A dual-well step drawdown method for the estimation of linear and non-linear flow parameters and wellbore skin factor in confined aquifer systems

Abstract

Summary In this study a method based on dual-well step drawdown test (i.e. a combination of an aquifer and a well performance test) for the determination of hydrodynamic parameters (namely storage coefficient and hydraulic conductivity), mechanical wellbore finite thickness skin factor, non-linear wellbore and non-linear aquifer parameters in an homogeneous confined aquifer is presented in order to put together aquifer and well tests. The interpretation procedure is based on the application of superposition principle to a large time logarithmic approximation of the solution. The advantages of this method, that can be considered an extension of Jacob step-test (1947) and Cooper–Jacob approximation (1946) , are that: (I) it is possible to determine simultaneously aquifer and well properties in a single test; (II) the method is based on a large time approximation and it is therefore independent from wellbore storage; (III) if the well skin is absent, the aquifer parameters (storage coefficient and hydraulic conductivity) can be derived just from a single-well test; (IV) the interpretation procedure is easy to apply and robust and does not require any specific numeric code or software. The same procedure can be easily adapted to gas well testing. It is also shown that, even in the presence of linear and non-linear flow, skin effect and wellbore storage, the hydraulic conductivity (and not the storage coefficient) of the aquifer can be correctly estimated by the Cooper and Jacob (1946) method applied to a single-rate pumping test, using exclusively the large time drawdown data measured at the pumping well.