Method for forming channels of high fluid conductivity in formation parts around a borehole

Claim 1

A method for forming channels of high fluid conductivity in a relatively soft acid-soluble formation about a cased well which penetrates such formation and which has its casing perforated along at least a part of the casing wall which faces such formation, comprising the steps of: (a) producing in the formation a fracture containing a viscous fluid which communicates with the perforations (b) injecting an acid solution through the perforations into the viscous fluid in 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; (c) continuing the injection of the acid solution through the perforations until channels have been etched in areas of the fracture walls; (d) injecting a viscous carrying fluid containing a propping agent through the perforations into the fracture at a pressure at which the fracture remains open, the viscosity of the carrying fluid being at least equal to the viscosity of the acid solution; (e) continuing the injection of the carrying fluid and the propping agent until propping agent is present in the fracture between at least part of those areas of the fracture walls wherein channels have been etched; and (f) lowering the fluid pressure in the fracture, thereby allowing the fracture walls to be displaced towards a closing position, in which position the walls of the channels are supported and held open by the propping agent.

Claim 2

A method for forming channels of high fluid conductivity in a relatively soft acid-soluble formation about a cased well which penetrates such formation and which has its casing perforated along at least a part of the casing wall which faces such formation, comprising the steps of: (a) producing in the formation a fracture containing a viscous fluid which communicates with the perforations (b) injecting an acid solution through the perforations into the viscous fluid in 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; (c) continuing the injection of the acid solution through the perforations until channels have been etched in areas of the fracture walls; (d) injecting a viscous carrying fluid containing a propping agent through the perforations into the fracture at a pressure at which the fracture remains open, the viscosity of the carrying fluid being at least equal to the viscosity of the acid solution; (e) continuing the injection of the carrying fluid and the propping agent until propping agent is present in the fracture between at least part of those areas of the fracture walls wherein channels have been etched; and (f) lowering the fluid pressure in the fracture, thereby allowing the fracture walls to be displaced towards a closing position, in which position the walls of the channels are supported and held open by the propping agent.