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.