Achieving Zonal Isolation in Extended Liner Cementing in Abu Tabul Field, Block 60 in Oman

Abstract

Abstract The ability to meet production goals in gas wells relies heavily on achieving effective zonal isolation, which becomes even more difficult when dealing with long-interval cementing operations. This paper discusses key insights and proven approaches from performing long-interval liner cementing in the Abu Butabul field, northern Oman, where operations involved multiple extended liners with perforations situated at the base of a 7-inch liner. Additional challenges arose due to the presence of loss zones in the open hole, which constrained the allowable hydrostatic pressure of the cement column, and presence of gas bearing zone. The approaches outlined in this paper address both slurry design and cement placement methodologies. Extended liners present a significant challenge due to the low fracture gradient, which heightens the risk of formation losses resulting from excessive hydrostatic pressure and high equivalent circulating density (ECD). To mitigate this, software simulation tools were utilized to determine the optimal cement volume required for complete coverage of the target zones. Centralizer placement was optimized using cementing software based on running and drag force analysis to maximize liner standoff, deviating from the conventional practice of omitting centralizers across shale intervals due to stuck-pipe risk. A comprehensive gas risk assessment was also performed to address potential gas migration and temperature sensitivity at the liner hanger, all of which will be discussed in detail in this paper. The subsequent phase focused on optimizing slurry design to achieve appropriate rheological properties and density hierarchies. Extensive preventive slurry testing was conducted, including thickening time adjustments to ensure sufficient time for tool release and liner packer setting, even with increased slurry volumes above the liner top to address potential losses and guarantee adequate zonal coverage. The paper also details measures taken to enhance compressive strength, as well as analyses of gas migration and temperature sensitivity. Extended liners have posed challenges for the operator, particularly when perforations are located just above the shoe of the 7-inch liner. The operator has decided to apply the lessons learned from these operations to future cementing jobs involving similar well profiles in Block 60 of the field.