A Thermal Casing Connection Test to Avoid Casing Failure in Geothermal Wells

Abstract

Determining the proper casing and its connection for geothermal wells is very crucial. The casing and its connection experience various loads not only during drilling operations but also during production operations. In the past, there were numerous papers published in relation to casing failures in geothermal wells that sometime is hardly explained. For more than 100 years of geothermal experience, geothermal wells are still designed driven by oil and gas practices including the selection of casing and its connection. There is no specific protocol or procedure on how to determine suitable casing especially on selecting the casing connection to avoid casing failure especially during production operations due to thermal loads. In geothermal, the thermal load caused by the temperature cycle is potentially the highest load experienced by the production casing and its connection. This paper presents the testing protocol used to qualify the 13-3/8”, 68#, L80 Type 1 with NS-CC Connection, an API interchangeable connection, that used for Production Casing which believe as the critical casing for geothermal well. The testing protocol is referred to the ISO/PAS 12835:2013, Thermal Well Casing Connection Evaluation Protocol (TWCCEP) with some abbreviation, that have been used for High Pressure High Temperature (HPHT) wells in oil and gas industry. The test was conducted using 2+2 casing specimens at PT Citra Tubindo testing facility in Batam, Indonesia. Total of 30 thermal load cycles at temperature range of 35º – 290º C have been used to anticipate geothermal well lifetime. This paper summarizes the testing process from beginning to the end and the successful testing result of the NS-CC Premium casing connection.