Enhancement of Current Methodologies Used for Tubular Connection Product Line Validation

Abstract

For high pressure/high temperature (HPHT) and thermal wells, it is important to verify that the selected tubular connection product possesses adequate structural integrity and sealing capacity under the demanding load conditions typically experienced by these wells throughout their life cycle. Individual premium connection designs are typically evaluated and qualified to broadly adopted industry standards, such as ISO 13679 (2019) and API RP 5C5 (2017) for HPHT wells up to temperatures of 180°C, and ISO 12835 (2013) for thermal wells that experience temperatures from 180°C to 350°C. Proprietary operator-defined protocols are also used by some operators for connection qualification. While the current standards recognize that it is neither necessary nor practical for manufacturers to complete full-scale physical testing of the connection design for every different tubular diameter, weight and grade as a means to achieve full product line validation, the development of a practical framework and effective guidelines to achieve this outcome continues to be a work in progress. The basic approach allows interpolation and extrapolation of the results established through combined testing and analysis programs completed on a selected subset of sizes and weights of the full product line of the connection design. This paper starts with a review of current standards for qualifying tubular connections for HPHT and thermal wells. It presents guidelines and an approach to facilitate the performance evaluation and product line validation of connection designs based on the use of Finite Element Analysis (FEA) methods and the recently established sealability criterion. To illustrate the approach, parametric FEA case studies were completed to determine the impact of different tubular sizes and weights on the sealability performance of gas-tight tubing and casing connections under HPHT and thermal well loading conditions. Based on the analysis results, recommendations and considerations for on-going research are made to improve the confidence in the use of interpolation and extrapolation methods presented in the current standards when conducting tubular connection product line validation exercises.

Small-scale Experimental Research on the Key Parameters Affecting Metal-to-metal Sealability

“…As mentioned above, connection sealability can be evaluated by comparing the sealing capacity and the sealing demand, and an evaluation model was also put forward by Xie [11,12]:…”

“…Francesc Pérez-Ràfols et al [10] performed experimental and numerical studies on the effect of surface roughness on sealing performance, and indicated that the role of real contact area and average interfacial separation is different for surfaces with realistic topography than for isotropic surfaces, due to the particular contact topology arising due to the waviness of the spiral groove. Xie et al [11][12][13][14] conducted an experimental test program on metalto metal seals wherein sealing capacity was determined by the magnitude and distribution of the applied contact stress over the seal region, an empirical model that correlates the measured gas seepage rates for different metal-to-metal seal configurations to contact stress was developed, but the model is only fit for gas pressure less than 100MPa, whether it fit for those exceed 100MPa is unclear.…”