Drilling for oil is much more complicated than just punching a hole in the ground. Before the hole is actually drilled a lot of preliminary preparation has already been completed. The first act by an oil company when drilling a well is to perform scientific experiments to find a suitable drilling site. After this is done then the company will prepare the site and hire a drilling contractor. The drilling contractor will complete the process by drilling the well. Even after the well is complete there is still no guarantee that oil will be discovered.
Before oil drilling begins, scientists have already done extensive testing of the proposed drill site. Scientists have been unable to discover a way to make an absolute determination of where oil will be found. However, there are many specialized experiments that scientist can perform that give them clues to where the oil is most likely to be. Although expensive, these tests are beneficial to the oil companies because it gives them a much better idea of where they may find oil.
The scientists will usually start out by using the cheapest methods available. They will look at regional surveys, surface geology reports, and other easily obtainable sources of information. This information will help the scientific team pinpoint an area on a map where oil is most likely to be. These pinpointed areas will become the focus of more extensive scientific testing.
When the scientists are done pinpointing areas then they will produce a geophysical survey. A geophysical survey is a contoured map of the subsurface. The most common way to create this type of map is by using a seismograph machine. To use the seismograph machine, the scientists will set off an explosion in the ground. The seismograph machine will record the shock wave set off by the explosion. From the record produced by the seismograph machine the scientific team will produce an electronic picture of the different layers of rock underneath the ground.
When they study the picture produced by the seismograph machine the scientists will look for anomalies in the rock known as "reservoir traps." A reservoir trap is a very unique type of formation where oil is normally found. There are about five different types of these formations, and each of them have permeable rock present in their makeup. Permeable rock is a type of rock that oil can flow through. Permeable rock makes it easier to pump the oil from the ground.
After the scientific report is finished then the oil companies need to prepare the site and hire a drilling contractor. Most oil companies do not have their own drilling team. The drilling is commonly done by independent drilling contractors. These drilling contractors are usually in high demand and their services are costly. To lower the cost of drilling, oil companies will do everything possible to get the drilling team on and off of their land as quickly as possible.
Once the contractor is hired and available then the drilling contractor will bring the drilling rig onto the property. A drilling rig is a steel derrick that can be as much as fifteen stories high. It has a high powered motor for raising, lowering, and turning the drilling pipe in the well hole. It also has a pump that helps fill the hole with specialized drilling mud to reduce friction. The extra pipes used for drilling are stacked within the derrick.
A platform is built at the bottom of the derrick which has a hole through it for the drill bit to pass through.
Cable tool drilling is the original method used to drill wells. This method has become outdated and is rarely used today. Using a cable tool is similar to using a hand pick to chip away at the rock. A large pointed bit is raised and dropped into the hole to break the rock into small pieces. The fragments left can be easily removed from the hole by a bailing device. It is extremely rare for any oil drilling company to use cable tool drilling today. This type of drilling has been replaced by the more modern practice of rotary drilling.
Rotary drilling involves a lot of complex and expensive equipment. To start off the process the drilling contractor will begin drilling the hole. Once the hole has been drilled only a few feet, the drilling team will lower a pipe into the hole to follow the bit as it works its way farther into the ground. This pipe shores up the hole preventing it from caving in.
An oil drilling bit looks nothing like a conventional wood drilling bit. It is actually made up of three hardened steel bits that are attached to the end of a rotating pipe. These bits are interlocking and move together to drill through the rock. When interlocked the bits look similar to a cluster of gears. The bit is hollow in the center to allow drilling mud to flow through the bit into the hole.
The mud cools the bit down by preventing it from overheating due to friction with the rock. Although commonly referred to as mud, the compound is actually an expensive mixture of chemicals and abrasive material. The cost for the mud can run anywhere from $40,000 to $250,000 for one oil drilling operation.
Since mud is extremely expensive most drilling rigs are designed to filter the used mud to remove any impurities and then to recirculate it.
The drilling team will periodically stop the drilling to take a sample of the rock. This sample will let them know what type of rock they are drilling through. If the test show that they are drilling through permeable rock then they will perform a drill stem test. Before they can start a drill stem test they must remove all of the mud from the hole. A special instrument is then lowered into the hole to check the pressure of the oil. If no oil flows into the pipe the device is pulled from the hole and drilling continues.
Often no oil is found when drilling for oil. This is especially true in newly explored areas where nine out of ten drilling operations are unsuccessful. When a drilling operation fails to find oil this is referred as a dry hole. When the project ends in a dry hole it doesn't necessarily mean that drilling in the area is over. The material recovered from the dry hole is tested and used to determine if there may be oil somewhere in the near vicinity. Due to the high cost of exploring for oil most companies will drill several wells in an area before abandoning the site.
If oil is found, the oil drilling team will remove the drilling bit from the hole, and lower in a new length of pipe. This new pipe is called the casing. The casing is permanently set into the hole by securing it to the side of the hole with cement. After the casing is set in place, they will use a machine to punch holes through the side of the casing in the area where the oil was found. Oil is usually naturally pressurized. When the holes are punched into the casing then the oil should flow into the casing through its own power.
After the oil begins to flow then the oil contractor will finish their job by capping the oil well. The cap is often referred to as a "Christmas Tree" because of its many lights and devices. The cap is a very complex piece of machinery which controls the flow of oil from the well. After the cap is in place, then the oil well can be attached to a pipeline or pumped directly into barrels for distribution.
Natural gas is usually also found when oil is discovered. It is necessary to have a pipeline hookup available to pump the natural gas from an oil well. If no pipeline is available then the oil companies will either pump the natural gas back into the underground reservoir or they will shut off the oil well until they can have a pipeline run into the area.
Many drilling operations do not pay off for oil companies. However, one producing oil well can easily regain the losses from several dry wells. Some oil wells will only produce oil for several years, but it is not uncommon for oil wells to run continually for over fifty years. Whether the well runs for a year or fifty years the oil companies are able to make a profit off of the well. So even though drilling for oil is an expensive and complex undertaking it is worth the effort when oil is discovered.
