Nestor J. Santi

Premium and Semi-Premium Connections Design Optimization for Varied Drilling-With-Casing Applications

As high resistance to fatigue loading together with high overtorque and compression capacities are at the top of a list of required features for connections to be used in new drilling and completion techniques such as casing drilling, then special connections with enhanced performance need to be developed. On the other hand, a cost-effective solution should be chosen to balance the performance when considering low-demanding shallow wells for which sophisticated premium connections could be uneconomical. This paper describes the development and evaluation of premium and semi-premium connections for tubing/casing which were developed to stand cyclic loads and reach an extended number of cycles under such conditions. The development process of an integral connection for casing sizes targetting very demanding applications comprised Finite Element Analysis (FEA) and Full Scale Fatigue Test (FSFT) showing Stress Concentration Factors (SCF) lower than 2. In addition, during the development of the semi-premium connection to cover less demanding applications, some of these techniques were used to optimize the results until getting SCF lower than 3, good enough when low doglegs are present. The results of the tests are plotted in S-N (Alternating Stress vs Number of cycles to failure) curve with a standard curve as a reference. As per the results, both types of connections achieved the objective set at the beginning of the development process now being suitable alternatives for low and high demanding drilling/completion operations.