This paper presents a case of study of cementing operations in extended reach drilling (ERD) wells on two artificial islands in UAE. The cementing objectives involved covering and isolating the shallower oil or water-bearing zone, sealing any potential crossflow interval between various reservoirs, and mitigating communication between the 13 3/8-in × 16-in. and 9 5/8-in × 12 ¼-in. annulus. Additionally, the cement will become a secondary barrier planned for the 9 5/8-in. casing to prevent potential exposure of the 13 3/8-in. casing in the event of injection gas percolation. For this case was necessary to design the cement with the necessary mechanical properties to extend the well life expectancy.
To accomplish the operation objectives, the formations, well design complexity, and possible complications were considered. Understanding these factors facilitated the improvement in the approach and design to obtain better cementing operations results. To achieve all of the targets, various enhancements were implemented systematically over time, which included adding fiber in the cement spacer to mechanically enhance mud removal, adding corrosion inhibitor and bactericide to protect the casing if fluid remained in the well. Various lead cement slurries were designed with tailored rheology to remain within the established narrow margin between the pore pressure and fracture gradient. A flexible and expandable tail cement slurry system was implemented to increase the likelihood of proper isolation. The expansion of the tail cement slurry after the cement sets and the tailored mechanical properties used to achieve the necessary resilience, provide support for the stresses encountered during the life of the well. Upgraded properties, such as fluid loss, reduced permeability, and static gel strength (SGS) development, were used to mitigate possible influx between formations. Both cement slurries were loaded with resilient fiber to enhance the cement ductility. These strategies combined with software simulations enabled equivalent circulating density (ECD) management, contamination avoidance, friction pressure hierarchy, discernment of the top of cement (TOC), determination of possible channels, and appropriate stand-off design.
The application of the solutions combined with outstanding consistent field operational performance enabled the following: Fine-tuning various practices, improving isolation across critical zones, achieving the planned TOC, sealing the formations that could create potential future issues, and reducing the probability of interzonal communication or crossflow. A systematic approach was necessary to achieve all the objectives in these challenging wells and determine which practices and technologies provide the appropriate results.
Cementing ERD wells with the challenges previously described is not a standard industry practice. This case study presents the staged application of the enhancements that improved the cementing results. These were inferred by evaluating the operational parameters (density, pumping rate, pressure, volumes, and surface returns) in conjunction with the availability of cement logs (CBL, VDL, ULTRASONIC). The results demonstrated the capability to achieve isolation; Furthermore, the continuous annulus surveillance showed no undesirable sustained casing pressure.