Efficient CO2 Absorption in Water-Saturated Porous Media through Hydraulic Fracturing

Storing CO2 in porous rock formations that are already water saturated, it is necessary for the CO2 to displace or to be dissolved into the fluid. In either case, it is necessary to force the gas into the formation. If we envision pumping the CO2 into drained oil wells and these simply consist of a cylindrical hole, the pressure head at the well-formation boundary needs to be large in order to push significant amounts of gas into the formation. However, if the contact area between the formation and the well is increased significantly, the necessary pressure head will be lowered correspondingly. The obvious way to increase the contact area is through inducing fractures in the formation that start at the well. The most efficient way to induce fractures i s through hydraulic fracturing. Originally, hydraulic fracturing was done in hard and strong formations with low permeability, but during recent years, it is also being applied to soft and weak rocks. It is important to be able to predict how and where fractures will grow. Modelling of fracture initiation and growth is often based on linear elastic fracture mechanics, with resulting predictions that fail to reproduce reality. This is particularly a problem in soft formations. One of the r easons for the mismatch may be that the microscopic aspects of the fracture initiation process is neglected, that the true elasto-plastic behaviour of the rock is not accounted for, that fluid - rock interaction is neglected, and that basic mechanisms of dynamic stress changes associated with fracturing is not realistically captured by the modelling tools used. We will combine discrete particle modeling with a mesoscopic approach to scale-up the fracture process. We will in particular be interested in m odeling acoustic emission data which will be calibrated against laboratory data. We will also further evolve fracture network characterization in order to device algorihms for large-scale simulation.