the latest technology to enhance mud removal is an important process to achieve a successful cementing job. However, in cases where the cement sheath will be exposed to considerable stresses related to temperature and pressure changes, the selection of cement slurries with adequate mechanical properties will enable the cement sheath to overcome these stresses and maintain zonal isolation during well lifetime. Determining the stress environment between casing/cement/formation vs. cement mechanical properties makes it possible to tailor the cement slurry design to ensure the cement sheath will survive downhole pressure and temperature changes during perforation, stimulation and production operations.Analysis of the offset well data from UAE offshore wells has shown that normal conventional cement systems and previously applied cement job designs have limited success in addressing those challenging complex requirements. Thus, a new approach was required that involved not only the revision of the previously used cement system and spacer, but also revisiting and evaluating every aspect of cementing practices to achieve the desired results. This included increasing the tail slurry density to 16.7 ppg in the horizontal section to overcome equivalent circulating density (ECD) limitations. Fiber-scrabbing spacer technology was introduced to enhance mud displacement and an engineered flexible and expanding cement system was added to achieve and maintain well integrity. The new approach was performed successfully in this case study, and zonal isolation was confirmed by inflow testing. The fiber-scraping approach was used in two wells in the field with excellent results. These successful wells were used to demonstrate the improvements obtained in zonal isolation behind production liners upon implementation of the newly engineered methodology.Numerical analysis modeling was used to simulate the stresses the cement sheath would experience over the well's lifetime and help calculate the cement's minimum required mechanical properties necessary to withstand these stresses. The set cement mechanical properties were then customized using a proprietary trimodal particle-size distribution technology to accommodate the expected downhole stresses. Hydraulic isolation improvement was achieved and confirmed by cementing evaluation logs.