Propagation of In Situ Horizontal Fractures in Shale Due to Steam Injection

Thermal recovery processes, such as cyclic steam stimulation and steam assisted gravity drainage, involve the injection of large volumes of steam into oil sand formations. Dilatation of oil sand formations due to steam injection induces stresses and deformations in the shale overburden. Natural horizontal fissures or extensive fractures with no tensile and cohesive strength are commonly found in the shale formation. New fractures will be initiated at these in situ horizontal fracture tips if the stresses and deformation induced by the steam injection are excessive. Reactivation and propagation of these in situ fractures in the shale formation could not only cause casing impairment problems, but could also cause an environmental hazard. This paper presents an analytical model to investigate the propensity for fracture propagation in shale due to steam injection under tensile (mode I) and shear (model II) fracturing. Practical numerical examples are presented along with a risk assessment and implications.