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A drilling rig is a machine which creates holes (usually called Borehole s) and/or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill Water Well s, Oil Well s, or Natural Gas extraction wells or they can be small enough to be moved manually by one person. They sample sub-surface mineral deposits, test rock, soil and groundwater physical properties, and to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures (such as Oil Platform s, commonly called 'offshore oil rigs'). The term "rig" therefore generally refers to the complex of equipment that is used to penetrate the surface of the earth's Crust . Drilling rigs can be:
Oil and Natural Gas drilling rigs can be used not only to identify geologic reservoirs but also to create holes that allow the extraction of Oil or Natural Gas from those reservoirs. An oil or gas pumping rig, sometimes called a derrick, is used to retrieve oil / gas from a reservoir. HISTORY Until Internal Combustion Engine s came in the late 19th century, the main method for drilling rock was muscle power of man or animal. Rods were turned by hand, using clamps attached to the rod. The rope and drop method invented in Zigong , China used a steel rod or piston raised and dropped vertically via a rope. Mechanised versions of this persisted until about 1970, using a cam to rapidly raise and drop what, by then, was a steel cable. In the 1970s, outside of the oil and gas industry, roller bits using mud circulation were replaced by the first efficient pneumatic reciprocating piston Reverse Circulation RC drills, and became essentially obsolete for most shallow drilling, and are now only used in certain situations where rocks preclude other methods. RC drilling proved much faster and more efficient, and continues to improve with better Metallurgy , deriving harder, more durable bits, and compressors delivering higher air pressures at higher volumes, enabling deeper and faster penetration. Diamond drilling has remained essentially unchanged since its inception. MOBILE DRILLING RIGS In early oil exploration, drilling rigs were semi-permanent in nature and were often built on site and left in place after the completion of the well. In more recent times drilling rigs are expensive custom-built machines that can be moved from well to well. Some light duty drilling rigs are like a mobile crane and are more usually used to drill water wells. Larger land rigs must be broken apart into sections and loads to move to a new place, a process which can often take weeks. Small mobile drilling rigs are also used to drill or bore Piles . Rigs can range from 100 Ton Continuous Flight Auger (CFA) rigs to small air powered rigs used to drill holes in quarries, etc. These rigs use the same technology and equipment as the oil drilling rigs, just on a smaller scale. The drilling mechanisms outlined below differ mechanically in terms of the machinery used, but also in terms of the method by which drill cuttings are removed from the cutting face of the drill and returned to surface. DRILLING RIG CLASSIFICATION There are many types and designs of drilling rigs, with many drilling rigs capable of switching or combining different drilling technologies as needed. Drilling rigs can be described using any of the following attributes: by power used
by pipe used
by height
by method of rotation or drilling method
by position of derrick
DRILL TYPES There are a variety of drill mechanisms which can be used to sink a s. Auger drilling Auger drilling is done with a Helical screw which is driven into the ground with rotation; the earth is lifted up the borehole by the blade of the screw. Hollow stem Auger drilling is used for environmental drilling,geotechnical drilling, Soil Engineering and Geochemistry reconnaissance work in exploration for Mineral deposits. Solid flight augers/bucket augers are used in construction drilling. In some cases, Mine shafts are dug with auger drills. Small augers can be mounted on the back of a utility truck, with large augers used for sinking piles for bridge foundations. Auger drilling is restricted to generally soft unconsolidated material or weak weathered Rock . It is cheap and fast. . These slow rigs have mostly been replaced by rotary drilling rigs in the U.S.]] Air core drilling Air core drilling and related methods use hardened Steel or Tungsten blades to bore a hole into rock. The drill bit has three blades arranged around the bit head, which cut the rock. The rods are hollow and contain an inner tube which sits inside the hollow outer rod barrel. The drill cuttings are removed by injection of compressed air into the hole via the hollow inner rod. The cuttings are then blown back to surface via the outer space inside the barrel where they are collected if needed, or discarded. Drilling continues with the addition of rods to the top of the drill string. Air core drilling can occasionally produce small chunks of cored rock. This method of drilling is used to drill the weathered Regolith , as the drill rig and steel or tungsten blades cannot penetrate fresh rock. Where possible, air core drilling is preferred over RAB drilling as it provides a more representative sample. Air core drilling can achieve depths approaching 200 meters in good conditions as the cuttings are removed inside the rods and are less likely to clog. However, this method is more costly and slower than RAB. Cable tool drilling Cable tool rigs are a traditional way of drilling Water Well s internationally and in the United States. The majority of large diameter water supply wells, especially deep wells completed in bedrock aquifers, were completed using this drilling method. Although this drilling method has largely been supplanted in recent years by other, faster drilling techniques, it is still the most practicable drilling method for large diameter, deep bedrock wells, and in widespread use for small rural water supply wells. Also sometimes called "spudders", these rigs raise and drop a drill string to finely pulverize the subsurface materials. The drill string is comprised of the upper drill rods, a set of "jars" (inter-locking "sliders" that help transmit additional energy to the drill bit and assist in removing the bit if it is stuck) and a drill bit. During the drilling process, the drill string is periodically removed from the borehole and a bailer is lowered to collect the drill cuttings (rock fragments, soil, etc.). The bailer is a bucket-like tool with a trapdoor in the base. If the borehole is dry, water is added so that the drill cuttings will flow into the bailer. When lifted, the bailer closes and the cuttings are then raised and removed. Since the drill string must be raised and lowered to advance the boring, casing (larger diameter outer piping) is typically used to hold back upper soil materials and stabilize the borehole. Cable tool rigs are simpler and cheaper than similarly sized rotary rigs, although loud and very slow to operate. The world record Cable Tool Well was drilled in New York to a depth of almost 12,000 feet. The common Bucyrus Erie 22 can drill down to about 1,100 feet. Since cable tool drilling does not use air to eject the drilling chips like a rotary, instead using a cable strung bailer, technically there is no limitation on depth. |
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