A mud pump is a large pump used to move heavy drilling fluid, known as mud, within a hole when drilling for oil. The pump circulates the mud by pushing it down into the hole and then moving it back up again. Mud pumps are reciprocating pumps, meaning that they use oscillating pistons or plungers to displace the fluid.
A mud pump is a single acting pump, so the fluid will move in only one direction. A hole, or well, is drilled into the ground, and the mud is pushed by the mud pump down piping to the bottom of the hole. The pressure then forces the mud up the annulus, or the space that surrounds the piping.
The "mud" used is drilling for oil consists of emulsified water or oil, clay and chemicals. For safety reasons, it is tailor-made to the particular chemical conditions of the drilling. Its purpose is to float rock cuttings out of the hole, clean the bottom of the hole and cool the drilling equipment. It also acts as the initial barrier in case of a blowout by resisting the pressure from any fluid within the rock that might enter the well.
Most modern mud pumps are triplex-style pumps, which have three cylinders. Older oil rigs, or those in developing countries, might still use duplex pumps that have only two cylinders. Some newer pumps have as many as six cylinders.
A mud pump is a crucial piece of machinery in the process of drilling for oil. On a drilling rig, the process of drilling begins by using a rotating drill to bore a hole in the ground. After a hole has been drilled, a pipe is inserted into the well in order to ensure that it maintains its shape and structure. Within that casing, a smaller drill bit is used to drill deeper, and another pipe, known as casing, is placed in that hole. It is common for up to five holes, each slightly smaller than the next, to be bored when drilling for oil.
As the drill cuts the rock, the mud pump moves those cuttings up the well. The rock cuttings are put through a "shaker" that removes them from the mud. The mud is then reused by the mud pump. This process continues until the well is drilled to its full depth.