Analytical Evaluation of Casing Connections for Thermal Well Applications

摘要

Thermal well technologies, such as Cyclic Steam Stimulation (CSS) and Steam Assisted Gravity Drainage (SAGD), are widely used for the exploration of heavy oil and oilsands resources. Casing connections are one of the most critical components in thermal wells in terms of the wellbore structural and pressure integrities. High temperature operation of thermal wells inevitably imposes significant axial loads on the casing connections, and as a result, a plastic strain design concept must be used for the casing and connections. In addition, thermal well design should consider the impact of formation shear movement that may be caused by changes in the stress state in the reservoir and overburden formations during thermal operations. To meet the design challenges posed by thermal wells, premium connections are usually preferred over API connections due to generally superior structural capacity and sealability. Rigorous engineering assessments, such as full-scale physical tests and analytical evaluations are often used to assess the performance of premium connections and to identify suitable connection designs for the intended applications. These engineering assessments typically consider the in-situ load conditions specified by operators, or the load cases recommended by industry guidelines, such as the recently released Thermal Well Casing Connection Evaluation Protocol (TWCCEP 2012). This paper presents approaches and considerations for using Finite Element Analysis (FEA) to conduct the analytical evaluation of casing connections for thermal wells. Such analytical evaluations serve to determine the worst-case specimen configurations (e.g. highest potential for galling or leaking) for full-scale testing programs under the load conditions specified in the Protocol, such as make-up and thermal cycles, as well as for understanding the connection performance under in-situ load cases as specified by operators, such as bending and formation shear. Analysis results provide useful insight into connection performance in terms of structural capacity, leakage resistance and galling potential. To demonstrate the use of the proposed analysis approaches and considerations, an example case with a generic premium connection geometry is analyzed and the results are presented.