Experimental Investigation and Parameter Inversion of Radial Solute Transport Accounting for the Skin Effect

Radial solute tracer tests are a key method for estimating aquifer parameters, yet their accuracy often is compromised by skin effects around the wellbore resulting from drilling or completion activities. A clear understanding of how skin influences radial solute transport remains limited due to a lack of targeted laboratory studies. Moreover, available inversion models still face two major limitations: an inability to couple wellbore mixing during tracer injection with skin effects, and difficulty in concurrently estimating multiple parameters for both the skin and formation zones. Therefore, this study conducted a series of laboratory sand tank experiments, based on which a mathematical model accounting for both mixing and skin effects was developed combined with particle swarm optimization (PSO) algorithm for parameter inversion. The results indicate that (1) perforated tubes enhanced the wellbore mixing process compared to the conventional pipes, thereby achieving a better match between the experimental results and the simulation that accounts for mixing; (2) wellbore-aquifer mass transfer is augmented and inhibited by negative and positive skins, respectively, and an increased injection rate suppresses the negative skin effect; (3) when using a skin-effect numerical model, small injection rate or proximal monitoring wells are recommended; and (4) the PSO algorithm performs well in the simultaneous estimation of both skin and formation zone properties. The findings of this study offer valuable insights for addressing radial solute transport and multi-parameter inversion challenges in field settings.