[QUOTE=completenoob;34254]What is this “mud” exactly? As it appears to be more or less toxic, what could be the consequence of pumping up to 50,000 gallons down into the well, with most of it being pushed out again? Of course, the leak has to be stopped no matter what – but is this another case of fighting pollution with even more pollutants (as with the Corexit dispersant)?
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The fluid pressures at depth are usually greater than those you would get from an equivalent column of seawater. As a result, drilling requires denser fluids to counteract the pressures in the formations and keep them from rushing into the wellbore. One common way to do this is to suspend finely ground dense minerals such as barite into the fluid to jack up the density. This is where the term mud comes from as you are essentially mixing dirt in the water. You can tweak the density by adjusting the exact types and quantity of fine solids in suspension. According to the press briefing a day or so ago they are using a water-based mud with barite as the primary solid. This combination should be relatively inert. They did say they had mixed in some minor additives to adjust the viscosity, but did not say what those were other than to say that they met EPA guidelines. There are cases where drilling requires potentially toxic oil-based mud, such as when the rocks contain odd minerals which react with fresh water, but that is not what is being used here. From an environmental standpoint I would hazard a guess that the drilling mud they are using is relatively benign compared to the oil which comes out of the well when they are not pumping.