Abstract: A down-hole tool provided with a transmitter system for inducing a transient electromagnetic field in an earth formation has an induction coil with a number of windings to generate essentially a magnetic dipole field. The number of windings is divided into two or more groups of windings arranged to cooperatively generate the essentially magnetic dipole field when energized. Switching means are arranged to essentially simultaneously terminate the energizing of the groups of windings. The groups of windings are electrically isolated from each other or connected in parallel to each other, at least when the energizing is terminated. A transient electromagnetic field may thus be induced in an earth formation by essentially simultaneously terminating energizing each group of windings by operating the switching means. A transient electromagnetic response signal may be recorded, and used in a method of producing a mineral hydrocarbon fluid.

Abstract: In accordance with the present disclosure, a system and a method are disclosed for measuring a time varying magnetic field. In one aspect, a system comprises a plurality of induction coils arranged to measure the time varying magnetic field using at least one voltage induced in at least one of the induction coils in the plurality of induction coils, a plurality of snubber circuits connected to the plurality of induction coils, each of the snubber circuits of the plurality of snubber circuits arranged to suppress a resonance of a respective one of the induction coils of the plurality of induction coils, and a summing circuit connected to each of the snubber circuits of the plurality of snubber circuits, the summing circuit arranged to sum voltages induced in each of the induction coils in the plurality of induction coils.

Abstract: A layer stripping method that quickly and robustly determines values of undetermined parameters that model a formation (F). The layer stripping method includes applying inversion methods to subsets (d) of measured data (d) and corresponding modeled responses such that the value of a parameter determined during the application of an inversion method to one subset of the data (d) and the corresponding modeled response can be used to reduce the inversion space of a modeled response that corresponds to another subset of the data (d), to which an inversion method is subsequently applied.

Abstract: A transmitter system for inducing a transient electromagnetic field in an earth formation comprises an inductive element to generate an electromagnetic field in response to a flow of electric current through the inductive element. Furthermore, switching means arranged to interrupt the flow of electric current through the inductive element, which switching means comprises a primary switch and an auxiliary switch arranged in series connection with each other. The auxiliary switch has a lower breakdown voltage than the primary switch. This induces a transient electromagnetic field in the earth formation. Delay circuitry may impose a time delay between switching of the auxiliary switch relative to switching of the primary switch. A transient electromagnetic response signal may be recorded, and used in a method of producing a mineral hydrocarbon fluid.

Abstract: A down-hole tool provided with a transmitter system for inducing a transient electromagnetic field in an earth formation has an induction coil with a number of windings to generate essentially a magnetic dipole field. The number of windings is divided into two or more groups of windings arranged to cooperatively generate the essentially magnetic dipole field when energized. Switching means are arranged to essentially simultaneously terminate the energizing of the groups of windings. The groups of windings are electrically isolated from each other or connected in parallel to each other, at least when the energizing is terminated. A transient electromagnetic field may thus be induced in an earth formation by essentially simultaneously terminating energizing each group of windings by operating the switching means. A transient electromagnetic response signal may be recorded, and used in a method of producing a mineral hydrocarbon fluid.

Abstract: In accordance with the present disclosure, a system and a method are disclosed for measuring a time varying magnetic field. In one aspect, a system comprises a plurality of induction coils arranged to measure the time varying magnetic field using at least one voltage induced in at least one of the induction coils in the plurality of induction coils, a plurality of snubber circuits connected to the plurality of induction coils, each of the snubber circuits of the plurality of snubber circuits arranged to suppress a resonance of a respective one of the induction coils of the plurality of induction coils, and a summing circuit connected to each of the snubber circuits of the plurality of snubber circuits, the summing circuit arranged to sum voltages induced in each of the induction coils in the plurality of induction coils.

Abstract: A method for using a tool in a wellbore in a formation to predict an anomaly in the formation ahead of the device, the tool comprising a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals. the method comprises a) bringing the tool to a first position inside the wellbore; b) energizing the transmitter to propagate a transient electromagnetic signal into the formation; c) detecting a response signal that has propagated through the formation as a result of the transient signal in step (b); d) calculating a derived quantity for the formation as a function of time based on the detected response signal for the formation; e) plotting the derived quantity for the formation against time; f) moving the tool to at least one other position within the wellbore and repeating steps (b) to (e); g) predicting an anomaly in the formation.

Abstract: A method for using a tool in a wellbore in a formation to predict an anomaly in the formation ahead of the device, the tool comprising a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals. the method comprises a) bringing the tool to a first position inside the wellbore; b) energizing the transmitter to propagate a transient electromagnetic signal into the formation; c) detecting a response signal that has propagated through the formation as a result of the transient signal in step (b); d) calculating a derived quantity for the formation as a function of time based on the detected response signal for the formation; e) plotting the derived quantity for the formation against time; f) moving the tool to at least one other position within the wellbore and repeating steps (b) to (e); g) predicting an anomaly in the formation.

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.

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: Method of analyzing a subterranean formation traversed by a wellbore. The method uses a tool comprising a transmitter antenna and a receiver antenna, the subterranean formation comprising one or more formation layers. The tool is suspended inside the wellbore, and one or more electromagnetic fields are induced in the formation. One or more time-dependent transient response signals are detected and analyzed. Electromagnetic anisotropy of at least one of the formation layers is detectable. Geosteering cues may be derived from the time-dependent transient response signals, for continued drilling of the well bore until a hydrocarbon reservoir is reached. The hydrocarbon may then be produced.