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In order to improve the cuttings transport ability and well hole purification effect of horizontal shale gas wells in the Sichuan and Chongqing area, a new type of aluminum alloy drill pipe is put forward, and the floatability is validated by theoretical analysis and actual parameter calculation. According to the cuttings migration mechanism, the cuttings cleaning simulation model of the new aluminum alloy drill pipe and the traditional steel drill pipe was established by Fluent, and the hexahedral mesh is used to divide the model. Thus, the mesh independence and convergence of the two models are verified. Then, the simulation model is verified by comparing the calculation results of the two simulation models with the experimental data of the indoor cuttings migration device. Finally, the rock-cleaning ability of the two drill pipes is analyzed under the conditions of changing the cuttings particle size, well inclination angle, displacement, and mechanical speed. Compared with the traditional steel drill pipe, the new aluminum alloy drill pipe can improve the borehole purification capacity by 13% on average. This research result is of great significance in reducing the quality of cuttings in the annulus and improving the borehole purification effect. [ABSTRACT FROM AUTHOR]

To study the working mechanism and failure causes of semi-sealed ram blowout preventer, the full-size simulation model of semi-sealed ram is established in this paper. The failure analysis and strength evaluation of semi-sealing ram are carried out. The simulation of the blowout preventer ram in the process of well sealing under different well pressure impacts is studied, and the stress and strain distribution law is found out, and the causes of rubber core seal failure are analyzed. The analysis results show that the groove root of the ram body just enters the yield deformation when the oil cylinder pressure exceeds a certain value, and the maximum von Mises stress occurs at the groove root of the ram body, and the stress concentration and fluid impact pressure lead to the premature fracture failure of the ram. It is also found that the stress concentration in the contact area between the rubber core and the upper end of the ram is the most obvious, indicating that the upper part of the rubber core is severely deformed due to extrusion because of well pressure, which will cause fatigue damage to the rubber core over time. Finally, the extrusion behavior of the contact part between the ram and the drill pipe is highly consistent with the shape of the high-stress zone in the simulation analysis, which proves that the simulation result is reliable. [ABSTRACT FROM AUTHOR]

Fatigue performance of a 165 ksi Grade Super High Strength Drill Pipe Steel was studied by rotary bending fatigue tests and fatigue reliability design method. Three common fatigue life distribution models were analyzed in this paper and the most suitable model was selected by comprehensive coefficient method to describe the distribution of test data. Based on the life distribution model and Basquin’s equation, probabilistic S–N curves in middle-long life regime were obtained. The probabilistic S–N curves were also extended to super-long life regime. Test results show that the most match model was the three-parameter Weibull distribution; two-parameter Weibull distribution ranked second; the last was logarithmic normal distribution. Fatigue limits under reliability 50%, 95% and 99% were 648.91 MPa, 632.28 MPa and 618.64 MPa respectively with 99% confidence level. Extended probabilistic S–N curves were lower than fatigue limits in super-long life regime. [ABSTRACT FROM AUTHOR]

• The fatigue optimization of the rubber core should meet its sealing requirements. • Yeoh model fits well with the uniaxial compression test data of the rubber. • Taguchi method combined with numerical simulation is used to optimize rubber cores. • The applicable working conditions are selected to reduce the risk of blowout. • The performance of the optimized rubber cores is evaluated in field applications. In the process of underbalanced pressure drilling, the drill pipe body and its joint repeatedly pass though the sealing rubber core of the rotating blowout preventer (RBOP), making the rubber core susceptible to alternating cyclic load, and prone to fatigue failure. Under the premise of effective sealing realized by the rubber core, to increase its service life, first the Yeoh constitutive model and constitutive parameters describing the material of rubber core were determined by uniaxial tensile and compression tests, and the finite element governing equation of the nonlinear large deformation of the rubber core was obtained according to the principle of virtual work; then a three-dimensional finite element model of the rubber core was established by ABAQUS software to simulate the dynamic sealing process, contact pressure and Mises stress distribution and variation on the sealing surface were analyzed, and the accuracy of the finite element analysis results was verified by comparing the existing test results; subsequently, the influence of structural parameters such as inner angle, outer angle and inner diameter on the sealing surface stress was studied, and these parameters were optimized through Taguchi experiment. The optimal combination of structural parameters was obtained as inner angle 29°, outer angle 69° and inner diameter 84 mm. The maximum Mises stress was reduced by 2.48 MPa and the Mises stress amplitude by 42% after optimization. Finally, the suitable conditions of the optimized rubber core were selected based on the applicability analysis to conduct the field application and result shows that the rubber core has good sealing performance and significantly increased fatigue life after optimization. [ABSTRACT FROM AUTHOR]

The rotating blowout preventer (RBOP) is an essential safety-ensuring equipment in underbalanced drilling. RBOP is vulnerable to fatigue failure resulted from being subject to a cyclic alternating load during pressure drilling. To enhance the lifespan of RBOP, this paper used a finite element simulation combined with experiments to realize a structural optimization of RBOP. The results showed that the optimal thickness of the iron frame for the stripper rubber is 34 mm, the optimal radius of the fillet is 12 mm, and the optimal inner diameters for the stripper rubber that seals 2–3/8″, 2–7/8″, 3–1/2″, 4″, 4–1/2″, and 5″ drill pipes are respectively 48 mm, 58 mm, 75 mm, 87 mm, 95 mm, and 100 mm. The optimized RBOP was examined in a test center and demonstrated a lifespan that was 2.18 times the national standard. When it was deployed in the drilling site, its lifespan was 2.8 times that before optimization. The improvement in the performance and lifespan of RBOP is very meaningful for ensuring security in the drilling site and lowering drilling cost for oil production. • Constitutive model of the rubber matrix is described. • A dynamic finite element model for stripper rubber is established. • The dynamic sealing process of stripper rubber is simulated. • The structure of the stripper rubber for failed parts was optimized. • The optimized stripper rubber was verified in the indoor and oilfield test. [ABSTRACT FROM AUTHOR]

• Rotary blowout preventer is the key equipment of underbalanced drilling. • The rubber core is prone to failure when subjected to alternating cycle load. • Simulate the rubber core sealing process based on finite element method. • Optimize the structure of rubber core and safe lower speed of drill pipe. • The optimized rubber core was verified in laboratory and field experiments. In the process of under-balanced drilling, the rubber core of rotating blowout preventer (RBOP) subject to the alternating cycle load was prone to fatigue failure. Firstly, the sealing principle of RBOP was analyzed and the stress of rubber core in dynamic sealing process was obtained. Then, the Yeoh constitutive model in the deformation process was established by the tensile test of the rubber core material. Then we used ABAQUS software to establish the finite element model of the dynamic sealing of the rubber core, and the simulation of the sealing process of the rubber core during the drilling and tripping operations and the optimization analysis of the factors affecting the fatigue life of the sealing surface of the rubber core were carried out. In this paper, the structure of the rubber core was optimized, and the optimal outer angle of the rubber core was 155°, the inner angle was 153°, and the base angle was 125°. Then the inner diameter size of rubber core that was matched with different outer diameter drill pipes was optimized and the best combination of rubber core was obtained. The paper also optimized the lowering and lifting speed of drill pipe under different wellhead pressures. The higher the well pressure, the more likely the rubber core fatigue failure would be. The safe lowering and lifting speed of drill pipe under different pressures was obtained. At last, according to the Chinese standard, indoor seal test and field application test were carried out in the Well Control Equipment Quality Supervision and Inspection Center of China national petroleum industry to confirm the reliability of finite element optimization, which was of great practical significance to improve the service life of rubber core and oilfield operation safety. [ABSTRACT FROM AUTHOR]