Investigation on critical load and sealing capacity of mandrel hanger wellhead

Abstract

The mandrel hanger is a major wellhead device for suspending the casing string, and its ultimate suspension capacity and sealing capacity determine the success or failure of the cementing operation. Firstly, the structure and working principle of the φ273.1 mm mandrel hanger was introduced, and the mechanical balance equation of the main seal and the casing head step was derived. Secondly, the method to determine the limit suspension load of mandrel hanger is innovatively put forward, which should meet two conditions. On the one hand, no plastic deformation occurs at the casing head step; on the other hand, the maximum equivalent stress on the metal seal ring does not exceed the critical value, 0.8 times the tensile strength of metal sealing material. Thirdly, the suspension process of casing in mandrel hanger is simulated by using finite element software. The stress and deformation of casing head step and metal seal ring are analyzed, and the theoretical limit suspension load value of mandrel hanger, 250t, is obtained. At the same time, the metal seal ring has a sealing capacity of 773 MPa at 250t suspension load, far greater than the design requirements (105 MPa). Lastly, the experimental limit suspension load of the mandrel hanger is 263t, which is only 13t different from the theoretical limit suspension load, with an error rate of 5.2%. Therefore, the correctness of the research method is proved by combining the theoretical and experimental results.