Computational Method for Hydraulic Fractures Spacing of Multi-Fractured Horizontal Well in Ultra Low Permeability Reservoirs

Abstract Hydraulic fractures spacing of multi-fractured horizontal well (MFHW) is an extremely important item for the optimization of MFHW in ultra-low permeability reservoirs. By adopting the maximum condition that fluid at the midpoint of the two adjacent hydraulic fractures is just able to flow, the mathematical model and computational method to determine the hydraulic fractures spacing of MFHW were established based on the non-Darcy flow theory, the elliptical seepage theory, and average mass conservation law. Then the influences of the reservoir permeability, thickness, hydraulic fracture half length and conductivity, producing pressure drop on hydraulic fractures spacing of MFHW were studied quantitatively. The results show that hydraulic fractures spacing increases as the permeability increases and they have a preferable double logarithmic linear relationship; the fractures spacing decreases as the reservoir thickness and fracture half length increases, and the influences of the reservoir thickness and fracture half length on the fractures spacing are related to the hydraulic fracture conductivity. When the fracture conductivity is high, the fractures spacing is relatively broad, but with the fracture conductivity increasing, the fractures spacing growth gradually slows. The relationship between the producing pressure drop and the fractures spacing is approximately linear. The larger the producing pressure drop, the broader the fractures spacing of MFHW.