Abstract: Amplifier comprising an input signal node for conveying an input signal having an input signal value and an output signal node for conveying an output signal having an output signal value. Amplifier circuitry is coupled to the input signal node and provided with a plurality of intermediate output signal nodes, each for conveying an intermediate output signal having an intermediate output signal value. The intermediate output signal value in each intermediate output signal node relates to the input signal value in accordance with predetermined signal gains. A signal selector selects one of the intermediate output signals and feeds the selected one to the output signal node. The amplifier may be comprised in an analogue to digital converter. The amplifier may be incorporated in a down hole tool. The method of amplification may be used in a method of producing a mineral hydrocarbon fluid.

Abstract: An electromagnetic response from a region in an earth formation is determined by lowering an electromagnetic measurement tool into a borehole in the earth formation. The tool comprises a transmitter antenna, a receiver antenna, and an electrically conductive support structure. The transmitter antenna is energized, resulting in receiver signal in the receiver antenna. A raw response signal, comprising the receiver signal, is measured at the receiver antenna. The raw response signal is adjusted using a reference signal obtained by measuring the response signal of the tool in a test environment having a resistivity that is higher than that of the region in the earth formation. This method can be employed during the drilling of the borehole which may be part of a method of producing a mineral hydrocarbon fluid.

Abstract: A method of imaging a subterranean formation traversed by a wellbore using a tool comprising a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals. The tool is brought to a first position inside the wellbore, and the transmitter is energized to propagate an electromagnetic signal into the formation. A response signal that has propagated through the formation is detected. A derived quantity for the formation based on the detected response signal for the formation is calculated, and plotted against time. The tool may be moved to at least one other position within the wellbore where the procedure may be repeated to create an image of the formation within the subterranean formation based on the plots.