I’ve had a lot of calls and emails/messages about mud lately, for some reason. The drilling kind, not the kind we get to drive in. Maybe things go in cycles. Anyway, I thought it might be a good time to go over some mud basics.
First, drilling mud, properly circulated, removes the cuttings as the bit drills. They circulate to the surface and most of them settle in the pits, or are expelled by the shale shaker and other solids control equipment. I say “properly circulated” because, in the water well business, it is common to drill very large holes with very small pumps. I once drilled a 48-inch hole with a 5½-by-8 pump. Talk about slow circulating times! The problem is a combination of low annular velocity and slip velocity. Slip velocity is the speed that cuttings fall in fluid. Obviously, the annular velocity must be higher than the slip velocity to clean the hole.