Well spacing design for low and ultra-low permeability reservoirs developed by hydraulic fracturing

In order to simulate non-Darcy flows in low and ultra-low permeability reservoirs, based on the black oil simulator, a three-dimensional, two-phase model was established considering two-phase start-up pressure, permeability sensibility and fracture conductivity decline. Then numerous simulations were run to analyze the elliptic drainage area induced by a fractured well, the results show that: for water fractured well, permeability is the dominant factor affecting the elliptic drainage area at the beginning, and pressure difference and start-up pressure have increasing effects as time goes by. However, no factor has a marked impact on the shape of elliptic drainage area. Parameters of elliptic drainage area can be calculated with GA-BP neural network improved by genetic algorithm. Aiming at acquiring maximum sweep efficiency, well spacing equations were deduced for rectangular pattern and diamond inverted nine-spot pattern. Field application demonstrated daily oil production enhanced 1.25 times after hydraulic fracturing, and the long time stimulation effect is substantial. Key words: low and ultra-low permeability reservoir, fractured well, elliptic drainage area, well spacing desig