A cleaning system that effectively displaces movable and immovable mud from the wellbore prior to cementing is key for a successful cementing job and for long term zonal isolation. If in addition, the cleaning system can help in minimizing losses while showing proper compatibilities with mud and cement both, this will provide another assurance for a competent cement sheath in the wellbore. This new spacer system was tailored as per the actual wellbore conditions for Saudi operations.
To analyze the behavior of the new spacer system under different conditions, fluid compatibilities were performed with diverse drilling fluids and cement slurries. The stability of the new spacer was also verified under static and dynamic conditions. Furthermore, this spacer was tested with and without Lost Circulation Material (LCM) through different slot sizes ranging from 500-5000 microns along with a Particle Plugging Apparatus (PPA). This test was used in determining the spacer's capability to plug the slots under different pressure and temperature ranges.
In this study, spacer design was optimized to maintain the rheological and density hierarchy requirement between three fluids - drilling fluid, spacer, and cement slurry. Spacer design was tailored to maintain the above-mentioned hierarchies at both surface and downhole temperatures. It was found that the new spacer system has improved compatibility results with different drilling muds and cement slurry systems even without adding any additional viscosifier agents. The tailored spacer proved its stability under high pressure high temperature (HPHT) conditions using a consistometer with no settling and zero free fluid. In addition, it shows to effectively plug a 500-micron slot disk and was able to seal up to 5000 microns when LCM was added across different pressure ranges (100, 500 and 1000 psi). In addition, field trials for wells encountering dynamic and static losses were performed where spacer with LCM was pumped after considering critical flow path and minimum flow area restrictions. As a result, the new spacer proved to be compatible at multiple densities, demonstrated its ability to bring cement to desired depths, and helped in improving Cement Bond Logs (CBLs).
The application of this engineered spacer system is extremely valuable for the fields having low fracture density formations. Pumping this spacer, will not only help in the effectively cleaning of wellbores prior to receiving the cement but also in forming a seal to reduce any loss circulation issues. This will help in bringing the top of cement (TOC) to the desired depth and ensuring placement of a dependable barrier throughout the life of the well.