Productivity of hydraulic fractures with heterogeneous proppant placement and acid etched walls

Abstract

Production estimation for hydraulic fractures with heterogeneous proppant placement is not straightforward and requires numerical solution. Contrasts in hydraulic conductivity are intentionally created by channel fracturing, when proppants are injected by pulses in stages, or as a result of fracture wall etching by acids. In both types of fracturing treatment, a connected network of open channels is expected to form within a fracture. The channels not only create primary pathways for producing fluids, they are also very compliant regions that are subject to closure and pinching under large effective stresses. We develop a numerical model of hydraulic fracture productivity considering heterogeneous distribution of conductivity and channels. For various geometries of proppant pillars and etched walls, reservoir properties, and size of perforation intervals, we calculate total production rates from a hydraulic fracture as a function of pressure drawdown. We evaluate other productivity indicators such as skin factor and effective dimensionless conductivity traditionally used by field engineers. We show that our numerical solution agrees with exact solutions of several problems with rectangular and circular fracture geometry, with uniform or stepwise conductivity profile. The presented model can be used for accurate evaluation of pressure-dependent well productivity after channel fracturing and acid fracture treatments. An important application of our model is the optimization of the pressure drawdown schedule to reach the maximum production rates in the created fractures, which is often ignored by oilfield companies.