Fracture cleaning: Experimental study on the unclogging process within a propped fracture under a dynamic stimulation

Abstract

This experimental study investigates the unclogging process of a propped fracture previously clogged, using a synthetic dynamic load. Pressure oscillations inside the fracture are expected to flush out the fine particles blocking the flow. Laboratory experiments are presented: fractures are clogged with crushed natural sand; after applying the dynamic load, a significant increase of the intrinsic permeability is observed. The highest recovery rate reached was 82%. X-ray CT scans provide images of the fracture before and after the dynamic load is applied. The results show that a high percentage of fines are flushed out of the fracture. The influence of the proppant characteristics and of the quantity of fine particles in the fracture are discussed. Flushing of fines is more effective with large-size proppant. As the density of proppant increases, it passes through a minimum for one layer of proppant which corresponds to a very dense particle distribution. Above one layer of proppant, particles stack onto each other which increases the propped fracture thickness and its conductivity. Finally, it is found that high frequencies and high amplitudes of the dynamic load promote unclogging.