Delivering a competent cement seal to provide wellbore zonal isolation for maximizing production is highly dependent on mud removal, which remains the perennial challenge. Non-aqueous mud is preferred during drilling to avoid formation swelling and for HTHP wells, but it is highly incompatible with aqueous-based cement fluid. More challenging, non-aqueous mud is customarily recycled and reused in multiple wells, contaminating it heavily and making it difficult to clean by many conventional spacers.
This paper presents a full-scale laboratory development to a successful field application of an unconventional spacer with a novel micromaterial that enhances mud removal and provides exceptional fluid stability (flat viscosity), important for long horizontals. Due to its differentiating chemistry combined with uniquely engineered physical properties (minimally abrasive yet non-damaging to equipment), the new micromaterial allows more efficient scouring of strongly adhered mud from casing/formation surfaces, which many traditional spacers have difficulty removing efficiently.
To demonstrate efficient mud removal, numerous standard rotor cleaning tests were performed with different muds from across North America. Free water and HPHT dynamic settling tests were used to evaluate thermal stability of the spacer. Wettability and API compatibility tests were completed. XRD and SEM analyses were used to characterize and understand the unique properties of the novel micromaterials that contribute to enhanced mud cleaning. First field application was successfully completed in the Permian Basin. Field trial has proven the new spacer (11.3 ppg design with 134 bbl total volume) to be highly stable when pumping down (5 bbl/min) into a wellbore of over 20,000 ft (6096 m) depth with ~12,000 ft (~3658 m) horizontal and 139°F (59°C) BHCT. Most of the oil-based mud used during drilling was recovered.