Challenging combination of CO2 geological storage and coal mining in the Ordos basin, China

摘要

In a CO2 storage project, CO2 may be able to escape from channels caused by the formation's uplift, fault reactivation, and wellbore failure owing to overpressure build-up and likewise, coal excavation during which equilibrium disruption of stress could possibly lead to floor heave, roof collapse, and surface subsidence. When the carbon capture and storage (CCS) project and coal mining engineering activity occur in the same location, coal mining may also induce wellbore failure if the stope border is too close to the well. This is a real and challenging problem for CO2 geological storage in the Ordos Basin in China. We consequently investigated four key problems for such a combination system. The main conclusions obtained from numerical simulations are as follows. (i) Permeability is the most important factor that affects the flow rate at the injection point and the reservoir pore pressure. (ii) The interfaces between the coal layers and their adjacent rocks are easy to damage the casing. Our work suggests that the coal pillar should be set aside at least 90 m to maintain the tensile strength of the casing below the designed value. (iii) No impact occurs to the caprock from coal mining; thus, a coal seam 440 m in depth could be excavated if the original caprock is intact and no complex geological structure exists in the location. (iv) Permeability is the most crucial factor affecting surface displacement, and CO2 injection permits a surface displacement reduction of 0.04136 m compared with individual coal excavation