Drilling requires one of several methods of fluid circulation to clear cuttings from the borehole. Several types of drilling methods are best classified by the type of drilling fluid used, and/or the way in which the fluid is circulated through the borehole.
Liquid Mud Circulation (Direct)
Liquid Mud circulation with drilling fluid (water or water with additives-mud like Barite or Bentonite) is pumped down the drill pipe and out through the ports or jets in the drill bit. The fluid then flows up the annular space between the hole and the drill pipe carrying cuttings in suspension to the surface.
The drilling fluid, much like the bit, is custom designed and chosen depending on what type of subsurface conditions are expected or experienced. The drilling fluid chosen must have a number of properties to allow it to accomplish its tasks.
It must be light and thin enough to circulate through the drill bit, cooling the bit as it drills as well as lubricating the moving parts. The fluid must be heavy enough to carry drill cuttings away from the bit and back to the surface. In addition, the drilling fluid must be thick enough to coat the borehole with a cake, which serves to temporarily seal the walls of the well until casing can be installed (cement can be used for stabilizing the casing pipe).
In direct circulation drilling the circulating system consists of a starting point, the mud pit, where the drilling fluid ingredients are stored. Mixing takes place at the mud pit or in a drum or mixer used for this purpose. After mixing or the addition of additives the fluid is forced through pumps up to the swivel and down all the way through the drill pipe, emerging through the drill bit itself. From there, the drilling fluid circulates through the bit, picking up debris and drill cuttings, to be circulated back up the well, traveling between the drill string and the walls of the well (also called the ‘annular space’).
At the surface the fluid is channeled into settling pits or tanks where most of the cuttings settle out. Clean fluid is picked up from the opposite end of the settling area. If portable mud pits are employed, a series of baffles is used to aid in the settling process. The drilling fluid is then re-circulated down the hole. The process is repeated until drilling is completed.
The drilling fluids most often used in liquid mud circulation contain clay additives (bentonite/barite) or polymer based additives. A combination of the two additives is also used. Drilling muds remove cuttings while cooling and lubricating the drill bit. The drilling fluid also stabilizes the borehole by the creation of a wall cake. While these 3 functions, cooling, clearing, & stabilizing are essential for successful hole completion, in water well drilling the overuse of additives can make the removal of the drilling fluid residues more difficult during well development.
As we have seen above, dry bulk materials (such as barite, bentonite and cement) are needed in the drilling process. Lion Bulk Handling (Ruyter Offshore) can supply several dry bulk handling systems or dry material management systems for the storage, loading and unloading of dry materials on board of offshore related vessels (jack-up rigs, Semi-submersibles, Drill ships, Platform supply vessels, anchor handling tug suppliers, etc.). We also can supply a completely integrated system together with the drilling fluid management. If you would like to know more about the possibilities for your applications, please contact us here.