This generic case history reviews how a common unplanned event during platform drilling escalated to a seabed gas broach and how a novel relief well intervention was utilized to safeguard the production platform. Fortunately the broach stopped after a few hours when the open hole collapsed around the drillpipe. The broach did not ignite and there was no apparent major surface or structural damage to the rig or platform. The blowout well was subsequently plugged and a replacement/pressure relief well was completed and the platform put back on production.
While attempting to bring an adjacent well on stream, however, it was discovered the tubing and all protective casing strings were open to the sea below the conductor and above the SSSV (flow-cut by the original broach). This situation left the well with a single well control barrier and no practical way to intervene. Leaving the problem well in the current state was unacceptable and surface intervention was considered too high a risk due to the unknown status of the problem well tubulars.
Specialists were contracted to evaluate the possibility of safeguarding the platform using relief well technology. The strategy utilized was to drill an intervention well from an adjacent platform and intersect the problem well at its production casing string both above and below the producing reservoir. After intersection was confirmed, a liner was set in the intervention well. With this accomplished, the upper and lower intersection zone were perforated through both strings using oriented perforating guns. A retainer was set just above the lower intersection and cement was circulated down the relief well drillstring, through the retainer, up the problem well’s production casing/tubing and back into the relief well’s annulus. With the intervention completed, the well was turned into a producer replacing the problem well.
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