A comprehensive analysis to illustrate complex migration behaviors of fluid along fault for CO2 geological storage

To investigate migration behaviors of fluids along faults for CO2 storage, a 3−D numerical model was proposed with two faults. Using this model, six stages were divided based on leakage rates of fluids along faults. At Stage 1, brines escape upward along Fault A, while freshwaters lose downward along Fault B. At Stage 2, brines escape upward along both faults, while freshwaters lose downward along Fault B. Freshwater losses disappear gradually at this stage. At Stage 3, brines escape upward along both faults massively, while freshwaters no longer lose downward. At Stage 4, CO2 leaks upward along Fault A, while brines escape upward along both faults. At Stage 5, freshwater losses appear again and brine escaping reduces gradually. At Stage 6, CO2 leaks along Fault A and freshwaters lose along both faults, while no brine escapes. Four phenomena attached to six stages were found. Phenomenon 1 is that brines escaping exaggerate before CO2 leakage but reduce and end after CO2 leakage, occurring at Stages 3–4. Phenomenon 2 is that freshwater losses disappear gradually with brine escaping exaggerating at Stage 2, but appear again with massive leakage of CO2 at Stage 5. Phenomenon 3 shows that the brine escaping (upward) and freshwater loss (downward) occur simultaneously, before CO2 plumes reach faults, occurring at Stages 1–2. Phenomenon 4 occurs after CO2 plumes reach faults (Stages 4–6), showing that CO2 and brines leak upward together when freshwaters lose downward. Finally, parametric analyses indicated that: (1) Stage 3 has a longer period for higher permeability of saline aquifers; (2) Stage 6 occurs much earlier and leakage amounts of CO2 and freshwater increase obviously under higher fault permeability; (3) Permeability of freshwater aquifers especially in the lower level has an obvious effect on leakage amounts of fluids.