Research On Well Integrity During Carbon Dioxide Geological Sequestration

With rapid development of economy in the world today, the fossil energy consumption is growing increasingly, which makes large amounts of CO₂ emission into the atmosphere. Carbon dioxide capture and storage（CCS） is one of the most promising solutions to the problem of climate change. But the carbon dioxide is of low density and low viscosity, therefore there is a risk of leakage after the injection of carbon dioxide into the underground. To ensure long-term storage security of carbon dioxide, it is necessary to solve the problem of CO₂ escape, so well integrity of the CO₂ buried area is the key to the safety of carbon dioxide geological sequestration.In this paper, the influence of CO₂ on wellbore integrity and leakage along cement sheath are studied. The mechanical/chemical action between CO₂ and cement will damage wellbore integrity. By experiments, the self-healing of salt rock with the existence of CO₂ has been studied: the permeability of salt rock decreased with the increase of CO₂ injection time. At the same time, the leakage of CO₂ along the cement annulus in the sealing process was studied in laboratory test, and the relationship among cement, formation, the type of the rock and the fluid was studied. The possible leakage path of carbon dioxide is studied, and CO₂ escape calculation model is established, and the calculation escape formula is deduced, thus the related numerical simulation is carried out accordingly. The research results of this paper will provide the basis for the safety study of carbon dioxide underground storage technology, and provide technical support for the field application.