Abstract: A method for monitoring structural changes in a binder in contact with a solid object, while the binder is curing. Conductivity measuring pick-ups are placed in the binder mass and at the boundary between the binder and the solid object. A low amplitude AC voltage is applied to each pick-up at a low frequency, and the pick-up output signals are compared by a differential inductive bridge. The difference between the output signals is indicative of the extent of adhesion of the binder to the solid object. Preferably, only those components of the pick-up signals which are in phase with the applied AC voltage are employed for the comparison.

Abstract: A device for applying plugging mix to well walls comprises installed in series and interconnected a piston having passages for the flow of a fluid and spring-biased locking members for fixing the position of the device with respect to a drilling string, and a head carrying vanes for applying plugging mix to well walls and a bit for drilling-off the mix installed at the distal end of the head. The head has passages for the flow of the fluid. The vanes are made in the form of two plates installed on opposite sides of the head at an angle with respect to its axis of rotation, the vanes being radially movable with respect to the axis of rotation. The piston, the head and the bit are of a diameter which is slightly smaller than the nominal inside diameter of the drilling string.

Abstract: A method for preparing a plugging material of an alumina-base cement, by mechanical stirring of alumina cement with additives of the pre-rated quantities to improve the physical and mechanical characteristics of the plugging material. The stirring is effected by magnetized working bodies in an alternating electromagnetic field. The resultant material is subjected to a batch forming by compression at a pressure between 50 and 120 MN/m.sup.2.