Bud's Offshore Energy (BOE)

There is a small cadre of experienced oil and gas professionals who have been following the Montara transcripts religiously, and I have received a number of email messages about the testimony.  Pasted below is a message from Tom Maunder, a well engineer working in Alaska.   Tom has extensive industry and regulatory experience, and actually lived on the Alexander Kielland while working offshore Norway.

I have highlighted a couple of Tom’s observations in bold.  Like the Montara Commission, I had largely dismissed the possibility that a seismic event was a contributing factor to the blowout.  Also, I don’t think the Commission has sufficiently considered the effect of the horizontal well section on the delayed gas migration and flow following the removal of the corrosion cap.

Based on the statements regarding GOC and OWC, it appears that the reservoir is saturated and stratified with a gas cap over oil over water as would be expected.  What went unstated is that at reservoir conditions, the oil contains some amount of solution gas. Based on the testimony, it seems clear that any cement inside the bottom of the casing was contaminated with sea water and likely oil based on where the shoe was set.  Some amount of seal probably was established by holding pressure to allow the cement to set.  Although the plugs were bumped, the float failure and subsequent “check” allowed cement and oil to be let into the casing and that also resulted in lifting at least the top plug some distance up into the casing.  It is possible that this lifting reversed the fins essentially making the top plug worthless as a separating device for the cement and sea water displacement fluid.  This would seem to be supported since the testimony indicates that it was not possible to rebump the plug.  There is much discussion regarding the pore pressure and displacement weights or EMW.  I believe the seawater did not have sufficient weight to counter the formation pressure.  If ther was any overbalance it was very slight.  In either Seadrill’s or PTTEP’s submissions and in recent testimony the possibility of some seismic event is considered and then dismissed.  Based on reported experiences in Cook Inlet Alaska, I believe the “event” was real and it was likely whatever cement seal that had been formed at the bottom of the casing finally failing.  There have been a couple of deep production casing failures on wells drilled from Cook Inlet platforms.  In each case, the people on the platform reported feeling a “jolt”. It is not unlike shooting drill pipe conveyed perforating guns.  There is also testimony regarding the “time delay” between removing the 9-5/8” PCC to the initial burp and then the final unloading.  I don’t think any one is considering the horizontal portion of the well.  Movement along that section would be significantly different and likely much slower than movement in the more vertical portion of the wellbore. With little vertical depth change the evolution of solution gas as the pressure drops would be slower in the horizontal section.  I remember that well control school problems were changed to incorporate separate calculations for the horizontal versus vertical sections since the pressure change per time or volume in the horizontal section would be much, much smaller than in the vertical.