Analytical Evaluation of Casing Connections for Thermal Well Applications

Abstract

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.

Leakage Resistance Envelopes of API 8 Round Casing Connections using FE Analysis

“…Murtagian et al [6] observed large influence of thread compound on the evolution of leakage rates in premium connections. Temperature is known to modify seal compound properties, and to induce axial stresses that impact sealability [7][8][9]. Also, it is recognized that nature of contained fluids affects sealing behavior [10,11].…”

FE simulation of sealing ability for premium connection based on ISO 13679 CAL IV tests

“…Some assumptions have been made for simplified models, such as ignoring the screw angle, assuming the load on the joints and so on. The influence of temperature effect on the performance of premium connections is seldom analyzed in accordance with the test steps of ISO 13679 (Tao et al , 2013; Zhang et al , 2016; Li et al , 2017). In order to truly reflect the integrity of premium connections in service environment, a three-dimensional finite element model of a premium connection commonly used in complex wells is established in ABAQUS finite element analysis software.…”

Envoltórias probabilísticas da estanqueidade de conexões de revestimento de poços

“…Análises de temperatura e flexão são pouco exploradas, mas pesquisadores ressaltam a necessidade de pesquisa neste campo. A temperatura aumenta proporcionalmente com a profundidade e induz ciclos de expansão e retração no aço, introduzindo esforços axiais de compressão que ocasionam plastificação da conexão (TAO; XIE, 2013;TAO, 2010). CHEN et al (2018) analisam a influência da flexão nas pressões de contato na rosca e ombro de contato de conexões proprietárias.…”

“…Em especial, a flexão reduz o selo de conexões proprietárias pela redução das pressões e área de contato no ombro (de contato). Solicitações de flexão têm sido avaliadas sobre modelos axissimétricos, através do uso de elementos finitos axissimétricos implementados com formulações especiais (CHANG, 2008;XIE, 2013). BAHAI (2001) utiliza submodelos axissimétricos para avaliar os efeitos da flexão na concentração de tensões nos vales dos filetes.…”

“…Sabe-se que a natureza do fluido contido afeta o desempenho do selante (API, 2002;ASSANELLI et al, 1997;ERNENS et al, 2019). Além disso, estudos verificam grande influência da temperatura, pois ocasiona modificações no comportamento reológico do composto selante, facilitando sua extrusão e, em consequência, afetando negativamente o selo (BADICIOIU;TEODORIU, 2007;MURTAGIAN et al, 2004;XIE, 2013;TAO, 2010). Adicionalmente, o composto selante diminui o desgaste e a mudança da topografia das superfície que formam o selo metalmetal no aperto, incorporando robustez ao selo (ERNENS et al, 2018(ERNENS et al, , 2019.…”