Wednesday, August 11, 2010

Dynamically positioned drilling rigs

     So, not that I have any experience in the " oil patch ", or the engineering of Dynamically Positioned deep-water drilling rigs, but I was looking over the design of the Deepwater Horizon after going back over the course of events in the sinking of the platform. As it's come out in the news, any of the normal measures to prevent gases from a blowout from invading the engine rooms where the generators are found, and "supercharging" the generators to the point of making them explode , were shut off. There is normally a series of alarms and switches that would normally trip and trigger preventive measures, ie, closing of intake vents and such .Of course, it has been acknowledged in the media as well, that these alarms were turned off by the personnel on the platform. One could say that had the alarms not been de-activated, that the sinking of the platform and subsequent almost uncontrollable blowout could have been avoided.

   After the initial explosion, the well continued to fuel the ensuing fire, then the platform sank. Basically, the tanks that are normally are  flooded/flushed with water to provide ballast/and total depth below the water-line, had overheated, and been cooled by surrounding vessels spraying seawater, that eventually, the metal expanded and contracted enough to allow water to invade and sink the rig.

What's wrong with this picture...?

   Why would a giant platform designed for all practical purposes, to be able to slowly sink into the water at varying depths, but still maintain buoyancy slowly burn and sink..? would think that there are many redundancies built into any type of complicated structure/machine that comprises a drilling rig in it's totality. . .but wait...there is cost efficiency analysis to be taken into consideration as well.

How expensive is how safe ?

Is it cheaper to locate backup generators next to the generators they are supposed to be " backing up "..?


 Especially when the alarms are shut off.

 Then there is no redundancy in power re-routing in case of failure either

 ....from the next layer of this onion...

POWERPLANT SESSION :The Deepwater Horizon
A Unique 10,000-ft Water Depth Dynamically
Positioned Semisubmersible Drilling Vessel

M. W. Cole, Cole Engineering, Inc.
C. V. Wolff, R&B Falcon
J. J. May, R&B Falcon
D. R. Weisinger, Vastar Resources, Inc

" Loss of an engine room "

" Loss of an engine room with its associated diesel engine/generator set and switchboard
due to fire or flooding will cause loss of the thruster and the 480V bus loads assigned to
that switchboard. "

Given that dynamically positioned rigs use GPS to calculate position and ,the vector-specific angle and momentum of thrust applied at the bottom of the platform, there are the problems of loss of positioning information due to solar activities, but in the event of a loss of one generator from explosive failure, having them all together prevents any emergency power from being diverted to ballast pumps in the case the event eventually destroys all generators in the area, ...which it did.

So why would an engineering firm and oil company spend so much for a piece of equipment, then allow engineers to be constrained by costs, when they are designing the system, especially considering it doesn't add that much to alter the placement of various components in a system, depending on the layout....but  a square should be pretty easy...compared to something like an assembly line.

So why would emergency thruster control and ballast operation not be designed into the system in the event of an evacuation of the platform when they operate on real-time information from satellites to keep them stably located in the first place...?

It would seem if you can operate a satellite from Earth, you could operate an oil rig from this planet too......just in the event of an emergency .

Here is some great info on the deepwater Horizon and DP rigs in general.