Non-Darcy's law-based analytical models for data interpretation of high-pressure packer tests in fractured rocks

Abstract

High-pressure packer test (HPPT) is an enhanced constant head packer test for characterizing the permeability or coupled hydromechanical properties of fractured rocks under high-pressure groundwater flow conditions. The interpretation of the HPPT data, however, requires further investigations due to the non-Darcy flow prone to occur in the tested rocks at high flow velocities. In this study, two analytical models were presented based on the Forchheimer's law and Izbash's law, respectively, for interpretation of the HPPT data, which can be readily reduced to Hvorslev equation in laminar flow condition. The proposed models were applied to data interpretation and hydraulic parameter estimation for the HPPTs performed in fractured sedimentary rocks located at about 450m depth in central Hainan Island, and validated by numerical simulations on the tests. The results indicate that both of the proposed models well reproduce the non-Darcy flow behavior observed in the HPPTs before the initiation of hydraulic fracturing. Overall, the Forchheimer's law-based model is advantageous for its clear physical meanings, but the Izbash's law-based model could be more convenient when the obtained P–Q curves are divided into different phases according to the flow conditions in the fracture system. Also pointed out were the theoretical flaws in an existing Izbash's law-based analytical model, which lead to a misestimate of hydraulic conductivity and an inconsistency between the analytical solutions and numerical results.