Abstract: Colloids and suspensions are frequently encountered in energy geo-engineering applications, from natural processes such as fine particles suspended in subsurface water and oil, to engineered fluids such as drilling muds and proppants. Transported particles can clog porous media and alter the medium permeability and flow paths. This research explores particle laden fluids using pore- and fracture-scale experimental, analytical and numerical techniques.Particle shape emerges as an important dimension in bridge formation at the pore-scale. Experiments show that cubical particles and 3D crosses are the most prone to clogging because of their ability to interlock and to develop torque-resisting contacts. Simulation results reveal the complex arch geometries and associated force chains formed by different particle shapes.A large-scale parallel-plate configuration mimics particle-laden radial fluid flow at the fracture-scale. Experimental and numerical simulation results show the development of a negative pressure annular zone away from the central injection point as a result of fluid inertial effects at high Reynolds numbers. Gravity and inertial retardation cause particles to deviate from the fluid streamlines, which changes the local particle concentration and enhances clogging.Conventional treatments prevent fluid leakage into the subsurface for small-aperture fractures, but are inefficient for large openings. Magnetically-controlled aggregation emerges as a viable clogging alternative. One approach tests a newly designed magnetorheological mud and shows that the suspended iron particles accumulate around magnetic poles and gradually form an iron plug that stops fluid flow (flow resumes once the magnetic field is removed). The second approach investigates the granular self-assembly of engineered magnetic particles to form large architectures in a bubble-column reactor; results show the stochastic nature of collision-limited aggregation and the role of boundaries in constraining potential configurations.Bentonite-cement-oil mixtures exhibit surprisingly fast hydration in contact with water, and may be used for fluid loss control into large-aperture fractures. Linear and radial flow experiments reveal the complex interactions between concurrent processes: spontaneous imbibition, the release of hydrated ions during cement hydration, bentonite flocculation, and enhanced permeability. Complementary oedometer and cone penetration tests show the evolving swelling pressure and plug strength.