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Analysis on Causes of a Well Casing
Coupling Crack
SHUAN-LU LV, College of Mechanical and Transportation Engineering of China University of Petroleum, Beijing, China
XUE-QING TENG, YAN-JUN KANG, AND CHENG-XIN YANG, Tarim Oil Field, Xinjiang, China
Tubular Goods Research Center of China, National Petroleum Corp., Xi'An, China
Xi'An Maurer Petroleum Engineering Laboratory, Xi'An, China XIN-HU WANG AND TERRY QIN-CHANG-YI,
YONG HAN AND GUO-ZHENG ZHANG,
A crack occurred in a well casing at a depth of 836.75 m in less than 70 days after installation. Tis article describes the investigation of the coupling crack, the quality of casing threading,
material performance, and connection make up. It was found that the coupling material toughness was too low, and the torque of the casing connection at the mill end was too high.
58 MATERIALS PERFORMANCE April 2012
A
n oil and gas well was completed at a depth of 5,590 m. Well test- ing was conducted 65 days after the casing was installed. It was
found that the 74th casing from the well- head was pulled out from the connection at the mill end. The pulled-out coupling was cracked and located at a depth of 836.75 m.
Running and Make Up of Production Casing
The 177.8-mm production casing
string was run to the depth of 5,456.86 m IVL \PM LMX\P WN \PM KMUMV\ ÅTT \WX _I[ 1,400 m. The grade of the production casing was V150, and the wall thickness was 11.51 mm. The make-up torque of \PM ÅMTL MVL WN \PM KI[QVO KWVVMK\QWV I\ the depth of 836.75 mm was 11.52 kNm. The thread compound applied at the ÅMTL MVL WN \PM KI[QVO KWVVMK\QWV _I[ CATTS101†
. The optimum make-up torque at the
mill end of the casing connection was 17.5 kNm, the minimum torque was 14.7 kNm, and the maximum torque was 20.4 kNm. The coupling thread was galvanized. The thread compound applied at the mill end was SHELL TYPE III†
. density of 1.16 g/cm3
The annulus of the casing above U _I[ ÅTTML _Q\P [IT\ _I\MZ _Q\P I after running and
before testing. Production was gas and oil, and the annulus between the casing and tubing contained a mixture of oil and gas during testing. The temperature at the production layer in this well was 120 °C, and 30 to 40 °C at the wellhead.
Internal Pressure Change in Tubing and Casing
Figure 1 shows the internal pressure change in the tubing and casing during testing.
†Trade name. NACE International, Vol. 51, No. 4