Digital monitoring of rotary-percussive drilling with down-the-hole hammer for profiling weathered granitic ground

Rock and geotechnical engineering investigations involve drilling holes in ground with or without retrieving soil and rock samples to construct the subsurface ground profile.On the basis of an actual soil nailing drilling for a slope stability project in Hong Kong,this paper further develops the drilling process monitoring(DPM)method for digitally profiling the subsurface geomaterials of weathered granitic rocks using a compressed airflow driven percussive-rotary drilling machine with down-the-hole(DTH)hammer.Seven transducers are installed on the drilling machine and record the chuck displacement,DTH rotational speed,and five pressures from five compressed airflows in real-time series.The mechanism and operations of the drilling machine are elaborated in detail,which is essential for understanding and evaluating the drilling data.A MATLAB program is developed to automatically filter the recorded drilling data in time series and classify them into different drilling processes in sub-time series.These processes include penetration,push-in with or without rod,pull-back with or without rod,rod-tightening and rod-untightening.The drilling data are further reconstructed to plot the curve of drill-bit depth versus the net drilling time along each of the six drillholes.Each curve is found to contain multiple linear segments with a constant penetration rate,which implies a zone of homogenous geomaterial with different weathering grades.The effect from fluctuation of the applied pressures is evaluated quantitatively.Detailed analyses are presented for accurately assess and verify the underground profiling and strength in weathered granitic rock,which provided the basis of using DPM method to confidently assess drilling measurements to interpret the subsurface profile in real time.

Drill bit wear monitoring and failure prediction for mining automation

This article introduces a novel approach for tricone bit wear condition monitoring and failure prediction for surface mining applications.A successful bit health monitoring system is essential to achieve fully autonomous blasthole drilling.In this research in-situ vibration signals were analyzed in timefrequency domain and signals trend during tricone bit life span were investigated and introduced to support the development of artificial intelligence(AI)models.In addition to the signal statistical features,wavelet packet energy distribution proved to be a powerful indicator for bit wear assessment.Backpropagation artificial neural network(ANN)models were designed,trained and evaluated for bit state classification.Finally,an ANN architecture and feature vector were introduced to classify the bit condition and predict the bit failure.

Research on Fe-based impregnated diamond drill bits strengthened by Nano-NbC and Nano-WC

In order to improve the matrix performance of impregnated diamond drill bit to better meet the drilling needs,the effects of the addition of nano-WC and nano-NbC particles on the matrix material together with the mechanical properties and microstructure of the diamond-matrix composite material of the Fe-based diamond drill bit were studied by using the method of uniform formula design,regression analysis and solution finding.An indoor drilling test was also carried out using the fabricated impregnated diamond drill bit.The results showed that after the addition of nano-NbC and nano-WC,the hardness and flexural strength of the matrix material got improved,as the flexural strength of the diamond composite material increased to 4.29%,the wear-resistance ratio increased to 8.75%,and the tighter the chemical bonding between the diamond and the matrix.This,indicates that the addition of nanoparticles has a positive significance in improving the performance of the diamond composite.The results of the drilling test showed that the mechanical drilling speed of the impregnated diamond drill bit after nanoparticle strengthening is 25.85%higher than that of the conventional drill bit,and the matrix wear was increased by 17.5%.It proves that nanoparticles can improve the drilling performance and efficiency of drill bit.

Tooth arrangement design of retractable DTH hammer bit used for drilling while casing

Down-the-hole(DTH)hammer with casing while drilling(CWD)is a technology that has been proven to be able to alleviate many of the problems faced by complex formations.However,the drill bit is suffered from rapid wear,low drilling efficiency,and high energy consumption due to the unreasonable tooth arrangement and impact energy selection in drilling process,which affect the application effect of this technology.ABAQUS software was used for numerical simulation of rock breaking behavior under impact load with the single,three,and five teeth arrangement drill bit respectively,to improve the application effect and solve the aforementioned technical problems.Based on the calculated parameters of tooth arrangement,we designed a novel drill bit for hard rocks and provided a theoretical basis for the tooth arrangement of largediameter drill bits.

Reliability analysis of retractable drill bit with air reverse circulation used for drilling while casing

Casing-while-drilling(CWD)with down the hole(DTH)hammer drilling technology has been widely used in unconsolidated formations,due to its advantages in protecting the borehole wall,excellent rock cuttings capacity,and fast penetration rate in hard rock.As an important component of the CWD system,the structure of the retractable drill bit needs not only to ensure to form stronger reverse circulation,but also to be expandable or retractable as needed,otherwise the drill bit cannot be lift and put down smoothly in the casing,and may lead to drilling accidents.This paper developed a new type of reverse circulation DTH hammer drill bit used for CWD drilling technology.The retractable performance of this type of drill bit is studied using ADAMS software.The results show that it is smoothly expandable and retractable as designed under the conditions of the weight of the bit(WOB)of 0.5–2.0 t and the rotation speed of 30–60 r/min.To investigate the reverse circulation effect of the drill bit,Fluent software was used to simulate the flow characteristic inside it.The simulation results indicated that it can form strong reverse circulation,and the entrainment ratio h can reach 9.5%.

Discussion of reasonable drilling parameters in impregnated diamond bit drilling

The impregnated diamond(ID)bit drilling is one of the main rotary drilling methods in hard rock drilling and it is widely used in mineral exploration,oil and gas exploration,mining,and construction industries.In this study,the quadratic polynomial model in ID bit drilling process was proposed as a function of controllable mechanical operating parameters,such as weight on bit(WOB)and revolutions per minute(RPM).Also,artificial neural networks(ANN)model for predicting the rate of penetration(ROP)was developed using datasets acquired during the drilling operation.The relationships among mechanical operating parameters(WOB and RPM)and ROP in ID bit drilling were analyzed using estimated quadratic polynomial model and trained ANN model.The results show that ROP has an exponential relationship with WOB,whereas ROP has linear relationship with RPM.Finally,the optimal regime of mechanical drilling parameters to achieve high ROP was confirmed using proposed model in combination with rock breaking principal.

Theoretical and experimental study of the pulling force of jet bits in radial drilling technology

Radial drilling technology, of which the jet bit is the key device, is a research focus in the field of oil drilling and production. This paper establishes mechanical equations for jet bits and analyzes the hydroseal of backward jets in bottom holes. Meanwhile this paper establishes a mechanical equation for a high pressure hose and analyzes the axial force distribution. Laboratory experiments indicate that the flow rate, the angle between the backward nozzle axis and the jet bit axis, and the hole diameter are the major influencing factors; the generation of the pulling force is mainly due to the inlet pressure of the jet bit; the backward jets can significantly increase not only the pulling force but also the stability of jet bits. The pulling force would reach 8,376 N under experimental conditions, which can steadily pull the high-pressure hose forward.

Core discing characteristics and mitigation approach by a novel developed drill bit in deep rocks

Core discing often occurs in deep rocks under high-stress conditions and has been identified as an important characteristic for deep rock engineering.This paper presents the formation mechanism of core discing firstly.Then,the interaction between diamond drill bits and rock was analyzed based on numerical modeling.A novel drill bit with an inner conical crown for the mitigation of core discing was designed and verified by simulation experiments.The mitigation method was applied in the cavern B1 of CJPL-Ⅱand satisfactory results had been achieved.The percentage of core discing had been obviously decreased from 67.8%when drilling with a rectangular crown drill bit,to 26.5%when an inner conical crown drill bit had been adopted.This paper gives full insight into core discing characteristics and provides a new method for core discing mitigation;it will potentially contribute to stress measurement in deep rock engineering.

Drilling signals analysis for tricone bit condition monitoring

This paper presents a novel approach to investigate the relations between drilling signals and bit wear condition in real world full-scale mining operations.This research addresses the increasing demand for automation in mining to increase the efficiency,safety,and ability to work in harsh environments.A crucial issue in fully autonomous unmanned drilling is to have a system to detect the bit wear condition through the drilling signals analysis in real time.In this work,based on extensive field studies,a novel qualitative method for tricone bit wear state classification is developed and introduced.The relations between drilling vibration as well as electric motor current signals and bit wear are investigated and bit failure vibration frequencies,regardless of the geological conditions,are introduced.Bit failure frequencies are experimentally investigated and analytically calculated.Finally,the effect of bit design parameters on the failure frequencies is presented for the application of bit wear condition monitoring and bit failure prediction.

Critical weight on bit of double-driven bottomhole assembly during vertical and fast drilling

It is difficult to determine the optimal weight on bit (WOB) of the double-driven bottomhole assembly (DD-BHA, with double stabilizers and a bent housing positive displacement motor (PDM)) which is employed during vertical and fast drilling. High WOB leads to well deviation out of control, and low WOB leads to low rate of penetration (ROP). So considering the rock physical properties, the anisotropy index function of polycrystalline diamond compact (PDC) bit was derived with the structure and cutting performance parameters of the bit, and the effect of natural hole deviation tendencies on the performance of DD-BHA resisting deviation was represented. The concept of elliptic deformation ratio was used to characterize the performance of DD-BHA resisting deviation. Eventually, a model calculating the critical WOB was established. By comparing the model predictions with the measured hole angle changes in the field, the results show that the model predictions are accurate with error less than 5.8%, which can meet the operational requirements in the projects. Furthermore, the model was adopted to justify and guide the operating conditions and parameters during drilling, which shows that the optimum WOB predicted by the model can not only control deviation but also improve ROP effectively. The model is independent on the formation characteristics of blocks, so it can be expanded widely to other oilfields.

THE LUBRICATING MECHANISMS OF LUBRICATINGDRILLING FLUIDS ON SYNTHETIC DIAMOND BIT

The functions of lubricants in diamond drilling were discussedin this paper. The influences of lubricant on drilling efficiency and bit′s life were compared and analyzed with simulated drilling test and lubrication test apparatus. Lubricating mechanisms were also discussed.

“Push back” technique: A simple method to remove broken drill bit from the proximal femur

Broken drill bits can be difficult to remove from the proximal femur and may necessitate additional surgical exploration or special instrumentation.We present a simple technique to remove a broken drill bit that does not require any special instrumentation and can be accomplished through the existing incision.This technique is useful for those cases where the length of the broken drill bit is greater than the diameter of the bone.

Finite Element Investigation of Flow Field Below Asymmetric Drill Bits for Reverse Circulation in Drilling Tight Oil and Gas Reservoirs

Development of unconventional tight oil and gas reservoirs such as shale pays presents a huge challenge to the petroleum industry due to the naturally low permeability of shale formations and thus low productivity of oil and gas wells.Shale formations are also vulnerable to the contamination of the water in the drilling and completion fluids,which further reduces reservoir permeability.Although gas-drilling(drilling with gas)has been used to address the issue,several problems such as formation water influx,wellbore collapse,excessive gas volume requirement and hole cleaning in horizontal drilling,still hinder its application.A new technique called gas-lift drilling has recently been proposed to solve these problems,but the optimal design of drilling operation requires a thorough investigation of fluid flow field below the asymmetric drill bits for evaluating the fluid power needed to clean the bottom hole.Such an investigation is conducted in this work based on the Finite Element Method(FEM)implemented in an open source computational framework,FEniCS.Pressure and flow velocity fields were computed for three designs of drill bit face characterized by radial bit blades and one eccentric orifice of discharge.One of the designs is found superior over the other two because it generates relatively uniform flow velocities between blades and provides a balanced fluid power needed to clean all the bit teeth on each bit blade.To quantify the capability of borehole cleanup presented by three drill bit designs,the energy per unit volume is calculated in each region of drill bit and compared with the required value suggested by the literature.In addition,the developed FEM model under FEniCS framework provides engineers an accurate tool for optimizing drill bit design for efficiently gas-lift drilling unconventional tight oil and gas reservoirs.

Similarity evaluation of stratum anti-drilling ability and a new method of drill bit selection

Considering the stratum anti-drilling ability,drill bit working conditions,drill bit application effect and drill bit economic benefits,the similarity of stratum anti-drilling ability was evaluated by grey relational analysis theory to screen out candidate drill bits with reference values.A new comprehensive performance evaluation model of drill bit was established by constructing the absolute ideal solution,changing the relative distance measurement method,and introducing entropy weight to work out the closeness between the candidate drill bits and ideal drill bits and select the reasonable drill bit.Through the construction of absolute ideal solution,improvement of relative distance measurement method and introduction of entropy weight,the inherent defects of TOPSIS decision analysis method,such as non-absolute order,reverse order and unreasonable weight setting,can be overcome.Simple in calculation and easy to understand,the new bit selection method has good adaptability to drill bit selection using dynamic change drill bit database.Field application has proved that the drill bits selected by the new drill bit selection method had significant increase in average rate of penetration,low wear rate,and good compatibility with the drilled formations in actual drilling.This new method of drill bit selection can be used as a technical means to select drill bits with high efficiency,long life and good economics in oilfields.

Whirl Interaction of a Drill Bit with the Bore-Hole Bottom

This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body with uneven surface. It is attached to the lower end of a rotating elastic drill string. In the perturbed state, the bit can roll without sliding on the bore-hole bottom, performing whirling vibrations (the model of dynamic equilibrium with pure rolling when maximum cohesive force does not exceed the ultimate Coulombic friction). To describe these motions, a nonholonomic dynamic model is proposed, constitutive partial differential equations are deduced. With their use, the whirling vibrations of oblong and oblate ellipsoidal bits are analyzed, the functions of cohesive (frictional) forces are calculated. It is shown that the system of elastic drill string and ellipsoidal bit can acquire stable or unstable whirl modes with approaching critical Eulerian values by the parameters of axial force, torque and angular velocity. The analogy of the found modes of motions with ones of the Celtic stones is established. It is shown that the ellipsoidal bits can stop their whirling vibrations and change directions of their circumferential motions in the same manner as the ellipsoidal Celtic stones do. As this takes place, the trajectories of the oblate ellipsoidal bits are characterized by more complicated paths and irregularities.

Study on drilling mechanism and optimization of percussion-extruding DTH hammer bit

The authors tested the percussion-extruding Down-the-hole(DTH)hammer bit with five different structures and mainly analyzed the drilling mechanism between conical bit and stepped bit.In addition,aiming at "the pile effect" in combination with the advantage of stepped bit,we design a new cam spinning bit and test it outdoors.The result shows that using cam spinning bit can solve the problem of "the pile effect",which can also obtain higher drilling efficiency than using conical bit in high confining pressure strata.It is characterized by novel structure and high drilling speed as well as good guiding,and it is significant for improving efficiency in percussion-extruding drilling technique.

Frequency Analysis of Drill Bit Whirlings on Uneven Bottoms of Deep Bore-holes

An incipient stage of a rotating drill string bit whirl motion proceeding on a well bottom surface is studied on the basis of kinematic （nonholonomic） models of mechanic interaction between the contacting uneven bodies. The bit is considered to be an absolutely rigid spherical or ellipsoidal body, the well bottom surface can be plane or spherical. It is assumed that the system coaxiality is disturbed through small initial curvature of the drill string, imperfections of the bit and bore-well geometry or the system mass debalance. Linearized equations of the bit whirling are deducted, the frequencies of periodic motions are calculated, and their modes are constructed for different geometric parameters of the spherical and ellipsoidal bits. It is demonstrated that, depending on the system properties, the bit motion can acquire the regimes of forward and backward whMings or to transit to the state of stationary spinning relative to an immovable center of velocities. The most unfavorable and atypical whirling modes are characteristic for oblate eilipsoidal bits and curvilinear surfaces of the well bottom.

万米深井上部大尺寸井眼钻柱动力学特性研究

油气勘探已向更深、更复杂的超深层的万米勘探新领域推进,但上部大尺寸井眼给万米深井的钻井提出了巨大挑战:岩石硬和返速低导致钻速慢,大尺寸井眼内剧烈振动导致钻具裂纹多发,钻压小则钻速慢,钻压稍大则下部振动快速加剧从而导致大尺寸钻具使用寿命远低于预期。为此,在对比研究了深地川科1井(以下简称SDCK-1井)和毗邻8000 m超深井上部井段钻柱振动问题基础上,基于全井钻柱系统动力学模型和数值仿真方法,针对性研究了大尺寸井眼中的钻柱动力学特性。研究结果表明:①井眼尺寸越大,钻头和下部钻具的振动越剧烈,SDCK-1井二开大尺寸井眼与邻井中等尺寸井眼相比(井深500 m处),其钻头及下部钻具振动强度均值分别增加了48.0%和41.5%,比SDCK-1井三开中等尺寸3000 m井深的钻头及下部钻具振动强度均值分别高了29.0%和2.9%;②相同井眼尺寸和岩石特性情况下,下部钻具组合比钻柱整体长度对钻头振动的影响更大,优化下部钻具组合能够明显改善钻头振动,保护钻头,同时还可以提高钻头破岩能量利用效率实现钻井提速;③在大尺寸井眼中钻头破岩激励向上传播,横向振动衰减慢于轴向振动衰减,大尺寸钻头扭矩更大且钻压和扭矩波动更加明显,因此从保护下部钻具的角度出发,大尺寸井眼钻具组合对抑制横振更加有效;④大尺寸井眼中下部钻具弯矩和弯矩波动更大,现场频繁出现的钻具裂纹除受控于整体振动强度较大以外,交变弯矩是裂纹发生的重要原因。结论认为,该研究成果揭示了超深井大尺寸井眼中钻柱的动力学特性,指出了应着重控制横振和交变弯矩,该认识可以为超深井上部大尺寸井眼钻井提供技术指导。

具有独立缓冲结构的PDC—牙轮复合钻头研制

油气勘探开发过程中,难钻地层钻井效率低、钻头寿命短是影响深井、超深井钻井周期和成本的瓶颈问题。钻头工作过程中切削结构轮流与井壁接触而产生的多边形效应是导致钻头不稳定工作、切削齿冲击失效的主要因素。为提高钻头工作稳定性,提出了具有独立缓冲结构的PDC—牙轮复合钻头新结构,并针对四川盆地茅口组Ø311.2 mm井段常规PDC钻头冲击失效严重的问题,设计了3+3+3型(3个主刀翼、3个牙轮以及3个独立缓冲刀翼)的独立缓冲结构复合钻头,开展了全尺寸钻头室内钻进对比实验,并在川渝页岩气区块茅口组—栖霞组地层进行了实钻应用。研究结果表明:①独立缓冲结构复合钻头在常规复合钻头的牙轮切削结构和固定切削结构之间的空隙部位增设独立缓冲刀翼,有效缓解了多边形效应,对PDC齿形成很好的缓冲保护,同时分担了过大的钻压,限制了切削齿吃入深度,进而防止了钻头产生粘滑振动;②独立缓冲结构复合钻头钻压和扭矩波动小,扭矩为PDC钻头的1/5;③独立缓冲结构复合钻头取得了单只钻头进尺170 m的记录,比邻井同层位单只PDC钻头最高进尺提高了73.5%。结论认为,独立缓冲刀翼对提高钻头的稳定性起到了关键作用,不仅提高了钻头寿命,而且有效提高了复杂难钻地层及复杂结构井的综合钻井时效,有效降低了油气勘探开发成本。

差压步进钻头提高破岩速度原理及现场试验

井底岩石承受较大的原地应力作用,且随着井深增加原地应力呈增大趋势。原地应力的存在增加了岩石的压实程度,导致岩石坚硬、可钻性差、研磨性强等问题,成为破岩工具切削效率低、使用寿命短和钻井速度慢的最主要原因之一。针对此背景,提出释放井底部分原地应力弱化地层抗钻特性提高破岩速度的理念,研发一种可释放井底部分原地应力弱化地层抗钻特性且能够集中钻压强化攻击能力的差压步进钻头,该钻头充分利用钻井过程中的井底钻压波动,实现扩眼钻头与领眼钻头钻压动态分配及钻进过程交替进行的目标,通过弱化地层、强化攻击及转化振动三重效果提高破岩速度。为验证差压步进钻头的应力释放效应,建立三维流固耦合的阶梯井底应力场模型,并在江苏油区某区块砾石层井段开展3口井的实钻试验。结果表明:阶梯井底能够使阶梯处岩石更易破碎;小直径领眼钻头应力释放效果较好;随着地层深度的增加,差压步进钻头应力释放效果更加显著,应力释放比约为60.2%;差压步进钻头提速效果显著,砾石层钻速较牙轮钻头提升可达161.89%,最高提速318.11%。