A drilling rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person and such are called augers. Drilling rigs can sample subsurface mineral deposits, test rock, soil and groundwater physical properties, and also can be used 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 platforms, commonly called 'offshore oil rigs' even if they don't contain a drilling rig). The term "rig" therefore generally refers to the complex equipment that is used to penetrate the surface of the Earth's crust.
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Small to medium-sized drilling rigs are mobile, such as those used in mineral exploration drilling, blast-hole, water wells and environmental investigations. Larger rigs are capable of drilling through thousands of metres of the Earth's crust, using large "mud pumps" to circulate drilling fluid (slurry) through the bit and up the casing annulus, for cooling and removing the "cuttings" while a well is drilled. Hoists in the rig, a derrick, can lift hundreds of tons of pipe. Other equipment can force acid or sand into reservoirs to facilitate extraction of the oil or natural gas; and in remote locations there can be permanent living accommodation and catering for crews (which may be more than a hundred). Marine rigs may operate thousands of miles distant from the supply base with infrequent crew rotation or cycle.
Until internal combustion engines were developed in the late 19th century, the main method for drilling rock was muscle power of man or animal. The technique of oil drilling through percussion or rotary drilling has its origins dating back to the ancient Chinese Han dynasty in 100 BC, where percussion drilling was used to extract natural gas in the Sichuan province.[1] Early oil and gas drilling methods were seemingly primitive as it required several technical skills.[1][2] The skills involved the availability of heavy iron bits and long bamboo poles, the manufacturing of long and sturdy cables woven from bamboo fiber, and levers. Heavy iron bits were attached to long bamboo cables suspended from bamboo derricks and then were repeatedly raised and dropped into a manually dug hole by having two to six men jumping on a lever.[1] Han dynasty oil wells made by percussion drilling was effective but only reached 10 meters deep and 100 meters by the 10th century.[1] By the 16th century, the Chinese were exploring and drilling oil wells more than 2,000 feet (610 m) deep.[2] Chinese well drilling technology was introduced to Europe in .[3] A modernized variant of the ancient Chinese drilling technique was used by American businessman Edwin Drake to drill Pennsylvania's first oil well in using small steam engines to power the drilling process rather than by human muscle.[1] Cable tool drilling was developed in ancient China and was used for drilling brine wells. The salt domes also held natural gas, which some wells produced and which was used for evaporation of the brine. Drake learned of cable tool drilling from Chinese laborers in the U.S.[4] The first primary product was kerosene for lamps and heaters.[5][6] Similar developments around Baku fed the European market.
In the s, outside of the oil and gas industry, roller bits using mud circulation were replaced by the first 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.
Oil and natural gas drilling rigs are used not only to identify geologic reservoirs, but also used to create holes that allow the extraction of oil or natural gas from those reservoirs. Primarily in onshore oil and gas fields once a well has been drilled, the drilling rig will be moved off of the well and a service rig (a smaller rig) that is purpose-built for completions will be moved on to the well to get the well on line.[7] This frees up the drilling rig to drill another hole and streamlines the operation as well as allowing for specialization of certain services, i.e. completions vs. drilling.
Mining drilling rigs are used for two main purposes, exploration drilling which aims to identify the location and quality of a mineral, and production drilling, used in the production-cycle for mining. Drilling rigs used for rock blasting for surface mines vary in size dependent on the size of the hole desired, and is typically classified into smaller pre-split and larger production holes. Underground mining (hard rock) uses a variety of drill rigs dependent on the desired purpose, such as production, bolting, cabling, and tunnelling.
In early oil exploration, drilling rigs were semi-permanent in nature and the derricks 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 short tons (91,000 kg) 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.
An automated drill rig (ADR) is an automated full-sized walking land-based drill rig that drills long lateral sections in horizontal wells for the oil and gas industry.[8] ADRs are agile rigs that can move from pad to pad to new well sites faster than other full-sized drilling rigs. Each rig costs about $25 million. ADR is used extensively in the Athabasca oil sands. According to the "Oil Patch Daily News", "Each rig will generate 50,000 man-hours of work during the construction phase and upon completion, each operating rig will directly and indirectly employ more than 100 workers." Compared to conventional drilling rigs", Ensign, an international oilfield services contractor based in Calgary, Alberta, that makes ADRs claims that they are "safer to operate, have "enhanced controls intelligence," "reduced environmental footprint, quick mobility and advanced communications between field and office."[8] In June the first specifically designed slant automated drilling rig (ADR), Ensign Rig No. 118, for steam assisted gravity drainage (SAGD) applications was mobilized by Deer Creek Energy Limited, a Calgary-based oilsands company.[9][10]
An auger drill is a spiral-shaped tool. Its main function is the drilling of holes in the ground and other materials - or surfaces such as ice, wood, etc. The design of an auger depends on the kind of material it's meant to drill into, hence there are different types of auger drills.[11] Auger drills come in varying sizes and can drill holes up to a depth of 95 feet below the ground. They are known to be quite versatile, saving time and energy during construction work or even personal projects. The auger is a helical screw made of steel casing with curved flights that rotates as it's pushed into the ground by a drill head. As the auger rotates, it brings excavated material to the surface, which helps keep the borehole open and prevents it from collapsing. Augers can be mounted on trucks or other machines and come in different lengths and diameters. Auger drilling is used in many fields, including construction, environmental studies, and geotechnical investigations. It can also be used for a variety of other purposes, such as:
There are different auger drilling methods, including hand auger drilling and hollow stem auger drilling. Hand auger drilling is a cost-effective method that's often used in areas with shallow soil, but it can be time-consuming and labor-intensive. Hollow stem auger drilling uses a large, hollow auger that removes soil as it drills.
Auger drilling is often quieter and less vibration-prone than other drilling methods, like drive drilling, so it can also be used in urban areas. When using an auger, it's important to take safety precautions, such as wearing protective equipment like gloves, eye and ear protectors, and closed-toe boots. You should also make sure the auger and attachments are secure, engage the drill's high torque gear, and start drilling slowly.
A drill bucket, or auger bucket, is a drilling head that accumulates spoil inside and can be lifted from the hole periodically to be emptied.[12]
This method is particularly effective for drilling through hard and compacted soils, as well as rocks, due to the bucket's cylindrical design with cutting teeth at the base, which excavates and retains soil or rock as it rotates. Drill buckets are commonly used in foundation drilling for constructing deep piles and shafts.[13]
They come in various sizes and configurations, tailored to specific ground conditions and project requirements, and can be equipped with wear-resistant components to enhance durability in abrasive environments. Additionally, modern drill buckets may include a vented bottom to release trapped air and facilitate faster spoil removal.[13]
Directional drilling is a broad term used to describe any boring that doesn’t go in a straight line vertically down. In fact, even in a vertical well, it might be necessary to deviate to avoid a geological formation or a previous stuck pipe, then return to the original path. In this instance, the driller uses sidetracking techniques.
In conventional drilling for oil and gas, the drill bit, drillstring, pipe and casing all go down in a straight line. If a driller aims away from the 180-degrees down, that’s technically directional drilling. Nowadays, however, it’s more likely that there’ll be a series of one or more carefully planned directional changes along the wellbore.
Directional drilling techniques have been employed for almost 100 years now. Over the past few decades, technological improvements have meant that angles, turns and underground distances covered are amazing feats of engineering.
Techniques such as multilateral, horizontal and extended reach drilling (ERD) are enhanced oil recovery (EOR) methods that can increase the yield of a downhole dramatically. It’s possible for ERD specialists to drill for more than 10 kilometers/6.2 miles. Students of petroleum engineering often get shown illustrations and diagrams that look like tree roots. If we imagine the rig as the trunk of the tree, the directional possibilities of the roots are endless. Even the branches of the roots are comparable to multilateral drilling.
Multiple down holes can be drilled from the same rig, minimising surface disturbance and environmental impact. Also, these boreholes can extend up to a mile down, and for more than five miles at shallower angles. In an oilfield with dispersed deposits, a large radius can be tapped, maximising the expensive asset which is the rig. Rigs and crews have day rates that run into the hundreds of thousands of dollars, one rig working up to five or ten square miles is very cost-effective in comparison to having a dozen or more vertical rigs, which may or may not be tapping into the same accessible reservoir deposits.
Geologists and engineers use terms such as an ‘oil reservoir’ or a ‘hydrocarbon reservoir’ to describe underground pockets of resources. Scientific terms give a label to help everyone understand each other, but Mother Nature has different ideas about the way she organises things.
People who perform well plans such as seismic geologists, geoscientists, exploration engineers and CAD experts join together to give the best idea of where oil and gas deposits may lie. Their estimates are based on different types of surveys, and past experience. What they’re unlikely to do is pinpoint the exact place where they’d access the maximum amount of resources.
When we see reservoirs of water, we can imagine dropping a giant straw into the middle and sucking up the entire lake. The flat surface area of the water and the likelihood of human-made dams and walls might give us a false idea of the topography of an underground reservoir. The bottom of the lake would provide a better insight into the random geometry of the dispersed resource. For example, if your imaginary straw happened to touch a shallow gravel bar in the middle of the lake, you might only extract a small percentage of the water.
On top of this randomness related to upper, lower and outer dimensions, there are plenty of other possibilities:
In fact, these ‘irregular’ reservoirs are very common. Now that relatively fewer elephant reservoirs are being discovered, and technology improves, directional drilling becomes more critical each year.
Another use for directional drilling is in the event of an uncontrolled, or ‘wild well’. If you imagine a well that has broken through the blowout preventer and is gushing, how can you cap it?
This depends on the amount of underground pressure. In some instances, a second control well is drilled so that it intercepts the same point where the original wellbore meets the reservoir. Once the new directional well is completed, it can be pumped with kill fluid.
If the well pressure isn’t too severe a relief well can help to release gas so that the original gusher reduces in intensity, allowing it to be controlled. Mud and water are pumped in from a different angle, to get the first well under control and back to proper working order.
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It’s not possible to see hundreds of metres underground, in fact, the drillers and engineers rely entirely on technology to ‘see’ where they are going. A directional driller has a guide that has been created by the engineers and geologists. Every 10-150 metres, (with 30-40 being typical), survey data is sent back to make sure that the original ‘blue line’ well path is being followed.
Directional drilling software receives input from multiple measurements while drilling (MWD) sensors in the drill bit, and at any branches or junctions. (Other measurement tools include Electromagnetic MWD and Global Positioning Sensors (GPS)). In addition to MWD technology, mud loggers use logging while drilling (LWD) sensors and software. The drill bit has vibration sensors that can detect the type of formation being drilled at any point. Collars can be added along the length of the well, sending back information to the surface regarding torque, weight and bending.
From the surface, electromagnetic sensors can also track the progress of the drill bit. When all of the data from the drill bit, collars, motors and the surface equipment enter the control panel, a complete representation occurs.
As well as being able to know what is going on, even a mile along the drill bore, drilling engineers can make adjustments in real-time that ensure that everything is going to plan. This is especially relevant when unexpected things occur concerning geology or severe equipment stress.
If you were to imagine the mechanics of directional drilling without seeing the technology, you might wonder how the drill could suddenly change direction. Since the motor that turns the drill is at the surface, how can the drill string continue to rotate at 360 degrees while going around a corner?
We now have downhole drilling motors, that can drive the drill bit in a completely different direction to the usual 180-degree downhole starting point. Turbodrills and rotary steering drills are employed in directional situations where they’re best suited.
The rotational speed of the drill and the weight and stiffness of the drillstring can also be used to influence direction. One of the original methods was jetting, a high-pressure nozzle shot water or drilling fluid from one edge to the drill bit, creating a weaker side in the formation.
Another traditional method was to use a whipstock. A whipstock is a type of wedge that can redirect the drill. At the desired depth the drill is withdrawn to the surface, a whipstock gets put in place, then the drill goes back down and gets redirected by the whipstock. Next, the drill is brought to the surface again, the whipstock pulled out and then drilling resumes and the bore changes path.
Drill bit sensors can tell the driller about external weight, and rotary speed that can also be used to influence the trajectory. Mud motors can also be used to change direction. With a steerable drill pipe, there’s a bend near the bit. The drillstring stops turning, and then there is plenty of time to use chosen directional techniques to reposition the bit to the desired trajectory. When it starts spinning again, it’ll start going in the direction that it’s now pointing towards. (More about steerable mud motors in the next section).
Specialised drillbits are used to improve performance and reduce the chance of failure. Schlumberger supply directional PDC drill bits for both push- and point-the-bit rotary steerable systems. Horizontal Technology, Inc. provides ‘Varel High Energy Series bits’ designed for the unique, rigorous conditions of horizontal directional drilling.
Mud Motors. Downhole steerable mud motors get positioned near the drill bit, which has a bend in it. What happens is that at the correct depth the drillstring stops rotating, then drilling fluid is pumped through the mud motor so that the drill bit starts to turn just due to the force of the liquid. This mud pressure pushes the drill bit into a different angle, and also begins to bite into the formation at a different angle to the central well trajectory. Once the sensors verify that the drill bit is pointing in the right direction, the drillstring starts to turn again.
Rotary Steerable Systems (RSS). Directional drilling by using the mud motor means that often the drill pipe needs to be slid forward while the drill is motionless. A rotary steerable system can drill and steer at the same time. This means that previously inaccessible formations can be accessed.
Bottom Hole Assembly (BHA) configurations are often bent in shape so that they can make turns by using physical manipulations. The video further up the page clearly shows the bend in the drill pipe.
Multi-Shot cameras are fitted inside the drillstring. They’re set to take regular pictures on a time-lapse setting. Then these images are sent to the surface control.
Custom whipstocks that work with downhole motors don’t need removing in between drilling. These are a significant advance on the old fashioned ones previously mentioned. More time can be spent drilling, and less time removing the drill bit and conventional whipstock.
Networked or wired pipe. The Intelliserve system from National Oilwell Varco is a broadband networked drilling string system. It can transmit data from the sensors back to the surface.
These are most of the specialist directional equipment used. Plus there is the three-dimensional measuring equipment mentioned previously in this article (MWD, LWD, etc.)
Well integrity is perhaps the most crucial aspect of directional drilling. Drilling at deeper, or extended distances, and especially changing direction causes a number of additional engineering challenges and stresses on the equipment.
For example, a downhole drilling motor will always be far smaller and less powerful than one connected to a robust drilling rig above ground. It’s more likely to fail, or have insufficient torque or speed to get through challenging geological formations.
The drillstring itself will be less stressed when going in a straight line, every degree of turn add extra friction and unbalanced pressure. If drillstring integrity isn’t maintained, the drillstring can snap or get jammed. It could mean that a brand new set of equipment is needed, and a new well might need to be drilled again in a slightly different direction.
Maintaining hydraulic pressure, and wellbore cleaning is much more challenging with these types of wells. Modern directional drilling equipment is so advanced, it can cope with high pressure/high-temperature HP/HT conditions, a mile away, after the wellbore has changed direction.
Computer simulation programmes are used to simulate the well plan. 2D and more recently 3D modelling programmes give the geoscientists and engineers a visualisation of the planned path. This software is created based on previous knowledge, current seismic and magnetic data, supplemented with real-time data from the MWD instruments.
There are a few different types of directional drilling. Multilateral drilling is where a downhole bore has multiple lateral (90 degrees) offshoots. For example, a well might be metres in depth but have numerous lateral wells connected to it. Extended reach drilling (ERD) is categorised by ever longer wellbores drilled from the rig.
Perhaps the most interesting type is horizontal directional drilling because it was the first type, and perhaps the most controversial.
Land tenders offer the right to explore and extract resources from a particular square meterage of land. It’s possible to purchase a lease for an oil patch, then drill horizontally into neighbouring territory. Close to a national border, it’s been known for drillers to drill into another country.
This is different from straightforward situations, where two territories happen to tap into the same reservoir. The industry has guidelines and regulations. Simultaneous operations (SIMOPS) and combined operations (COMOPS) have strict procedures for situations where well interference can occur.
The oil industry is aware of the ability to horizontally tap deposits under other peoples leases, lawsuits related to this started way back in the s.
Of course, the majority of horizontal drilling is done for good reason, not to cross borders of ownership or sovereignty. Sometimes horizontal directional drilling is the only possible way to tap a reservoir, such as the case of dilling under a town or nature reserve. Other times it’s a cost-saving exercise, to drill under a salt dome or mountain. Lastly, drilling horizontally can be the best way of maximising extraction by reaching more sections of a reservoir.
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