Integrated design and control technology of liner completion and drilling for horizontal wells

Aiming at the problems of large load of rotation drive system,low efficiency of torque transmission and high cost for operation and maintenance of liner steering drilling system for the horizontal well,a new method of liner differential rotary drilling with double tubular strings in the horizontal well is proposed.The technical principle of this method is revealed,supporting tools such as the differential rotation transducer,composite rotary steering system and the hanger are designed,and technological process is optimized.A tool face control technique of steering drilling assembly is proposed and the calculation model of extension limit of liner differential rotary drilling with double tubular strings in horizontal well is established.These results show that the liner differential rotary drilling with double tubular strings is equipped with measurement while drilling(MWD)and positive displacement motor(PDM),and directional drilling of horizontal well is realized by adjusting rotary speed of drill pipe to control the tool face of PDM.Based on the engineering case of deep coalbed methane horizontal well in the eastern margin of Ordos Basin,the extension limit of horizontal drilling with double tubular strings is calculated.Compared with the conventional liner drilling method,the liner differential rotary drilling with double tubular strings increases the extension limit value of horizontal well significantly.The research findings provide useful reference for the integrated design and control of liner completion and drilling of horizontal wells.

Dynamic Response of Two-Degree-of-Freedom Riserless Drill String for Vortex-Induced Vibration Suppression and Enhancement

The mechanical behavior,dynamic evolution,and flow-field distribution of a two-degree-of-freedom riserless drill string were simulated numerically by using FLUENT fluid simulation software with the user-defined function embedded.The rotation angular velocities before and after the critical rotation angular velocity were used as independent variables,and the reduced velocity range was 3-14.Fluid-structure coupling was realized based on the dynamic overset grid and the SST k-ωturbulence model.Results reveal that the dynamic response of the riserless drill string was considerably affected by rotation and flow velocity,which are coupled with each other.The cross-flow average dimensionless displacement increased with the rotation angular velocity,and rotation considerably enhanced the in-line maximum average dimensionless displacement.However,the cross-flow amplitude caused by vortex-induced vibration was suppressed when the rotation angular velocity reached a certain value.The in-line and cross-flow frequencies were the same,thereby causing the trajectory to deviate from the standard'figure-eight'shape and become a closed circle shape.The vortex did not fall behind the cylinder at low reduced velocity with high-rotation angular velocity,and the structure of the near-wake vortex remained U-shaped.The wake of the cylinder was deflected along the cross-flow direction,thereby leading to vibration asymmetry and resulting in increased vibration instability and disordered vibration trajectories,especially at high-rotation angular velocities.

Calculation of the Gas Injection Rate and Pipe String Erosion in Nitrogen Drilling Systems

Detailed information is provided for the design and construction of nitrogen drilling in a coal seam.Two prototype wells are considered.The Guo model is used to calculate the required minimum gas injection rate,while the Finnie,Sommerfeld,and Tulsa models are exploited to estimate the ensuing erosion occurring in pipe strings.The calculated minimum gas injection rates are 67.4 m^(3)/min(with water)and 49.4 m^(3)/min(without water),and the actual field of use is 90–120 m^(3)/min.The difference between the calculated injection pressure and the field value is 6.5%–15.2%(formation with water)and 0.65%–7.32%(formation without water).The results show that the Guo model can more precisely represent the situation of the no water formation in the nitrogen drilling of a coal seam.The Finnie,Sommerfeld,and Tulsa models have different sensitivities to cutting densities,particle size,impact velocity and angle,and pipe string hardness.

Observer-based State Feedback Control to Suppress Stick-slip Vibrations in Oil Well Drill-string

In drilling field, stick-slip vibrations of the drill-string are the main reason for the failure of the drilling system. To suppress the undesired stick-slip vibrations, an observer-based state feedback control method is proposed. The drilling system is described by a lumped parameter model including a Karnopp friction torque model. A state observer is designed to estimate the bit velocity in bottom hole and a state feedback controller is proposed to control the top drive velocity. By simulation, the performance of the control algorithm is demonstrated. Based on the control algorithm, a stick-slip vibration control system is developed. Test results show that the control system can effectively eliminate stick-slip vibrations of the drill-string and can be applied to the drilling field.

The Effects of Fluid Rheology and Drillstring Eccentricity on Drilling Hydraulics

Accurate determination of hydraulic parameters such as pressure losses, equivalent circulation density (ECD), etc. plays profound roles in drilling, cementing and other well operations. Hydraulics characterization requires that all factors are considered as the neglect of any could become potential sources of errors that would be detrimental to the overall well operation. Drilling Hydraulics has been extensively treated in the literature. However, these works almost entirely rely on the assumption that the drill string lies perfectly at the center of the annulus—the so-called “concentric annulus”. In reality, concentricity is almost never achieved even when centralizers are used. This is because of high well inclination angles and different string geometries. Thus, eccentricity exists in practical oil and gas wells especially horizontal and extended reach wells (ERWs) and must be accounted for. The prevalence of drillstring (DS) eccentricity in the annulus calls for a re-evaluation of existing hydraulic models. This study evaluates the effect of drilling fluid rheology types and DS eccentricity on the entire drilling hydraulics. Three non-Newtonian fluid models were analyzed, viz: Herschel Bulkley, power law and Bingham plastic models. From the results, it was observed that while power law and Bingham plastic models gave the upper and lower hydraulic values, Herschel Bulkley fluid model gave annular pressure loss (APL) and ECD values that fall between the upper and lower values and provide a better fit to the hydraulic data than power law and Bingham plastic fluids. Furthermore, analysis of annular eccentricity reveals that APLs and ECD decrease with an increase in DS eccentricity. Pressure loss reduction of more than 50% was predicted for the fully eccentric case for Herschel Bulkley fluids. Thus, DS eccentricity must be fully considered during well planning and hydraulics designs.

Influence of friction on buckling of a drill string in the circular channel of a bore hole

Enhancement of technology and techniques for drilling deep directed oil and gas bore hole is one of the most important problems of the current petroleum industry.Not infrequently, the drilling of these bore holes is attended by occurrence of extraordinary situations associated with technical accidents. Among these is the Eulerian loss of stability of a drill string in the channel of a curvilinear bore hole. Methods of computer simulation should play a dominant role in prediction of these states. In this paper, a new statement of the problem of critical buckling of the drill strings in 3D curvilinear bore holes is proposed. It is based on combined use of the theory of curvilinear elastic rods, Eulerian theory of stability, theory of channel surfaces, and methods of classical mechanics of systems with nonlinear constraints. It is noted that the stated problem is singularly perturbed and its solutions have the shapes of localized harmonic wavelets. The calculation results showed that the friction effects lead to essential redistribution of internal axial forces, as well as changing the eigenmode shapes and sites of their localization. These features make the buckling phenomena less predictable and raise the role of computer simulation of these effects.

Critical Buckling of Drill Strings in Cylindrical Cavities of Inclined Bore-Holes

Notwithstanding the fact that the problem of drill string buckling （Eulerian instability） inside the cylindrical cavity of an inclined bore-hole attracts attention of many specialists, it is far from completion. This peculiarity can be explained by the complexity of its mathematic model which is described by singularly perturbed equations. Their solutions （eigen modes） have the shapes of boundary effects or buckles （harmonic wavelets） localized in zones of the bore-hole that are not specified in advance. Therefore, the problem should be stated in the domain of entire length of the drill string or in some separated part including an expected zone of its buckling. In the paper, a mathematic model for computer analysis of incipient buckling of a drill string in cylindrical channel of an inclined bore-hole is elaborated. The constitutive equation is deduced with allowance made for action of gravity, contact, and friction forces. Computer simulation of the drill string buckling is performed for different values of the bore-hole inclination angle, its length, friction coefficient, and clearance. The eigen values （critical loads） are found and modes of stability loss are constructed. The numerical results for the case when the inclination angle equals friction angle coincide with ones obtained analytically.

Exploration and determination of the principles of rotary-percussive underground slimhole drilling

A possibility of the efficient use of rotary percussive drilling to provide drilling smaller diameter holes(40–70 mm) both in mining and prospecting is disclosed herein. A new construction designed for the nipple thread connection is described. The relative amplitude variation, change of power pulse time and energy in their propagation throughout the drilling tool are determined. A possibility of the efficient power pulse transfer along the drill string to the rock destruction tools with new nipple connections which allow automating the make-up and breakout system of drill pipe was supported by experiments.

Improved Methods for Acoustic Transmission along the Drill String and Other Periodic Media

Acoustic telemetry along the drill string helps to know the physical and chemical characteristics of the formation and drilling fluid.A time-domain algorithm is developed for the propagation of one-dimensional axial stress waves with the inner and outer viscous fluid.The algorithm simulates the passbands,stopbands and spikes due to the presence of the discontinuous boundaries of drill string.Then the effects of transmitted pulses and transceivers on acoustic transmission are analysed.The simulated results show that the raised cosine pulses and optimal placements of transceivers improve system performance.Moreover,dual PZT receivers can exclude signals propagating in a direction opposite to the transmitted signals. It is obvious that the uses of the available modeling and signal processing techniques can make the drill string as a waveguide for transmitting information at high data rates.

METHOD OF EQUILIBRIUM DIFFERENTIAL EQUATION FOR ANALYSIS OF STRENGTH OF LARGE DEFLECTION DRILL STRING

To counter the strength problem of drill string in well of large curvature and small diameter, well axis was taken as datum mis. Based on description of deflection of well an's and on analysis of three dimensional forces of a small section of drill string, equilibrium differential equations of large deflection drill string were established. The internal forces were found by Longe-Kutta method. The stresses were found by using them and the strength prerequisite was established. Stresses of drill string in lateral horizontal well H767 were computed. The results are in agreement with those of finite element model and soft-rope rigidified model. But the method is simpler for computation than finite element model and is more perfect than soft-rope rigidified model. Curvature of the well is too large and there is stress concentration so that the fraction accident of drill string occurs.

NEW METHOD FOR GEOMETRIC NONLINEAR ANALYSIS OF LARGE DISPLACEMENT DRILL STRINGS

Based on the actual measured well depth, azimuth and oblique angles, a novel interpolation method to obtain the well axis is developed. The initial stress of drill string at the reference state consistent with well axis can be obtained from the curvature and the tortuosity of well axis. By using the principle of virtual work, the formula to compute the equivalent load vector of the initial stress was derived. In the derivation,the natural （curvilinear） coordinate system was adopted since both the curvature and the tortuosity were generally not zero. A set of displacement functions fully reflecting the rigid body modes was used. Some basic concepts in the finite element analysis of drill string were clarified. It is hoped that the proposed method would offer a theoretical basis for handling the geometric nonlinear problem of the drill string in a 3-D larg edisplacement wellbore.

Numerical Characterization of the Annular Flow Behavior and Pressure Loss in Deepwater Drilling Riser

In drilling a deepwater well,the mud density window is narrow,which needs a precise pressure control to drill the well to its designed depth.Therefore,an accurate characterization of annular flow between the drilling riser and drilling string is critical in well control and drilling safety.Many other factors influencing the change of drilling pressure that should be but have not been studied sufficiently.We used numerical method to simulate the process of drill string rotation and vibration in the riser to show that the rotation and transverse vibration of drill string can increase the axial velocity in the annulus,which results in the improvement of the flow field in the annulus,and the effect on pressure loss and its fluctuation amplitude.In addition,there are also multiple secondary flow vortices in the riser annulus under certain eccentricity conditions,which is different from the phenomenon in an ordinary wellbore.The findings of this research are critical in safely controlling well drilling operation in the deepwater environment.

Mechanism and prevention method of drill string uplift during shut-in after overflow in an ultra-deep well

Drill string will sustain large uplift force during the shut-in period after gas overflow in an ultra-deep well, and in serious case, it will run out of the wellhead. A calculation model of uplift force was established to analyze dynamic change characteristics of the uplift force of drill string during the shut-in period, and then a management procedure for the uplift risk during the shut-in period after gas overflow in the ultra-deep well was formed. Cross section method and pressure area method were used to analyze the force on drill string after shut-in of well, it was found that the source of uplift force was the "fictitious force" caused by the hydrostatic pressure in the well. When the fictitious force is in the opposite direction to the gravity, it is the uplift force. By adopting the theory of annular multiphase flow, considering the effects of wellbore afterflow and gas slippage, the dynamic change of the pressure and fluid in the wellbore and the uplift force of drill string during the shut-in period were analyzed. The magnitude and direction of uplift force are related to the length of drill string in the wellbore and shut-in time, and there is the risk of uplift of drill string when the length of drill string in the wellbore is smaller than the critical drill string length or the shut in time exceeds the critical shut in time. A set of treatment method and process to prevent the uplift of drill string is advanced during the shut-in period after overflow in the ultra-deep well, which makes the risk management of the drill string uplift in the ultra-deep well more rigorous and scientific.

Attenuation of microwave transmission in a diameter-variable drill string bore

With the drill string hole being regarded as an ultra-long irregular lossy cylindrical waveguide, the optimal frequency point for microwave transmission was calculated according to the electromagnetic wave coupling theory, the attenuation law and efficient transmission distance of microwave channel were obtained and the microwave mode in the waveguide was analyzed. Furthermore, the channel model and signal attenuation model were established by the microwave transmission equivalent circuit method. The power attenuation coefficient per unit of length was proposed to simplify the analysis on effective transmission distance for the ultra-long drill string. The optimal frequency points of 139.7 mm(5.5 in) and 127 mm(5 in) API drill pipes are 2.04 GHz and 2.61 GHz, respectively, and there are several inner diameter varying sections and break points in the drill string hole along the axial direction. The microwave transmission suffers a lot of reflections. The channel impedance change is a key factor affecting the transmission quality. The lab and field tests reveal that the attenuation model established in this paper is accurate, and it is applicable to the design of microwave transmission measurement while drilling system.

THREE-DIMENSIONAL NONLINEAR ANALYSIS OF DRILL STRING STRUCTURE IN ANNUI US

Three-dimensional nonlinear analysis of drill string structure in annulus of curvedwellbore is done by using the theory of finite element and Newton-Raphson method.According to the characteristics of its deformation,a method of the description andcomputation of taking different forms of elements for different parameters is advanced.The penalty function method is applied for finding the unknown boundary .the nonlinear effects of curvature of wellbore on the side forces on bit ae shown by thecomputation.

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。

超深井工程理论与技术若干研究进展及发展建议

超深井工程受到高温高压、复杂地层、超长井眼和腐蚀介质等多重因素约束,其安全高效作业面临全方位的技术挑战。为此,针对超深井工程的安全高效设计控制问题,介绍了该工程的发展概况与技术特点;选取井眼轨迹预测与防斜打快、钻柱振动特性分析与减振控制、钻井延伸极限预测与设计控制,以及套管失效风险评估与安全控制等几个重要理论与技术问题,介绍了国内外的相关研究进展及笔者团队的最新研究成果;然后,针对超深井工程提出了若干创新发展建议。研究结果表明,超深井工程理论与技术的发展整体呈现出体系化、科学化、多学科交叉、地质与工程一体化等基本特点。建议在基础理论问题、关键核心技术、技术协同关系、技术迭代模式和多学科交叉融合等方面加强创新研究,以持续推进超深井工程基础理论与关键技术创新发展。

考虑深井井下动力钻具影响的钻柱粘滑振动规律

油气勘探开发统计数据显示,深井钻井过程中粘滑振动频发,占钻进时长的50%以上,严重影响了钻井井下安全,延长了钻井周期,增加了钻井成本。由于深井钻柱结构较为复杂,井下动力钻具应用普遍,但动力钻具对井底钻头粘滑振动的影响规律缺乏深入研究,目前尚未有学者提出深井动力钻具下的钻柱全尺寸动力学模型。为此,基于弹簧集中质量原理,建立了包含井下动力钻具的粘滑振动仿真模型和螺杆钻具输出参数的计算模型,研究了螺杆钻具、扭力冲击器及两种工具复合使用对钻头粘滑振动的影响,并基于模型分析了现场实钻案例。研究结果表明:(1)使用螺杆钻具复合钻进时,转盘转速与螺杆转速对粘滑振动影响较大,复合转速越大,越有利于消除粘滑振动;(2)钻压和钻头尺寸越大,需要消除粘滑振动的转速就越大;(3)在保证水力参数的情况下,螺杆输出较高的扭矩和转速,能够有效地抑制钻头粘滑;(4)扭力冲击器和螺杆钻具复合使用情况下,当螺杆钻具的输出参数不足以抑制粘滑振动时,提高扭力冲击器的冲击扭矩和冲击频率,可降低螺杆钻具的临界转速,抑制井底粘滑振动。结论认为,该动力学模型可以为深井合理使用动力钻具、避免粘滑振动和提高机械钻速提供有效的技术支撑,该理论新认识在指导钻井现场钻进,提高钻井效率和降低钻井成本等方面具有重要的现实意义。

钻柱腐蚀疲劳寿命评价和影响因素分析

油气钻井过程中钻柱受力复杂,容易发生断裂情况,根据现场情况评价钻柱腐蚀疲劳寿命可以为钻柱安全使用提供依据。从现场实用角度,通过轴向力、循环应力和疲劳极限的计算,对比了基于疲劳系数、寿命百分数和旋转计数的钻柱疲劳评价方法,并考虑了腐蚀的影响。分析结果表明,当在严重狗腿度的井段钻进时,弯曲应力和屈曲增加将加快钻柱疲劳失效;当对应的机械钻速降低、转速增加时,钻柱的剩余使用寿命将进一步降低;当发生较严重的腐蚀时,钻柱剩余使用寿命将迅速降低。在高抗拉井段和狗腿度变化大的井段的钻柱应定期倒换使用,以保障现场钻具安全规范使用。

钛合金/钢钻杆复合钻柱动力学特性分析与优化设计

钻井深度的持续增加使钻柱面临的载荷工况越来越严苛。钛合金具有密度小、屈服强度高和弹性模量低等特点,基于井口钻杆抗拉余量设计要求,设计3种钛合金/钢钻杆复合钻柱,即复合钻柱1(Φ101.6 mm钻杆段全段使用钛合金钻杆)、复合钻柱2(Φ101.6 mm钻杆上半段使用钛合金钻杆)和复合钻柱3(Φ101.6 mm钻杆下半段使用钛合金钻杆)。为了探究钛合金/钢钻杆复合钻柱(简称为复合钻柱)的动力学特性,基于Hamiton原理建立复合钻柱的动力学模型,并采用节点迭代法和Newmark-β法对模型进行求解,分析3种复合钻柱的涡动特征、动态应力和振动特性,并与常规钢钻柱进行比较。结果表明:钛合金钻杆的使用可有效减缓钻柱涡动速度、动态应力,其中复合钻柱3的涡动速度、动态应力最小;基于振动特征强度对钻井作业参数进行优化,形成复合钻柱3的钻井作业参数推荐图版并给出合理的施工参数范围。