A shortened and simplified summary from information provided in the DNV report:
- The Upper Variable Bore Rams (VBRs) were closed prior to the Emergency Disconnect Sequence (EDS) activation at 21:56 on April 20, 2010.
- A drill pipe tool joint was located between the Upper Annular Preventer (closed) and the Upper VBRs (also closed). Forces from the flow of the well pushed the tool joint into the Upper Annular element. Because the tool joint was trapped beneath the closed annular preventer (and could not move upward), forces from the flowing well caused the pipe to push upward and buckle.
- The drill pipe deflected until it contacted the wellbore just above the Blind Shear Ram (BSR). The portion of the drill pipe located between the shearing blade surfaces of the BSR was off center and held in this position by buckling forces.
- A portion of the pipe cross section was outside of the intended BSR shearing surfaces and did not shear as intended.
- As the BSR closed, a portion of the drill pipe cross section became trapped between the ram block faces, preventing the blocks from fully closing and sealing.
- Since the deflection of the drill pipe occurred from the moment the well began flowing, trapping of the drill pipe would have occurred regardless of which means initiated the closure of the BSR.
- In the partially closed position, flow continued through the drill pipe trapped between the ram block faces and subsequently through the gaps between the ram blocks.
- When the drill pipe was sheared on April 29, 2010, using the Casing Shear Ram (CSR), the flow expanded through the open drill pipe at the CSR and up the entire wellbore to the BSR and through the gaps along the entire length of the block faces and around the side packers. The CSR was designed to cut tubulars, not seal the well bore.
sheared off-center drill pipe
Bud's Offshore Energy (BOE) 
Interesting to note that neither the upper annular and upper VBR upper variable pipe rams closed, these 2 barriers did not manage to stop the flow, which is surprising.
The pressure on Macondo was not very high based on final kill pressure, in any case the BOP rating was 15,000 psi WP , and most body components are tested at 22,500 psi. which held together very well after flowing thru for 4 months, and no leaks after the capping worked.
The 2 other VBR’s lower and middle and lower annular were not operated.
One explanation about the Riser EDS Emergency Disconnect System and deadman failures was the loss of elect/hyd. communications due to damages after the deck explosions.
Is the protection of umbilicals in moonpool areas on MODU similar to the level of protection for control system on floating production vessels, with blast walls and segregated conduit for power supply ?
JL,
My sense is that much of the early flow was through the drill pipe. The extent of flow through the closed VBR still seems to be unclear. The Bly report implies that the upper VBR was closed but not sealing. With time, erosion would have increased flow that leakage/flow. Hopefully, we will learn more about flow patterns (over time) during the upcoming hearing.
Will be interesting to see how they incorporated the weight of 5000 ft of drill pipe inside the riser with no top tension (rig unoperational) ? and the free fall of the 20 ” Dia x 5000 ft of riser bending both drill pipe and riser at 90 deg. angle with the drill pipe inside.
Forces / stress concentration on what ever was closed on BOP must have been transferred by the drill string jammed in.