A novel experimental approach for fracability evaluation in tight-gas reservoirs

• Brittleness, natural fracture, stress sensitivity, and AE activity number are integrated to evaluate the ability to generate complex fracture.
• Natural crack density is calculated by non-interactive assumption theory and establish a linear relationship between fracability index and calculated crack density.
• The model are verified with 90 shale core samples and field application.

Hydraulic fracturing is an effective stimulation method for the economic development of tight-gas reservoirs in which extremely low matrix permeability requires complex fracture networks. Petrophysical/mechanical experiments and XRD/SEM analyses demonstrate that volcanic sedimentary rock is characterized by developed natural fracture, strong brittleness, stress sensitivity, AE activity, weak anisotropy, and fluid sensitivity. Fracability index is often utilized as a key parameter to evaluate the ability to generate fracture networks. In this study, a new systematic experimental approach and a new mathematical model are established for the comprehensive evaluation of the fracability of tight-gas formations. These two methods integrate natural fracture, stress sensitivity, rock anisotropic nature, AE activity and crack density. The results indicate that the fracability index (FI) and the calculated crack density (CRD) are positively linearly correlated. The method is successfully applied to evaluate the fracability of the Yingtai gas field in northeast China.