| Scientific drilling is implemented for the purpose of geological research, is the most effective and intuitive way for human to access to earth’s internal information. It is through the scientific detection of the organizational structure, material composition, formation mechanism of the crustal lithosphere, biosphere, hydrosphere, to conduct various types of research. The continental scientific drilling, by increasing the degree of deep geological research, which can solve the problems mankind is confronted with, the issues of resources, such as oil and gas, solid minerals, and geothermal energy, the disasters, such as earthquakes and volcanoes, the environment problems, such as meteorite impact and nuclear waste disposal, and other issues. In addition, just like sending satellite into space, the continental scientific drilling need high-tech support and huge amount of capital investment, but can get the major scientific and technological achievements of the world-renowned, reflect the national comprehensive strength and improve its international image.The scientific ultra-deep drilling is a systematic project, involves a very wide field of research, for some of the problems that may be encountered in the implementation process, the reference instance at home and abroad was limited. Currently, the study on physical and mechanical properties of the rock under high temperature and pressure conditions in deep ultra-deep, and the rock breaking mechanism under these conditions, our country has carried out a little work, the abroad has done some, but less information can be investigated. Therefore, a further study on the rock fragmentation mechanism of diamond drilling in crystalline rock, the friction and wear characteristics between bit matrix and rock under these conditions is appeared very necessary. The core technology of scientific ultra-deep drilling is drill coring technology, high ROP footage, back time long, better coring effect, small drill string axial vibration, low power consumption as well as little disturbance to the borehole wall were required. To meet this requirement, a set of bit selection program and drilling procedure that based on the physical and mechanical properties of the deep strata must be put forward, and designed drilling tools for deep rock. Therefore, a task force of the faculty of engineering of China University of Geosciences (Wuhan), undertake a project which named the pre-study of the broken rock methods and tools in scientific ultra-deep drilling process, it belongs to part of pre-study of the scientific ultra-deep drilling technology scheme (No.SinoProbe-05-06), which is the sixth task of continental scientific drilling site and drilling experiment (No.SinoProbe-05), which is the fifth project called special project of deep detection technology and experimental studies.This paper’s topics are rely on the subject, the main contents are: researched the change rule of mechanical properties of rock when confining pressure and temperature changed, and determine the rock’s drillability level under different conditions. Proposed the bit technical scheme apply to diffident well section of13000m ultra-deep drilling. Summarized the frictional characteristics occurred between impregnated diamond bit and rock under high temperature conditions. Researched the rock breaking mechanism of the impregnated diamond core bits which with different shapes of the end, that is to provide theoretical support for the structural design of impregnated diamond core bit used in ultra-deep drilling. Through the research and analysis of the results, it will be helpful to our deep drilling project development in a certain degree, and provide certain support and reference in theory.The bottom temperature of scientific ultra-deep drilling which is going to implement by China is about400℃, the bottom hole pressure reach160～280MPa and confining pressure is124.8MPa. through research on the drilling technical date in connection with deep drilling, ultra-deep drilling, geothermal well drilling from home and abroad, especially the kola super-deep well in the former Soviet Union (SG-3), Germany KTB and China’s continental scientific drilling (CCSD-1), have a in-depth understanding of the rock’s mechanical properties and drilling characteristics under high temperature and high pressure, and the requirements and influence to the bit. By understanding and analysis the drilling tools’ operating characteristics, put forward the broken rock methods and tools can be used in different interval in scientific ultra-deep drilling. The impregnated diamond core bit is suitable for drilling crystalline rock stratum with a higher level of drillability, is the first choice for deep core drilling. So its design and production is an important element in the study of ultra-deep drilling project. In the deep well section of ultra-deep well, the bottom of the well with a high-temperature and high-pressure environment, how to improve the quality of the impregnated diamond core bit and drilling effect, what king of the end shape of the bit easier to rock breaking, how the friction and wear characteristics between bit matrix and rock under high temperature conditions, are have become the important factors must take into account when bit is designed.Based on the basic theory of friction and wear, blank matrix samples and diamond matrix samples were produced with the impregnated diamond bits’ commonly used matrix formula in deep well drilling, the making method is hot-pressing and the specifications is8.5mm×8.5mm×15mm, and then wear test was carried out on MG-2000friction and wear test machine with a20 ℃、100℃、200℃、300℃、500℃ambient temperature condition, the drilling condition is load p=400N an speed n=400r/min. Using scanning electron microscopy (SEM) to observe mole and the morphology of friction track, with electronic measuring the amount of wear, studied the friction wear regularity of the matrix under different temperature conditions. The test results show that: the friction coefficient is closely linked to the type of rock, in the case of the same composition as the matrix, the friction coefficient of the test sandstone always less than test granite. The ambient temperature has a obviously influence on rock, when it up to400℃, regardless of what kind of matrix, the test sandstone all can be into a massive rupture in less than two minutes. The influence of ambient temperature on the friction coefficient and friction power is also larger, namely in different matrix and rock wear combination conditions, as the temperature increases, the friction coefficient and friction power generally showed a trend of decrease. The amount of wear and wear stroke is proportional to the relationship, whether blank matrix sample or diamond matrix sample, when tested a dry friction with granite and sandstone, there are the same rule, namely as the temperature increases, the wear amount have a upward trend in general. When the ambient temperature exceeds400℃, the wear amount of diamond matrix combined with granite rose sharply, but wear amount of blank matrix combined with granite reduced, and show that the difference in composition of matrix have a greater impact on the amount of wear. Higher the ambient temperature, the more stronger abrasive ability sandstone to bit matrix. The wear mechanism of blank matrix and rock is mainly adhesive wear and surface fatigue wear. When wear itinerary and ambient temperature increases, the blank matrix will appear adhesion phenomenon in surface under the action of friction heat. The adhesive advantageous for solid self-lubricating phase (graphite) of matrix is transferred to the rock surface, that the amount of wear is reduced within a certain range. So the wear mechanism between blank matrix and rock is a hybrid form of adhesive wear and surface fatigue wear. The wear mechanism between diamond matrix and rock also is mixed mode which are abrasive wear, adhesive wear and fatigue wear in surface. The abrasive grain is the cutting that cut by diamond and shed diamond. It will cut the metal surface in the wear interface so that the amount of wear increases. Along with the wear itinerary and ambient temperature increases, the diamond matrix appear spalling that is fatigue wear. So it can be said the wear mechanism of diamond matrix is hard item cutting and abrasive wear, and appears s a failure trend by adhesive wear and fatigue wear in the role of time and temperature.The impregnated diamond core bit design includes many aspects, the shape of the end design is an important part of the drill bit design. Based on analyzing the rock breaking mechanism of impregnated diamond bits and PDC bits, three methods to optimize the shape of the end of the bit was summarized by this paper, they were change shape to increase the free surface of the lip surface cutting rock, reduce the lip area to increase a single diamond’s drilling pressure and use super hard materials to enhance the effect of rock breaking. Three impregnated diamond core bits with typical lip surface shape were selected, they were flat-shaped, flat-bottomed shape which containing AKTM and gear-shaped respectively. Then numerical simulation technique was used to simulate the rock drilling under the same drilling procedure condition. The analysis results show that:under the same drilling procedure conditions, the drilling speed of the bit from small to large respectively is:flat-bottomed bit, AKTM bit and gear bit. The rock mass’s warming phenomenon is not obvious overall and the temperature value basic didn’t have much change, only appeared a small amount of temperature concentration within a small range of the bottom of the well and the borehole wall. For flat bit and AKTM bit, the diamond top temperature is relatively higher than the matrix temperature, but the diamond root temperature is higher than diamond top temperature to gear bit. With the same rotating tangential direction, the front edge temperature on the segments of the bit was higher than the rear edge of diamond and matrix. A gear drill lip surface temperature higher than the other two bits lip surface temperature. In the process of broken rock, the equivalent stress value is relatively large around the rock crushing area. The farther away from the rock crushing area stress value is reduced accordingly. When flat-bottomed bit and AKTM bit crushing the first layer of rock, the front edge stress value on the segments of the bit was larger than the rear edge which with the same rotating tangential direction, the stress value tend to be consistent with the drilling, gear bit lip surface stress have been relatively average.The bench test and field drilling test has been used as the most effective means to detect the bit’s drilling effect. In this paper, impregnated diamond core bits with flat-shaped, containing AKTM cutting teeth and gear bit were made by hot pressing method, their specification is (?)75/49mm, they have the same matrix formula. Then indoor bench test and two field drilling tests were carried out. Firstly the thin-section analysis and mechanical properties testing to the rock and formation would be drilled were carried out, their mineral composition, texture, structure and the drillability grade were determined. The bench and field drilling test results show that:AKTM bit’s penetration rate is2times to flat bit within the P=2.5KN, n=222r/min drilling procedure, which show that AKTM poly crystal played a role of shear broken rock like clad composite sheet. The two field test results show that, according to the average mechanical drilling rate descending sort: gear bit, AKTM bit, flat-bottomed bit, the test result and numerical simulation test results are consistent.Overall, this paper through research material, theoretical analysis, numerical simulation and a large number of tests, basically achieved the purpose of the research. But for the restriction of personal experience and test conditions, many parts in the thesis were not satisfactory, the deficiency mainly displays in:the drillability of deep strata in Ultra-deep drilling is unpredictable, will encounter a variety of rock and precipitating factors in the actual drilling process, the final drilling process and BHA should be decided according to the actual situation. When doing the friction and wear test between bit matrix and rock under high temperature and high pressure conditions, due to the restriction of the use conditions of the friction and wear tester, no drilling fluid circulation and pressure-loading device, belong to the dry friction of the matrix and rock under high-temperature conditions, it is far cry from the actual deep well bottom hole drilling situation, it is concluded that the friction and wear rule have certain reference function, but still needs further examination in the ultra-deep drilling process. The testing machine need to continue be improved to enable it to real simulate bottom hole high temperature and pressure environment. In addition, this paper only do the matrix of impregnated diamond bit and rock friction and wear testing, the PDC bit, cone bit, and other types of bits will be used in drilling process, suggest the follow-up work to do some friction and wear tests according to these bits, to reveal their wear rules under different temperature and pressure conditions. The impregnated diamond core bit design includes a lot of content, end shape design is only one aspect, the adaptability of the matrix of bit and the rock drill should be taken into account. When simulating bit drilling rock, just take into account the influence of drill pressure, temperature and penetration rate, the follow-up studies should be added to the confining pressure of the bottom of the well, drilling fluid circulation and boundary conditions. |
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