A generalized non-Darcian model for packer tests considering groundwater level and borehole inclination

Abstract

Packer test is a tool that has been long developed and widely used for characterizing the permeability of formation. The flow in the tested formation tends to transition from laminar to non-Darcian regime with increasing flow velocity and hydraulic gradient. But as the non-Darcian effect becomes important, how the borehole inclination and groundwater level influence the interpretation of packer test data remains unclear. In this study, a Forchheimer's law-based analytical model incorporating the effects of groundwater level and borehole inclination was presented by image method and velocity integration, which can be immediately reduced to Zangar's (1953) equation for vertical borehole under laminar flow condition and approximately reduced to Chen's (2015b) model when the test interval is at a moderate depth below the groundwater level. The proposed model was validated by numerical simulations. Parametric and error analyses indicate that the hydraulic conductivity will be overestimated while the non-Darcy coefficient will be underestimated if the effects of groundwater level and borehole inclination are neglected. The proposed model was applied to data interpretation of packer tests performed in fractured sedimentary rocks in Hainan Province, China. The results show that significant non-Darcian flow occurred in the tests. The borehole inclination has little influence on the estimation of hydraulic parameters, but demonstrates the anisotropy and heterogeneity of the rocks. • A generalized non-Darcian model was proposed for packer test data interpretation. • The influences of groundwater level and borehole inclination were evaluated. • Previous models overestimate permeability but underestimate non-Darcian coefficient. • Chen et al.'s (2015b) model applies as the depth becomes moderate from groundwater level.