Stress release mechanism of deep bottom hole rock by ultra-high-pressure water jet slotting

To solve the problems of rock strength increase caused by high in-situ stress,the stress release method with rock slot in the bottom hole by an ultra-high-pressure water jet is proposed.The stress conditions of bottom hole rock,before and after slotting are analyzed and the stress release mechanism of slotting is clarified.The results show that the stress release by slotting is due to the coupling of three factors:the relief of horizontal stress,the stress concentration zone distancing away from the cutting face,and the increase of pore pressure caused by rock mass expansion;The stress concentration increases the effective stress of rock along the radial distance from O.6R to 1R(R is the radius of the well),and the presence of groove completely releases the stress,it also allows the stress concentration zone to be pushed away from the cutting face,while significantly lowering the value of stresses in the area the drilling bit acting,the maximum stress release efficiency can reach 80%.The effect of slotting characteristics on release efficiency is obvious when the groove location is near the borehole wall.With the increase of groove depth,the stress release efficiency is significantly increased,and the release range of effective stress is enlarged along the axial direction.Therefore,the stress release method and results of simulations in this paper have a guiding significance for best-improving rock-breaking efficiency and further understanding the technique.

Insights into the radial water jet drilling technology-Application in a quarry

In this context, we applied the radial water jet drilling(RJD) technology to drill five horizontal holes into a quarry wall of the Gildehaus quarry close to Bad Bntheim, Germany. For testing the state-of-the-art jetting technology, a jetting experiment was performed to investigate the influence of geological heterogeneity on the jetting performance and the hole geometry, the influence of nozzle geometry and jetting pressure on the rate of penetration, and the possibility of localising the jetting nozzle utilizing acoustic activity. It is observed that the jetted holes can intersect fractures under varying angles, and the jetted holes do not follow a straight path when jetting at ambient surface condition. Cuttings from the jetting process retrieved from the holes can be used to estimate the reservoir rock permeability. Within the quarry, we did not observe a change in the rate of penetration due to jetting pressure variations.Acoustic monitoring was partially successful in estimating the nozzle location. Although the experiments were performed at ambient surface conditions, the results can give recommendations for a downhole application in deep wells.

NUMERICAL SIMULATION STUDY ON ROCK BREAKING MECHANISM AND PROCESS UNDER HIGH PRESSURE WATER JET

The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling model suited to analyze the whole process of water jet breaking rock were established with continuum damage mechanics and micro damage mechanics. The numerical results show the dynamic response of rock under water jet and the evolvement of hydrodynamic characteristic of jet during rock breaking is close to reality, and indicates that the body of rock damage and breakage under the general continual jet occurs within several milliseconds, the main damage form is tensile damage caused by rock unload and jet impact, and the evolvement of rock damage shows a step-change trend. On the whole, the numerical results can agree with experimental conclusions, which manifest that the analytical method is feasible and can be applied to guide the research and application of jet breaking rock theory.

EXPERIMENTAL STUDY OF ROCK BREAKING EFFECT OF STEEL PARTICLES

Particle impact drilling is an efficient drilling technology for deep-well hard formation, With this technology, the rock is cut mainly by high-speed spherical particle impact under hydraulic action. In this article, the influence of jet flow factors, hydraulic factors and abrasive factors on rock breaking is studied through indoor experiments of impact by steel particles. The results indicate that the particle water jet has an optimal standoff distance and particle concentration; the rock breaking effect declines with the increase of the confining pressure and the decrease of the pump pressure and particle diameter. This study will provide some food of thought for the development of particle impact drilling technology.

高压水射流凿岩过程的理论研究(英文)

Based on analyses of experimental results of water jet drilling, the fluid motion law in rock pores and the tendency of energy distribution, the rock-breaking process under high pressure water jet drilling has been studied systematically. The research indicates that the main interaction between the rock and water jet is interface coupling, that the impacting load and the static pressure of the water jet act together to make the rock break, and that the stress wave is the main factor. Water jet drilling can be divided into two stages: At the initial stage, the stress wave plays the main role and most of the rock breaking takes place; at the later stage, the existing rock defects, for instance, micro-holes and micro-cracks, are propagated and merged to make macroscopic damage, and then the diameter of the jet-drilled hole is expanded.

水射流辅助硬质合金钻头切割岩石过程的刀具温度分析

通过对硬质合金钻头切削岩石过程中热量转换、传递过程分析,建立了前刀面的温度方程。根据对水射流与刀片间传热过程的热力学分析分别建立了水射流与刀片表面对流换热微分方程组和热源与刀片间的稳态导热微分方程,推导出水射流对刀片的换热功率表达式和刀片内温度场表达式。研究表明,在无水射流情况下,钻头切削岩石前刀面温度变化与切削速度vq的平方根成正比;水射流的存在可以大幅降低刀具的温度,水射流对刀片的换热功率Φ与射流压力p的四次方根成正比,刀片平均温度的变化与p-1/4成正比。一定条件下的试验结果表明,采用水射流辅助硬质合金钻头切削岩石,当射流大于适当压力,钻头破损程度大幅下降,从而有效地提高钻头寿命。

多孔喷嘴破岩钻孔特性的实验研究

采用自行研制的实验装置研究了孔数和水力参数(冲蚀时间、喷嘴压降、喷距、围压)对多孔喷嘴破岩效果的影响规律。结果表明:喷嘴孔数越多,成孔形状越圆整;破岩效果随着射流压力的增大而呈线性增加;0围压条件下多孔喷嘴存在获得最大破岩体积和孔深的最优喷距约为5～6倍喷嘴当量直径。在围压条件下,多孔喷嘴破岩效果随着围压的增大而大幅下降;当量喷嘴直径相同时,破岩效果随孔数的增加而减小;在保证钻孔孔径的情况下,减少孔眼数量有利于提高多孔喷嘴破岩效率。实验结果可为超短半径水平钻孔射流钻头设计提供依据。

超高压水射流辅助破岩钻孔研究进展

将喷嘴出口压力大于140MPa定义为超高压水射流。介绍了早期超高压水射流钻孔试验及其应用,综述了超高压水射流辅助深井钻孔技术的发展状况,概括了超高压水射流辅助破岩机理和岩石性质与水射流结构参数对破岩效果的影响规律。在此基础上,对今后超高压水射流辅助破岩技术的研究提出了一些建议。

围压对射流破岩特性影响的试验研究

围压是石油工程中影响射流动力学特性的重要参数之一。应用高压井筒模拟试验装置进行了围压对常规连续射流、空化射流和磨料射流破岩效果影响的试验，最高围压达到20MPa。试验结果表明，围压对常规连续射流和空化射流破岩效果影响明显，破碎体积随围压的增大而减小，减小的速度随围压增大逐渐变缓；而对获得最大破碎体积的最优喷距影响不大，为3～5倍喷嘴直径，说明围压对射流基本结构特性影响不明显。当围压小于15MPa时，磨料射流射孔深度随围压的增大而近似呈线性减小。该试验可为射流参数的优选提供依据。

超高压水射流作用下岩石损伤破碎机理

由于水射流的高紊动与岩石材料的复杂性,水射流作用下岩石破坏机理的研究一直都是难点问题。运用全解耦流固耦合理论,建立超高压水射流冲击岩石介质的数值分析模型,射流采用标准k-ε模型和控制体积法,岩石采用线弹性和有限元法,计算分析淹没条件下岩石介质在水射流冲击作用下内部的应力分布规律。其次,根据岩石介质内部应力分布特征,基于岩石微元强度遵循Weibull分布的概率理论,将Mohr-Coulomb破坏准则作为随机分布变量,建立岩石损伤变量演化方程和连续损伤统计本构模型及用量纲一破坏系数来表征岩石破坏的准则。再次,按建立的流固耦合分析模型、岩石损伤模型和破坏准则,运用分阶段法对水射流的破岩过程进行了数值分析。最后,运用扫描电镜对水射流切割岩石断口形貌进行观测试验,分析岩石在超高压射流作用下微观破坏机制,主要有穿晶断裂和剪切错动两种形式,进一步验证数值模拟分析的结果,建立起水射流破岩过程中岩石微观破坏机制和宏观断裂分析的桥梁。

高压水射流破岩的数值模拟分析

采用非线性动力有限元法和岩石动态损伤模型对高压水射流破岩过程进行了模拟,结果表明,水射流破碎岩石主体所用的时间为毫秒量级,普通连续水射流破岩的主要形式是卸载及射流冲击所产生的拉伸破坏,并呈“阶跃式”发展。在此基础上,探索了水射流参数对破岩效果的影响,数值计算与试验结果吻合良好,表明利用该方法分析水射流破岩过程和机理是可行的,所得结论可作为水射流破岩体系设计和优化的依据。

径向水平钻孔直旋混合射流钻头设计与破岩特性

为解决高压水射流径向水平钻孔时孔径和孔深相互矛盾的问题,设计了一种兼具直射流和旋转射流特点的直旋混合射流钻头。给出了射流钻头设计方法,通过破岩实验,分析了直旋混合射流钻头结构对其破岩特性的影响。结果表明,直旋混合射流结合了直射流和旋转射流优点,比锥形喷嘴圆直射流扩孔能力强,比纯旋转射流钻孔深度大。影响直旋混合射流钻头破岩效果的结构参数较多,存在最优破岩效果结构参数,可通过不同参数组合调节破岩钻孔特征。需要进一步开展流场结构与破岩机理分析,为径向水平钻孔中射流钻头的设计提供更好的指导。

煤岩体水射流破碎机理

假设非均质岩体微元的弹性模量和抗压强度均服从Weibull分布,用愈渗理论推导了非均质岩体的水射流破坏准则和水射流破碎非均质岩体的门槛压力;数值模拟了水射流在非均质煤层中的连续钻孔过程;并进行了水射流的破煤实验.研究表明,在水射流作用下,煤岩体中强度较弱的一系列微元首先破坏,形成裂隙.进入裂隙空间的水射流对裂隙发生的水楔作用,使裂隙尖端产生拉应力集中,导致裂隙迅速发展和扩大,裂隙与裂隙连通后使得大块的煤岩体脱落,形成破碎坑.当水射流压力为60 MPa时,煤体破碎距离达到0.5 m以上.

石门揭煤钻孔布置优化分析及应用

为优化突出煤层石门揭煤钻孔布置,在理论分析射流割缝影响半径的基础上,提出基于高压脉冲水射流割缝技术的钻孔布置的新工艺。在理论分析圆形紊动射流结构的基础上,研究了射流冲击破碎煤体时射流速度分布,基于动量守恒定律得出射流作用于煤体的应力分布。并选取重庆某煤矿K1煤层煤体制作原煤煤样进行孔隙率测试和单轴压缩实验,得出煤体的初始损伤和煤体力学参数,基于损伤力学对煤体发生损伤破坏的门槛值进行了计算,得出射流冲击煤体的最大深度和钻孔切缝后影响半径,并应用于重庆某煤矿+175N2号石门揭煤工程。应用结果:钻孔数量减少32个,减少钻尺718.4 m,钻进工程量减少35.7%。

空化水射流破碎岩石的机理研究

在不同泵压和淹没压力条件下,针对不同类型的空化喷嘴,对空化水射流的空泡云特性和破碎岩石机理进行了一系列实验研究,探讨了空化水射流的空泡云与冲蚀能力之间的相互关系。优化空化喷嘴结构和工作条件以减小泵压,从而降低输入能量。空泡云的可视化研究显示缩放形喷嘴产生的空化云的长度和宽度比收敛形喷嘴的大。研究表明,空化水射流切割破碎岩石主要是由空泡的溃灭引起的,空泡云的长度等于靶距与切割深度之和;在切割破碎岩石时冲蚀效果只在开始几秒内发生,冲蚀深度并不随时间而增大。

高压水射流作用下岩石破碎机理及过程的数值模拟研究

根据连续介质力学和有限元理论,给出了高压水射流破岩系统中流体和岩石的控制方程,并建立了相应的有限元列式.运用连续损伤力学和细观损伤力学理论,建立了适用于水射流破岩全过程分析的岩石损伤模型以及宏细观损伤的耦合模式.数值计算的结果较真实地反映了水射流破岩过程中,岩石的动态响应以及水射流动力学特性的演化过程,普通连续水射流破碎岩石主体所用的时间为毫秒量级,破岩的主要形式是卸载及射流冲击所产生的拉伸破坏,并呈“阶跃式”发展.数值计算与相关试验结果基本吻合,表明该分析方法是可行的,可用来指导高压水射流破岩理论的进一步研究及应用.

基于CFD的自进式喷嘴参数优化

为了有效穿透井眼污染带,扩大泄油面积,提高油藏采收率,最终实现增产增注的目的。通过建立喷嘴三维模型,采用Fluent软件进行模拟,研究自进式喷头在不同前后喷嘴直径、前后喷嘴角度下的流场特性,利用流场中速度的分布规律结合公式计算出反冲力、破岩力、推进力的变化趋势。结果表明:随着后喷射角直径和前喷射角角度的增大,反冲力、推进力增大,破岩力减小;随着前喷射角直径和后喷射角度的增大,反冲力和推进力减小,破岩力增大。最终得到喷嘴的匹配方案,为实际生产提供了可靠依据。

井下增压超高压射流钻井技术研究进展

随着浅层油气资源勘探开发程度越来越高,深层油气资源成为中国油气资源战略接替的重要领域。而深井、超深井钻井勘探过程面临钻速慢,成本高等亟待解决的问题。应用超高压喷射钻井技术来提高深井超深井钻井速度是一种行之有效的方法,而实现超高压射流最主要的工具是井下增压器。通过国内外文献调研,主要介绍了国内外井下增压器工艺和增压机理以及超高压射流辅助破岩机理的研究进展,指出了前人研究的不足或尚未完善之处,在此基础上指出了井下增压器及其超高压射流辅助钻井破岩机理的研究方向。

煤层水力自旋转射流钻头设计

高压旋转水射流技术在钻大井径、长连续孔方面具有明显优势,在煤层中钻井又具有高效、节能、钻孔大、成孔规则、破岩效率高等优点,因此在煤层气地面径向水平井技术和井下采空区钻长直井技术中广为应用。主要从理论上分析了旋转射流和射流旋转各自的流动规律、破岩过程及破岩机理,并在此基础上分析了旋转射流钻头各设计参数的取值范围,结合已有的经验值,优化设计了可控外壳旋转内导叶轮、可控中心轴旋转内导叶轮、偏置可控外壳自旋转、偏置可控中心轴自旋转等4种水力旋转式钻扩孔射流钻头。这些钻头适用于在煤层中钻孔及安全排放瓦斯气体。

环空流体吸入式自激振荡脉冲射流大涡模拟研究

发展新型破岩钻井技术对于促进油气田高效开发具有重要意义,高压水射流是提高破岩钻井效率的一个重要手段,脉冲射流是一种高效射流形式。为了充分利用井底水力能量,提出了一种环空流体吸入式脉冲射流的技术构想。基于自激振荡原理设计了相应射流调制工具,并对工具的流场和动力学特性进行了大涡模拟研究。研究结果分析揭示了环空流体吸入式自激振荡脉冲射流调制的机理,并发现合理的水力结构可以在振荡腔内实现局部负压,使得环空流体被吸入,参与调制生成高效脉冲射流。与非吸入式脉冲射流相比,吸入式脉冲射流振荡更加剧烈,破岩能力更强。研究结果得到了实验验证,为实际钻井工具的研制和相关工艺技术的开发提供了依据。