In cooperation with the US Minerals Management Service (MMS), the International Association of Drilling Contractor's (IADC) Deepwater Well Control Task Force (OGJ, Mar. 8, 1999, p. 58) has quickly responded to conditions that initiated three accidental drilling riser disconnects.
As a result, guidelines have been formulated that will reduce the risk of such incidents in the future. In the first two cases, the MMS and IADC cited human error as the main cause. The last case, however, involved a software glitch.
Altogether, these actions show the kind of positive response that can occur between industry and the government as drilling operations head into deeper waters.
The ability to close a well in automatically then disconnect the lower marine riser package (LMRP) plays an extremely important role in offshore drilling operations, both for safety and environmental reasons (Fig. 1).
First, this system of hardware and procedures allows the rig to disengage quickly from the riser in the event dynamic positioning is lost. This loss can produce a condition in which the rig drifts or even drives off location with the riser, LMRP, and BOP still attached.
Second, this system provides a means for protecting the integrity of the well during and after the disconnect. Thus, this procedure provides a means to protect the environment by halting the release of drilling fluid or hydrocarbons into the ocean.
The basic steps for a disconnect are:
- Operator initiates disconnect sequence at the BOP system control panel.
- BOP rams shear the casing or drill pipe and close off the wellbore.
- Connector found at the base of the LMRP, positioned above the shear rams, releases and allows the rig to drive off with the riser and LMRP trailing behind.
According to MMS's Notices to Lessees and Operators No. 2000-G07, (http://www.gomr.mms.gov/homepg/regulate/regs/), the first incident, which took place Jan. 19, 2000, involved an employee who "inadvertently pushed the LMRP connector unlatch button instead of the blind-shear ram button on the control panel." Although both were labeled appropriately, each button was colored the same.
Unfortunately, by initiating the LMRP disconnect out of sequence, the pod stabs did not retract and the blind-shear rams did not close. Fortunately, the wellbore was cased, and a well-control event did not occur through a loss of riser hydrostatics. To resolve this issue, all drilling vessels operating in the GOM began installing guards over the LMRP's control switches.
Unfortunately, a second incident occurred on Feb. 28, 2000, when one of the drilling contractors began installing the lock-out devices. During the procedure, the crew member accidentally brushed against the LMRP button and initiated an out-of-sequence disconnect similar to the first event.
But this time the rig was running a liner across an open hydrocarbon-bearing zone. In turn, the release of drilling fluid and loss of riser hydrostatic pressure allowed a short release of hydrocarbons. The drilling crews then immediately closed in the well by setting the liner packer and reinstalling the LMRP.
The third accident, which took place June 28, 2000, began when a control panel light bulb shorted out. The software then read a drop in voltage that in turn initiated the emergency disconnect sequence. The software glitch, which was found on only two drilling vessels after a GOM audit, was modified to prevent a subsequent occurrence.
In response to the accidental disconnects, the Task Force has developed a comprehensive set of revisions to the Deepwater Well Control Guidelines that were submitted to MMS with suggested changes to hardware and procedures (Deepwater Well Control Guidelines, Supplement 2000).
These suggestions, to be reviewed and acted upon by the MMS later this year, focus on two key areas: preventive measures and mitigation options (Tables 1and 2). In summary, the first set of measures focuses on ergonomic means to prevent human error, and the second focuses on technologies that will allow crews to regain control quickly.
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