Innovative Spacer Solution to Control Losses While Cementing in Permeable and Depleted Formations

Drilling and cementing across permeable, naturally fractured, and depleted formations have become some of the most common challenges across the world. A major operator in Offshore Brunei was facing similar challenges across such formations. The primary objective of the cementing job across this difficult formation was to isolate shallow hydrocarbon zones. Achieving desired top of cement (TOC) without inducing losses was the major design challenge. Drilling across such formation generally leads to loss circulation scenarios. This makes subsequent cementing operation more challenging. In order to minimize losses during the cement job, an innovative tailored spacer system was designed and pumped immediately before the cement slurry. This tailored spacer system not only helped in mud removal and wellbore cleaning but also helped to mitigate losses during cementing. Spacer and cement slurry density and rheology was optimized with the help of an advanced hydraulic simulator and industry leading computational fluid dynamics (CFD) software. To check the effectiveness of the spacer system, several laboratory tests were conducted to determine the spacer system's ability to plug a porous medium. Specialized particle suspension analysis was conducted to assure that the spacer design can maintain the fluid system's solid transport stability under both dynamic and shutdown periods. This helped to avoid plugging off restrictions such as critical flow paths in float equipment and the liner hanger. To validate the spacer design, several field jobs were executed for surface, intermediate and production casing scenarios. For each job the spacer design was tailored for the wellbore condition based on the severity of losses. For such jobs, initial purely hydraulic simulations predicted the possibility of losses. No losses or substantially reduced losses were noted for the cement jobs where this tailored spacer system was used. These results validated that the tailored spacer helped to mitigate the loss potential from the hydrostatic pressure. Top of cement was also validated based on fluids returns to surface and final displacement pressure. The first cement job using this innovative spacer system was executed for a 13-3/8inch surface casing job in Q3-2020. 100 bbls of an 11 ppg spacer was pumped across a permeable formation ahead of the cement slurry. Cement returns were observed at surface. Since the first job, 14 cement jobs using this innovative spacer system have been successfully executed in offshore Brunei for various casing sizes.