Anisotropic Permeability Estimation by Horizontal Well Tests

A horizontal well drilled along the principal permeability k x direction is often assumed in horizontal well test interpretation. However, the orientation of well affects well test interpretation significantly, particularly in horizontally anisotropic reservoirs. A new form of horizontal well solution which incorporates the well orientation effects is presented in this paper. The permeability anisotropy usually forms an ellipse in the horizontal plane and an ellipsoid in the 3D space, with the principal permeabilities as its three axis. By using the new solution, the true permeability anisotropy can be obtained for an arbitrarily oriented horizontal well. Two methods are demonstrated for determination of the true reservoir anisotropy (permeability ellipse), a graphical method and a numerical method. Two tests from two horizontal wells of different azimuths are needed in determining the reservoir anisotropy by these methods.