The Permian basin has been one of the main drivers leading the recovery of recent drilling activity on U.S. land. It has been a focus for drilling activity that has targeted conventional reservoirs since the first well was drilled in 1925. Through the depletion of conventional reservoirs, fracture pressure in these zones has decreased due to the reduction in pore pressure. Some of these previously drilled reservoirs throughout the Permian Basin have been selected for the reinjection of produced water which has caused abnormal pore pressures to occur. The combination of having both loss and injection zones exposed in the same drilling interval has resulted in challenges for operators as they have to navigate the resulting mud weight windows of highly developed fields of the Midland and Delaware Basins. As development throughout the Permian basin continues, these mud weight windows will only become more difficult to manage.
In one of Chevron's highly developed Midland Basin fields, managing the exposed injection and loss zones in the intermediate hole section proved to be challenging. This hole section had routinely experienced severe to complete losses upon entering the Upper Spraberry formation as a result of trying to manage higher pressures inflicted by the San Andres formation, a shallower injection zone. The mud weight could not be reduced to mitigate these losses without inducing an influx from the San Andres. Circulation could often not be reestablished upon entering the Spraberry formations which resulted in mud cap or blind drilling in order to reach section total depth (TD). These losses and overall wellbore conditions introduced higher risk and consequences in the form of well control events, wellbore instability, and mechanically or differentially sticking 9-5/8" casing prior to reaching planned set point. The immediate solution to isolate the wellbore problems was to implement a contingency liner, which comes at a premium and decreases drilling and completions efficiencies of the production hole section.
Managed pressure drilling techniques were identified as a solution to simultaneously navigate a shallow injection zone and a deeper loss zone within the same hole section. The necessary equivalent mud weight profile was established through the reduction of MW and the addition of surface back pressure. This enabled a higher equivalent mud weight to be held at the shallow injection zone and a lower equivalent mud weight to be held across the loss zones. Additionally, managed pressure cementing techniques were used to achieve a similar pressure profile during cementing operations in order to increase the likelihood of maintaining returns while placing cement across the loss zones.
Managed pressure drilling and cementing techniques implemented in this field contributed to the elimination of contingency liners and significant non-productive time in hole sections where both injection zones and loss zones were exposed. As laterals are extending beyond 10,000’ across the Permian Basin, the team has collectively proven the concept that the MPD system is part of an equipment package that can eliminate contingency liners and deliver the preferred sizes of production hole and production casing that is crucial to successfully reaching TD and efficiently placing hydraulic fracturing jobs at optimal rates.