Land-Based Oil Rig
Like all oil rigs, land based ones are used to drill holes in the earth to find oil in underground reservoirs. They can be small and portable like the ones used in mineral exploration drilling, or large and able to drill thousands of feet below the earth's surface. Land-based rigs are usually powered electrically, mechanically, hydraulically, or pneumatically; it really depends on the location, type and size of the rig, and the type of oil well being drilled into. Likewise, there are different methods of drilling that are used to create holes in the earth to reach the oil. The main ones include auger, air core, cable tool, diamond core, direct push rig, hydraulic rotary, percussion rotary air blast, reverse circulation, and sonic drilling.
The amount of people needed to operate a certain drilling rig also greatly depends on the size and type of rig as well as the type of well being drilled into. Anywhere from six to hundreds of people can work at a single rig. A standard 20,000 foot land rig take about a year to make and a mobile one take approximately 2 years. These rigs can cost anywhere from one to 100 million US dollars dependig on their type and size. Most oil rigs are able to operate 24/7.
In order to drill for oil, the crew sets up the oil rig and initiates the drilling process. Primarily, a specific depth is drilled down to from a surface hole above where oil is believed to be located. Upon reaching the predetermined depth, the casing must be cemented by placing casing-pipe sections with spacers around the outside keeping them centered inside the hole, in order to prevent it from collapsing in on themselves. The cement is then pumped down the casing pipe using a bottom plug, cement slurry, top plug and drill mud. Pressure from the drill mud has the effect of moving the cement slurry through the casing and into the space between the outside of the casing and the hole. Finally, the cement is allowed to harden and then tested for such properties as hardness, alignment and a proper seal.
Drilling occurs in stages: drilling, then running and cementing new casings, then drilling again. When rock cuttings from the mud reveal oil sand from reservoir rock, it is an indicator that the desired depth may have been attained. At this point, the drilling apparatus is removed from the hole and several tests are performed to verify this, including “Well logging” (process of lowering electrical and gas sensors into the hole to take measurements of the rock formations), “Drill-stem testing” (process of measuring the pressure within a hole by lowering a device which divulges whether or not reservoir rock has been reached), and “Core samples” (process of obtaining samples of rock in search of reservoir rock characteristics).
Upon reaching the final depth, an oil well is instituted to permit oil to flow into the casing in a controlled way. A perforating goes into the well to the production depth. Gun has explosive charges to generate holes in the casing through which oil can run. After perforating the casing, small-diameter tubing is inserted into the hole as a means for oil and gas to course from the well. Outside of the tubing, a tool called a packer is used. At production level, it was expanded to make a seal around the outside of the tubing. Then, multi-valve structures called a Christmas trees are cemented to the top of the tubing as well as to the top of the casing. The Christmas tree enables them to control the gush of oil from the well. Once the well is complete, the flow of oil into the well must be initiated. After the oil is flowing, the oil rig is removed from the site and production equipment is set up to remove oil from the well.