Abstract

Tarim Basin is the biggest oil and gas bearing basin in China. The ultra-deep formations in the North Border of Tarim Basin is characterized by ultra-high temperature, high pressure, and ultra-thick composite salt-gypsum formations, are widely distributed, 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.

A numerical model is used to analyze the impact of temperature decrease and salt rock creep on injection well integrity in this process of CO2 injection and obtain a critical temperature drop value. A set of new ideas for casing selection was proposed based upon long-term corrosion rate of different materials calculated by De. Warrd corrosion prediction model. Well B in Tarim Oilfield was designed in this method, and design results were verified by performing laboratory experiments.

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. A set of methods is proposed for casing material selection in CO2 corrosion environment is proposed: corrosion rate of different materials is calculated and converted into long-term corrosion rate. Then the maximum allowable wear extent of the casing is calculated according to casing strength requirement. Finally, casing selection material is determined. 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.

This new method can effectively reduce cost of casing material selection and make for guaranteeing oilfield development and CO2 sequestration while maintaining wellbore integrity and controllable well control safety.

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