When oil drilling, a hole is drilled into the surface of the earth, that is created to retrieve petroleum oil hydrocarbons for us to use. In most cases, natural gas is produced along with the oil.
The well is produced by drilling a hole from anywhere from 5" - 40" in diameter into the earth with a drill rig, that rotates a drill string with a diamond core bit attached. Once the hole is completed, sections of steel pipe or otherwise known as casing, that is slightly smaller in diameter than the borehole, are lowered into the hole. The casing provides structural integrity to the newly drilled well, and isolates any potentially dangerous high pressure zones from each other and the surface.
When these zones are safely isolated and the formation is protected by the casing, the oil well can be drilled deeper with a smaller drilling bit, and then cased with a smaller diameter casing. These wells typically have two to five sets of smaller diameter hole sizes drilled inside one another, each cemented with casing.
How to drill the oil well:
- Drilling fluids, or "drilling muds", are pumped down the inside of the drill rods and exit through the drilling bit. The main functions of the drilling muds include cooling the bit, lifting rock cuttings to the surface, stabilizing the rock in the borehole walls and overcoming the pressure of fluids inside the bedrock so that these fluids do not enter the borehole. The main components of drilling fluid are usually water and clay, but it also typically contain complex mixtures of fluids, solids and even chemicals that must be carefully calculated to provide the correct physical and chemical characteristics to safely drill the oil well. In some cases oil wells can be drilled with air or foam as the drilling fluid, to cool the drill bit and carry the drill cuttings to surface.
- The rock "cuttings" are carried up by the drilling fluid as it resurfaces outside the drill pipe. The fluid then goes through "shakers" which strain the cuttings from the good fluid and then returned to the mud pit. Watching for abnormalities in the returning cuttings and monitoring pit volume or rate of returning fluid is important to catch any "kicks" early. A "kick" is when the formation pressure at the depth of the bit is more than the hydrostatic head of the mud above, if this is not controlled temporarily by closing the blowout preventers and ultimately by increasing the density of the drilling fluid would allow formation fluids / mud to come up through the annular space uncontrollably.
- The rods or drill string that the bit is attached is gradually lengthened as the well gets deeper by adding additional 30-foot (9 m) sections of pipe under the topdrive of the drill rig at the surface. This is what they call in the industry as "making a connection". These connections can be combined for more efficient tripping of the rods when pulling out of the hole and creating stands of multiple connections. A conventional triple, would be to pull pipe out of the hole three connections at a time and stacking them in the derrick. Some modern rigs, called "super singles," trip pipe one at a time, laying it out on drill racks as they go.
This process is all done by a oil drilling rig which would contain the equipment to circulate the drilling fluid, hoist and turn the pipe, control downhole drilling, remove cuttings from the drilling fluid, and generate on-site power for all drilling operations.
