Underbalanced Drilling

Sand control screens deployed during underbalanced conditions

An innovative inflatable bridge plug system has overcome the challenges of deploying screens in an underbalanced environment

George Arnold and Enrico Suwandi, Baker Oil Tools 

Underbalanced drilling (UBD) is now routine in fields with low bottomhole pressures (BHPs), or formations where skin damage may occur due to overbalanced drilling. UBD advantages are offset, however, by more challenging on-site operations brought by continuous pressure at the wellhead. 

One requirement is that all tool strings be lubricated into the well before commencing operations. Because the required screen length typically exceeds the lubricating device's length, sand control screens cannot be installed in an underbalanced condition. The option to kill the well before deploying the screens subjects the formation to damaging overbalanced conditions. This dilemma has been resolved with the development of an inflatable deployment system. The new system was used successfully on a recent UBD project in Brunei.