Until now, the third generation is still the major method for directional and horizontal drilling. The development of directional techniques after Han Although the tool face is fixed, directional accuracy and operational efficiency are too low, and the borehole is always polyline. The tool face is impacted by untwist angle, which makes its fixation very difficult. Due to the wiggle of tool face, the borehole trajectory is always screwy.
The tool face is still impacted by untwist angle, but it can be fixed in a certain scope. Due to the wiggle of tool face, the borehole trajectory is still screwy. The tool face is no longer influenced by untwist angle, and it can keep stable. Most of down-hole equipment for directional and horizontal drilling are usually same with vertical drilling, such as the drill pipe, heavy weight pipe, compressive pipe, drill collar, fluted spiral drill collar, substitute sub, short pony drill collar, stabilizers, and so on.
Clearly, without advanced directional tools, it might not be physically possible to drill a given well, the well might be drilled in a suboptimal location or it might be more expensive or risky. The directional technique development is driven by advanced directional tools.
According the development history of directional techniques, the main directional tools can be summarized as follows: deflector, down-hole motor, RSDS, and vertical drilling system. The deflection tools can be defined as a wedge-shaped steel tool having a tapered concave groove down one side to guide the whipstock bit into the wall of the hole. There are two types of whipstocks available Inglis ; Short ; Chen :. The schematic diagram of removable and permanent whipstock. The permanent whipstock is mainly used in cased hole for sidetracking around a fish or by-passing collapsed casing Inglis As shown in Fig.
After setting the whipstock in the required direction and shearing the retaining pin, the milling operation begins. Once the window has been cut, the mill is pulled out of the hole and a small diameter pilot bit is run on the bottom. The pilot hole is subsequently reamed out to full size. The next step is to run a rotary building assembly to continue the sidetracking.
The most common deflection technique in current use involves running a down-hole motor, including PDM and turbo-drill, to drive the bit without rotating the whole drill-string. The deflection is provided by a special sub placed above the motor to create a side force on the bit. PDM tools are used more commonly in directional and horizontal drilling. In the s, the first PDM tool is designed by Smith drilling tools.
In the s, the commercialized PDM tools began to appear and apply in the directional drilling. Due to a successful application in the directional and horizontal drilling, PDM tool is applied more and more wide ranges. The number of lobes is a very important aspect of motor, increasing the number of lobes increases speed and reduces torque for a given size, so the common motors use one rotor and two lobes for high torque. PDM tools also have a wide range of speeds about — RPM, the most common operational speeds vary about — RPM, due to there are a large number of drill bits available.
In addition, the material of the stator is also a critical factor for PDM tools, various rubber and elastomer materials have been tried and tested. But most of the elastomer components are susceptible to high temperatures, and they are also affected by oil-based muds, which cause swelling Inglis ; Short Turbo-drill tools are also can be used for both vertical and directional wells.
In , a single-stage turbo-drill is patented in Chicago, but there is no actual using record. Until the s, the researches and developments of the turbo-drill were revived again in the United States and the Soviet Union. In the s, further developments took place for the turbo-drill by the Soviet Union, and most of the oil and gas wells in the USSR were drilled using the turbo-drills.
Turbo-drills also can operate with the cone bit and PDC bit to drill vertical, directional, horizontal, extended-reach, and multi-branched wells. To accomplish directional drilling, the turbo-drills need operate with a bent sub or a new type of bent housing.
The disadvantages include high rotational speeds, low torque, short bearing life, too many quick-wear parts, and short bit life. In order to overcome these disadvantages of the common turbo-drills, many special turbo-drill had been developed, such as the turbo-drill with low speed and high torque, the turbo-drill with gearbox, the turbo-drill with spiral housing, and other new turbo-drills.
Currently, the major application of turbo-drill is to drill extended-reach wells and to improve ROP. In addition, due to the effect of high temperature, there is a defect for geothermal drilling using PDM tools, the rubber-lined cavity cannot work under the high temperature conditions.
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The bent sub forces the bit and down-hole motor to drill in an appointed direction that depends on the tool face, which makes the amount of deflection lies on the stiffness of the down-hole motor, the offset angle of the bent sub and the hardness of the formation. The schematic diagram of types of bent housing PDM tools. The down-hole motors also can be used in either sliding and rotary drilling, the rotary drilling with down-hole motors also called as composite drilling or rotary drilling.
The use of down-hole motors is greatly dependent on financial efficiency.
In vertical drilling, the down-hole motors may be used solely to increase ROP, or to minimize erosion and wear on the drill-string, since the drill-string does not need to be turned as fast. The majority of down-hole motor use is in the directional, including directional wells, horizontal wells, extended-reach wells, multi-branched wells.
Although other methods may also be used to steer the bit to the desired target zone, they are more time consuming which adds to the cost of well construction. During directional operation, the sliding drilling mode is adopted to steer the bit to the desired direction; while the composite drilling or rotary drilling mode can be adopted to improve the drilling problems, such as the high risk of stuck pipe, high drag, poor hole cleaning, low ROP, high cost, and etc.
The VDS is another type of directional tool, and it is used to prevent deviation and drill vertically and quickly, as a result, increasing the ROP for deep, ultra-deep wells. Although the conventional techniques, such as the eccentric-axis assembly, eccentric rigid-flexible assembly, steerable assembly, anti-pendulum assembly, pre-bending dynamics, and etc.
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The VDS can avoid frequent straightening and automatically keep the borehole vertical. The directional survey technique, a key aspect of trajectory control, measures the inclination and direction at various depths. The tool face measurement is required to determine the direction of a whipstock, a bent sub or bent housing. Thus, the survey technique is also the key of directional drilling, which is classified as two groups, the more prevalent measurement while drilling MWD tools and the less mature post-drilling measurement tools Short ; Chen ; Han ; Wu To overcome this problem, the MWD tools were developed to measure the wellbore trajectory during drilling.
The key techniques of MWD include survey technique and transmission technique. MWD tools have been applied almost all of the directional wells all over the world. But the single-shot and multi-shot instruments are applied the vertical wells.
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We will focus on the MWD techniques:. There are three kinds of down-hole information, directional information, drilling engineering information and formation information, which need to be measured during drilling Wu ; Ma and Chen ; Ma et al. The directional information can be measured using the conventional MWD tools.
The measurement of drilling engineering was developed from the conventional MWD technique, while the measurement of formation information was developed from the conventional logging technique and mainly used for geo-steering drilling to adjust the geological target in real time. The MWD tools are generally capable of taking directional surveys in real time. The accelerometers and magnetometers are utilized to measure the inclination and azimuth, and the information of inclination and azimuth are transmitted from the measuring location to the surface.
The trajectory and location of wellbore can be calculated using the survey data.
The directional information can help the directional driller to know where the well is going, and what the effects of his steering efforts are Mitchell ; Chen In order to prevent down-hole accidents and improve drilling efficiency, the MWD tools also have been designed to measure the drilling engineering information, such as the down-hole pressure, WOB, torque on bit TOB , rotational speed, vibration, impact, temperature, mud flow volume, and etc. Ma and Chen Under the supporting of this information, the down-hole conditions and the working status of drilling tools can be identified in real time, which makes the drilling operation more efficient, safe and economic.
In addition, this information is also valuable to Geologists responsible for the well information about the formation which is being drilled Mitchell The following formation information is usually available, such as the natural gamma-ray, density, porosity, resistivity, acoustic-caliper, magnetic resonance, formation pressure, and etc.
Due to the effect of the length, include down-hole motors, sub and LWD tools, the measuring point of directional information have to move up, which makes the control precision of well path lower. Thus, a near-bit inclination tool was developed to measure directional information at the drill bit. The near-bit measurements, such as gamma ray, inclination and azimuth, allow the operator to closely monitor drilling progress Felczak et al.
The conventional MWD tool allows these measurements to be transmitted and evaluated in real time, which makes the geo-steering can be realized. The geological target also can be adjusted according to the evolution of the formation properties, this is so-called the geo-steering drilling Wu Near-bit measurements, such as gamma ray, inclination and azimuth, allow the operator to closely monitor drilling progress. According to the transmission medium, the transmission technique of down-hole data can be classified as three types: mud-pulse telemetry, electromagnetic telemetry and wired drill pipe, their main features can be sorted in Table 3.
calamiherre.gq Three kinds of mud-pulse telemetry methods. Negative-pulse MWD tools: as shown in Fig. Once the valve is opened, there is a decrease in pressure that received at the standpipe. Thus, this method is called as the negative-pulse. Continuous wave MWD tools: as shown in Fig. Any digital modulation scheme with a continuous phase can be used to impose the information on a carrier signal. The most widely used modulation schemes are continuous phase modulation Wu Current mud-pulse MWD tools are mainly the positive- and negative-pulse, although the transmitting rates 0.
The transmitting rate drops with increasing length of the wellbore and is typically as low as 1. In addition, once aerated underbalanced drilling is used or drilling fluid is aerated, the compressibility of drilling fluid is increased, which makes the transmitting ability of drilling fluid also lower. In this case, the electromagnetic MWD or wired drill pipe telemetry is recommended.
The schematic diagram of wired drill pipe after Edwards et al. Deep formations are broken apart mechanically by cutting elements called as tooth or cutter of the bit by scraping, grinding or localized compressive fracturing Chen On this basis of the cutting mechanism, the industry classifies drill bits into two groups: the roller cone bits, the fixed cutter bits and the hybrid bit. The milled tooth bits, also called as steel-tooth bits, have cones that have wedge-shaped teeth milled directly in the cone steel itself Centala et al. The TCI bits have shaped teeth of sintered tungsten carbide press-fit into drilled holes in the cones, the tungsten carbide material is applied to the surfaces of the teeth to improve durability due to its extreme hardness.
The TCI tooth also has been applied in some types of milled tooth bits. To further improve the durability of drill bits, some advanced materials also be developed, such as the alveolate diamond material and the double cemented tungsten carbide. The cones rotate on bearings that are usually sealed by rotary O-ring or metal face sealing to against the down-hole drilling fluid environment.
For deep or geothermal drilling, the high temperature roller cone bit can be specially designed to endure high-temperature drilling environments like geothermal wells for extended periods. The drag bit was the first type of drill bit that used in rotary drilling, but it just can be used in soft formations, so it has seldom been used in petroleum drilling now.
The PDC bit is the most common drill bit in use today, due to the advantages of high ROP, long life and long drilling footage. The PDC bit consists of body, cutter and nozzle. The PDC cutter tooth is a sintered tungsten carbide cylinder with one flat surface coated with a synthetic diamond material. The cutters are arranged on the blades of the bit in a staggered pattern with the diamond coated cutter surface facing the direction of bit rotation to provide full coverage of the borehole bottom Bruton et al.
The natural diamond bit and impregnated bit are similar, the biggest difference is the cutters. The natural diamond bit employs the natural industrial-grade diamond cutters to imbed within the bit body matrix, while the impregnated bit employs the thermal stable polycrystalline TSP diamond cutters. Due to the diamond is featured by greatest hardness and high durability, which makes it can adapt to the hard abrasive formations.
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These bits are available in a variety of styles for both motor and rotary drilling in hard or abrasive formations. Although the diamonds are expensive, the durability of bits also enough high, which makes them have strong competitiveness in petroleum drilling.
The natural diamond bits have been widespread used in RSDS drilling, turbo-drills drilling and core drilling.
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