Abstract: An acoustic logging tool sleeve with a preferably discontinuous, alternating structure that is acoustically opaque in some zones, and acoustically transparent in others. The sleeve may be modular, with several stages connected together. The multiple stages provide a sleeve that may be useful with a variety of borehole logging tools to reduce or eliminate the transmission of noise to the receiving elements.

Abstract: Tools for investigating an earth formation in the presence of either oil-base or water-base mud are provided and includes a circuit which induces current into the formation in a focused manner, and a sensor electrode which is isolated from the circuit, at least partially surrounded by the circuit, and located in the area in which the current is focused. The current inducing circuit may be an oppositely polarized double-dipole circuit to which voltage is applied with the two dipoles sharing a common radiating element over which a focused area is formed. Insulators are provided that separate the outer electrodes of the double-dipole circuit from the common radiating element. Alternatively, the current inducing circuit is a coil arranged in a partial toroidal configuration in an insulated area that at least partially surrounds the focused area and which separates the focused area from return electrodes.

Abstract: A method for estimating the time varying mechanical properties of a material comprising: propagating acoustic waves through a sample of material; measuring signals corresponding to acoustic waves after they propagate in the sample; and characterised by: comparing attributes from the measured signals with attributes from corresponding signals provided by a calculating model, the calculating model accounting for at least initially estimated acoustic properties of the material; using the differences between the measured and calculated signals to update the initially estimated acoustic properties of the material in the calculating model; processing N iterations of the comparison and updating either until the differences between measured and calculated signals are within a given tolerance factor or when the number i reaches a prescribed maximum; and calculating the time varying mechanical properties of the material from the final iterated acoustic properties.