Hydraulic fracturing in a penny-shaped crack. Part II: Testing the frackability of methane hydrate-bearing sand

摘要

This work examines the susceptibility of methane hydrate in sand to fracture. The task is made difficult because of two challenges: (1) the means to conduct hydraulic fracturing experiments under high pressure and low temperature conditions, and (2) the formation of high saturation hydrate-bearing sand. The apparent fracture toughness (K-Q) of a material is usually determined via conducing standard tests such as three-point bend on notched beams or pull test on compact specimens. In Part I, Too et al. (2018), hydraulic fracturing in a penny-shaped crack was found able to determine K-Q and estimate the tensile strength of frozen sand. As such, experiments were conducted using the similar approach on the synthesized high saturation methane hydrate-bearing sand specimens (approximately 50-75%) with sample size of 80 mm in diameter and 150 mm in length. The range of K-Q determined is between 0.3 and 1.4 MPa root m while the tensile strength estimated ranges between 6 and 12.5 MPa for the hydrate saturation range. The possibility of creating artificial fractures in synthetic methane hydrate-bearing sand may present an opportunity to improve the gas production from natural occurring hydrate-bearing sand.