Still Pumping Heavy Mud Against a Pressure Gradient

Update: From Bit Tooth Energy

Admiral Allen, who is the Government head of the effort to cap the flowing well in the Gulf, and to oversee the cleanup operation, commented this morning that the well had reached a point where the internal pressure difference between the mud pumped in and the reservoir pressure was very low. However, with the relatively high volume of leakage that was passing through the BOP, the plan now included a try at blocking some of that leakage path by injecting debris (for which likely read rubber strips and small spheres) in the hope that these will lodge in the flow path within the BOP and reduce the leakage of fluid.

The leakage rate is significant (I calculated earlier that it was around 17,000 bd, which lies within the newly reported range of 12,000 to 19,000 bd, and may have been higher than BP were actually anticipating. (Though the leak may also have increased a little as the mud was injected at higher pressures). The operation has already used all the mud on one of the supply boats, and has moved to the second (there is a third standing by so they won't run out). The concern, however is now with the volume of cement that will be required for the seal.
_BitTooth

In other words, they need to do something to stop the leakage of injectant (mud or cement) out of the top of the blowout preventer, or they may not have enough cement on hand, when it comes time to switch from the mud to cement (when mud pressure balances the oil/gas reservoir pressure). Some type of "junk shot" may be attempted to slow the leak out of the top of the BOP.

More here

The top kill procedure of pumping heavy kill mud against the pressure of a gushing oil well, has been ongoing for about 24 hours. It is still too early to tell whether the pressure of the oil will drop low enough to allow the injection of cement into the blowout preventer. At least the Gulf of Mexico has had almost a day's respite from the relentless high pressure injection of oil and gas into its depths.

Oil Well Stabilizes but Top Kill Continues

Oil and Gas no Longer Gushing, too early to declare success

Effort to stop spill "going according to plan"

Another "pre-mortem post-mortem", from WSJ

More: Best estimate of oil leak before top kill: 12,000 to 19,000 barrels per day.
The range of 12,000 to 19,000 bpd is higher than the earlier USCG / NOAA estimate of 5,000 barrels per day, but is far lower than the fantastical estimates by academics from Purdue, UCB, and other universities who estimated flow rates to 100,000 barrels per day and higher. The higher spill rate would put the Deepwater Horizon spill above the Exxon Valdez in total volume spilled -- although that is not taking evaporation into account.

Journalists and Obama -- who are looking for "an unprecedented disaster -- want to compare the spill to the Exxon Valdez in order to prove that the apocalypse has come. But the Deepwater Horizon spill is not comparable to the Exxon Valdez spill for many reasons: a deep undersea leak far offshore vs. a surface container spill close to shore; a lighter crude with high proportions of gas vs. a heavier crude; the warm fertile waters of the Gulf of Mexico vs. the frigid waters of Prince William Sound; the active Gulf Loop Current into open seas vs. the relatively closed waters of the Sound . . . and so on.

Journalists, politicians, and activists are clearly too stupid to look beneath sloppily constructed surface realities. But that doesn't let the rest of us off the hook.