Operating environment complicates deepwater well test
During a deepwater exploration well test, where the water depth exceeded
1,500 m and currents exceeded 3.5 m/s, an operator encountered challenges
aboard a dynamically positioned rig. With the gas well live and flowing
hydrocarbons during the cleanup phase, the rig experienced an initial partial
power blackout, and later suffered a full power blackout. For a reservoir where
pressures exceeded 6,500 psi, the operator knew it was important to rapidly
control and shut in the well as safely and efficiently as possible as the rig
began to drift.
Subsea test tree enhances safety during critical period
As the rig began to lose power during the initial partial blackout, the
rig’s dynamic positioning (DP) system continued to operate. As a
precaution, the operator decided to close the test valve within the
well’s IRDV dual valve to bleed off pressure. Approximately 15 min later,
power returned, but the IRDV valve was kept closed, and roughly 4 min later,
the rig lost power completely and started to drift.
Following the loss of DP functionality, the second emergency shutdown
system (ESD-2) was activated and the SenTREE 3 test tree with an
electrohydraulic deepwater control system (DWCS) disconnected the landing
string in 11 s. The rig had drifted 150 m off the well center to a riser angle
of more than 5.7° when the LMRP disconnected.
Landing string relatched on first attempt following rapid
In an operating environment with high surface currents it was unknown if
the latch skirt had been damaged due to the angle of disconnection; it was
later determined that the latch skirt had not been damaged. The operator ran
the original tool following a surface inspection and resumed operations after
approximately 5 days of being off the well.
Enabled by local technical support,
the relatch was successful on the first attempt. All samples were collected
before the well was killed and testing resumed seamlessly after having been
suspended, without environmental incident.