Title : Enhancing cement sheath quality via high efficiency oil based mud removal using advanced spacer systems
Abstract:
They key components of an OBM spacer – surfactant and mutual solvents – have been used for a long time to facilitate mud removal. However, these spacers are not always capable of removing OBM films on the formation and casing. The spacer system under review, was specifically formulated to overcome the challenges of oil-based mud (OBM) removal by implementing tailored “scouring” and “scrubbing” additives to provide enhanced OBM removal. It was designed to physically disrupt OBM films and increase the likelihood of restoring water-wet surfaces, thereby enhancing cement bonding to both casing and formation. The system was subjected to a series of targeted laboratory tests, including mud removal trials, wettability assessments, and mud-cement compatibility evaluations under simulated downhole conditions, before deployment to field. The scouring effect effectively disrupted gelled OBM, while the powerful surfactant reduced interfacial tension and restored water-wet conditions on both casing and formation surfaces.
The study presents the design process, field execution and results of the advanced spacer system on different well conditions and casing/liner sizes. Cement evaluation results demonstrated that the advanced spacer system significantly improved oil-based mud (OBM) removal compared to conventional spacers. These improvements led to notably enhanced cement bond strength, as verified through modified rotor tests to determine the mud removal efficiency in the laboratory and post-cement operation ultrasonic cement evaluation. Field trials confirmed the laboratory findings, showing improved cement bonding and zonal isolation on cement bond logs compared to offset wells. The spacer system is adjustable across a wide range of densities, supporting flexible application in various well conditions. Overall, the system enhances cement sheath integrity, reduces the likelihood of gas migration and remedial squeeze jobs, and supports long-term well performance in OBM-drilled sections. The application of this advanced spacer system represents a significant development in ensuring long-term zonal isolation in wells drilled with OBM by improving cement sheath quality and wellbore integrity.
Key Words: Zonal Isolation, Cement Placement, Scrubbing spacer, OBM removal, mud filter cake, cementing, spacer.
