Copyright 2005 IPTC
Presented at the International Petroleum Technology Conference held in Doha, Qatar, 21-23 November 2005.

The increasing demand to drill wells having narrow pore pressure and fracture gradient margins and the increasing concern that irreparable damage from extreme overbalanced drilling negatively impacts productivity and recoverable reserves, requires a new method of controlling bottomhole pressure while drilling, beyond the current capability of conventional drilling techniques. Where the dynamic pressure or equivalent circulating density can be supported, a solution has been developed to drill with a relatively constant bottomhole pressure equal to the dynamic conditions rather than static conditions, thereby reducing the maximum bottomhole pressure. The method also establishes a continuous method of well control that should reduce the risk of taking a kick.

Shell International Exploration & Production Research & Development has developed a robust solution using a flow model running in real time coupled to an automated choke control system to continuously maintain the bottomhole pressure at a relatively constant value. Several applications of this method have been implemented or proposed, including fractured reservoirs where it is difficult to control losses, HPHT wells subject to ballooning and wells with narrow pore pressure and fracture gradients margins subject to kicks and losses. Underbalanced drilling is another application where increased control of bottomhole pressure to limit inflow and decrease the potential for borehole instability can be realized. The development, testing, application and results of this automated system will be presented.