Abstract: The productivity calculation formulae for low permeability reservoir developed by vertical well integrated with horizontal well patterns including inverted 4-spot, inverted 5-spot, inverted 7-spot and inverted 9-spot patterns are theoretically deduced using hydroelectricity similarity principle and equivalent filtrational resistance method, considering starting pressure gradient, and four kinds of formulae for calculation of productivity of horizontal wells by these patterns are offered. And the factors affecting the productivities from these different patterns are analyzed in terms of penetrating proportion, reservoir thickness and starting pressure gradient. The results show that the different well patterns' productivity ratios by horizontal well process will be reduced for existence of starting pressure gradient; with the increase of penetrating proportion, the ratios will be increased; with the increase of reservoir thickness, the ratios will be decreased in view of low permeability reservoir. These conclusions can be used for design of field development program and prediction of these productivities.

Key words: low permeability reservoir, horizontal well, well pattern, productivity, starting pressure