Multiphysics modeling of thermo-hydraulic fracturing during CO2 sequestration in multilayered reservoirs at Ordos, China

The increase in CO 2 injectivity and shifting of CO 2 -absorbing layers in multilayered geological CO 2 sequestration (GCS) reservoirs in Ordos, China indicate significant permeability variations in certain layers. To capture these system changes, a numerical model incorporating all 21 aquifers and internal aquitards was developed. The monitored pressure was well matched through multiphase and thermal-hydraulic-mechanical (THM) coupling numerical simulations by introducing permeability variations. The results revealed that the permeability in the second layer increased on approximately day 13 due to the abrupt pressure buildup and temperature decrease. Even such a low rate of CO 2 (2.8 kg/s) injected into the low permeability system initiated some fractures and the permeability in the second layer around the wellbore increased by 722 times. The second critical system change occurred on approximately day 386. As demonstrated in the numerical simulation, the substantial injection of cold CO 2 induced strong thermal stress, leading to rock contraction and the initiation of several cracks. The permeability of the first layer around the wellbore unexpectedly increased by 4 orders of magnitude. Since no additional pressure could drive the CO 2 into the remaining 17 layers, the total storage capability of the multilayered system was reduced. A whole picture of the system variation is fully presented and the underlying mechanisms are analyzed. It is believed that the phenomenon of thermal-hydraulic fracturing observed in this field and the simulation procedures will benefit other fluid injection and production works in various geotechnical settings.