Abstract: Joshi’s horizontal well productivity formula was analyzed in this paper, and its two disadvantages were presented. One is an existing inconsistency between the hypothesis and the potential applied in vertical radial flows, the other is a conditional formula in anisotropism formation. By coordinate transformation
and with different choices of permeability in perpendicularity and horizontal direction, Joshi horizontal well productivity formula was modified. A new horizontal well productivity formula in isotropism and anisotropism reservoirs were developed. Furthermore in contrast with an oil field example, the results show that the production predicted by new formula is in good agreement with the flied.

Key words: Joshi’s horizontal well productivity, vertical radial flows, anisotropism, contrast