Horizontal radial flow is a flow regime that occurs only in a horizontal well after linear horizontal or elliptical flow, and before the occurrence of boundary effects. The purpose of analyzing horizontal radial flow data is to determine horizontal permeability (kxy).
The equations and theory for analyzing horizontal radial flow data are identical to that for radial flow. The only difference is the permeability obtained and shown in the equations is replaced by horizontal permeability (kxy).
It is important to note that in a horizontal well, two radial flow regimes occur. One at early time which occurs in the vertical plane of the formation, and the second at late time in the horizontal plane. Thus, it is important to analyze the proper region of data to obtain correct results. The plots below show the distinction between vertical and horizontal radial flow on the semi-log and derivative plots, as well as the correct placement of the analysis lines.