On the horizontal-well pumping tests in anisotropic confined aquifers

A method that directly solves the boundary problem of flow to a horizontal-well in an anisotropic confined aquifer is provided. This method solves the point source problem first, and then integrates the point source solution along the horizontal well axis to obtain the horizontal well solution. The short and long time approximations of drawdowns are discussed and are utilized in the semilog analysis of the drawdown. A closed-form analytical solution of geometrical skin effect at the wellbore is derived. Type curves and derivative type curves of horizontal pumping wells are generated using the CHOW program. This program also calculates the drawdown at any given observation well at any given time. The horizontal-well type curves are different from the vertical-well type curves at early time, reflecting the different nature of flow to a horizontal-well and to a vertical-well. The horizontal-well type curves converge to the vertical-well type curves at late time, showing the similar nature of flow to a horizontal-well and to a vertical-well at late time. The sensitivity of the type curves and derivative type curves on monitoring well location, aquifer anisotropy, horizontal well depth, and horizontal well length is tested. These type curves and derivative type curves can be used in the matching point method for interpreting the pumping test data. (C) 2001 Elsevier Science B.V. All rights reserved.