Solid material required at a subterranean location is supplied from the surface suspended in a carrier liquid and agglomerated below ground by means of a binding liquid. Agglomeration is achieved by arranging that the binding liquid and the particulate solid are similar to each other but opposite to the carrier liquid in hydrophilic/hydrophobic character. The solid and the binding liquid may both be hydrophobic while the carrier liquid is hydrophilic, or vice versa. The solid may be hydrophobically surface modified to render it hydrophobic. The binding liquid may be provided as a precursor which converts to the binding liquid below ground to trigger agglomeration after arrival at the subterranean location. The agglomerates may function as proppant heterogeneously placed in a fracture of a reservoir, or may serve to block an unwanted path of flow. The binding liquid may polymerise after agglomeration so as to stabilise and strengthen the agglomerates.