The ultra-deep formations of Tarim Basin is characterized by ultra-high temperature, high pressure, and ultra-thick composite salt-gypsum formations, so it will bring great challenge to well integrity during CO2 sequestration. Therefore it is necessary to evaluate the impact of temperature decrease and salt rock creep on injection well integrity.
Firstly, the numerical simulation method could be used to analyze the influence of temperature drop and salt rock creep on the integrity of the wellbore during CO2 sequestration. The actual stress of the wellbore cement sheath was equivalent to the simulated wellbore cement by the stress equivalent method. Secondly, CT scanning technology was used to detect the internal structure of the cement sheath, revealing its failure mechanism. Lastly, with the help of GMI and WELLCAT software, the optimization of design parameters during CO2 sequestration is realized.
The results show that under some circumstances the micro-annulus between casing and cement sheath can be changed by salt creep or self-healed. The mechanism of casing damage in salt layers was preliminarily revealed. CT scans were performed on the cement sheath before and after the experiment. By comparing the gap volume changes of the casing cement sheath, it was found that there was a micro-annulus between the casing cement sheath. The mechanism of casing damage in salt layers was preliminarily revealed during CO2 sequestration. It is indicated that casing damage is mainly caused by the non-uniform load induced by the creep of salt-gypsum layers, the low temperature, and the poor cementing quality. Finally, a series of measures were proposed to prevent casing damage during CO2 sequestration in the areas with a salt formation.
This new method can effectively reduce cost of casing material selection and make for guaranteeing oilfield development efficiency and CO2 sequestration while maintaining wellbore integrity and controllable well control safety.