Abstract: This method consists in introducing within the well or pipe (C) a mandrel (1) equipped with an inflatable membrane (2) which can expand radially under the effect of an internal pressure, in positioning said mandrel opposite the portion to be treated, in introducing a pressurized fluid (L1) within the membrane (2) such that its end regions form annular bulges pressing firmly against the wall, whereas its mid-region expands to a lesser degree, forming a peripheral annular space (?) into which is then injected a cement (L2) which is liquid but able to harden, in leaving the cement to set so as to form a solid sleeve, in deflating the tubular membrane (2), and then in withdrawing the mandrel (1) together with the deflated membrane (2). The method can be used in the oil sector, particularly for repairing and/or plugging a portion of casing.