Page 43 - 4822
P. 43
Figure 4.4 -Drilling Rig
Drilling mud is also the key to preventing blowouts. If the
drill bit penetrated a porous and permeable fo rmation containing
oil and gas under high pressure, the oil and gas would naturally
tend to rush out of the formation and up the borehole. But in order
to do this, it would have to overcome the downward pressure
exerted by the thousands of kilograms of slowly circulating mud.
What usually happens in such a case is that only small traces of oil
or gas will flow out of the formation and circulate back to the
surface with the mud. This result is actually useful to the wellsite
43
