Optimal spacing of staged fracturing in horizontal shale-gas well

Shale reservoirs have low or ultra-low permeability and porosity, and require achieving economic production rates by creating fracture network. The spacing between fractures is thought to be a major factor in the success of horizontal well completions. The opening of a propped transverse fracture in horizontal wells causes a reorientation of in-situ stresses in its neighborhood, which in turn affects the creation and distribution of stress-relief fractures. In this paper, the extent of stress reorientation has been calculated for fractured horizontal well using two-dimensional numerical model of the stress interference induced by the creation of propped fracture. Staged fracturing in horizontal well is simulated based on an alternate sequencing of transverse fractures. By mapping the angle of stress-relief fractures generated by different fracture stages, we calculate the network area that is the extent of the intersection of stress-relief fractures. Our results demonstrate that the network area has a peak value with the varying fracture spacing and therefore, the associated spacing is optimal fracture spacing. The effect of in-situ stress contrast and net pressure on the optimal fracture spacing has been investigated. It is shown that optimal fracture spacing will increase with lower stress anisotropy or larger net pressure. Finally, the effect of proppant on optimal spacing is investigated. The results presented in this paper can offer some new insights on the completion designs, such as optimizing fracture spacing and improving the conductivity of rock matrix. (C) 2015 Elsevier B.V. All rights reserved.