Hydraulic fracturing in methane-hydrate-bearing sand

Abstract

Knowledge of the fracturing behaviors in gas-hydrate-bearing sediments is essential to understand the accumulation mechanism of gas hydrates in fractured sediments and to apply hydraulic fracturing as a well stimulation method when considering gas recovery from gas hydrate reservoirs. We present an experimental study of hydraulic fracturing involving methane-hydrate-bearing sand formed in a triaxial pressure cell. The injection pressure rapidly increased after the start of distilled water injection from the core top through a small port, but suddenly decreased afterward. X-ray computed tomography revealed that laminar fractures, which were oriented in a plane perpendicular to the minimum principal stress, were generated after this pressure drop. The fracturing pressure was 2.9–3.9 MPa above the minimum principal stress. Although the host sediment was unconsolidated, the observed fracture behavior yielded a consolidated-rock-like fracturing mode, i.e., the tensile failure mode. It was affected by the low-permeable feature of hydrate-bearing sediments. The permeability was increased after fracturing and was maintained even after re-confining and closing the fractures. The results indicate that hydraulic fracturing is a promising well stimulation method for low-permeable gas hydrate reservoirs.