Experimental Study for Establishing Metal-to-Metal Seal Evaluation Criteria for Tubular Connections in Thermal and HPHT Applications

Abstract

Abstract Qualification of tubular connections is an important task in well completion design for thermal wells, which experience peak temperatures of 180°C to 350°C, as well as high pressure and high temperature (HPHT) wells, which experience peak temperatures up to 180°C and pressures greater than 70 MPa. Industry protocols (such as ISO/PAS 12835:2013 for thermal wells, and ISO 13679:2019 and API RP 5C5:2017 for HPHT wells) have been developed for the purposes of evaluating the structural integrity and sealability of premium connections. In recognition of the the time and capital expense associated with completing "product line validation" for a connection design per these standards for multiple physical configurations (i.e for combinations of various sizes, weights, and grades), industry is developing a hybrid approach that supplements results from physical qualification tests with numerical simulation, such as Finite Element Analysis (FEA). To facilitate numerical modeling, extensive research work has been performed recently (e.g. Xie, Matthew, and Hamilton (2016) and Xie and Matthew (2017)) to establish a constitutive relationship for evaluating metal-to-metal sealability. It was noted in previous studies that further experimental work is required to better understand connection sealing behavior, especially the effects of surface roughness and thread compounds. This paper presents an experimental study with a series of small-scale metal-to-metal seal tests under various levels of seal contact stress and gas pressures representative of thermal and HPHT operational conditions. These tests incorporated the effects of surface roughness and thread compound. FEA was performed to model the stress conditions in the test specimens. Based on the experimental and analytical study, an updated metal-to-metal seal evaluation criterion with calibrated parameters is proposed for tubular connections used in thermal and HPHT applications.