Case History from 65 Wells in Deepwater Offshore Project of Eastern India – Tailored & Engineered Cementing Solution for Mitigating Deep-Water Shallow Flow Hazards for Riserless Surface Casing Cementing Job

Abstract The deepwater offshore region of eastern India contains massive hydrocarbon potential beneath water depths that range from several hundred meters to several thousand meters. This region includes some of the most complex offshore wells drilled globally. The operator drilled a total of 65 wells as part of the world's largest deepwater development project, with water depths between 700 and 1200 m. Shallow flow hazards were anticipated, and the challenge intensified because of the close proximity of overpressurized zones to the mudline. A 12 1/4-in. pilot hole and a subsequent 26-in. main hole, located 50 m apart, both encountered severe shallow gas flow. This condition necessitated a resilient zonal isolation barrier to preserve well integrity. Standard solutions, such as optimized slurry designs with fluid loss less than 50 cc/30 minutes and transition time less than 45 minutes, proved insufficient because of the severity of the gas flow. The primary challenge was to drastically minimize slurry transition time, a requirement complicated by low seabed temperature, to establish a dependable seal and maintain well control. Based on hydraulic simulations and the low fracture gradient of the shallow formation, the plan called for cementing the section with a 12-lbm/gal lightweight, high-strength cement slurry. Two lightweight additives (glass beads and cenospheres) were available for the formulation of such slurries. Given the water depth, glass beads were selected to help prevent crushing the lightweight material under downhole pressure. To mitigate shallow flow, a proprietary liquid additive was used in the cement slurry. This additive provided a shorter transition time and effective fluid loss control at temperatures less than 80°F, which supported suitability for the deepwater environment. The slurry transition time decreased to 11 minutes, a result not possible with conventional anti-gas migration additives. The additive maintained compatibility with seawater and other commonly used cementing additives. The cement operation was successfully executed with no operational issues. After the appropriate wait on cement, ball valves on the subsurface wellhead were opened, and no bubbles were observed around the wellhead. The blowout preventer was then lowered, and the well was completed successfully without shallow flow migration issues. The successful use of a lightweight cement solution in a deepwater well in an eastern offshore field of India at water depths near 700 m is discussed. Use of a tailored single additive for this deepwater environment, along with glass beads, mitigated shallow flow risk at low temperature and provided zonal isolation during drilling of the well.