Parametric optimization of vector well patterns for hydraulically fractured horizontal wells in tight sandstone reservoirs

In this paper, a generalized and pragmatic framework has been developed to optimize the vector well pattern in tight sandstone reservoirs. More specifically, the maximum principal formation stress, natural fracture orientation, and principal permeability orientation are identified as the three key factors associated with well productivity, while both micro-elements of fractures are summed up and coefficients of the same fracture are combined according to the angle between the principal permeability orientation and direction of the hydraulic fractures to form an equation matrix. The sensitivity analysis is then conducted to examine effect of the maximum horizontal principal stress and the principal permeability on horizontal well production while determining the optimal orientation of the horizontal wellbore. Subsequently, theoretical calculation is performed to design and optimize the well pattern as well as fracture properties. It is found that the orientation of a horizontal wellbore should be perpendicular to the direction of the maximum horizontal principal stress if the angle (theta) between the orientation of the principal permeability (k(x)) and the direction of the maximum horizontal principal stress is less than 30 degrees. If 30 degrees <= theta <= 60 degrees, the orientation of the horizontal wellbore should be perpendicular to the direction of the maximum horizontal principal stress for a weak anisotropic reservoir (k(x)/k(y) < 2), while it should be perpendicular to the orientation of principal permeability (k(x)) for a strong anisotropic reservoir (k(x)/k(y) >= 2). The orientation of a horizontal wellbore needs to be perpendicular to the orientation of the principal permeability (k(x)) if 60 degrees <= theta <= 90 degrees. In addition to improving the recovery factor compared with that of the conventional well spacing, it is found from a field application that the optimized vector well pattern can effectively extend the stable production period, reduce water-cut, increase oil recovery up to 4.5%, and improve the overall reservoir performance.