Mechanical performance analysis of downhole safety valve of completion string under typical working conditions

The downhole safety valve is an important barrier to maintain the well integrity, and its working performance and mechanical behavior are vital for safe production. With the downhole safety valve commonly used in deep wells of China’s western oilfields as an example, a three-dimensional finite element analysis model of the safety valve was established. Localized mesh refinement of the model was performed during pre-processing, according to the structural characteristics of each geometric body of the model, and the spring in the model was replaced equivalently by the spring simulation function of the finite element analysis software. Considering four typical working conditions, namely, setting, fracturing, opening and closing, the working procedure and mechanical properties of the safety valve body and key components were analyzed. The results show that the downhole safety valve presents the highest stress under the fracturing condition, representing the harshest condition, with a difference of more than 250 MPa from the stresses of most parts. Although the overall safety factor of stress intensity is above 1.41, the stress distribution of key parts is uneven. The stress difference in most parts of the central tube exceeds 200 MPa, which leads to the peak of the line plot of stress distribution. Moreover, the stress difference at a few millimeters near the end of the central tube exceeds 70 MPa, which results in a rapid increase in stress distribution from one point. The stress difference in most parts of the lower joint is over 300 MPa, and the stress difference near the corners is over 150 MPa. The overall stress of the force transmission cylinder is relatively uniform, but the local stress of the end face presents a sudden change with a magnitude exceeding 200 MPa. The findings of this research provide guidance for improving the design and application of safety valves and similar downhole tools.