Using Particle-Size Distribution Technology for Designing High-Density, High-Performance Cement Slurries in Demanding Frontier Exploration Wells in South Oman

Abstract

Abstract A promising oil source in South Oman is providing challenges to successful cementing operations. The formation is approximately 4200m deep with bottom hole pressure of 13000psi. There is a very narrow margin between the formation pore and fracture pressures. Also salt saturated mud with weights up to 17.5 lbm/gal is routinely required to drill these wells. There has always been a conflict with conventional oilfield cements between optimizing slurry properties for mixing and placement and resulting mechanical properties of set cement necessary for long-term zonal isolation. This conflict is even more evident in high-density environment where achieving slurry which is stable, mixable and pumpable frequently results in sacrificing set cement mechanical properties as compressive strength, permeability and porosity. The challenge has been successfully dealt with in cementing high-pressure wells in South Oman using a technology adapted from the concrete industry. Particle Size Distribution (PSD) optimizes both slurry and set cement properties simultaneously. Extensive lab testing and yard trial prior to field application demonstrated the superior performance of High Density High Performance Slurries (HDHPS) over conventional cements in both the liquid phase and when set. To date eight jobs have been performed and following improvements have been seen. Average waiting on cement time has been reduced by 50% for plugs. Much higher success for plug setting compared to three successful plugs out of the previous seven with conventional slurries. Reduced difference between the planned and actual cement heights for plugs. Well cemented critical production liners shown by Cement Bond Logs. Details of the slurry technology are presented along with data documenting the jobs done to date in South Oman. The system is widely accepted by operator in Oman and is the preferred system for critical high pressure cementing.