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In the past we heard a lot about “peak oil” and how the world would soon run out of oil. That is not going to happen for many years, if ever, and one the main reasons is the use of directional drilling. We asked Dr David Maddison to take a look at the topic and this is his report. The big energy breakthrough: Horizontal drilling for oil D irectional drilling, also known as slant drilling, is chances of finding oil from around 10% in early times to a technology which gives the ability to drill a hole about 50% today. One of the most significant historical incidents involving into the ground in any desired direction (bearing) and angle, toward a predetermined location. It is widely directional drilling was when Iraq accused Kuwait of stealused for oil and gas production, for “Surface in Seam” ing its oil via this method. This resulted in Iraq occupying (where a well is drilled horizontally into a coal or shale Kuwait and subsequently led to the First Gulf War. Directional drilling has specific applications as follows: seam to extract gas) and for underground utility cable or pipe installation. (a) Multiple wells from a single location In the past, oil wells were drilled over easily-accessible In the case of an off-shore drilling platform, directional deposits. Early prospectors did not really know what to drilling enables multiple wells to be drilled from a fixed look for in terms of geological formations, so they would location, saving the huge expense of moving the platform drill wells near places such as natural oil seeps. or building another. Many oil fields would not be economic As knowledge improved, prospectors could look for without this capability. certain types of (b) Lack of suitageology known ble surface locato be associated tion for a drilling with oil deposplatform its. Beyond that, An oil or gas the development deposit may lie of remote sensbeneath a town, ing technologies city or a mountain which detected or some other area magnetic, graviunsuitable for a tational and seisdrilling platform. mic properties Another examimproved the ple is offshore deability to find deposits which can posits at greater be accessed from depth. an onshore drillThe only sure ing rig where the way to know if Sources: US Energy Information Administration and US Geological Survey deposit is relativethere is oil or Fig.1: several oil and gas drilling scenarios showing, from left to right, a well ly close to shore. gas is to drill a that has been drilled vertically and then steered into a seam of hydrocarbon One example hole – but mod- rich shale; a well that has been steered to intersect gas deposits within sand; of drilling and reern technology a conventional vertical well to extract coal bed methane and on the far right a covery of oil from has improved the traditional oil and and gas well drilled vertically. 16  Silicon Chip siliconchip.com.au Image source: www.pdgm.com/solutions/well-planningdrilling-engineering-and-geosteering/well-planning/ Fig.2: image generated with Paradigm Sysdrill well planning software showing planned locations of directionally drilled wells. beneath a city is in the Beverly Hills Oil Field, part of the City of Los Angeles (see Fig.3 below). through a salt dome can be problematic. A well can be drilled in such a way as to avoid going through such domes. (c) Drilling around obstructions This is known as side-tracking. The directional drilling technique is used to drill around an obstruction in a well, such as a broken-off string of pipe or a drill bit. (Such pieces of debris are known as “fish”.) Side-tracking can also be used to invigorate an old dry well by using part of the existing well and then side-tracking out of the original well casing to access possible untapped deposits. (g) Drilling relief wells Relief wells are often required to kill an oil or gas well that has “blown out”. A blow-out is an uncontrolled flow of gas, oil or other well fluids from the well. A nearby well is drilled to intercept or pass close to the bottom of the blown well and a special high density “kill fluid” is then injected to block the blowing well. (d) Drilling in heavily faulted rock formations Heavily faulted rock formations can cause deflection of a vertical well during drilling. Also, a fault might slip, breaking the drill pipe. Directional drilling allows a better and safer approach angle to the deposit. (h) Straightening a crooked well A conventionally drilled vertical well might drift off course. Directional drilling techniques can be used to redrill the well from the point of deviation, to realign it to the correct direction. (e) Intersecting multiple deposits with a single well In some cases it might be most economical to have a single well intersect multiple hydrocarbon deposits. This saves having to drill multiple wells. (f) Drilling in an area of salt domes Oil deposits are often associated with salt domes but drilling siliconchip.com.au Fig.3: the Beverly Hills Oil Field is providing oil from a most unexpected location. Oil recovery is via directional drilling from four “drilling islands”, hidden away beneath structures designed to disguise them. (i) Recovery of coal seam or shale gas or oil Huge quantities of gas and oil are now being extracted by horizontally drilling through coal, shale or oil-bearing seams. For an example of such drilling see Fig.6. (j) Utility cables and pipes Directional drilling techniques can also be used to install utility cables and July 2016  17 Fig.4: seismic survey of a deposit in Queensland showing a variety of possible oil, gas and coal deposits, demonstrating the great detail that can be produced describing structures within the Earth. Directional drilling technology can ensure that no economically recoverable deposit is inaccesible. pipes. One application is to run these utilities under a river, thus saving the cost of a bridge; or running utilities under roads and footpaths without having to excavate. Naturally, one must check plans for existing services or detect existing services with special equipment. Many cables for the National Broadband Network (NBN) are being installed by this method. Fig.5: simplified view of a drilling rig showing the main components. Components of a drilling rig The drilling rig imparts rotary motion to a drill string. It contains pumps to circulate drilling fluid or “mud” to facilitate the drilling process and has equipment to add or remove sections of pipe to or from the drill string. The drill string comprises the components of the drill pipe, transition pipe and the bottom hole assembly. The bottom hole assembly comprises a drill bit, drill collars which are heavy thick walled tubes for applying extra weight to the drill bit, components such as down-hole motors or a rotary steerable assembly and various sensor packages. Transition pipe makes a flexible connection between the drill collars and drill pipe. Drill pipe is hollow tubing which compromises the majority of the length of the drill string. How is the drill steered? There are several ways in which a drill can be “steered” to a desired direction and angle using “deflection tools”. The basic principle involves applying side-force to the drilling bit, causing it to deviate from its straight line course. The most common tools for directional deviation are steerable motor assemblies and rotary steerable systems which are placed at the end of the drill string. Other systems Fig.7: drill string showing drill pipes, bottom hole assembly (BHA) and the drilling bit but not showing the transition pipe. Fig.6: plan of horizontal drilling into gas bearing shale formation around Glenfarne in Ireland. Each set of wells has a common origin at a drilling pad indicated by a small red rectangle. Note the 1km scale marker indicating the massive scale of the horizontal drilling. 18  Silicon Chip siliconchip.com.au History of Directional Drilling Apart from drills accidentally deviating from the vertical (or possibly deliberately deviating from the vertical to steal someone else’s oil!) one of the first legitimate applications of directional drilling was to relieve pressure on a well that was undergoing and uncontrollable fire in Texas. A slanted well was drilled into which water was pumped which extinguished the fire at the wild well. This saved the oil field. This work appeared on pages 40, 41 and 117 in the May 1934 issue of Popular Science Monthly. You can read it yourself at Google Books: https://books.google.com.au/books?id=wygDA AAAMBAJ&lpg=PP1&pg=PA40#v=onepage&q&f=false The article stated “Only a handful of men in the world have the strange power to make a bit, rotating a mile below ground at the end of a steel drill pipe, snake its way in a curve or around a dog-leg angle, to reach a desired objective.” The method used to deviate the drill was with a whipstock, (see Fig.8 at left). Fig.8: a whipstock. It is like a wedge placed in an existing bore hole that forces a special drilling bit to deviate off into unbored rock. The steps are as follows: 1) A packer is placed in the borehole at the desired location. 2) The whipstock is oriented to the desired angle. 3) A hole is milled through the side of the existing borehole. The tool can bend because of a flexible joint. 4) The whipstock is retrieved. in use are whip stocks to sidetrack out of existing cased (lined) bore holes and jetting systems. A whip stock is like a wedge placed down an existing borehole to apply lateral force on a special drill assembly, causing it to deviate through the side of the bore (see Fig.8). Another method is to have a drill bit with a jet on it which cuts out a pocket of material using high pressure hydraulic fluid in the direction of desired travel. This is mainly of use in softer rock formations. There are two more complex methods of directional drilling. One is a so-called steerable motor assembly and the other involves an assembly at the end of the drill train that can exert force on one side of the borehole to steer the bit, a so-called rotary steerable system. Steerable motor assmblies A steerable motor assembly contains a motor at the end of the drill string which is attached to a “bent-sub”, a relatively short length of pipe that is at a slightly different angle to the rest of the drill pipe. Under normal circumstances of straight drilling, the entire drill string (comprising the drill pipe, the bent-sub and drill bit plus any electronics packages) is rotated as for a conventional drilling operation. The bend in the pipe does not affect anything as forces are applied evenly and the bore is cut in a straight line. The motor is not electrical but is driven by high pressure Fig.9: typical dimensions of a steered motor assembly. siliconchip.com.au Illustration from 1934 “Popular Science” article about how directional drilling was used to put out a major oil well fire. The next major development in directional drilling came in the 1970s with the development of the steerable motor assembly. Beyond that, rotary steerable systems were developed in the 1990s but were still considered an exotic technology until the 2000s. The massive increase in computer power and remote sensing technology has since enabled extremely detailed maps of subsurface terrain. Computer power also allows the planning and the steering of the bore holes in any desired direction. July 2016  19 How much oil is left in the world? This is a commonly asked question, especially since the predictions of the date of Peak Oil (the time of maximum extraction of oil is reached after which it declines) keeps getting pushed back and has done so since 1919, when the chief geologist of the US Geological Survey predicted peak production of US oil would be reached within a few years. That’s not to say that the time won’t come, but we just keep finding more oil and have also started utilising unconventional sources such as tar sands. In 1981 world consumption of oil was 60 million barrels per day and proven reserves were 700 billion barrels. On this basis it was predicted the world would be out of oil by December 2013. By then, global production of oil was 46% higher than in 1981 and proven reserves were one trillion barrels greater. Today’s current prediction, by BP, is that current proven reserves form around another 53 years supply. The 53 year prediction is based on the concept of proven reserves which are what companies believe they can extract out of the ground at current prices with current technology and still make a profit. As prices rise, formerly uneconomic reserves may become profitable or new technology (such as directional drilling) might make otherwise uneconomic reserves economic to recover. New discoveries will also be made. Actual proven reserves are a small proportion of the the oil left in the ground. Fig.10: the two processes involved when directional drilling using a steerable motor assembly. On the left the drill string is stationary and the mud motor rotates the drill bit during the “sliding” process. On the right, the entire drill string rotates and the well is drilled in a straight line. Due to the bend in the pipe, the bore will be greater than the diameter of the drill bit. Note that the angle of the bend can be adjusted as circumstances dictate. Image from Deepak Choudhary’s blog at http://directional-drilling.blogspot.com.au/ Rotary steerable systems Unlike a steerable motor assembly, the drill string of a rotary steerable system constantly rotates even during steering operations and there is no bent-sub (length of pipe with a bend in it). Instead, there is a series of typically three pads around the circumference of a motor assembly which, under computer control, move in and out in rapid succession at a particular point in the drill string rotation. This exerts a sideways force at one point on the bore hole to force a change in the drilling direction. During straight drilling these pads are retracted. As an alternative to separate pads, elliptical rings are used in some systems which are rotated to apply force on a particular side of the bore hole. There is also the hybrid Schlumberger PowerDrive Archer rotary steerable system that has a motor within it thus giving advantages of both a steerable motor assembly and a rotary steerable system. Steerable motor assemblies versus rotary steerable systems Diagram from the US Energy Information Administration showing the small proportion of proven reserves compared to the total amount of oil left. As prices rise or technology improves more oil becomes available. “mud” forced through a spiral-shaped cavity or stator in which resides a matching rotor. There is a continuous seal along the matching edges of the stator and rotor and when mud is forced through the cavity, the rotor turns, causing the drill bit to rotate (see Fig.11). This type of motor is known as a mud motor or progressive cavity positive displacement pump. Another type of mud motor uses a turbine instead of a rotor. When a change in direction is required, the drill string is stopped from rotating but mud continues to flow through the mud motor. As there is a bend in the pipe and the whole pipe is no longer rotating, the cut will be in the direction of the bend. This operation when the drill string is not rotating is known as “sliding”. The key to this operation is knowing the way the bend is oriented since obviously it has to be steered toward a required direction. This is determined by “measurement while drilling” instrumentation located behind the drill bit, such as accelerometers, magnetometers and other instruments. Such instrumentation will be discussed later. 20  Silicon Chip Steerable motor assemblies are older technology than rotary steerable systems but nevertheless are reliable and in many cases more economical to use. However, rotary steerable systems can be used to drill wells which would be extremely difficult or impossible with a steerable motor assembly. A key advantage of rotary steerable systems is the fact that the entire drill string turns at all times which prevents the possibility of the string becoming stuck against the borehole wall by friction, as could happen when using steerable motor assemblies during the process of sliding, when the only rotation is of the drill bit and mud motor but not the drill string. In addition, this friction can result in less than the desired weight transfer to the drilling bit causing slower penetration rates. A further disadvantage of steerable motor assemblies is that during the process of sliding (when the drill string is stationary), drill cuttings tend to pack in around the bottom assembly. This is because there is no vortex created around a rotating drill string which tends Fig.11: mud motor and drill bit assembly. The rotor assembly for the mud motor is visible at the left and the drill bit is on the right. siliconchip.com.au to keep the particles in suspension, making them easy to carry away to the surface. There is also less drag with rotary steerable systems and a smoother hole which contributes to greater directional control. Logging-while-drilling, the process of obtaining bore hole data such as direction during the drilling process is also possible with this system. Higher accuracy is also a feature, enabling extremely small target zones to be reached such as in a layer that is only 45cm thick. While rotary steerable systems have many advantages, one disadvantage is their cost. If precise directional control is not needed then a steerable motor assembly would be the preferred choice. Also, the rotation of the rotary steerable The Weatherford Revolution® rotary steerable system. system is generally dependent on the drilling rig as they generally do not have their own motor, unlike steerable motor assemblies, so possibly a higher performance drilling rig would be required than with a steerable motor assembly. There is also a more limited range of drilling bits available and much greater mechanical and electronic complexity. If a rotary steerable system is lost down a bore hole as happens from time to time, its replacement could cost over US$1 PILOT HOLE PRE-REAMING PULL-BACK Method for trenchless installation of pipe under a river using directional boring. First a pilot hole is drilled and steered in the desired direction, then a reamer is pulled through that pilot hole from the opposite direction to expand the diameter of the hole and then the pipe is pulled through. Photo at left shows the horizontal boring machine and at right a length of pipe is prepared for the pull-back process. siliconchip.com.au July 2016  21 Some videos on directional drilling “Horizontal Directional Drilling / Boring (HDD): How the Drill Bit is Steered” https://youtu.be/cl8BBoCV7gU “Directional Drilling 3D Animation.avi” (silent video) https://youtu.be/raTMsTpD3Pg “Complete directional drilling operation” (silent video) https://youtu.be/tUxkx48HRIo “Horizontal Directional Drilling - how it works” https://youtu.be/ufYMgHa0d18 This video shows the installation of an underground pipeline. “Horizontal Directional Drilling - Pullback 48’’ Steel Gas Pipe” https://youtu.be/o-1kBFJLXSY “Horizontal Directional Drilling, The Next Generation (HDB)” https://youtu.be/zr6pgRv6RDo “Geo-Pilot® Rotary Steerable System from Halliburton” https://youtu.be/uVrw3InxPyc “The Revolution Rotary-Steerable System - How It Works” https://youtu.be/9TEyYRAu2Uk The Halliburton Geo-Pilot Dirigo rotary steerable system. million compared with an average replacement cost of a steerable motor assembly of US$168,000. Bore hole data It is important to measure various parameters to do with the drill string and the rock formations through which the well is being bored. Some measurement systems work in real time and others require drilling to be stopped while a probe is lowered down the hole. The instruments have to be extremely rugged and have to withstand temperatures up to 175°C, pressure up to 170MPa (25,000 psi) and 500G acceleration for 0.5ms. Power is supplied to the measurement system either by non-rechargeable lithium thionyl chloride batteries or a turbine and alternator system driven by the flow of the drilling mud. There are two general categories of real-time measurements. Both require sensor instrumentation which is part of the bottom hole assembly. Note that in some cases the sensor packages transmit some data while other data is recorded in memory and analysed when the bottom hole assembly is bought to the surface, due to the limited data rate available with some data transmission methods. The first category is called measurement while drilling and relates to drilling mechanics and survey of the position of the drilling bit. Measurements include the inclination and direction of the drill bit, rotational speed, vibration of the drill string, temperature, torque on the drill bit, weight on drill bit and mud flow rate. The second category is called logging while drilling and relates to properties of the rock formation being drilled. Measurements made include rock density and porosity, electrical resistivity. acoustic properties, magnetic resonance and formation pressure. Logging while drilling enables the following measurements to be made, including: • Gamma radiation from the rock; • Density of rock and photoelectric index; • Neutron porosity to indicate hydrogen content in a reservoir; • Bore size and shape; • Electrical resistivity of rock to help distinguish between formations containing salty water and hydrocarbons; • Sonic logging to measure the ability of the bore hole to transmit sonic waves; • Bore hole imaging; • Testing and sampling of rock formation; • Nuclear magnetic resonance to test a formation’s porosity and permeability and • Seismic measurements while drilling to determine optimal path of bore hole. The Schlumberger PowerDrive Archer which is a hybrid rotary steerable system with its own motor, combining advantages of both systems. The background image is a three dimensional map showing the directionally drilled bore holes in red and the underground structure in a grid pattern. 22  Silicon Chip 22   siliconchip.com.au Max3Di™ Drilling optimisation software that displays various drilling data sourced both at the surface and from the bore hole during the measurement while drilling process. Mud-pulse telemetry Several methods are used to transmit data from the bottom hole assembly instrument packages to the surface. Mud pulse telemetry involves encoding data in the form of a modulated pressure pulse in the drilling mud which is measured at the surface and then decoded. The pressure pulse is generated with a valve in an instrument package near the drill head to momentarily restrict the flow of drilling mud. It can be in the form of either a positive or negative pulse, depending upon conditions inside the borehole. There is also a form of mud pulse telemetry involving encoding data on a continuous wave via sinusoidal pressure variations. Data rates of up to 40 bits per second are possible but this diminishes with distance and can drop to as little as 1.5 bits per second at a well bore length of 12,200 metres. Electromagnetic telemetry involves sending either a magnetic or electrical pulse from the drilling tool which is detected on the surface. The data rate is higher than for mud pulse telemetry but it does have depth limitations and a signal may be undetectable at depths beyond 1000 metres or in certain rock formations. High speed data transmission can be effected by using wired drill pipe. Connections are made between different sections of pipe via electromagnetic induction through an inductive loop. Very high data rates of up to 1 Mbit per second or more are possible. In addition, it enables a local area network to be established with the ability to make siliconchip.com.au various instrument and tools on the drill string individually addressable. The technology was first deployed in 2006 and is known by the trade name of IntelliPipe for the physical pipe and IntelliServ for the network architecture. Utility cabling and pipes Apart from its use in oil and gas drilling, directional drilling or more correctly, directional boring (also known as horizontal directional drilling) is used to install utility cables, conduits and pipelines without having to dig trenches and with minimal environmental impact. Of course, before proceeding it is vitally important to do a site survey first to determine the location of other underground services. Unlike directional drilling in the oil and gas industry A look inside an oil well Here is a fascinating collection of video clips from a camera sent down various oil wells to look at different problems. Note that the term “fish” used in the video refers to undesired debris in the well such as broken pipe. In these videos the wells have been shut down (sealed off) to reduce the flow of gas and oil to enable inspection to take place. “Oil Well Downhole Camera Video (1/2)” https://youtu.be/ZzDrheWDhGw “Oil Well Downhole Camera Video (2/2)” https://youtu.be/5diKdBZ8EOI July 2016  23 Intellipipe® concept for high speed data transmission. A data connection is made across sections of pipe via electromagnetic induction across the pipe joint while a cable runs within the section of pipe. The concept also establishes a local area network within the drillstring enabling individual sensors and tools to be addressed. MWD stands for measurement while drilling. where the initial direction of the bore is roughly in the vertical direction, directional boring is closer to horizontal. A bore hole is initiated at a shallow angle and then steered into a more horizontal position. Typically, a tapered cutting bit is used and it provides the steering mechanism. When a direction change is required the drill string is stopped from rotating and the taper oriented to move the drill in the direction required. Then the drill string is thrust forward and rotation of the drill string begins. Jetting or a steering process similar to the sliding of a mud motor can also be used. The choice of a tapered head, jetting or mud motor depends on the nature of the subsurface structure. It is obviously important to know the location of the drill head and this is done via one of four methods. In the walk over locating system, a transmitter located at the bore head electromagnetically transmits data to the surface concerning angle, rotation and direction data and this is received by a hand held receiver over the general vicinity of the bore head. The received data is then used by the boring machine operator to make any corrections required. Magnetic guidance is a method utilising magnetometers and accelerometers at the drill head to calculate the directional heading and location of the drill head. In some urban environments there is a lot of magnetic interference and so an artificial magnetic field is generated at the surface. A secondary system of location that can be used with magnetic guidance involves the use of a DC coil placed on the surface to generate a magnetic field which is sensed at the drill head. Very high accuracy of location is possible with this method. A gyroscope-based system is also available that works in real time and provides directional data to autonomously steer the drill head. Pipes can be installed in a diameter range from 75mm to 2000mm and multiple smaller pipes or conduits can be installed at once during the pull back process. Pipes can be installed using smaller machines at a depth of up to 4.5m but this is a limitation of the surface tracking system. Larger machines can install pipes down to about 60m in depth. The length of pipe that can be installed ranges from around 120m to 4570m (maximum diameter and length figures are for a HERRENKNECHT HK600T machine). A video of the directional boring process can be viewed at https://youtu.be/FQBVTlcl20c “Prime Drilling - Horizontal directional Drilling explained”. Conclusion Directional drilling enables oil and gas to be extracted from formations which would be unreachable or uneconomic by conventional drilling methods and enables more energy to be extracted from the earth to feed our energy hungry civilisation. Directional boring enables conduits and pipes to be installed relatively inexpensively without needing to dig SC expensive trenches. A Ditch Witch JT60 directional boring machine. The drill string is initially bored into ground at a shallow angle. In this case the drill string can be seen coming out to the left of the machine. Extra lengths of drill pipe visible on the machine are added as the boring progresses. Such machines are available in a wide range of sizes. 24  Silicon Chip siliconchip.com.au