The construction of petroleum wells is becoming more and more complex and challenger. Drilling and completion in deep and ultra deep water requires use of dynamic positioning rigs increasingly sophisticated. Despite all the technology, an emergency disconnection may occurs at any time in dynamic positioning drilling rigs, sometimes in a surprising and unexpected way, be by human error, adverse environmental conditions or blackouts. The selection of proper EDS (Emergency Disconnections Sequence), followed by well thought operational decisions, is primordial to reduce the potential damage caused by disconnections. Unfortunately, the needed EDS is not always available at moderns rigs.
Emergency disconnection guidelines were established for various drilling and completion operations, to be studied and discussed previously activities with BOP / Xtmas Tree connected to the wellhead. Additionally, this work suggests new EDS options for different operations and BOP configurations (number/type of shear rams available).
Operational safety and minimization of damage are the focus of this work. It will be presented some informations on emergency disconnections occurred over 30 years of operations in Brazil DP rigs, obtained through information gathered in one of the largest databases of DP incidents worldwide.
Zero emergency disconnection is the goal of all DP rig, but it is something that is still far from achieving. Reduce losses, putting the well in safe condition facing the possibility of disconnection, avoiding environmental tragedies as happened in Macondo well is the prime directive of any oil company. The incorporation of new configurations of EDS by manufacturers of BOP and the use of guidelines for emergency disconnection certainly contribute to create situations where emergency disconnection can be executed with more confidence.
Over the last two decades drilling and completion from DP rigs has become common practice in Brazil, especially with the growing activity in ultra deep water. In order to guarantee safety, it has been necessary to put more and more focus on the ability to perform safe disconnection independent of the operation occurring in the well.
Loss of position without safe disconnection could result in critical damage to the well barrier as well as to exposed subsea equipment. The ultimate consequence could be a well blowout and/or severe damage to subsea production systems like production templates resulting in risk to personnel, environmental damage, financial loss and harm to the reputation of the company .
In general terms, an unsuccessful emergency disconnection can result in:
Abrupt discontinuation of operations in progress, with high possibility of serious operational problems in the well (stuck pipe, fishing, kick, etc).
Underground blowout or subsea blowout in the case of wells without riser safety margin and as a result of not closing properly the BOP, Xmas Tree or other equipment.
Total loss of the well.
Break and falling of drilling and completion risers on the well, flowlines, manifolds or other Xmas Tree.
Severe injury or damage.