Nonlinear groundwater flow during a slug test in fractured rock

•Nonlinear flow was identified regime during slug tests in fractured rock.•The degree of nonlinearity increased with an increasing the initial head displacement.•An equation was utilized to estimate the hydraulic property in a linear flow regime. A series of slug tests with various initial head displacements was carried out to investigate the influence of nonlinear groundwater flow on a slug test in fractured rock. To identify the nonlinear flow regime during a slug test, a representative Reynolds number (Re) was calculated using the slug test results and the fractures identified from geophysical logging and core logs. The Forchheimer equation and cubic law were used to determine the critical Re where nonlinear flow arose in the test zone. Our results showed that nonlinear flow arose when the initial displacement was over 1.0m. Then, the degree of nonlinearity increased and the estimated hydraulic conductivity from the test results decreased with increasing initial displacement. The study also suggested that the Forchheimer and cubic law can be used to estimate the hydraulic conductivity in a linear flow regime using data from the slug tests in a nonlinear flow regime.