Abstract:Flexure shaft is a key component for torque transfer between the joints of ultra-short radius flexible motor units. Aiming at the failure phenomena such as fracture of flexure shaft in the drilling process of ultra-short radius flexible motor， this paper carries out mechanical modelling and design strength checking of the internal flexure shaft of the flexible motor， uses finite element simulation to carry out stress analysis on the stress state of the flexure shaft in the torque transmission process of the flexible motor， and tests the mechanical properties of the flexible motor through indoor teststo analyse the mechanical properties of flexure shafts. The results show that the root and spline contact surfaces of the flexure shaft are the stress concentration areas in torque transmission， and the fatigue life of the flexure shaft can meet the requirements of continuous downhole operation. The finite element analysis and indoor tests show that the flexure shaft can transmit torque of 500N·m， which can realise the internal torque load transmission of the flexible motor under alternating bending and torsional stresses. This provides an important theoretical basis for the drilling process of ultra-short radius flexible motors in the development of horizontal wells， and provides a new type of technical means to improve the drilling length and drilling efficiency of the horizontal section of ultra-short radius horizontal wells.

Abstract:The support chassis of large drilling equipment， serving as the support platform， is commonly assembled by welding numerous steel plates together. The residual stresses and deformations caused by welding have a certain impact on the strength and stiffness of the chassis. In this study， the finite element analysis method is applied. A finite element model is established for a representative T-type welded joint in the large support chassis， using a Gaussian moving heat source. Four different welding sequences and welding speeds are adopted to analyze their effects on welding stresses and deformations. Optimized welding sequences and welding speeds are obtained. Based on this， an overall welding scheme for the chassis is optimized. A comparative analysis is conducted on the welding stresses and deformations before and after optimization. The results show that the residual stress is reduced by approximately 7% and the maximum deformation is reduced by approximately 26% after optimization. The research results can provide reference for the formulation of welding processes.

Abstract:In order to achieve the scientific research goal of drilling through the ice sheet and directly obtaining subglacial bedrock samples， this paper designs an aluminum alloy double-wall drill pipe for polar drilling， which can meet the drilling requirements of air reverse circulation， hydraulic reverse circulation， and matching with wire-line core drilling in different formations such as overlying snow layer， ice layer， ice-rock interlayer and subglacial bedrock on the polar region. According to the stress of aluminum alloy double-wall drill pipe under the condition of ultimate tensile and ultimate tensile torsion， the finite element analysis of double-wall drill pipe was carried out， and the tensile test and torsion test of the connection specimen between the outer pipe of the double-wall drill pipe and the steel joint were carried out. The finite element analysis results show that the maximum stresses generated in the aluminum alloy double-wall drill pipe under the combination of ultimate tensile and extreme tensile torsion conditions are 183.8MPa and 161.9MPa， respectively， which are less than the yield strength of 489.99MPa of aluminum alloy material. The test results of the specimen strength test of the connection between the outer pipe of the double-wall drill pipe and the steel joint also show that the ultimate bearing tensile force of the tensile specimen during failure is 399.5kN， which is much greater than the tensile force required to lift the 1000m double-wall drill pipe （208.11kN）； the limit bearable torque during torsional specimen failure is 8264.7N·m， which is also greater than the maximum torque of the drill pipe in the normal drilling process （1990.56N·m）. The above results show that the design scheme of aluminum alloy double-wall drill pipe for polar drilling can meet the requirements of polar drilling.

Abstract:To provide guidance for structural design and optimization of the functional sub in the drill string， the model of the mud pulser sub in Type 675 instrument string is simplified and the finite element analysis model is created in the case of the extreme working condition under the combined load of compression， bend and torsion. Considering the structural characteristics of the mud pulser sub in Type 675 instrument string， different mesh division methods are adopted for different sections of the mud pulser sub. Fixtures are added on both sides of the model for composite loading， while equivalent loading is applied for the bend load in the combination of compression， bend and torsion load by calculating the maximum deflection under the limit dogleg. The simulation results show that under the combined load of compression， bend and torsion， the stress concentration phenomenon mainly occurs in the drill collar and the electronic framework， and weak positions such as openings， grooves. Based on the analysis results， suggestion is put forward on the structural improvement of the mud pulser sub in 675 instrument string. The analysis method and design experience presented in this paper can provide reference for the design and optimization of the functional sub of the same kind.

Abstract:Polycrystalline diamond compact （PDC） has been widely used in geological exploration and oil drilling industries due to its significant advantages such as high hardness， high elastic modulus， high thermal conductivity， isotropy and good wear resistance. In recent years， with the increasing exploitation of deep and ultra-deep wells， PDC has been applied to the drive shaft of screw drills. In this paper， the PDC thrust bearing on the drive shaft of screw drill is taken as the research object. From the perspective of statics and the manufacture process of PDC bearing， the finite element analysis of SolidWorks Simulation software is used to explore the failure modes of PDC thrust bearing under different static pressure， temperature， torque and weld width. The variance analysis of the simulation results shows that temperature， torque and weld width have significant effects on the failure of PDC thrust bearing. Among them， temperature has a high significant effect on the deformation of PDC thrust bearing in three directions. Torque has a significant effect on the deformation of bearing in x and y directions. Weld width has a significant effect on the deformation of bearing in x and z directions.

Abstract:At present， both at home and abroad are facing serious casing damage problems， so it is necessary to study the influencing factors of casing strength. By establishing a three-dimensional finite element model of casing and cement sheath， and using Ansys finite element analysis software to study the influence of cement sheath parameters， casing eccentricity and ovality on casing strength. The simulation results show that only when the elastic modulus of the cement sheath exceeds a certain value， increasing the thickness and elastic modulus of the cement sheath can improve the strength of the casing， otherwise the equivalent stress of the inner wall of the casing will be increased， and the effect of the cement ring on the strength of the casing is a function of the diameter-thickness ratio of the casing. In addition， the strength of the casing decreases significantly with the increase of the eccentricity and ellipticity of the casing， which can easily cause yield failure of the casing.

Abstract:The mast is an important part of the drill. This paper describes the structural design of the mast of the 4000m core drill independently developed by Institute of Exploration Technology. In order to ensure that the mast meets the requirements of working conditions such as strength， wind load， the mast model is created with SolidWorks， and ANSYS Workbench is used to carry out the finite element analysis for the mast assembly to verify the strength and rigidity of the mast structure， and perform the modal analysis to obtain the first 10 intrinsic vibration frequencies and modes. They are compared with the excitation sources， and the results show the first and second intrinsic frequencies overlap with the frequencies of the drilling turntable and hoisting system， which may cause resonance； thus， the rotating speed of the drilling rig turntable and hoisting system is adjusted to avoid resonance. As a result， the deformation amount is small at the maximum deformation position during vibration， indicating that the mast structural design is reasonable， and can meet the actual application requirements； therefor it has some value in engineering application.

Abstract:The square chisel is an important trench cutting tool for the underground diaphragm wall. This paper briefly introduces the structural design， construction method and application of a new square chisel. The integral frame of the new square chisel is welded with proper structure， and its size can be adjusted according to the needs of users. It has the advantages of good guidance， large water passage， high impact power per unit area and ease for fishing. After the successful development of the chisel， it has been used on percussive reverse circulation drilling rig with air-lift reverse circulation for subway construction in Xiamen and Shenzhen with significant construction efficiency， achieving good economic and social benefits. The successful development of the new type square chisel provides a better trenching tool for the construction of underground diaphragm walls.

Abstract:In order to ensure the sealing function of expandable liners in φ120mm boreholes, based on the proper design of an “8” shape section corrugated pipe, the hydrodynamic expansion forming process of the corrugated pipe with different wall thickness and materials is simulated by using the finite element theory, and the indoor hydrodynamic expansion test is carried out. Under the condition of satisfying the extrusion strength and internal pressure strength, the thinner the wall thickness of liners, the better the expansion effect; the “8” shape section liners suitable for 120 mm boreholes should meet the following conditions: yield ratio≤0.6, elongation≥25%, tensile strength σb≥410MPa; the minimum diameter of the liners after expansion can meet the requirements of subsequent mechanical expansion, and the maximum expansion pressure is 13.6MPa, which meets the requirements of drilling site operation. This provides technical support for field test of the liners.

Abstract:Expandable profile liner （EPL）technology is mainly used to solve technical problems such as frequent accidents in complex deep boreholes and limitation of casing tiers. Hydraulic Expansion of EPL is a key link in the application. In order to study the mechanical properties of expandable profile liners under hydraulic expansion, and improve the treatment of downhole accidents, the finite element numerical simulation and indoor laboratory tests were combined to study the hydraulic expansion process of expandable profile liners (EPL). Through multiple laboratory tests on hydraulic expansion of EPL, and comparison of the results with those of the finite element theoretical analysis, it was found that both methods obtained basically consistent results. The elastic deformation pressure of EPL is 0 to 2.5 MPa, and the displacement rate of the key points on the cross-section is larger when the pressure of the liner string is 3 to 9 MPa; the hydraulic expansion pressure of EPL is 14 MPa; and the maximum and minimum diameter for the cross-section dimension of EPL after expansion Xmax are 136.98 mm and 104.58 mm; which meet the requirement of the cross-section size for mechanical expansion of EPL. It provides important theoretical basis and technical support for field experiment and industrial application of EPL.