Understanding the effect of single-fracture heterogeneity from single-well injection-withdrawal (SWIW) testsComprendre l’effet de l’irrégularité d’une fracture isolée à partir de tests d’injection-pompage dans un puits uniqueConocimiento del efecto de la heterogeneidad de una fractura única a partir de pruebas de un solo pozo de extracción e inyección (SWIW)对单井回灌-抽水试验(SWIW)中非均质单裂隙影响的认识Compreendendo o efeito da heterogeneidade de uma fratura única a partir de ensaios de injeção e extração em furo único (SWIW)

The single-well injection-withdrawal (SWIW) tracer test is a method used to estimate the tracer retardation properties of a fracture or fracture zone. The effects of single-fracture aperture heterogeneity on SWIW-test tracer breakthrough curves are examined by numerical modelling. The effects of the matrix diffusion and sorption are accounted for by using a particle tracking method through the addition of a time delay added to the advective transport time. For a given diffusion and sorption property (Pm) value and for a heterogeneous fracture, the peak concentration is larger compared to a homogeneous fracture. The cumulative breakthrough curve for a heterogeneous fracture is similar to that for a homogeneous fracture and a less sorptive/diffusive tracer. It is demonstrated that the fracture area that meets the flowing water, the specific flow-wetted surface (sFWS) of the fracture, can be determined by matching the observed breakthrough curve for a heterogeneous fracture to that for a homogeneous fracture with an equivalent property parameter. SWIW tests are also simulated with a regional pressure gradient present. The results point to the possibility of distinguishing the effect of the regional pressure gradient from that of diffusion through the use of multiple tracers with different Pm values.