The Sprayberry field, situated in Midland County, Texas, is notorious for formations vulnerable to fluid losses. When drilling in the horizontal section of the Joe Mills formation, operators commonly contend with total drilling fluid losses and open-hole instability. Drilling a shallow depth intermediate casing string can expose pressure-depleted formations in the vertical section of the wellbore. This routinely leads to drilling fluid losses, wellbore instability, and challenges in running the production casing to total depth (TD).
An intermediate casing string was set at a relatively shallow depth of approximately 6,400 feet, which exposed the pressure-depleted formations situated above the kick-off point (KOP) and the curve of the horizontal well. This operation presented a tight window for the drilling fluid density, which ranged from 8.9 to 9.1 ppg. The operator utilized a brine drilling fluid system. Throughout the drilling process, there were significant fluid losses, raising serious concerns about wellbore stability.
In response to the drilling challenges, several measures were adopted. Star Shield® wellbore shielding® technology was consistently maintained at a specific concentration in the brine fluid system. If any losses were detected during the process, sweeps of both Star Shield and Star Shield 3000 were promptly utilized. Additionally, the viscosity of the brine drilling fluid system was tailored to remain around 30 cP. Despite challenges such as fluid losses, poor rate of penetration (ROP), and a bit trip beyond the curve section, the operator was able to reach TD and run production casing. By pre-treating the brine drilling fluid system with 5 ppb of Star Shield, and by adding a similar concentration of Star Shield 3000 to manage severe drilling fluid losses, the operator mitigated losses, maintained wellbore stability, and achieved total drilling depth. This plan improved the ROP from around 60 feet per hour to approximately 110 feet per hour. The operator further addressed fluid losses of around 60 BPH using Star Shield and Star Shield 3000 sweeps, which paved the way to drilling to planned depth.
By maintaining an effective concentration of Star Shield and supplemented with Star Shield 3000 in the 9.0 ppg brine drilling fluid system, the operator successfully reached total depth in the horizontal Joe Mills formation with improved wellbore stability and without a significant lost circulation event. The operator successfully ran production casing to bottom and cemented with full returns.