超声波振动频率对花岗岩破碎规律影响的研究

发布时间：2017-12-27 07:19

本文关键词：超声波振动频率对花岗岩破碎规律影响的研究　出处：《吉林大学》2017年博士论文　论文类型：学位论文

【摘要】：随着矿产资源勘探深度的增加,复杂地层与难钻地层钻遇率升高,硬岩层所占比例越来越大,现有钻探技术已不能完全满足当今钻井作业需求。尤其是在硬岩地层的钻进中,常规钻探方法存在钻头寿命短、钻进效率低、钻探成本高的技术问题。因此,亟须研究一种高效碎岩技术来解决这一钻进难题,从而提高钻进效率,降低钻进成本。本文针对上述钻进难题,提出采用超声波振动辅助碎岩的方法。超声波振动的频率较高,可以达到硬岩的固有频率,岩石在共振条件下会产生较大的振幅,此时岩石内部裂纹裂隙极易发育、扩展及贯通,造成岩石破碎难度的大幅度下降。但是,随着岩石力学性能劣化现象的产生,其固有频率的下降规律以及其本身的固有频率范围还有待测试研究。因此,进行超声波振动频率对硬岩破碎规律的研究很有意义,通过研究岩石的破碎规律,一方面可以估算硬岩的固有频率,另一方面可以确定岩石频率的改变规律,用以确定超声波振动频率的加载范围及加载方式,为超声波振动辅助硬岩钻进提供理论指导及技术支持。本文的研究对象为花岗岩,以试验研究为基础,辅以理论分析及数值模拟分析的研究手段,开展超声波振动频率对硬岩破碎规律的研究。本论文的主要研究内容及成果如下:(1)结合断裂力学理论和共振碎岩理论,从理论上分析超声波振动下岩石破碎的机理。建立超声波振动力学模型,开展超声波振动频率对岩石破碎影响规律的分析。研究结果表明在固有频率范围之内对岩石进行振动加载能更有利于岩石的破碎,系统的阻尼越强则对振动的抑制效果越强。(2)采用ANSYS/WORKBENCH软件对模型进行了有限元模拟分析。研究岩石内部裂纹参数对模型模态频率、谐响应频率、应力强度因子以及应力应变变化规律的影响。研究发现裂纹的走向、尺寸、数量均会造成岩石颗粒模型的模态频率降低的现象,并且岩石应力、应变的峰值随着振动频率的增加呈现先增大后降低的趋势,在振动频率为35KHz时出现最大值。(3)研制了超声波振动试验台,对花岗岩样品进行超声波振动试验,并对试验前、后的花岗岩样品进行核磁共振检测以及单轴抗压强度测试。观察不同试验条件下花岗岩样品孔隙度、孔径分布、T2谱图以及单轴抗压强度的变化情况,分析超声波振动频率对岩石力学性能的影响规律。试验中发现花岗岩样品的核磁测试结果与其单轴抗压强度的结果相吻合,并且采用孔隙度表征岩石的损伤程度,能较好的反映出岩石抗压强度的强弱;花岗岩样品的固有频率在30KHz和35KHz之间,但更加接近30KHz。(4)研制微钻试验台,选择频率为20KHz的超声波换能器进行超声波振动回转钻进先导性试验。对比适当频率的超声波振动回转钻进方法与常规钻进方法的差异,并总结钻进压力对超声波振动回转钻进方法的影响规律。在钻进试验中发现,随着钻压的增大,钻进速度的增大幅度呈先增加后减小的趋势,增幅范围在13.93%~38.11%之间。
[Abstract]:With the increase of exploration depth of mineral resources, the drilling rate of complex strata and hard drilling strata is increasing, and the proportion of hard rock is bigger and bigger. The existing drilling technology can no longer meet the needs of drilling operation today. Especially in the drilling of hard rock formation, the conventional drilling method has the technical problems of short drilling life, low drilling efficiency and high drilling cost. Therefore, it is urgent to study a high efficient rock breaking technology to solve the drilling problem, so as to improve the drilling efficiency and reduce the drilling cost. In this paper, the method of using ultrasonic vibration to assist rock breaking is put forward in view of the problem of drilling. The higher frequency of ultrasonic vibration can reach the natural frequency of hard rock, and the rock will generate larger amplitude under resonance condition. At this time, the cracks and cracks inside the rock are easy to develop, expand and connect, resulting in a great decline in rock fragmentation difficulty. However, with the deterioration of mechanical properties of rock mechanics, the decline law of natural frequency and the natural frequency range of its own need to be tested. Therefore, it is meaningful to study the ultrasonic vibration frequency of breakage of hard rock, the rock fragmentation rules of natural frequency, one can estimate the hard rock, on the other hand can determine the change law of rock frequency, range and load loading method is used to determine the ultrasonic vibration frequency, to provide theoretical guidance and technical support for ultrasonic vibration assisted drilling in hard rock. The research object of this paper is granite. Based on the experimental research, supplemented by theoretical analysis and numerical simulation analysis methods, we carry out the research on the rule of ultrasonic vibration frequency on the hard rock fragmentation. The main contents and achievements of this paper are as follows: (1) combined with fracture mechanics and resonance rock fragmentation theory, the mechanism of rock fragmentation under ultrasonic vibration is theoretically analyzed. The mechanical model of ultrasonic vibration is set up, and the influence law of ultrasonic vibration frequency on rock breaking is analyzed. The results show that vibration loading of rock in the natural frequency range is more conducive to rock fragmentation, and the stronger the damping of the system is, the stronger the effect of vibration suppression is. (2) the finite element simulation analysis of the model is carried out by using ANSYS/WORKBENCH software. The influence of the internal crack parameters on the modal frequency, harmonic response frequency, stress intensity factor and stress and strain variation of the model is studied. It is found that the trend, size and number of cracks all cause the decrease of modal frequency of rock particle model. The peak value of rock stress and strain increases first and then decreases with the increase of vibration frequency, and the maximum value occurs when the vibration frequency is 35KHz. (3) the ultrasonic vibration test rig was developed, and the ultrasonic vibration test for granite samples was carried out. The granite samples before and after the experiment were tested by NMR and uniaxial compressive strength. The porosity, pore size distribution, T2 spectrum and uniaxial compressive strength of granite samples under different experimental conditions were observed, and the effect of ultrasonic vibration frequency on the mechanical properties of rock was analyzed. The test found that magnetic test results of granite samples and uniaxial compressive strength are consistent, and the damage degree of rock porosity, can reflect the compressive strength of the rock strength of granite samples; natural frequency between 30KHz and 35KHz, but closer to 30KHz. (4) developing a micro drill test rig, selecting the ultrasonic transducer with a frequency of 20KHz to carry out the pilot test of the ultrasonic vibration drilling. The difference between ultrasonic vibration rotary drilling method and conventional drilling method is compared, and the influence rule of drilling pressure on ultrasonic vibration rotary drilling method is summarized. In the drilling test, it is found that with the increase of drilling pressure, the increase of drilling speed increases first and then decreases, and the range of increase is between 13.93%~38.11%.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P634.1

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