Liquid Loading within Hydraulic Fractures and its Impact on Unconventional Reservoir Productivity

Slick-water fracturing has emerged as the preferred technique for fracturing and proppant placement in ultra-low permeability unconventional gas reservoirs. However, significant proportions of all these completions fail to perform as well as expected. This could be due to poor reservoir quality, inefficient completions or non-optimal flow back controls. A major concern with using water as the fracturing fluid is that of fluid retention in the tight reservoir matrix due to high capillary pressures and presence of water sensitive clays. High water saturation in the invaded zone near fracture face reduces gas relative permeability and impedes gas productivity. Fracture cleanup in itself plays an important role in achieving maximum productivity. Historically it is assumed that as long as fracture is infinitely conductive, any water within the fracture is cleaned up readily. Most of the previous studies have ignored the effect of gravity in fracture cleanup. However, in this study a 3D numerical simulation approach is adopted to investigate the effect of gravity on frac-water recovery. It is shown that under scenarios with low gas flow velocities, the water may load at the fracture bottom and maybe difficult to unload for months. This will impact the early time fracture cleanup and therefore, the gas productivity.