FREMGANGSMAADE TIL DANNELSE AF KANALER MED HOEJ VAESKELEDNINGSEVNE I FORMATIONSDELE OMKRING ET BOREHUL

A method for forming channels of high fluid conductivity in relatively hard acid-soluble formation parts around a borehole, said method comprising the sequential steps of: 1) installing a casing in the well, and introducing in the wall of the casing a plurality of perforations arranged over at least part of said well where facing the formation; 2) inducing in the formation a fracture containing a viscous fluid with propping agent at a fluid pressure at which the fracture is kept open; 3) injecting an aqueous acid solution through the perforations into the fracture at a pressure at which the fracture remains open, the viscosity ratio between the viscous fluid and the acid solution being chosen such that the viscous fluid is displaced in the fracture in an unstable manner by the acid solution; 4) continuing the injection of the acid solution through the perforations until channels have been etched in areas of the fracture walls that face each other; 5) lowering the fluid pressure in the fracture, thereby allowing the fracture walls to be displaced towards each other; and 6) lowering the viscosity of the viscous fluid.