Numerical modeling of deformations caused by carbon dioxide sequestration in coal seams.

摘要

Atmospheric concentrations of CO2, as the most prevalent greenhouse gas, have been dramatically increased due to the anthropogenic emission mainly from fuel combustion. Geologic sequestration of CO2 in coal seams is an attractive choice to mitigate global CO2 emissions and its consequences. It can also provide secondary benefits such as enhanced coalbed methane production.Three coal sites from Appalachian basin and Black Warrior basin were selected to numerically study the effects of CO2 injection in coal seams on overburden deformations. Finite element method was used for the analysis of overburden response. The analysis consisted of two phases---CO 2 injection and pore pressure dissipation after the termination of injection. The selected sites have differential geologic characters. The distribution of pore pressure from the analysis indicates that injected CO2 was primarily confined within the target coal seam. Modeling results show ground heaving in response to CO2 injection. Effects of elastic modulus, reservoir permeability and injection pressure on CO2 sequestration in coal seams were investigated. Results show that elastic modulus has a significant influence on the amounts of injected CO2 and the propagation of CO2 plume. Injection pressure is proportional to the injection amount of CO2.Deformation of the strata overlying the injection points can be one of the concerns related to high-pressure injection. Small vertical displacements at the ground surface were observed during the numerical analysis of all the selected sites. In fact, the overburden deformations at ground surface CO 2 can be expected to be very small due to the depth of injection points. However, constant measurements of surface deformation can be used to monitor the movement of CO2 plume to detect large amount of CO2 leakage.The screening criteria for selection of sites should include reservoir properties such as elastic properties, permeability, porosity, reservoir thickness and depth. Also, these properties for overburden strata can influence the overburden response during and after geologic sequestration of CO2 in coal seam.