Backflow from the drill pipe is a normal occurrence when a connection is broken at the rig floor. Backflow can result from the density differential of warm (low density) surface water pumped down the pipe against cold (denser) water in the ocean, air that has been trapped during connections and pumped down the pipe, dense cuttings or mud in the annulus flowing back (“U-tubing”) to equalize hydrostatic pressure, and so on.

Backflow into the pipe is usually reduced by the closure of the downhole float valve but also occurs while retrieving core barrels and through the bit nozzles. Hydrocarbons, hot acidic fluids, H2S, and/or cuttings and debris from the hole may backflow into the pipe and plug the pipe or bit nozzles or jam the downhole float valve open. Backflow will usually gradually decrease within a short time as the pressure differential is equalized.

Minor Flow:
A relatively minor or weak flow of gas or liquid hydrocarbons could seep into the hole from a formation that has been penetrated and go completely undetected for the duration of drilling operations in deep water. A minor flow could manifest itself in unstable hole conditions and “packing off” around the drill string. If a flow is suspected, the PDR could be used to look for suspicious plumes in the water column. it might be possible to run the VIT televiewer to look for gas bubbles or liquids escaping from the hole, which might be detectable as white hotspots on the Mesotech sonar. An attempt should be made to kill such a suspected flow if it appears to be a safe operation.

Major Flow:
In the event that a hydrocarbon flow is detected, coring or drilling operations will be terminated immediately. The Operations Manager, Transocean OIM, Staff Scientist, and Master, in dialog with the Co-Chief Scientists, should review the situation and agree on a plan of action. ODP is a self-regulating program with a long history of pollution-free scientific ocean drilling and is committed to maintaining an environmentally sound, pollution-free operation. However, if the Operations Manager, Transocean OIM, or Master feel that a kill attempt is too risky to the ship or personnel, the bit should be pulled above the seafloor and the ship should be moved off location upwind in dynamic positioning (DP) mode before the remainder of the drill string is recovered. On the positive side, environmental damage from shallow gas blowouts is usually limited because the soft sediments in shallow holes tend to collapse and kill the flow after a relatively short time.