Abstract: Horizontal well productivity equations of Borisov's, Joshi's, Giger's and Renard-Dupuy's formulae are analyzed comprehensively, and then their differences and similarities are compared. Actually, there are some problems to be improved in Joshi's formula. 3-D analytical productivity equation of horizontal well in infinite-acting reservoir with sealed boundary is derived. For the problem of Joshi's formula without π in the denominator of vertical seepage resistance term and the treatment of eccentricity as well as the differences between 2-D and 3-D seepage flow field, the corresponding improvement method is proposed. The study indicates that the error caused by the simplification of seepage flow field is not obvious. However, the problem of Joshi's formula without π and the treatment of eccentricity should be improved.

Key words: horizontal well, productivity, formula