The rock breaking and ROP increase mechanisms for single-tooth torsional impact cutting using DEM

Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.

TORSIONAL IMPACT RESPONSE OF A PENNY-SHAPED CRACK IN A FUNCTIONAL GRADED STRIP

The torsional impact response of a penny-shaped crack in a nonhomogeneous strip is considered. The shear modulus is assumed to be functionally graded such that the mathematics is tractable. Laplace and Hankel transforms were used to reduce the problem to solving a Fredholm integral equation. The crack tip stress field is obtained by considering the asymptotic behavior of Bessel function. Explicit expressions of both the dynamic stress intensity factor and the energy density factor were derived.And it is shown that, as crack driving force, they are equivalent for the present crack problem. Investigated are the effects of material nonhomogeneity and (strip's) highness on the dynamic fracture behavior. Numerical results reveal that the peak of the dynamic stress intensity factor can be suppressed by increasing the nonhomogeneity parameter of the shear modulus, and that the dynamic behavior varies little with the adjusting of the strip's highness.

Study of Torsional Impact Problem of Orthotropic Hollow Cylinder

A simple integral transform method was presented to solve the torsional impact problem of orthotropic hollow cylinder with mixed boundary condition. The analytical solution for the torsional impact problem of the orthotropic hollow cylinder was got. Some examples were calculated and discussed.

THE IMPACT TORSIONAL BUCKLING OF ELASTIC CYLINDRICAL SHELLS WITH ARBITRARY FORM IMPERFECTION

A perturbation analysis for the impact torsional buckling of imperfective elastic cylindrical shells subjected to a step torque is given The imperfection is supposed to be small and has arbitrary form. It is shown that only the imperfection which has the shape of static torsional buckling mode could influence the critical step torque. Finally a formula is presented for the critical step torque.

Impact Buckling and Post-Buckling of Elasto-Viscoplastic Cylindrical Shell Under Torsion

The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell is studied. By the usage of the Bodner-Partom constitutive relation, the present visco-plastic problem is treated as an orthotropic elastic problem. Based on the nonlinear large deflection shell therory, the governing dynamic buckling equation is solved by the Runge-Kutta method, and the critical buckling stress is determined by the B-R criterion. The present paper is mainly focused on the imperfection sensitivity, the strain rate sensitivity, and the dynamic post-buckling characters for the shell loaded dynamically with a constant shear strain rate. Numerical results show that the critical shear stress and imperfection sensitivity will increase with the increase of strain rate. It is found that the elastic buckling stress is more sensitive to imperfection than the visco-plastic buckling. The present research also reveals some dynamic post-buckling characters for the cylindrical shell, and it is shown that the shell will vibrate with the amplitude proportional to the strain rate in elastic buckling but improportional to the strain rate in visco-plastic buckling. An interesting phenomenon is found that when the strain rate is sufficiently high, there is no dynamic visco-plastic buckling occurrence and the shell produces a harmonic oscillation with a very small amplitude.

STUDY ON INFLUENCE OF BENDING-TORSION COUPLING IN AN IMPACTING-RUB ROTOR SYSTEM

A mathematical model of an impacting-rub rotor system with bending-torsion coupling was established. It was compared with the model without bending-torsion coupling through the modem nonlinear dynamic theory . It is observed that periodical, chaotic, period adding phenomena in them and the two models have a similar bifurcation process in their bifurcation figures . But the influence of bending-torsion on the dynmaic characteristics of the system is not neglected. The results have considerable meanings to analyze and improve the characteristics of an impacting- rub rotor system .

机械式复合冲击器的工作特性分析

常规冲击器采用的水力脉冲方法存在的冲蚀问题对冲击器的工作寿命影响较大。为此,提出一种机械举升及碟簧蓄能冲击方法并设计了一种机械式复合冲击器,通过实例模型验证了机构的可行性,在此基础上采用理论计算与数值分析相结合的方法对其压缩蓄能、扭冲、轴冲特性展开分析。研究结果表明:在10~100 MPa轴向压缩下,数量为11的碟簧组其总变形量增长率是数量为5的碟簧组变形量的约2.66倍,但其等效应力曲线特性相近;扭冲特性与径向冲击力成正比,下轴体端面总速度和总变形量与冲击力均呈线性相关,4对扭转冲击力作用的端面总速度约是2对的2.54倍;摆线轨迹线的举升座在30 r/min的运动状态下,12 mm冲程的最大冲击速度为0.2 m/s,最大冲击加速度为5.6 m/s^(2),为防止冲击过程接触应力过大需合理选择冲程大小,可通过增加扭冲对数、提高组合碟簧数量来增强冲击特性。研究结果可为复合冲击器的设计选型提供理论支撑。

钻井提速工具在南海东部深部地层应用分析

南海东部地区近几年一直延续使用的提速方法是马达+聚晶金刚石复片钻头(PDC)复合钻井技术和旋转导向配合PDC钻头,提速效果较为明显,但随着降本增效的压力越来越大,需要进一步提高机械钻速,提高作业时效,降低作业费用。基于此,分析了在南海东部某井试用的两种提速工具,分别是液力锤和扭冲工具,对这两种提速工具的工作原理及提速效果进行了深入的分析;认为提速工具的提速效果主要取决于工具与地层及钻头的配伍性;建议后续应用提速工具时需首先分析工具与地层和钻头的配伍性。

短路冲击下的船用柴油机瞬态扭振特性分析

[目的]为提出船用柴油发电机组的轴系扭振参数优化方案,需分析其在短路冲击下的瞬态扭转振动特性。[方法]采用Newmark法,以某型20 V柴油发电机组的短路冲击工况为例,对比不同轴系参数对轴系瞬态扭振特性的影响规律,进而基于参数优化结果来确定新的机组减振器刚度与联轴器刚度选配方案。[结果]研究结果表明:发生短路冲击时,轴系扭振特性将显著恶化;经优化之后(将扭振减振器刚度、联轴器刚度分别优选为原始值的0.9和0.70倍),短路冲击工况下的电机轴瞬时最大附加应力、联轴器瞬时最大扭矩、曲轴各轴段瞬时最大应力分别降低了13.43%,10.51%,5.29%。[结论]该参数优化方案可以有效降低轴系的瞬态扭振水平,研究成果可为柴油发电机组的减振降噪设计提供参考。

旋转配流式扭转冲击钻具设计与分析

为了减轻硬地层PDC钻头的黏滑振动,实现提速增效,研制了一种新型旋转配流式扭转冲击钻具。基于工具结构与工作原理的分析,建立了摆锤运动数学模型,研究了摆锤的运动规律,分析了水力参数和结构参数对其冲击性能的影响,并通过室内实验验证了工具结构的可行性。结果表明,摆锤在不同的阶段均做非线性加速运动,摆锤冲击功、冲击功率均与钻井液排量和摆锤转动惯量呈正相关,而摆锤固有冲击频率与钻井液排量呈正相关,与摆锤转动惯量呈负相关。研究结果为工具的结构优化和推广应用提供了理论支撑。

基于离散元法的PDC钻头切削复合地层黏滑振动特性研究

针对煤矿井下钻孔时钻头穿层钻进过程中遇到坚硬岩层而发生黏滑振动的问题,借助离散元数值模拟技术开展了PDC齿在5种典型硬度地层中切削破岩性能及黏滑振动特性研究。结果表明:钻头黏滑现象随着地层硬度的增加愈发明显,PDC齿切削极硬岩层时在岩石表面滑移而无法有效钻进;提高钻头转速在一定程度上能够减弱黏滑振动,但对提高钻进性能无明显增益效果;增加钻压能够显著提高钻头钻进效率,但同时会导致更严重的黏滑振动;采用扭转冲击方法能够有效减弱甚至抑制钻头的黏滑振动且能够提高钻头的钻进性能,但过大的扭转冲击会导致钻头所受冲击载荷增加。

PDC钻头复合冲击钻进动力学研究

深部地层的环境温度高,岩石硬度大、研磨性强。采用PDC钻头常规钻井方式,钻头的破岩效率低、机械钻速慢。介绍了1种轴扭复合冲击破岩工具的结构和工作原理。建立PDC钻头破岩理论模型和数值分析模型,并进行对比分析,得出了常规钻进和轴扭复合冲击钻进过程中PDC钻头的运动轨迹和岩石破碎过程应力变化规律。分析发现,复合冲击作用下岩石裂纹发生快,更容易产生体积破碎,岩石表面能够形成连续均匀的破碎坑,相比常规钻进能够提速30%左右。该研究为轴扭复合冲击破岩提供了理论依据,对深井油气田开发具有重要意义。

压扭超材料填充柱壳撞击固壁的动态力学行为研究

航天器着陆时的冲击防护是保证航天器安全着陆的关键技术,针对航天器腿式着陆器对缓冲装置的需求,文章提出了一种新型能量吸收结构——将压扭双螺旋超材料填充于圆柱壳内部,并基于ABAQUS软件建立了该吸能结构的有限元计算模型,模拟了其撞击固壁时的动态力学行为,开展了系统的参数化研究分析。模拟和分析结果表明:1)由于耦合作用,填充了压扭双螺旋超材料的圆柱壳吸能盒的能量吸收能力逐渐会大于压扭双螺旋超材料和圆柱壳能量吸收的线性叠加;2)圆柱壳吸能盒壁厚和压扭双螺旋超材料连杆个数是影响其动态力学特性和能量吸收的关键参数。上述结论可为内充压扭超材料圆柱壳式吸能盒在航天器着陆器中的应用提供一定技术参考。

元坝地区陆相地层钻井提速配套技术

四川盆地元坝气田天然气资源丰富,是中国石化的重点勘探开发区块,但钻速慢、钻井周期长是该区深井—超深井所面临的共同难题,该区域陆相侏罗系沙溪庙组—三叠系须家河组地层岩石致密、硬度高、可钻性差,此井段钻井周期约200d,占全井钻井周期的45%,严重制约了钻井提速提效。为此,开展了扭力冲击器配合PDC钻头、涡轮配合孕镶金刚石钻头、气体钻井等新技术应用试验,在试验效果的技术经济分析基础上,提出了延长气体钻井应用井段和深度的方案;对于不宜开展气体钻井的钻井液井段,如侏罗系自流井组中上部以浅地层或钻井液密度较低的地层推荐采用扭力冲击器提速,自流井组中下部—须家河组地层推荐应用涡轮钻具提速的方案。YB27-1H等11口井第三次开钻的314.1mm井段平均进尺1 885.29m,钻井周期缩短到166.18d,较前期平均值缩短34d。采用上述配套技术后,无论是钻井周期、日进尺均优于前期施工井,陆相地层提速提效取得了显著效果。

钻头扭转冲击器在元坝10井的试验

针对川东北地区尤其是元坝地区陆相下部地层常规钻井机械钻速低、单只钻头进尺少的难题,在元坝10井进行了"钻头扭转冲击器+PDC钻头"钻井试验,试验井段3 233.30～3 503.82 m,进尺270.52 m,纯钻时间81.0 h,平均机械钻速3.34 m/h,与同地层牙轮钻头钻进相比机械钻速提高3.04倍,与该井"螺杆+PDC钻头"复合钻进相比机械钻速提高2.59倍,PDC钻头工作寿命延长53 h。试验结果表明,钻头扭转冲击器配合PDC钻头钻井可解决复杂地层钻头寿命不高和机械钻速低的难题,拓宽了PDC钻头的应用范围。介绍了钻头扭转冲击器的技术背景、工作原理、特点和技术参数及在元坝10井的试验情况。

高研磨性硬地层钻井提速技术

川东北陆相自流井组和须家河组地层岩性致密、研磨性强,机械钻速低、钻头消耗量大,是制约该区域钻井提速的关键层段。为实现提速,各种新型井下工具得到了试验应用,但效果参差不齐。通过计算分层段岩石可钻性,推荐自流井组至须家河组采用孕镶金刚石钻头提高破岩效率;为降低硬地层和软硬交互层段钻头失效导致的钻速低问题,开展了三开井段典型钻具组合扭转和纵向振动理论分析,提出东岳庙段以浅地层采用扭力冲击器配合PDC钻头降低黏滑,珍珠冲段含砾岩层段需使用减震工具或改变钻具组合降低纵振,砂泥岩互层段需推广使用双向减震器或水力加压器降低纵振;采用高速螺杆+孕镶金刚石钻头的复合钻进,提高自流井组至须家河组大井眼定向速度。5口井现场实施后,机械钻速成倍增加、钻头新度提高30%,须家河组?311.2 mm井眼定向速度提高1.32倍。

高频扭转冲击钻进的减振与提速机理研究

高频扭转冲击钻井是一种能大幅提高钻井效率的新兴钻井技术,但由于对其破岩机理认识不清,使得高频扭转冲击钻井技术未能在国内推广应用。基于弹塑性力学和岩石力学,采用Drucker-Prager准则作为岩石的本构关系,塑性应变作为岩石破碎的失效判据。通过有限元方法建立全尺寸PDC钻头动态破岩的非线性动力学三维仿真模型,分析了高频扭转冲击作用下硬地层中钻头的动态破岩过程。结果表明,高频扭转冲击钻进硬地层时拉应力与压应力区域交叉出现且以拉应力为主,较以压应力为主的常规钻进可大幅提高钻头的机械钻速;高频扭转冲击钻进有效地减弱了硬地层中钻头处的粘滑振动,大大地提高了钻头的破岩效率。研究成果有助于深化对高频扭转冲击破岩的认识,为高频扭转冲击钻井技术的应用提供理论依据。

SLTIT型扭转冲击钻井提速工具

在我国钻井大提速的背景下,提出了一种集机械剪切、水力和扭转冲击3种破岩方式共同作用的复合钻井工艺新技术及装备。旋转钻井过程中,在不影响钻进的情况下,扭冲工具利用钻井液驱动内部冲击锤做反复的扭转冲击,将部分流体能量转换成一定频率、周向扭转、冲击型的井底机械破岩能量,并直接传递给钻头。5口井的现场试验结果表明,扭转冲击复合钻井技术与装备适合我国的钻井技术环境,能够有效消除PDC钻头的卡滑现象,减轻钻柱扭转振荡,能够有效保护钻头和钻具等配套部件,有效降低钻井成本。

扭转冲击钻具设计与室内试验

常规钻具在钻硬地层时机械钻速低,钻头失效快,钻井成本高。为此,设计了扭转冲击钻具。该钻具可将流体的液压能转换成扭向的、高频的机械能并直接传递给PDC钻头,给钻头施加周期性的低幅高频扭转冲击,当与钻柱稳态扭矩相结合时,能对钻头施加高效的破岩扭矩,大幅减小或消除钻头的粘滑振动,在保证井身质量的同时提高机械钻速,延长钻头寿命。对扭转冲击钻具的关键部件——扭转冲击副的运动可行性分别进行了仿真分析和室内试验。结果表明,扭转冲击副运转顺利,滑动块与传动轴周期性的碰撞可对传动轴施加周期性的低幅高频扭向冲击。

TorkBuster扭力冲击器在元坝地区的试验应用

元坝地区是继普光气田之后,中国石化在川东北地区发现的又一大型海相气田。元坝地区下部陆相地层岩石研磨性强、可钻性差、且存在高压气层,机械钻速低,成为元坝地区钻井工程面临的最大挑战。PDC钻头+TorkBuster扭力冲击器钻井技术就是为了解决这一问题而引进应用的一项关键技术,截止到2011年5月31日,已试验应用了11口井16次,取得了明显的提速效果,已经成为元坝地区下沙溪庙组、千佛崖组地层钻井提速的一种有效手段。