As one of the leading products of oil and gas well drilling, according to incomplete statistics, the drilling footage of roller bits currently accounts for about 20% of the total drilling footage. Roller bit has the function of impacting, crushing and shearing formation rocks when rotating. Through reasonable selection of bit structure, it can be used to drill into medium-hard strata at low speed, and it is a kind of bit with good broad spectrum, especially in recent years, roller bits with diamond inserts and metal seals have been used in soft-hard staggered strata. Practice has proved that in open hole section, roller bit has high drilling efficiency and satisfactory bit life. In the large-diameter reaming drilling in the upper part of deep well, roller bit shows its manufacturing technical advantages. The drilling efficiency and service life of hard crystalline rock in medium-deep hole section are low; In ultra-deep hole, the special requirements for embedded roller bit include: selecting the type of roller bit suitable for hard abrasive crystalline rock layer; Bit structure with as little or no shaft offset as possible; The drill bit shall be equipped with sealed rolling and sliding bearings; Standard and variable cutting edge (insert tooth) embedding method, with the number, form and geometric shape of simultaneous insert teeth; The most effective measures to protect the diameter are to reduce the shift wheelbase as much as possible and increase the outer insert and gauge insert; Adopt materials suitable for hole depth and temperature conditions; Cone-shaped, oval-shaped and spherical blades are especially suitable for drilling in crystalline rocks, while chisel-shaped teeth, spoon-shaped teeth and super-spoon-shaped teeth are easy to break. The weak link of roller bit is its moving part-bearing. When drilling in deep wells, its life and temperature resistance should stand the test.
(2)PDC bit
PDC bit is a new type of cutting bit, which is made of artificial polycrystalline diamond cutting teeth welded to the bit matrix or bit steel body. It uses self-sharpening PDC cutting teeth as cutting edges, and can obtain high penetration rate at low WOB, which is twice as high as that of roller bit. Long service life, 4 ~ 6 times that of roller bit, mainly used for drilling soft to medium hard stratum. With the improvement of PDC composite quality and welding technology, the application range of PDC bit is extended to the formation with drillability of grade 9. In the past, PDC bits were not used in Tangke drilling in China, ultra-deep drilling in Kola and KTB drilling in Germany, because the drilling rocks were hard.
Diamond compact can be used to drill into soft and hard strata at low speed by pressing in and shearing rocks and selecting the bit structure reasonably. It's a little broad-spectrum. With the great improvement of PDC performance in recent years, drillers have higher and higher expectations for PDC bits, and the demand for PDC bits is also increasing. According to statistics, the drilling footage of PDC bits accounted for 26% of the total drilling footage in 2000.
The research progress of PDC bit is very fast, which can be summarized as follows:
1) bit hydraulic system. Using advanced optical testing technology PDA combined with CFD method to study the bottom hole flow field of PDC bit has become a new direction of bit hydraulics research. CFD is a technique for solving fluid flow developed with the progress of computer technology in recent years, but the research in this field is relatively scarce in China.
2)PDC bit design. Personalized design is carried out according to different geological conditions, such as multi-size pick bit design and double torque concept design bit. Advanced modeling method is used to establish accurate digital model, and PDC bit is optimized by CFD and CAD.
3) 3) Processing technology of PDC bit. Realize NC machining, and integrate CAD computer aided design technology with CAM computer aided manufacturing technology.
4) Soft die forming technology of 4)PDC bit. At present, it is widely used by foreign advanced bit manufacturers and domestic oil well bit manufacturers. After NC machining of jig is realized, this method can greatly improve production efficiency and ensure dimensional accuracy.
PDC composite bit has played an important role in drilling soft to medium hard formations and made breakthrough progress.
200 1, American Hughes Christensen company used BD536PDC composite bit, which set a world record of 6,994 m in one trip. The M9 1P PDC bit produced by Smith Company set a world record of the highest ROP of 202m/h, and STR554 PDC bit tripped 65,438 times, with a cumulative footage of 21405 m..
In recent years, scientists and technicians have been devoted to studying the interaction between cutting tools and strata, the dynamics of cutting tools and the dynamics of lower drilling tools. According to the development of drilling technology and the actual needs of drilling site, various PDC cutting teeth, special PDC bits and related technologies have been designed and developed by major bit companies in the world. In 2005, Robert Claytom of American DBS Company published the article "New bit design and cutting tool technology expand the application of PDC bit in hard rock drilling" at the American Society of Petroleum Engineers, and put forward the viewpoint of energy balance in bit design, that is, the reasonable arrangement of cutting tools (PDC) on the bit can minimize the radial resultant force formed by the bit, which is also a necessary condition for drilling in hard rock. With the successful development of a new generation of cobalt-filtering and heat-resistant PDC cutting teeth, the performance of PDC bit has changed greatly. When drilling hard strata, the average footage of the new generation of cobalt-filtering and heat-resistant PDC bit with cutting teeth is 2 times higher than that of the conventional PDC bit, and the ROP is 65,438 0.5 times higher, thus expanding the application range of PDC bit in hard rocks.
(3) The surface of natural diamond is inlaid with a drill bit.
At present, in the deep hole coring drilling of hard rock, the traditional natural diamond surface-mounted coring bit has been gradually replaced by impregnated bit or other new diamond coring bits. The reason lies not only in the high price of natural diamond surface coring bits, but also in the fact that the service life and average penetration rate of new diamond coring bits such as impregnated bits are higher than those of natural diamond surface coring bits, which is proved by the rock crushing mechanism and a large number of practical data at home and abroad.
The experiment of drilling the first well in Continental Science shows that the drilling effect of natural diamond surface-mounted bit is not ideal, and the ROP is not high, especially after drilling for a period of time, the aging decreases rapidly. After drilling, it was found that some natural diamonds were broken and most of them became dull, and almost no complete natural diamonds could be seen.
The matrix of natural diamond surface-mounted drill bit has high hardness, strong wear resistance and strong erosion resistance, which is more suitable for drilling conditions with large pump capacity and high pump pressure in oil drilling. The natural diamond surface-mounted drill bit has high cutting edge, coarse diamond particles, high drilling efficiency in sedimentary rocks and long service life.
For Kezuan 1 well, the rocks encountered are crystalline rocks with high hardness and abrasiveness. In order to obtain high drilling speed, it is necessary to adopt high rotating speed and WOB, and the complex vibration of the drill bit will inevitably increase, which is unfavorable to the drill bit with surface inlay, which will make the diamond above the blade break or collapse and gradually lose its working ability. Many drilling facts also show that the natural diamond surface-mounted bit is not only expensive to drill, but also not suitable for drilling in hard rocks and broken strata.
In order to improve the drilling efficiency, hydraulic hammer percussive rotary drilling is designed, and the diamond with a bit embedded in its surface has a high cutting edge. Under the action of large impact energy, the reaction force of hard rock is large, high-edge natural diamond is easy to crack, diamond can not fully play its role, and the service life of the bit is not long. Therefore, it can be considered that natural diamond surface-mounted drill bit is not suitable for drilling in hard rock, nor for impact rotary drilling in hard rock.
(4) electroplated diamond coring bit
According to the test of electroplated diamond coring bit in Continental Scientific Drilling, the bit showed better performance, longer service life and higher penetration rate at the initial stage of the test. With the change of coring drilling mode, the bit began to be unsuitable for impact rotary drilling, and the working layer of the bit fell off, and the performance of the bit was not fully exerted. Some only drilled once, some only drilled twice, and only two wireline coring bits were used in the main interval.
(5) impregnated diamond bit
The impregnated diamond bit can drill medium-hard to hard rocks, and can drill all kinds of rocks with abrasiveness and various integrity. In other words, the impregnated diamond bit has wide adaptability to crystalline rocks and good drilling technical indicators. Most impregnated diamond bits use synthetic diamond, and the drilling cost is low.
The impregnated diamond bit is much thinner than the diamond particles embedded in the bit, and the diamond cutting edge embedded in the matrix is small, as if it were embedded by multi-directional stress, so it can bear impact load without breaking, and is suitable for impact rotary drilling.
The design and manufacturing technology of impregnated diamond bit is mature, with decades of experience and understanding. The impregnated diamond bit is beneficial to single-acting double-tube coring drilling, with high core recovery rate and good core quality, which can well meet the construction requirements of scientific drilling. Therefore, the impregnated diamond bit is the first choice for coring drilling in Kedriller 1 Well.
Motion characteristics and coring quality of coring impregnated diamond bit: Because of its small cutting edge, fine particles and more diamonds, impregnated diamond bit cuts into the rock in a limited depth, and the amount of broken rock per revolution is small. Therefore, when it rotates at the bottom of the hole, it will not vibrate because of the movement of the tool itself, like a roller bit. Generally, in order to obtain effective drilling speed, the drill bit must rotate at high speed. When the rotating body rotates at high speed, it will produce gyro effect (simply speaking, the centrifugal force when the object rotates will keep itself in balance), so the diamond bit is much more stable than the roller bit when it rotates at the bottom of the hole. The practice also shows that the core surface drilled by diamond bit is smooth and continuous, the core is more complete and the coring quality is better.
Practice has proved that it is most suitable for drilling crystalline rock strata with high drillability; High ROP, good drilling effect, long service life and low comprehensive cost; The drill bit has high heart rate and good core quality; It has the best performance in double-tube coring drilling driven by hydraulic hammer, the screw motor of Kedriller 1 Well. German KTB, Chinese mainland Scientific Deep Drilling, the most commonly used is impregnated diamond coring bit.
(6) Reaming bit
Roller teeth break rocks through impact, extrusion and shearing, which produces volume rock breaking effect in hard strata. Especially in the reaming drilling stage, due to the free surface formed by small holes, the free surface can be effectively used under the impact mode, resulting in greater volume rock breaking effect. If the diamond bit is used to drill holes, the cutting amount per revolution is very small, which requires a higher rotation speed, which can not be met by on-site rotary table drilling. If PDC bit is used, because the stratum is extremely hard, the cutting edge is difficult to enter the stratum, and the scraping effect is difficult to achieve. The unevenness of the stratum will also lead to the fracture of this tool under impact load during rotation.
In reaming drilling, the stress condition of the bit cutting tool is very bad, so the cone palm with larger diameter must be used as much as possible. However, using too large bit palm will reduce the connection area between the bit guide body and the bit body, thus reducing the strength of the bit.
Reaming bits can be made into three-cone, four-cone and six-cone. Four-cone reaming bit has poor stability and is easy to vibrate when drilling. Three-cone and six-cone reaming bits have good stability when drilling, but if the number of cones is relatively large, choosing a larger cone palm in a limited layout space will inevitably affect the connection strength between the guide body and the body, which is not conducive to improving the overall strength of the cutter and the bit (Jian Kang, 2008).
The No.1 well of Kezuan adopts the guiding three-cone reaming bit. The main hole of KTB adopts three-cone reaming bit, and the following measures should be taken when reaming: adopting metal sealing bearing and optimum alloy tooth profile to optimize bit design, giving priority to bit structure design and material, and strengthening bit gauge protection; Take shock absorption measures to minimize the vibration of drill string system to ensure the stability of drilling process and the long life of tools; Diamond reamer is used to keep the borehole diameter stable for a long time. When making reaming bit in No.1 well of Kezuan, the cone palm selected has the following characteristics: the bearing has a pressure balance lubrication system, which is suitable for deep drilling; Bearing seal adopts metal floating seal structure with excellent performance.
(7) Turbine motor
Because almost all parts of turbine motor are made of metal materials, turbines equipped with proper bearings are basically frictionless and can be used in the temperature range of 275 ~ 300℃. In order to adapt to the use of high temperature, a special sliding bearing is developed. The contact surface between the bearing and the stator and rotor is inlaid with synthetic diamond (PCD). In order to avoid damage caused by impact load as much as possible, PCD bearing adopts the structure of ram bearing. The turbine motor with this bearing has been successfully used in geothermal well drilling where the temperature is as high as 280℃.
The biggest advantage of turbodrill is that it does not contain rubber parts and is resistant to high temperature (working temperature can reach 250 ~ 300℃). Suitable for drilling deep wells, ultra-deep wells and high temperature and high pressure wells. Turbodrill also has some inherent shortcomings, which limit its application. For example, the turbine diameter is large, so it is difficult to manufacture small-diameter and high-power turbine drilling tools; The turbine speed is very high, so it can't directly drive the drill bit, and it often needs a reducer to slow down, which increases the complexity of the device and reduces the reliability. Therefore, turbodrill has been used in some vertical wells, but it is not convenient to use it in directional inclined wells, small diameter wells and horizontal wells with relatively small bending radius.
In order to improve the footage of roller bit and successfully apply turbodrill to deep well drilling, the rotational speed of turbodrill should be reduced as much as possible and the torque on its shaft should be increased. At present, low-speed decompression turbodrill, hydraulic brake turbodrill and planetary reducer turbodrill have been successfully adopted.
According to the rotating speed of turbodrill assembly, it can be divided into high-speed turbodrill assembly, medium-high speed turbodrill assembly and medium-low speed turbodrill assembly. The high-speed combined turbodrill is not equipped with a reducer, so the bit speed is high; Medium-high speed and medium-low speed combined turbodrill is equipped with a reducer between the bearing joint and the drill bit, which can reduce the output speed of the turbine. At this time, the corresponding rotational speeds are: 600 ~ 1000 rpm, 300 ~ 600 rpm, 100 ~ 300 rpm.
In actual operation, the working speed of turbodrill (including reducer turbodrill) can be adjusted according to the needs of the site. Therefore, turbodrill can be used not only for roller bits (low working speed), but also for PDC bits and various types of diamond bits (relatively high working speed, up to 1200 ~ 2000 r/min).
The working speed of large torque, low pressure and short length variable diameter turbodrill is 100 ~ 300 r/min, which is suitable for roller bits and PDC bits with different speeds. The working speed of high-torque medium-speed turbodrill is 300 ~ 500 r/min, which is suitable for PDC bits and natural diamond bits. The working speed of high-torque high-speed turbodrill is 500 ~ 2000 r/min, which is mainly suitable for impregnated diamond bits.
Using turbodrill-reducer system for bottom-hole driving drilling is one of the three technical characteristics of deep well drilling in the former Soviet Union. The output speed of turbodrill is high, so it can only be used to drive roller bit after deceleration. When the turbodrill is used, it is equipped with a speed telemetry system, which is installed above the turbine motor. After measuring the speed of the motor, the information is transmitted back to the ground in the form of mud pressure pulses. According to this information, the ground staff can adjust the pump quantity and control the motor speed to ensure the best drilling progress.
(8) Screw motor
Screw motor is a downhole power machine powered by drilling fluid, and it is a positive displacement motor. The drilling fluid output by the mud pump enters the screw motor through the bypass valve, forming a certain pressure difference at the inlet and outlet of the motor, driving the rotor of the motor to rotate, and transmitting the rotation speed and torque to the drill bit through the universal shaft and the transmission shaft, thus achieving the purpose of rock breaking.
The working characteristics of screw motors are quite different from those of turbine motors. They have hard characteristics, such as large torque and low speed. The rotational speed is only related to the displacement and structure, and has nothing to do with the working conditions (WOB, torque, etc.). ). Its rotating speed is directly proportional to the input drilling fluid flow, and its output torque is directly proportional to the motor voltage drop, regardless of the rotating speed. The greater the pressure drop, the greater the torque, but the speed changes little when the pressure drop and torque change. Therefore, it is not difficult to know that when the screw motor is used in drilling operation, the pump pressure gauge can be used as a monitor of downhole working conditions, and the downhole working conditions can be judged and displayed through pressure changes, and the rotation speed can be adjusted by adjusting the displacement. The stator of screw motor is made of rubber, which has poor high temperature resistance. Generally, nitrile rubber is used, and its temperature resistance is about 150℃. If you need high temperature resistance, you need to use special rubber, which is costly.
In the drilling construction of Kedriller 1 well, the screw motor is used as the bottom hole rotary driving device of diamond coring drilling system.
In oil and gas exploration and development, with the development and practice of drill bit and downhole tool technology, a set of technical approaches to improve ROP has been gradually introduced abroad, that is, a specially designed synthetic diamond impregnated drill bit is combined with downhole power (high-speed screw and high-speed turbine) to improve ROP by strengthening drilling parameters. Compared with roller bit, this technology can improve the ROP by more than 3 ~ 10 times, which greatly improves the ROP.
From the current market research, using imported turbodrill and impregnated diamond bit is the best way to improve drilling speed, and good results have been achieved. In the future, through the research on the cutting structure design, matrix material, manufacturing method and manufacturing technology of the bit, the impregnated diamond bit will play a great role in the stratum with high hardness and strong abrasiveness.
See Table 6. 1 for the rock breaking modes and performance characteristics of various drills.
Table 6. 1 Types and characteristics of rock-breaking tools