Abstract: Based on percolation theory, the formulae of interwell on-way pressure and pressure gradient distribution for vertical injectorhorizontal producer hybrid pattern system are deduced for the first time, and their variations are analyzed. Integrated with mathematic expression of the start-up pressure gradients given by physical modeling experiment, the method for well spacing of this hybrid pattern in low permeability reservoir is proposed, by which the influences of injection-production pressure differential, permeability and horizontal section length on this well spacing are analyzed. The study shows that the producing pressure differential required by this hybrid pattern system is much smaller than that by vertical well pattern. It is easier to create an effective displacement compared with vertical wells pattern, and larger injection-production well spacing can be taken.

Key words: low permeability reservoir, hybrid well pattern, pressure gradient, effective displacement, injection-production well spacing