Variation laws of elastic modulus and yield strength of V150 drill pipe under high-temperature environment of ultra-deep well

Abstract:

To address the issue of strength and stiffness degradation of drill strings under high-temperature conditions in ultra-deep well drilling， which affects drillstring safety and deviation control， high-temperature tensile and thermal expansion tests were conducted on V150-grade drill pipe material. The elastic modulus and yield strength at different temperatures were obtained， and a mathematical model describing their variation with temperature was established. Combined with a transient wellbore temperature field model calibrated with measured data， the temperature distribution along a specific ultra-deep well was analyzed. Integrating the material model and the temperature field model， the effects of parameters such as geothermal gradient， drilling fluid flow rate， drilling fluid density， and inlet temperature on drill pipe performance were systematically investigated. The results show that both the elastic modulus and yield strength of V150 drill pipe decrease significantly with increasing temperature， with the yield strength decreasing by approximately 15% at 250 ℃. Conventional design models， which do not account for this temperature effect， overestimate the actual strength of the drill string. The sensitivity indices of the parameters affecting yield strength follow the order： inlet temperature > drilling fluid flow rate > geothermal gradient > drilling fluid density， while for elastic modulus the order is： geothermal gradient > drilling fluid density > inlet temperature > drilling fluid flow rate. The design of drill strings for ultra-deep wells must consider performance degradation due to high temperatures， and safety can be enhanced by optimizing flow rate and inlet temperature. The research findings provide technical support for the design and operation of drill strings in ultra-deep wells.