Quantification of non‐Darcian flow observed during packer testing in fractured sedimentary rock

[1] High-precision straddle packer tests were conducted in boreholes in a fractured dolostone aquifer using constant rate injection (Q) step tests to identify the conditions of change from Darcian to non-Darcian flow on the basis of Q versus the applied head above ambient (dH), where the ambient head represents static conditions. The linear portion, representing Darcian flow, passes through the origin, but after the onset of non-Darcian flow, there is proportionally less Q per unit dH, and the transmissivity (T) calculated for the test interval using Darcy's law-based models can be substantially underestimated. Onset of nonlinear flow depends on the test interval length and permeability, typically beginning at injection rates less than 0.5 L min−1 for a relatively transmissive (2 × 10−5 m2 s−1) 1.5 m test interval. In studies of nonlinear flow during pumping tests, the Forchheimer equation is commonly used to describe nonlinear flow near the well using a Q2 versus dH relationship. However, for packer tests in fractured rock, we propose the Darcy-Missbach equation, which relates Qn to dH, as an alternative equation. While both equations accurately predict the observed dH within the range of flows used, the Darcy-Missbach exponent (n) describes the degree of deviation from the linear regime; moreover, all calculated exponents were less than 2, implying that the flow is nonlinear but not quadratic in nature. This quantification of the linear to nonlinear flow relations provides for a more accurate identification of the Darcian range, resulting in better T estimates.