The Process

Drilling fluid (mud) is used to control subsurface pressures, lubricate the drill bit, stabilize the well bore and carry the cuttings to the surface, among other functions. Mud is pumped from the surface through the hollow drill string, exits through nozzles in the drill bit and returns to the surface through the annular space between the drill string and the walls of the hole.

As the drill bit grinds rocks into drill cuttings, these cuttings become entrained in the mudflow and are carried to the surface. In order to return the mud to the recirculating mud system and to make the solids easier to handle, the solids must be separated from the mud. The first step in separating the cuttings from the mud involves circulating the mixture of mud and cuttings over vibrating screens called shale shakers. The liquid mud passes through the screens and is re-circulated back to the mud tanks from which mud is withdrawn for pumping down-hole.

The drill cuttings remain on top of the shale shaker screens; the vibratory action of the shakers moves the cuttings down the screen and off the end of the shakers to a point where they can be collected and stored in a pit for further treatment or management.

Most drill cuttings collected by the shale shakers are still coated with so much mud that they become difficult to handle and are unsuitable for the next reuse and for disposal. Constituents of the cuttings or the mud coating them (e.g., oil, metals) may leach from the waste, making them unsuitable for land application or burial approaches.