China began to introduce PDC bits since the early 1980s. After the 1990s, major oil fields began to use PDC bits and achieved good results. Although PDC bits have many advantages and are widely used, the hydraulic problems of PDC bits are even more pronounced than other bits: On the one hand, PDC bits break the rock in a shear manner, and the drilling speed is fast. A large amount of cuttings needs to be removed in time; On the one hand, the temperature
Sensitive PDC cutters require rapid cooling. If the clear rock and cooling effect are insufficient, it will not only cause bits of mud, repeated cutting, resulting in a sharp decline in the penetration rate, but also will make the PDC cutting teeth rapidly wear out in the bottom of the high temperature environment, which will seriously affect the use of PDC bit life. Therefore, research and improvement of the effect of PDC bit bottom hydraulics has always been one of the most concerned issues for PDC bit researchers and users.
PDC bit cutting teeth have two kinds of composite structure and tooth column structure. The composite chip cutting tooth is formed by welding the composite piece directly in the reserved groove on the bit body, and it is mainly used for the carcass drill bit; the tooth post type cutting tooth is to weld the composite piece on the tungsten carbide tooth post and Formed, when installed, the studs are inlaid or welded in the tooth space on the drill body. It is mainly used for steel body drills and also for carcass drills. Foreign countries have always attached great importance to the research of new cutting teeth. Using the different shapes of cutting teeth, a variety of new products have been developed. Typical examples are double-edged cutting teeth (TEC), pre-chamfer edge-enhancing teeth (CES), and overlays. Protective layer cutting teeth, composite structure teeth (MC), wedge teeth (SC), etc. [2 ~ 4]. Under the application of certain specific conditions, the cutting performance of these special morphological structures has been significantly improved. In recent years, research on PDC bits has progressed rapidly and can be summarized as follows.
1. Research advances in bit hydraulics For the study of the velocity field, the flow pattern in the downhole flow field of the rotating PDC bit is very complex. Usually the nozzle has a high-speed jet nozzle, and the jet is affected by many factors such as the shape of the drill bit and the shape of the flow channel. Therefore, the flow of this complex flow field is difficult to directly - 70 body clear rock and cool cutting teeth capacity; 3 reduce the impact of the vortex and jet on the cutting teeth to prevent broken teeth. The current research method is to analyze the similarities and differences of the flow field under different bit shape and hydraulic parameters through experiments and numerical calculations, in order to find the direction to improve the hydraulic parameters of drill bit shape adjustment.
PDC oil drill bit is a combination of materials science and drilling engineering in recent decades. The shape of PDC oil drill bit has also undergone several changes. The current form of bit shape is fully studied by solid mechanics, but it should not be final. shape. At present, the fluid mechanics problems appearing in the faults of the PDC bit gradually increase. The author believes that the use of personalized PDC bit will be the development trend of the drilling industry. With the development of CFD technology and computer hardware technology, the author believes that further work should be done in the following areas.
(1) Different personalized PDC bits are designed for different geological conditions. Using CFD and CAD to optimize specific PDC bits, this method is very meaningful both in terms of efficiency and cost.
(2) Design a multifunctional PDC bit. During drilling, surface drilling, deep drilling, and final drilling operations often require the use of different drill bits. If a multifunctional drill bit is designed to adjust various parameters of the drill bit, drilling efficiency can be improved and expensive drilling can be reduced. cost.
(3) Adopt advanced modeling methods to establish accurate digital models. In order to study the performance of a PDC bit under specific conditions and its optimization plan, it is necessary to establish an accurate model that can describe the geometry of the bit, including the precise geometrical surface of the chip tooth and the surface profile.
(4) Non-Newtonian liquids were used for numerical simulation and experimental study. Due to the complexity and difficulty of using non-Newtonian liquids for numerical simulations and experimental studies, the authors used clear water for numerical simulations and experiments. However, in order to accurately describe the flow of the bottomhole, non-Newtonian liquids should be used for numerical simulation and experimental research.
(5) At present, due to the limitation of the experimental hardware conditions, certain changes have been made to the experimental device, and the working conditions of the drill bit have also been simplified. With the experimental conditions permitting, experiments should be conducted under practical conditions. As for prediction, it can only be understood and analyzed through experiments or calculations. Traditional experimental methods, such as dyeing method, painting method, bubble display method, silk thread method and high-speed photographic particle tracing method, are mostly directed to a specific structure. The drill bit is researched by flow display. These methods are limited by the experimental conditions and equipment, and measurement accuracy is difficult to guarantee. With the rapid development of test technology and computer technology, the bottom hole flow field of PDC bit has been studied by using advanced optical testing technology PDA (Parti-cleDynamicAnalyzer) or PIV (ParticleImageVe-locimetry) combined with Computational Fluid Dy-namics (CFD) method. Has become a new direction of bit hydraulics research. Test Technology PDA and PIV are advanced optical test technologies with high measurement accuracy and large data volume.
2. Development of PIV and PDA research methods and applications Since the laser speed measurement technology was introduced in 1964, it has become more and more advantageous due to its many advantages such as non-contact measurement, non-interfering flow field, high spatial resolution, fast dynamic response, and high measurement accuracy. Widely used in various measurement areas. Particle Image Velocimetry (PIV) is a new flow velocity measurement technology developed in the last decade or so. It is based on the flow display, Laser Speckle Velocimetry (LSV), which emerged in the late 1970s. Since its evolution, it has integrated computer image processing and optical technology. It has broken through the limitations of space single-point measurement technology, and can record relevant information of the entire measurement plane at the same time, and thus can obtain the instantaneous plane velocity field of flow, Vorticity field et al. . As a non-perturbation, transient and full-field velocity measurement method, PIV has been widely applied to the single-phase flow velocity field measurement of liquid or gas. The Laser Dynamic Particle Analyzer (PDA) was developed based on the Laser Doppler Velocimeter (LDV) and is currently recognized as the most effective instrument for simultaneously measuring particle size and velocity. The principle of LDV is based on the fact that the Doppler frequency is proportional to the vertical velocity of the intersecting region (measurement volume) of the particles to be measured that are intersected by the two laser beams. By calculating the Doppler frequency, the motion speed of the particle is inversely calculated. PIV and PDA testing technologies have now become
For mature technologies, it is widely used in various industries such as physics and power.
3. CFD Research Progress CFD is a technology that has been developed in recent years with the advancement of computer technology to solve the problem of fluid flow. It describes the motion of a large number of fluids in the form of a grid and uses numerical iterative methods to solve and calculate fluids. Speed, pressure, and other variables in each grid. Through computer numerical calculation and image display, the system including the phenomena of fluid flow and thermal conduction and other related physical problems was studied. Compared to traditional test methods, CFD methods have a cost
Low, short cycle, and ability to flexibly change calculation conditions. The visualization of CFD calculation results mainly includes the display of the calculation domain, the calculation process, and the display and analysis of the calculation results. Visualization technology can be specifically divided into visualizations of scalar, vector, and tensor fields, of which the visualization of scalar fields is currently quite mature.
4. PDC bit design progress At present, on the basis of the existing PDC bit, in some specific applications [10 ~ 12], design some new PDC bit.
(1) Thermally stable polycrystalline diamond drill bits The so-called thermally stable polycrystalline diamond drills are polycrystalline diamonds that retain their physical and mechanical properties at high temperatures (1 200 °C). Due to the use of a silicon alloy binder or no binder, the critical graphitization temperature of diamond is greatly increased, and the thermal properties of silicon carbide and diamond are more consistent, which significantly improves the performance of polycrystalline diamond.
(2) PDC + Diamond Pregnancy Block Mixing Drill Bits The main cutting teeth of this drill bit are PDCs, and diamond studs are inserted behind the PDC cutting teeth to support the PDC cutting teeth and enhance the breaking strength of the PDC. This drill bit cuts the formation from the PDC as it drills into the soft formation, and when drilling in a hard or abrasive formation, the diamond impregnated block comes into contact with the formation and shoulders the crushed rock as the PDC wears. This drill has a wide range of applications and at the same time has a high penetration rate as a PDC bit and a lifetime similar to a natural diamond drill.
(3) PDC + TSP mixed tooth bit This type of drill consists of PDC teeth and TSP teeth of the same shape and size, the ratio is generally 40 (PDC): 60 (TSP), can be drilled in the hard ~ hard and hard rock sandwich Formation. Under the same conditions, the drill performs better than conventional PDC bits and roller cone bits.
(4) Large cutting teeth PDC bits Usually, this drill has only 8 to 9 large PDC cutters. Due to the large cutting teeth, the total cutting area is 35% larger than that of conventional drills, and cuttings are 3 times more cuttings. about. The advantage is that the cutting teeth do not fall off easily and are resistant to erosion. The drill has achieved significant economic benefits in applications in the United States, the North Sea, and Southeast Asia.
(5) Diamond-enhanced Pregnancy Inserts The cutting teeth of this type of drill are cemented with 3 layers of polycrystalline diamond composite layer of about 0.76mm thick on cemented carbide post, so that the cutting teeth also have high wear resistance of diamond. The high impact resistance of cemented carbide and the ability to effectively drill into hard and abrasive formations with grinding and impact. In the development of the new PDC bit, it is particularly important to use fluid mechanics to analyze the hydraulic field at the head of the PDC bit after the material and structure have reached a certain level. It may even become a decisive factor in improving the drilling speed and service life of the PDC bit. factor. The main research purposes are: 1 to prevent bit mud packs, in order to improve the ROP and prolong service life; 2 to make the flow smooth and improve the flow