The oil and gas industry is continuously evolving, and expectations to efficiency, safety and environmental awareness continue to increase. In addition, limits are being pushed as rigs are operating in harsher weather conditions.
As such, it is crucial to incorporate better systems that ensure the safety of the crew and the environment, as well as the equipment.
In this blog article we will discuss how an Automatic Disconnect System (ADS) can prevent catastrophic consequences due to drift-off/drive-off in harsh weather on a Dynamically Positioned (DP) operated drilling rig.
Avoiding a catastrophe during drift-off/drive-off
It is crucial that a DP operated drilling rig maintain its position over the well as close to the vertical as possible. The shallower water depth, the more critical the station keeping becomes.
Deviation from the vertical (called drift-off or drive-off) implies that the marine riser which connects the drilling rig to the BOP on the seabed, will be forced off the vertical line and bending forces will be imposed to it.
For each specific drilling location, allowable drift-off/drive-off is calculated based on e.g. water depth, rig specific parameters and weather/environmental criteria. If the drift-off/drive-off exceeds certain predefined limits, safety procedures require that the rig initiates the Emergency Shutdown Disconnect Sequence (EDS).
This operation will i.a. discontinue drilling operations, disconnect the riser and LMRP from the BOP, and secure the well by closing the BOP (in addition the hydrostatic pressure of the mud will act as a barrier to control the well pressure).
Typically, the EDS will involve a number of steps including manual intervention which again initiates automatically initiated operations. In a critical situation which may require EDS to be initiated, it may be challenging to maintain necessary overview, and/or rig crew may not be in position to take required actions manually.
If, for some reason a drift-off/drive-off beyond predefined limits occurs and a controlled disconnect is not invoked as required, consequences are potentially catastrophic.
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Automatic Disconnect System (ADS)
As an extra safety measure to avoid potential unwanted incidents related to drift-off/drive-off while drilling a well, installing an automatic disconnect system is a direct investment on safety system redundancy.
An ADS is designed for water depths up to 1000 meters and is an additional and independent safety system mounted on the lower flex joint above the BOP.
The ADS is a standalone mechanical device which automatically will trigger the EDS system and activate disconnection of the riser/LMRP if the angle measured between the flex joint and the riser exceeds a pre-set angle.
In an emergency situation and if other systems fail, the ADS will automatically trigger the EDS to disconnect the riser/LMRP, secure the well by closing the BOP, avoid damage to the rig, and not at least avoid potentially catastrophic environmental impact.
The ADS has been used for many years on a vast number of rigs and has a proven record of performance.
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Uncontrolled drift-off/drive-off during drilling operations on a floating drilling rig can have catastrophic consequences for personnel, equipment, and the environment.
An ADS represents a modest investment and will introduce an extra safety layer which will automatically invoke the EDS systems and secure the well in an emergency situation.