Interaction analysis for CO2 geological storage and underground coal mining in Ordos Basin, China

The CO2 geological storage in Ordos Basin and coal mining activities occurring simultaneously at the same location is a highly challenging coupled thermo-hydro-mechano-chemical (THMC) problem. To address this problem, an in-house program named "AEEA Coupler" was developed by linking two commercial software packages, Simulia ABAQUS and Schlumberger ECLIPSE, both of which are widely used and highly recognized in their respective fields. The applicability and accuracy of the developed coupler were tested by benchmark studies. A coupled multi-physics analysis was conducted based on real formation data of the Ordos and Shenhua CCS Demonstration Project with an injection rate of 0.1 Mtpa (Million tonnes per annum). A larger injection rate of 1.0 Mtpa was also investigated to explore the potential for the commercialization of large-scale CCS projects in the area. The primary conclusions that were obtained from the numerical simulations are as follows: (a) The pore pressure and displacement at the top of the reservoir increase with CO2 injection, and the displacement continues to increase even after the termination of the CO2 injection due to the coal mining activity. (b) The displacement of the wellbore peaks at the coal seam floor where the axial strain of the well soars abruptly. Our work suggests that the distance between coal pillars should be at least 90 m to ensure that the Mises stress of the casing is below the designed safe value. (c) The tensile stress and shearing stress increase significantly in the caprock as a result of the coupling of the two engineering activities; therefore, damages in the caprock occur more easily. (d) After CO2 injection, only the strata with a depth of less than 769 m are affected by the coal mining activity. (e) The combined activities achieve a surface subsidence reduction comparable to that of only coal mining. Finally, several recommendations are given regarding the actual engineering implementation of the combined activities. (C) 2015 Elsevier B.V. All rights reserved.