Abstract
Synthetic oil and oil-based mud (SBM and OBM) have been used extensively to drill problematic and producing formations due to their robust performance and thermal stability. The high cost and the growing environmental concerns of SBM and OBM drove the industry towards more adoption of water-based mud systems (WBM). However, using conventional WBM to drill problematic formations, such as shale formations, is still challenging. Long laterals are required to maximize production and reduce drilling costs. Borehole instability, higher torque and drag, and a lower rate of penetration are encountered when drilling with WBMs, affecting drilling time and cost. This study evaluates new high-performance polymer additives developed to help drill challenging formations, where salinity and temperature limit the use of natural polymers and conventional partially hydrolyzed polyacrylamide (PHPA) products.
The mud systems were formulated in the laboratory with various densities (8.5 ppg to 16 ppg) to account for the flexibility of drilling envelopes. The systems comprise saturated brines with newly designed polymeric additives called HPPs to improve drilling fluid performance, particularly suspension, stability, rheological, and filtration properties. The developed polymers were evaluated by measuring rheological and suspension properties, thermal stability, fluid loss, shear degradation, and clay inhibition. The new polymers were challenged by increasing the testing temperature up to 350°F, and thermal stability was evaluated for extended drilling time.
The HPPs showed excellent thermal stability at up to 350°F for 5 days, low fluid losses (7 ml to 14 mL), good suspension properties (LSYP = 8-12 & VSST < 1.0), and high shear resistance and salt tolerance. Low shale dispersion rates were observed with reactive clay samples for extended drilling time (16 hrs). More than 95% of clay cuttings were recovered with the introduced mud systems, while less than 1% was recovered with fresh water.
The excellent performance observed with these polymers in terms of rheology, suspension, thermal stability, fluid loss control, shear resistance, and salt tolerance make them excellent viscosifier that can be suitable for various drilling and completion applications, especially for challenging downhole conditions.
