Investigation of the Impact of Fracture Spacing and Fluid Properties for Interfering Simultaneously or Sequentially Generated Hydraulic Fractures

Abstract

Summary Using a fully coupled (flow and mechanics) hydraulic-fracture propagation model, we investigate the critical in-situ and treatment factors controlling geometry in multiple-fracture horizontal wells. Fracture net pressure is calculated by considering continuity of flow rate and pressure equilibrium in the fracture and the wellbore between injection points. A 2D displacement-discontinuity method, with correction for finite fracture height, was used to calculate fracture aperture, accounting for mechanical interaction between multiple propagating fractures. Stress-shadow effects change the local stress field in the surrounding rock, influencing fracture geometry. A sensitivity study for simultaneous propagation was performed, including fracture spacing, velocity exponent, in-situ differential stress, fluid viscosity, and pump rate. The results show that closely spaced hydraulic fractures can cause significant fracture-width restriction, increasing the likelihood of premature screenout. Exterior fractures have greater lengths than interior fractures, and the length difference is more significant for poor injection control. At a low in-situ differential stress, multiple fractures tend to extend away from one another to reduce the negative mechanical interaction; however, increasing the stress difference can make fractures propagate along a straight line. Compared with gel hydraulic-fracturing treatments, slickwater treatments generate narrower and much longer fractures with lower net pressure. In the case of simultaneously generating multiple fractures, these slickwater fractures cause less mechanical interference with each other. Increasing pump rate enlarges fracture width slightly and reduces the length. Finally, simultaneous and sequential injection methods were examined showing that these two methods create slightly distinct fracture trajectories.