While operating for Total E&P offshore Angola, the 1999-built Ensco DS1 drillship was running their blowout preventer (BOP) to the wellhead in 4,318 feet of water.  Unfortunately, they forgot to open the blind shear rams while doing so.

After lowering the BOP 3,970 feet down, the hook load began to increase unexpectedly.  With the blind shear rams closed, the riser had not been able to fill with water as it was lowered into the ocean, and as the hydrostatic differential continued to build, the pipe collapsed in on itself.

The following images were sent to us from an anonymous gCaptain contributor:

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

riser collapse Ensco DS1

After discovering the failure on their ROV cams, French energy major Total, which had contracted the rig, continued to lower the BOP to the wellhead where the BOP was made up, and the Lower Marine Riser Package (LMRP) was unlatched and brought to the surface.  The collapsed riser joints were then replaced.

The deepwater drilling process in a very small nutshell

When drilling a deepwater well, the drilling rig will “spud in” or begin drilling, with large rock bit (the ones with big teeth on them), perhaps 26 inches in diameter, and it will drill (nozzle) a few hundred feet down in order to set the 30 or 36 inch conductor casing, which is the biggest and heaviest-walled casing string that is lowered into the well.  This string is lowered at the same time as the drill bit is nozzle-ing into the mud.

After it’s set, the top section of the well is drilled to a certain point, perhaps a few thousand feet down depending on the geology, where the well is then cased off using a 22 inch steel pipe.

This casing string forms the high pressure wellhead, which is locked into the low pressure wellhead (the 30″ or 36″) and subsequently cemented into place.

After the 22 inch wellhead is in place, the blowout preventer (BOP) with an 18 3/4 inch inside diameter (ID) is lowered down to the wellhead and locked into place.

From then on, oil-based mud is used to drill progressively narrower holes down into the earth while the cuttings are captured and the mud is recirculated down into the well via the center of the drill pipe.

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  • Ole M. Amundsen, Jr.

    Thanks for the explanation of the process…and the graphic photos of what pressure is being dealt with in undersea drilling.

    • jason

      Wrong! Might wanna check that again buddy

    • Walt

      Hydrostatic pressure at that particular depth would be: 1776 psi

      8.54 ppg X .052= .44408
      .44408 X 4000′ = 1776.32 psi

      Fluid weight(ppg) X .052 (lb per in^2 constant) X depth in TVD(ft)

  • W nicol

    Hi read ur article ,can I ask why was the rams not opened,is there not a set procedure for the operation? Also were the choke and kill lines ok or did they collapse as well?

  • iain

    choke n kill lines are rated at 10s of thousands of psi pressure they would never collapse imagine pressure needed to cut a drill collar with shear rams

    • W

      your operating pressure will max out at 5k psi on the shear rams, choke and kill lines can be rated up to 15k psi on a deepwater rig like this, but these are two very different pressures and fluids. Also, companies sell items called riser fill up valves for this exact reason. This device allows seawater into the riser if the differential pressure reaches around 300 psi. Obviously this rig did not have one.

  • Dag Vavik

    Great pictures and good experiance transfer :-) One question do you know the wall thickness (0,75″, 0,875″, etc..?) of the riser in use and the OD (21″)???

  • Sw

    Few things should have prevented this .
    # open rams in work procedure ( obviously)
    # driller should have spotted weight was not right for depth
    # fill valve as previously mentioned.
    # last but far from least how would you ever get to 4000 ft depth without testing riser , most company’s. test every 5 or 10 joints , bad practise to run. 4000 foot with no test. Perhaps they just test choke and kill lines? I’m sure in future the will do main tube as well
    Hind sight is always 20 20

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  • Ken

    What is the thickness of collapsed risers?

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