摘要
The casing damage is a serious problem when the steam-injection method is applied in the oilfields. In this work, the commercial software ANSYS is used to predict the thermal expansion and the thermal stresses of casings in steam-injection wells under different conditions, including steam channeling, well shut-in and cavitation in cement ring. The results indicate that nearly no temperature change occurs in oil-layer areas 4.0 m-6.0 m away from the casing center. When steam channeling appears, the maximum Mises stress of both the casing and the cement ring occurs on the interior wall. During the shut-in operation, while the maximum thermal expansion ocurs within the temperature-transition area, the maximum thermal stress will be on the interior wall of casing, exceeding the thermo-elastic yield ultimate stress of N80 steel. Besides, the thermal stress is much higher than the elastic strain limit if certain amounts of cavitations appear in the cement ring. Based on the results, some preventive measures against casing damage are proposed, which are verified through the successful application of TP120TH casings during well completion in Liao＇he oilfield.
The casing damage is a serious problem when the steam-injection method is applied in the oilfields. In this work, the commercial software ANSYS is used to predict the thermal expansion and the thermal stresses of casings in steam-injection wells under different conditions, including steam channeling, well shut-in and cavitation in cement ring. The results indicate that nearly no temperature change occurs in oil-layer areas 4.0 m-6.0 m away from the casing center. When steam channeling appears, the maximum Mises stress of both the casing and the cement ring occurs on the interior wall. During the shut-in operation, while the maximum thermal expansion ocurs within the temperature-transition area, the maximum thermal stress will be on the interior wall of casing, exceeding the thermo-elastic yield ultimate stress of N80 steel. Besides, the thermal stress is much higher than the elastic strain limit if certain amounts of cavitations appear in the cement ring. Based on the results, some preventive measures against casing damage are proposed, which are verified through the successful application of TP120TH casings during well completion in Liao＇he oilfield.
