here's a little piece on basic oil exploration.
Finding Oil and Gas
The task of finding oil and gas that is deeply embedded in the earth is first assigned to a geologist. Modern day geologists start their search for oil and gas by examining surface rocks and terrain with the help of satellite images. By surveying and mapping the surface and sub-surface characteristics of a certain area, the geologist can extrapolate which areas are most likely to contain a petroleum or natural gas reservoir. They also use a variety of other high tech equipment such as onshore seismology, gravity meters, magnetometers and sand sniffers.
Gravity meters measure tiny changes in the Earth's gravitational field that can indicate flowing oil. Magnetometers measure tiny changes in the Earth's magnetic field which can give clues to local deposits of oil and gas. Sniffers are sensitive electronic devices which detect the smell of hydrocarbons, which can indicate the presence of oil. Perhaps the most common method used by geologists to find oil is seismology. Seismology creates shock waves that pass through hidden rock layers. Geologists then interpret the waves that are reflected back to the surface to determine if oil and gas are present.
Preparing the Land
Once a geologist has selected a site, it must be surveyed to determine its boundaries and studies to determine any possible environmental impact must be done. Lease agreements, permits, titles and right-of way access for the land must also be obtained. For off-shore sites, legal jurisdiction must be determined. Once the legal issues have been settled, a crew goes about preparing the land. The land is cleared and leveled, and access roads are built. A well pad must be constructed to separate the wildlife, crops or residences from the well. The pad must be large enough to accommodate emergency, maintenance and construction equipment necessary for operations and repairs during the life of the well. Because water is used in drilling, there must be a source of water nearby. If there is no natural source, a well must be dug. Once the land and well pad have been prepared, several holes are made to support the rig and its 90 foot derrick or mast. Some rigs are built on ships or barges when there is no foundation to support a rig (as in marshes or lakes). Depending upon the location of the drill site and its access, ancillary equipment is then transported to the site by truck, helicopter or barge.
Casings and Cementing
Prior to the arrival of a big drilling rig, workers install "conductor casing". Conductor casing, which is usually no more than 20 to 50 feet long, is installed to prevent the top of the well from caving in and to help in the process of circulating the drilling fluid up from the bottom of the well. The casing is usually 16 to 20 inches in diameter. The hole for the casing is usually drilled with a small auger on the back of a truck. The casing is then cemented in place.
Once the conductor casing is in place and the rig has arrived, workers start drilling a 600 to 1000 foot hole to accommodate the "surface casing". Surface casing is a large diameter, low-pressure pipe that is designed to protect the earth's aquifer from contamination during drilling. The casing itself comes in 40-foot sections, which are threaded at both ends. Workers, or "roughnecks", attach the sections with a "collar" which also is threaded .The roughnecks then tighten the collar with a large pipe wrench. Once the surface casing has been run into the hole, special cement is pumped in. The cement seals the area between the surface casing and the side of the hole.
Drilling the Well
Once the surface casing is in place, workers can actually begin drilling for oil. The well is drilled by a rig rotating pipe (or drill pipe) with a bit attached to the end. Drill pipe is added in 30 foot lengths at a time. Weight is applied to the bit through the use of drill collars or thick walled tubular pieces made from solid pieces of steel. A liquid consisting of fresh water and bentonite, also called drilling mud, is circulated in the hole during drilling to remove cuttings and maintain pressure. Blow out preventers or BOPs are installed at the surface to control any unexpected changes in pressure.
Logging
Once the hole reaches the desired depth, logging begins. Logging is the process of determining which of the formations between the surface and the bottom of the well contain oil and gas and which formations contain merely water. An electrical cable and a "logging tool" are lowered into the hole, and the tool sends electrical charges into the formation. The tool then sends geological information to a "logging" truck where a computer processes the information. The information which can be derived from logging includes rock type, porosity, and resistivity.
The Casing Point Decision
Once this information is gathered and studied, a decision is made to either plug or complete the well. This is called the "casing point decision". If a decision is made to complete the well, then more casing is lowered in to reach the bottom of the hole. Cement is once again pumped into the hole to seal the area between the surface casing and the side of the hole. However, the cement to hold this casing stops at least 500 feet below the surface to prevent natural gas leaks. Setting this casing is the final step before well stimulation can begin.
Well Stimulation
Well stimulation consists of various techniques used to loosen the oil that is trapped in the porous rock. Hydraulic fracing (pronounced fracking) is the most commonly used method. Fracing involves pumping water at extremely high pressure into the hole until a crack develops in the rock formation. Water and sand are then pumped into the crack. The sand holds the cracks open until all the oil escapes the rock and flows into the casing.
Well Completion
Well stimulation consists of various techniques used to loosen the oil that is trapped in the porous rock. Hydraulic fracing (pronounced fracking) is the most commonly used method. Fracing involves pumping water at extremely high pressure into the hole until a crack develops in the rock formation. Water and sand are then pumped into the crack. The sand holds the cracks open until all the oil escapes the rock and flows into the casing.
Production
Once the well has been completed, it moves to the production stage. The oil and gas streams are separated. The gas flows into a gas pipeline that carries it to processing plants and then onto the consumer for purchase. Meters are installed from the wellhead to measure the amount of gas that is being purchased. The oil that is separated flows into tanks and is stored until it trucked or shipped via pipeline to a refinery.
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