Failure Mechanism Analysis of CO2 Flooding Wellbore Tubing

Carbon dioxide flooding enhanced oil recovery technology has been tested in many major oil fields in the world. It can not only improve oil recovery but also realize long-term geological storage of some carbon dioxide. In the process of low temperature carbon dioxide injection, heat is exchanged with the wellbore assembly, and the ice volume of water in the oil casing annulus expands, resulting in frost heaving force which damages the tubing casing and shorens the life of the wellbore. Based on the theory of fluid-solid heat transfer and phase transformation, a tubing-casing - cement ring - formation assembly model is established in this paper. The damage mechanism of frost heaving force on tubing is studied, and the changes of tubing force and wellbore temperature field under the action of frost heaving force are analyzed. The analysis results show that the frost heave force caused by the freezing of water in the annulus is the main cause of the tubing damage during the low temperature carbon dioxide injection. 1. INTRODUCTION CO2 flooding enhanced oil recovery technology has been widely tested in major oil fields in the world, and the oil displacement efficiency has been significantly improved, and part of the carbon dioxide geological storage can be realized in the process of oil displacement, which is of great significance to restrain the greenhouse effect. It is also an important part of CCUS. In the process of carbon dioxide flooding, the temperature of liquid carbon dioxide injected at the wellhead is generally 223.15K to 253.15K, and the daily injection volume is 20-40 tons. In the process of low temperature carbon dioxide injection, heat is exchanged with the wellbore assembly. The water in the annulus of tubing and casing will freeze and expand, resulting in frost heave force, which significantly increases the risk of tubing damage increases significantly well integrity being compromised and shortens the life of wellbore. Among them, Sheng li Oilfield in Taizhou, China carried out low-temperature CO2 injection operation for more than two months, and its injection temperature was 253.15K. Practical engineering problems of tubing damage occurred in some test Wells (Fig. 1). According to the field situation, the actual situation of tubing damage in the process of low temperature CO2 injection is known, and the wellbore integrity failure is caused by pipe string damage, and the life of the wellbore is greatly shortened. Therefore, it is of great practical significance to study the failure mechanism of low temperature CO2 injection tubing.