Pemboran Sumur (Drilling Well)

The well is created by drilling a hole 5 to 36 inches (127.0 mm to 914.4 mm) diameter into the earth with a drilling rig which rotates a drill string with a bit attached. After the hole is drilled, sections of steel tubing (casing), slightly smaller in diameter than the borehole, are placed in the hole. Cement may be placed between the outside of the casing and the borehole. The casing provides structural integrity to the newly drilled wellbore in addition to isolating potentially dangerous high pressure zones from each other and from the surface.

With these zones safely isolated and the formation protected by the casing, the well can be drilled deeper (into potentially more-unstable and violent formations) with a smaller bit, and also cased with a smaller size casing. Modern wells often have 2-5 sets of subsequently smaller hole sizes drilled inside one another, each cemented with casing.

To drill the well

* The drill bit, aided by the weight of thick walled pipes called "drill collars" above it, cuts into the rock. There are different types of drillbit, some cause the rock to fail by compressive failure. Others shear slices off the rock as the bit turns.
* Drilling fluid (aka "mud") is pumped down the inside of the drill pipe and exits at the drill bit. Drilling mud is a complex mixture of fluids, solids and chemicals which must be carefully tailored to provide the correct physical and chemical characteristics required to safely drill the well., Particular functions of the drilling mud include cooling the bit, lifting rock cuttings to the surface, preventing destabilisation of the rock in the wellbore walls and overcoming the pressure of fluids inside the rock so that these fluids don't enter the wellbore.
* The generated rock "cuttings" are swept up by the drilling fluid as it circulates back to surface outside the drill pipe. The fluid then goes through "shakers" which strain the cuttings from the good fluid which is returned to the pit. Watching for abnormalities in the returning cuttings and monitoring pit volume or rate of returning fluid are imperative to catch "kicks" (when the formation pressure at the depth of the bit is more than the hydrostatic head of the mud above, which if not controlled temporarily by closing the blowout preventers and ultimately by increasing the density of the drilling fluid would allow formation fluids and mud to come up uncontrollably) early.
* The pipe or drill string to which the bit is attached is gradually lengthened as the well gets deeper by screwing in additional 30-foot (10 m) joints (i.e., sections) of pipe under the kelly or topdrive at the surface. This process is called making a connection. Usually joints are combined into 3 joints equaling 1 stand. Some smaller rigs only use 2 joints and some rigs can handle stands of 4 joints.

This process is all facilitated by a drilling rig which contains all necessary equipment to circulate the drilling fluid, hoist and turn the pipe, control downhole pressures, remove cuttings from the drilling fluid, and generate onsite power for these operations.




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