Achieving Top of Cement; An Engineered Solution for Loss Zone Wells in the Bakken

Abstract

Primary cementing across the Williston basin Mission Canyon formation, a depleted zone with a low fracture gradient, can require alternative cementing techniques to achieve reduced equivalent circulating density (ECD) to minimize losses during cement placement. Achieving top of cement in this zone is challenging, and has historically required some form of remedial cementing. Some solutions have been foamed and two-stage cementing techniques; however, these techniques can be operationally complex. The solution used is a lightweight, high-performance cement slurry. This solution uses an engineered, high-crush-rated hollow sphere particle as a cement extender, thus providing the slurry with reduced density and increased solid volume fraction upon comparison to conventional slurries. This slurry is used in combination with a fiber-based loss circulation material (LCM.) The combination of the increased solids content of the cement and the fiber LCM improves the plugging efficiency across the loss circulation zone. This cementing package allows for cement to be effectively placed across the Mission Canyon loss circulation zone with single-stage cement techniques. Both case study wells sustained losses in the Mission Canyon at approximately 9,500 ft, with target true vertical depths (TVDs) approximately 10,800 ft. The average mud weight used in these wells was 10 ppg, and an aggressive LCM package was used prior to drilling into the Mission Canyon formation. Casing running rate was modified in order to reduce risk of inducing losses. Using the previously discussed design, a low-density, high-performance lead slurry was employed to cover these loss zones. A significant increase in solids content was achieved by extending this slurry with a manufactured, hollow sphere particle. This system gave an overall reduction in ECDs when compared to conventional slurries across the zone of interest. This lightweight, high-performance system was used with a fiber-based LCM package to maintain good circulation throughout cement placement. Critical job parameters were recorded throughout cementing and compared to design ones to support the observation of consistent returns to surface throughout placement. Ultrasonic cement evaluation was used to confirm top of cement post placement. The novel solution, supported by two case studies, shows the successful use of a lightweight, high -performance cement system, along with fiber-based LCM. This cementing package was used to successfully achieve required top of cement during primary cementing across depleted or naturally fractured zones in the Williston basin during a single-stage cement placement.