Modeling the flow of carbon dioxide during the drilling of oil, gas, and geothermal energy

Abstract

Using carbon dioxide as a resource for enhancing the exploitation of fossil energy and geothermal energy, while realizing the geological storage of carbon dioxide, is an important direction in carbon dioxide capture, utilization, and storage studies. A carbon dioxide wellbore flow model is developed by considering the wellbore heat transmission, fluid dynamics, potential energy, and viscous friction heat. The flow characteristics of carbon dioxide and the controllable influence factors of the bottom hole pressure under different geothermal gradients are analyzed. The results indicate that the liquid carbon dioxide pumped into the drill-string enters the supercritical state at a depth of 454.8 m, and returns to the liquid state at a depth of 439.8 m in the annulus under the conditions stated here. The geothermal gradient has a significant influence on the density, pressure, and state of carbon dioxide in both the drill-string and the annulus. A larger choke pressure at the wellhead and a higher flow rate are required to obtain the same target bottom hole pressure under a high geothermal gradient. The injecting temperature has little influence on the pressure profile in the annulus. We herein establish a solid theoretical foundation for drilling technology with carbon dioxide.