Rotary drilling method
The rotary drilling method is a method used for geological drilling and is mainly used for vertical or slightly inclined deep drilling for crude oil , natural gas or for geothermal drilling . The main feature of the rotary drilling process is a rotating drill pipe. While a rotary table drive and a classic pyramid-shaped tower (rig) were used for a long time in the 20th century and much work had to be carried out manually, modern systems often work with masts, the drill rod is driven by a power rotary head and the work is highly mechanized.
Components of a classic drilling tower with rotary table drive
The rotary drilling process was developed and perfected primarily in the USA, so that many English-language terms are used untranslated in German. The German language also has its own technical terms or technical terms from mining that must first be explained in order to understand the individual processes involved in drilling.
- If the rods are screwed together or to the pulling cap or the chisel, the screw connection must be tightened with a high torque . This is called countering. This torque must be released again when screwing apart. This is called breaking. In the classic rotary process, the high torque is applied using rotary tongs, also known as machine tongs.
- If the drill bit has to be changed, the entire rod must be pulled from the Kelly or the drill rod on the power rotary head to the chisel and then reinserted. This process is called a round trip. When pulling the drill rod, the flushing head is exchanged for the elevator , a gripper that grabs the head of the rod. In the highly mechanized process with a power rotary head, the elevator is usually pivoted hydraulically in front of the rotary head.
- The move: During the round trip, not all of the rods are unscrewed in the case of higher drilling rigs, but rather they are placed in groups of several rods (depending on the height of the drilling tower, two rods for the double stand, three rods for the higher triple stand) in the finger platform. Such an association is called a train. No trains can be parked in the Single, at best the individual boring bars.
- If the drill string has to be supplemented with another rod, this is called repositioning.
- Tank or pond for the drilling fluid
- Vibrating sieve Shale Shakers and centrifugal separators Desilter and Desander '. Here the cuttings, i.e. the drilled rock, are separated from the drilling fluid.
- Suction pipe of the irrigation pumps
- Irrigation pump
- Derrick drive (mostly diesel engines)
- The high pressure hose section between the flushing pump and standpipe is called vibrating hose because it can hit or vibrate strongly due to the pressure surges of the pump.
- Elevator as the main pull
- Standpipe
- Hose to the flushing head, Kelly hose Kelly pants
- Goose Neck , pipe elbow for the flushing hose, also called gooseneck
- Kloben Traveling Block . The block is the lower block of the hoist's pulley.
- Rope of the Drilling Line elevator
- Tower roller bearing Crown Block . The tower roller bearing is the top block of the hoist's pulley system.
- Derrick itself derrick
- Monkey platform, boom platform or hanging platform Monkey Board : Here, the stage man detaches the trains from the elevator during the round trip and places them in the finger platform, which is directly connected to the monkey platform.
- Pulls of the drill pipe Stand (of drillpipes)
- Bottom of the warehouse for the trains, usually made of wood, so that the threads of the trains are not damaged.
- Flushing head
- Kelly , the drive rod. The Kelly is a prismatic tube with a square, hexagonal or octagonal base. At the top and bottom of the Kelly are the tapered threads usual for the drill pipe.
- Turntable. The turntable or drilling table is, in simplified terms, a horizontal circular plate with a central hole, which was located on the working platform in the early days, in more modern systems is embedded in the working platform and through which the drill rods are retracted. The turntable is guided by a large ball bearing and is set in rotation by the derrick drive. It has holes for the pins of the driver, which then turns the Kelly.
- Working platform or table
- Bell nipple flush spout
- and 24. Well control device Blow-Out-Preventer (BOP)
Not shown here, next to the turntable, there is a tube leading slightly into the ground at an angle, in which the next drill rod is held to extend the rod, the mousehole. Some derricks have a second storage tube in which the Kelly can be placed, which is then referred to as a Rathole.
The derrick has other important equipment that is not shown:
- In addition to the hoist, the tower has additional chain hoists or rope hoists as auxiliary winches, the so-called air winches. With a horizontal cable or spill on the monkey stage, the collars are brought into the finger stage by two stage men. The pliers and other heavy tools hang on their own air winches. The individual drill rods are pulled with an air winch from the horizontal rod store of the catwalk over the ramp (pipe ramp) through the door and placed in the mouse hole.
- The slips are placed on the table with which the drill pipe is intercepted so that it does not fall back into the borehole when it is pulled out of the borehole. When repositioning a boring bar, the hand wedges are used, with the round trip there are also automatic wedges that remain in the hole of the turntable during the trip and so do not have to be lifted up again and again.
- With the rotary pliers, the rods are tightened (locked) and released from each other (broken) after they have been screwed together. Originally, the tubes were screwed with the spinner chain and then countered with the pliers. Later, this method used mechanical aids to turn the tubes, the spinners such as z. B. the spinnerhawk and the Kelly spinner for the Kelly bar , and the not entirely harmless work with the spinner chain was limited to exceptional cases . In the beginning the pincers were operated with muscle power, later the force to counter or break was applied with spills and today with mostly hydraulically driven rope or chain hoists, which are called cat heads (catheads). As the mechanization of work progressed, hydraulic tongs were introduced first. Finally, the spinner and tongs for the Iron Roughneck, also called Hydraulic Roughneck, were combined, a hydraulic breaker / counter device.
Processes and technical developments
The greater the depth into which a borehole is to be driven, the greater the technical effort. Roughly it can be said that as the depth increases, a larger borehole diameter must be started. So it is understandable that the boring bars could still be countered and broken by hand with the chain pipe wrench from 1901 on in the first rotary bores, but today power-operated tools such as heavy tongs that are operated via cat heads, hydraulic pipe wrenches or iron roughnecks can be used for countering and breaking must be used.
The length of a normal drill rod is approx. 9 m. If the entire drill rod has to be pulled out after the chisel is worn, this means that with a medium-deep drill hole of approx. 2000 m depth, 222 rods have to be pulled, broken, unscrewed, parked, screwed together and countered. The work of the workers called Roughnecks on the work platform and of the worker called Derrick Man on the monkey platform is not without risk from the point of view of work safety, heavy parts have to be moved, one works in the vicinity of unprotected parts that move with high forces and energies, sometimes at dizzying heights, and especially when it comes to drilling, time is money. In addition, a deep borehole can cause highly flammable gases and liquids to break out. Technical progress in the Rotary process was therefore primarily related to efforts to make work faster and safer and to get by with as few staff as possible. Regardless of the properties of the rock to be drilled through, the time required for screwing and countering or for breaking and unscrewing the rod as well as the speed of the hoist determines the trip speed (roughly corresponding to the English terms trip speed or tripping speed ) and is an important one Cost factor of a deep well. If a time of 2 minutes is specified for pulling or repositioning a rod or a strand, 30 strands can be repositioned in one hour. In the English-speaking world, a tripping speed of 30 stands per hour would be specified (30 trains per hour). German manufacturers indicate the trip speed in meters per hour. The length of the train is also included here. This performance measure of a derrick shows that its performance depends, among other things, on its height, because the higher a derrick is, the longer the trains that can be parked. Oil rigs are classified according to the length of their trains, among other things:
- Single corresponds to a pipe, this corresponds to 30 feet or 9 m
- Double corresponds to two pipes, this corresponds to 60 feet or 18 m
- Triple equals three pipes, this equals 90 feet or 27 m
There were also isolated reports of systems with trains of four pipe lengths.
A single would have a tripping speed of 270 m / h at a tripping speed of 30 trains per hour. A double has a trip speed of 540 m / h at the same tripping speed and a triple can even reach 810 m / h. For comparison the performance of a modern system: Streicher indicates the performance of his VDD 370 with a single mast with a trip speed of up to 400 m / h. This may seem relatively slow, as a team of well-trained Roughnecks can expand a train into a triple in just under 2 minutes, but it must be taken into account that modern, highly mechanized systems get by with considerably fewer staff.
Drill
While initially only so-called fishtail chisels were used, which caused a very high torsional stress on the drill rod (the bolted pipe string), today roller chisels or crown chisels are used. Roller bits usually have three toothed tapered rollers which are arranged at an angle to one another. When the drill bit is set in rotation, the tapered rollers roll on the bottom of the borehole and crush the rock to be drilled in the process. For hard rock there are roller chisels whose teeth are studded with hard metal pins . PDC chisels (without moving parts) with artificial diamonds , cutting ceramics or hard metal are also used , especially with hard rock .
The crushed rock is continuously removed by a flushing fluid that is fed in through the drill pipe and exits at the bit and reaches the surface of the earth in the annular space between the borehole and the drill pipe. The drilling fluid mostly consists of water and clay powder with an addition of barite powder , which due to its high density increases the gravity pressure in the liquid to such an extent that it stabilizes the uncased borehole and the rock that has been crushed by the drill bit can be transported to the surface of the earth . In addition, the flushing fluid, in conjunction with powerful flushing pumps , enables the drilling performance to be increased significantly, as the fluid emerges from nozzles in the drill bit at speeds of over 100 meters per second and thus contributes significantly to the removal of rock. The clay rinse also has the property that its viscosity varies depending on the flow rate ( thixotropy ). If the flushing pumps fail, the flushing stops and changes to a gel-like state after a certain time. This prevents the cuttings located in the annulus from sinking in the direction of the bottom of the borehole and thus prevents the bit from becoming stuck.
The rinsing liquid that has reached the top is cleaned of the rock material brought along by means of vibrating sieves (shale shaker) and centrifugal separators (desander and desilter) and can thus be used again and again after supplementing the admixture losses.
In the rotary process, the drill bit is set in rotation by the drill pipe.
In the case of very deep or directional bores , the rotary drilling method is usually not used, but a drilling turbine (or an underground drilling motor ), which is located directly above the drill bit. In this case, the drill rod does not rotate, but only serves to advance the bit and to supply the flushing fluid, which also drives the turbine.
In the classic rotary drilling process, the drill string was usually rotated by means of a so-called turntable on the working platform of the drilling rig. The upper end of the drill rod is formed by a square, hexagonal or octagonal driver rod (Kelly), which transfers the rotary movement from the turntable to the rod via the driver, which is coupled to the turntable by means of pegs, and on which the flushing liquid is also supplied.
Today's drilling rigs are equipped usually with a power rotary head (engl. Top Drive ), whereby the drive rod is eliminated and so the constantly necessary extension of the drill string, the repositioning is simplified.
Follow up
As already mentioned, the drill rod usually consists of sections of 30 feet each (because of the origin of the drilling technology from the USA ; approx. 9 m). After every 9 m drilling progress , the entire drill string is first raised by means of the hoist, a block and tackle , for the purpose of which the derrick exists, so that the entire drive rod and a good 1 m of the top drill rod protrude from the borehole. Then the drill string is secured against falling below the flange point to the driving rod by means of hand wedges on the turntable and the driving rod is broken and unscrewed. The drive rod is then screwed and countered with a rod element that is available next to the turntable in the Mousehole. Then the drive rod with the new rod element is screwed back onto the drill rod and locked, the rod is raised until the hand wedges are free, then the wedges are removed and the entire pipe string is lowered again until the chisel with the necessary pressure the Reached the sole. A further 9 m can be drilled. The change process described takes 1.5 to 4 minutes.
Breaking or countering the drill pipe with the turntable is too dangerous and therefore prohibited. For unscrewing after breaking, the turntable is mostly used, the lower tube is rotated. To screw on the new pipe, the upper pipe must be turned. In the past, this was done partially by hand with small pipe diameters, later with a spine chain, whereby fingers, hand or arm could easily be squeezed or wound against the pipe if handled inappropriately. Therefore this is only allowed in exceptional cases. The collars were sometimes tightened with the chain pipe wrench, which was time-consuming. Over time, powered devices appeared that could rotate the upper linkage, known as spinners such as the Kelly spinner and the spinnerhawk. Modern systems have the Iron Roughneck described above with tongs and spinner, which only has to be brought up to the rod to be screwed and then carries out the tong work controlled by operating levers.
Round trip
To change a worn or defective drill bit, the entire rod must be pulled out of the already drilled borehole. This is usually done in trains of 2 to 4 rod elements, that is, 2 to 4 rod elements remain screwed depending on the height of the derrick. The complete pulling and reinsertion of the drill string is called a round trip . In the German drilling language, which is hardly used today, this process of catching up, changing chisels and letting in was called the chisel march .
history
As early as 1844, the Briton Robert Beart registered a patent for a drilling method that largely corresponds to modern rotary deep drilling technology. The rock, which has been shredded by a rotating chisel, is continuously removed by a flushing liquid that is pumped down through the drill rod and emerges from the chisel. The high technical demands (transmission of a large force to a movable drill rod, continuous supply of the flushing fluid into a constantly rotating pipe, need to regulate the load acting on the drill bit) prevented the implementation of the concept for a long time. Even after solving most of the problems, the rotary method was considered to be too susceptible to failure and thus inferior to the hammer drilling method until after the First World War .
The first famous application of the Rotary method was the drilling on Spindletop Hill near Beaumont (Texas) , which on January 10, 1901, encountered high-pressure crude oil at a depth of 347 m. A huge eruption ensued, as a result of which around 100,000 barrels of crude oil were ejected uncontrollably from the borehole and siphoned off from the oil lake that had formed. Suddenly, US oil production had tripled.
Commonly known as Spindletop Gusher or Lucas Gusher (after the hole by leading geologists Anthony Lucas - named - native Antonio Luchich) known event was in Texas a petroleum boom with lasting effects on the economy of the United States to escape.
literature
- Springer, FP: On the history of deep drilling technology from the perspective of textbooks and specialist books , Erdoel-Erdgas-Kohlen Heft 7/8, 2009 pp. 308–314.