As the drilling industry has pursued more horizontal wells in water-reactive shales, the challenges from wellbore instability and high friction (e.g., stick slip, reduced Rate of Penetration [ROP], stuck pipe, severe doglegs) have led to increasing use of oil-based (OBM) and synthetic (SBM) muds. While costs associated with materials and waste-management for O/SBMs may make them more than twice as expensive as water-based muds (WBM), efforts to develop advanced WBMs that can broadly stabilize shale and lubricate have seen mixed results and limited applicability. To address these challenges, we have developed a novel methodology to control pore pressure transmission and reduce interfacial tension to rapidly and comprehensively deliver shale inhibitors within the near borehole shale pores while simultaneously targeting lubrication to high friction areas.
Leveraging complex nano fluid technology as a chemical platform to convert water imbibition in shale pores into a pro-active tool dramatically reduces capillary pressures and focuses delivery of shale inhibitors within the near borehole shale pores. The combined features of reduced capillary pressure and inhibited clay platelets mitigate elevated pore pressure destabilization of the wellbore. As we have previously described, using polysaccharide-encapsulated oil targets lubrication to points of friction throughout the borehole strong enough to break the encapsulation. Laboratory and field observations indicate that these technologies can be used together to enable drilling with aqueous systems in water-reactive shale.
The use of these two technologies was associated with significant reduction (40 %+) in dynamic linear swell meter testing relative to incumbent aqueous shale stabilization technologies (e.g., KCl polymer) and a 76 – 91% reduction in coefficient of friction. In field testing, the technologies have been associated with keeping a wellbore stable for over 90 days (compared to an average of 12–14 days with KCl Polymer drilling fluid in the same field) and the reduction in drilling torque from 11 – 45 % in highly deviated wells.
Results in the laboratory and field indicate that control of pore pressure transmission, objective inhibitor delivery and encapsulation of lubricant can be used in WBM to drill operationally and economically efficient in water-reactive shale. When employed throughout the build section of a highly deviated well the system can continue to be employed as a drill-in fluid because of its reservoir stimulation features4,6 .