Abstract

Recent interest in horizontal wells has been increasing because of improved completion and technology. There are several analytical solutions available in the literature for predicting the productivity. Some equations were originally derived for isotropic reservoirs. The effect of anisotropy was accounted for by modifying the vertical axis.

This paper presents new steady state and pseudo-steady state flow equations derived by simply considering a reservoir that consists of linear and radial flow systems put in series. Any vertical anisotropy could therefore be incorporated in the derivation.

By putting the linear and the radial systems in series, equations for fluid flow in a reservoir producing oil through horizontal well could then be solved. In the derivation, the transformation for accounting for any vertical anisotropy introduced by Muskat and used by previous authors was unnecessary. Instead, the anisotropy factor by itself comes out from the derivation. Furthermore, the magnitude of skin factors in horizontal wells can be proved to be influenced by reservoir anisotropy and thickness and horizontal well length.

The two equations derived have been used to estimate productivity indices of horizontal wells. The results were compared with those of other studies. The comparison are in good agreement even with results of the numerical simulation studies. Results of the effect of skin damage on productivity will also be presented.