This book investigates the key geomechanical processes associated with fluid flow in the underground environment. The major phenomena assessed include deformation, fracturing and erosion of the subsurface in response to high fluid pressure perturbations, fluid flow, and interactions with pre-existing naturally occurring and artificial subsurface structures. The inter-relationships and effects of well operation variables on rock formation behaviour are examined. Some controls have been established which inform the understanding of reservoir/rock formations and are pivotal to reservoir operations such as enhanced coal bed methane production (ECBM), enhanced oil recovery (EOR), enhanced gas recovery (ECR) and CO2 sequestration.