Application of non-linear flow laws in determining rock fissure geometry from single borehole pumping tests

Abstract This paper deals with the effect of non-linear flows on the results of constant pressure well tests in single fractures. The non-linearity results from kinetic effects as flow leaves the laminar regime and enters the mixed laminar/turbulent flow regime. Well test designs are considered that use the long term steady flow in addition to designs using the transient period. A multistage steady flow test using as few as three pressure steps can be used to determine the extent of turbulent flow as well as fracture aperture, roughness, and, under some conditions, the distance to a constant pressure boundary. Finite element simulations are used to develop type curves for transient flow analysis where non-linear flow may exist. Unique curves can be developed only for specific values of relative roughness, aperture, and dimensionless well pressure. Non-linear flow strongly affects the magnitude of flow but does not change the form of the transient-flow-curve greatly, hence neglecting possible non-linear flow may lead to errors as much as an order of magnitude in estimation of transmissivity. Transient tests using a range of pressures, including sufficiently low pressure for laminar flow, can be used to deduce relative roughness, aperture and the distance and nature of fracture boundaries.