On January 28, 1969, well A-21, the 5th well to be drilled from Union Oil Company’s “A” platform began flowing uncontrollably through fractures into the Santa Barbara Channel.
The absence of any well casing to protect the permeable, fractured cap rock meant that the operator couldn’t safely shut-in a sudden influx of hydrocarbons into the well bore (i.e. a “kick”). Shutting-in the well at the surface would create well bore fractures through which oil and gas could migrate to shallow strata and the sea floor. The probability of an oil blowout was thus essentially the same as the probability of a kick (>10-2). Compare this with the historical US offshore oil blowout probability (<10-4) and the probability of <10-5 for wells with optimal barrier management.
Here, in brief, is the well A-21 story:
- Well drilled to total depth of 3203′ below the ocean floor (BOF).
- 13 3/8″ casing had been set at 238′ BOF. The well was unprotected from the base of this casing string to total depth.
- Evidence of natural seeps near the site suggested the presence of fracture channels
- The well was drilled through permeable cap rock and a small high pressured gas reservoir before penetrating the target oil sands.
- When the well reached total depth, the crew started pulling drill pipe out of hole to in preparation for well logging.
- The first 5 stands of drill pipe pulled tight; the next 3 pulled free suggesting the swabbing of fluids into the well bore..
- The well started flowing through the drill pipe. The crew attempted to stab an inside preventer into the drill pipe, but the well was blowing too hard. The crew then attempted unsuccessfully to stab the kelly into the drill pipe and halt the flow.
- The crew dropped the drill pipe into the well bore and closed the blind ram to shut-in the well.
- Boils of gas began to appear on the water surface. Oil flowed to the surface through numerous fracture channels. The sketch below by a former colleague depicts the fracturing, which greatly complicated mitigation of the flow.
Here is the link to an excellent US Geological Survey report from 1969 that describes the geologic setting, well activities, and remedial measures after the blowout.
We need to continue studying these historically important incidents, not just the technical details but also the human and organizational factors that allowed such safety and environmental disasters to occur. The idea is not to shame, but to remember and better understand.
Bud's Offshore Energy (BOE) 