A Simple Scaling Approach to the Spontaneous Clearing Time of Water Block

Hydraulic fracturing causes water to invade reservoir rock. This invaded water is called a water block as it lowers the effective permeability of the rock to oil. Field and laboratory results show that the water block is temporary. We hypothesize that (a) the clearing is caused by capillary-dominated advection of water, and (b) the clearing takes place when the water saturation drops at the fracture face. We test this hypothesis with laboratory experiments, analytic solutions, and numerical simulations to a capillary-driven model. In particular, we determine how the clearing time scales with the permeability of the rock and the amount of water invaded, and this scaling matches experimental observations. From this match, we develop an equation that estimates clearing time and test how the leading coefficient of this equation depends on rock constitutive parameters (e.g., capillary pressure, relative permeability).