Abstract: A method for interpreting transient electromagnetic survey data includes measuring response of subsurface Earth formations to a plurality of time separated transient electromagnetic fields imparted thereto. An amplitude time decay of a selected one of the measured responses is modeled. An amplitude from the modeled amplitude time decay is added to a one of the measured responses later in time than the selected measured response if the amplitude is less than a selected threshold. The method includes at least one of storing and displaying a result of the adding.

Abstract: An instrument is disclosed for measuring resistivity of Earth formations from within a conductive pipe inside a wellbore drilled through the formations. The instrument includes a plurality of housings connected end to end and adapted to traverse the wellbore. At least one electrode is disposed on each housing. Each electrode is adapted to be placed in electrical contact with the inside of the pipe. The instrument includes a source of electrical current, a digital voltage measuring circuit and a switch. The switch is arranged to connect the source of electrical current between one of the electrodes and a current return at a selectable one of the top of the pipe and a location near the Earth's surface at a selected distance from the top of the pipe, and to connect selected pairs of the electrodes to the digital voltage measuring circuit. The pairs are selected to make voltage measurements corresponding to selected axial distances and selected lateral depths in the Earth formations.

Abstract: A method for interpreting transient electromagnetic survey data includes measuring transient response of a medium over a plurality of switching events. The measured transient response to a first one of the current switching events is modeled. Transient response to the model for at least one current switching event prior in time to the at least a first current switching event is calculated. The calculated transient response is summed with the first event measured response and the sum is compared to the electromagnetic survey measurements. The model is adjusted and the calculating summed transient responses is repeated until a difference between the summed calculated responses and the survey measurements falls below a selected threshold.

Abstract: A method for interpreting transient electromagnetic survey data includes measuring transient response of a medium over a plurality of switching events. The measured transient response to a first one of the current switching events is modeled. Transient response to the model for at least one current switching event prior in time to the at least a first current switching event is calculated. The calculated transient response is summed with the first event measured response and the sum is compared to the electromagnetic survey measurements. The model is adjusted and the calculating summed transient responses is repeated until a difference between the summed calculated responses and the survey measurements falls below a selected threshold.

Abstract: A method for interpreting electromagnetic survey data includes acquiring electromagnetic survey data near a top of a portion of the Earth's subsurface. An initial model of the portion of the Earth's subsurface is generated. The model includes at least spatial distribution of formation resistivity within the portion. The initial model is applied to an artificial neural network trained to generate expected electromagnetic survey instrument response to the initial model. The acquired electromagnetic survey data are compared to an output of the artificial neural network. The initial model is adjusted, and the applying the model to the artificial neural network and the comparing are repeated until differences between the output of the network and the acquired survey data fall below a selected threshold.

Abstract: A method for interpreting transient electromagnetic survey data includes imparting an electromagnetic field in the Earth's subsurface by passing electric current through a transmitter antenna. The electric current includes switched direct current at a selected switching frequency. Voltages induced in a receiver corresponding to electromagnetic effects induced in the Earth's subsurface are detected. Frequency domain electromagnetic response of the Earth's subsurface is determined from the detected voltages and transient electromagnetic response of the Earth's subsurface is determined from the detected voltages.

Abstract: A method for subsurface Earth surveying includes acquiring seismic data over a selected region of the Earth's subsurface. Seismoelectric data are acquired over a selected region of the Earth's subsurface. Electroseismic data are also acquired over a selected region of the Earth's subsurface. At least one type of electromagnetic survey data is acquired over a selected region of the Earth's subsurface. Survey volumes of the seismic data, the seismoelectric data, the electroseismic data and the electromagnetic data are matched, and a model of the Earth's subsurface is generated that accounts for all of the seismic data, the seismoelectric data, the electroseismic data and the electromagnetic data.

Abstract: A method for determining spatial distribution of properties of the Earth's subsurface includes obtaining seismic data over a survey area of the Earth's subsurface. Controlled source electromagnetic survey data are obtained over substantially the same survey area. An initial model of the Earth's subsurface for each of the seismic data and the electromagnetic data is generated. Further data may include gravity, magnetics, seismics any type and borehole data. Each model is optimized on at least one model parameter. Consistency is determined between the models; and the at least one model parameter is adjusted and the optimizing and determining consistency are repeated until the models are consistent. Constraints are successively derived from the data sets and also cross checked against reservoir data where available.

Abstract: A method for subsurface Earth surveying includes acquiring seismic data over a selected region of the Earth's subsurface. Seismoelectric data are acquired over a selected region of the Earth's subsurface. Electroseismic data are also acquired over a selected region of the Earth's subsurface. At least one type of electromagnetic survey data is acquired over a selected region of the Earth's subsurface. Survey volumes of the seismic data, the seismoelectric data, the electroseismic data and the electromagnetic data are matched, and a model of the Earth's subsurface is generated that accounts for all of the seismic data, the seismoelectric data, the electroseismic data and the electromagnetic data.

Abstract: A method for determining spatial distribution of resistivity of Earth formations surrounding a wellbore having a conductive pipe therein includes measuring resistivity of the Earth formations using measurements of current leakage along the pipe at selected axial positions. Electromagnetic properties of the Earth formations are measured from within the pipe. The measurements of electromagnetic properties correspond to a larger axial distance and to a greater lateral distance than the measurements of resistivity from current leakage. The current leakage and electromagnetic measurements are jointly inverted to obtain a model of the spatial distribution.

Abstract: A method is disclosed for determining spatial distribution of resistivity of Earth formations surrounding a wellbore having a conductive pipe therein. The method includes measuring resistivity of the Earth formations using measurements of current leakage along the pipe at selected axial positions. Electromagnetic properties of the Earth formations are measured from within the pipe. The measurements of electromagnetic properties correspond to a larger axial distance and to a greater lateral distance than the measurements of resistivity from current leakage. The current leakage and electromagnetic measurements are jointly inverted to obtain a model of the spatial distribution.

Abstract: A method for controlled source electromagnetic Earth surveying includes deploying a plurality of electromagnetic sensors in a selected pattern at the top of an area of the Earth's subsurface to be surveyed. At least one of a transient electric field and a transient magnetic field is applied to the Earth in the vicinity of the sensors at a plurality of different positions. At least one of electric field amplitude and magnetic field amplitude at each of the sensors is recorded each time the transient electric field and/or magnetic field is applied. Each recording is adjusted for acquisition geometry. An image is generated corresponding to at least one sensor position using at least two stacked, adjusted recordings.

Abstract: An apparatus is disclosed for measuring formation resistivity through a conductive pipe in a wellbore. The apparatus includes a sonde adapted to be moved through the wellbore, and a plurality of voltage measurement electrodes are disposed on the sonde at spaced apart locations. At least one current source electrode is disposed on the sonde. All the electrodes are adapted to make electrical contact with the pipe. The apparatus includes a digital voltage measuring circuit controllably coupled to selected ones of the voltage measurement electrodes and digitally controlled current sources.

Abstract: A method is disclosed for determining spatial distribution of resistivity of Earth formations surrounding a wellbore having a conductive pipe therein. The method includes measuring resistivity of the Earth formations using measurements of current leakage along the pipe at selected axial positions. Electromagnetic properties of the Earth formations are measured from within the pipe. The measurements of electromagnetic properties correspond to a larger axial distance and to a greater lateral distance than the measurements of resistivity from current leakage. The current leakage and electromagnetic measurements are jointly inverted to obtain a model of the spatial distribution.

Abstract: An apparatus is disclosed for measuring formation resistivity through a conductive pipe in a wellbore. The apparatus includes a sonde adapted to be moved through the wellbore, and a plurality of voltage measurement electrodes are disposed on the sonde at spaced apart locations. At least one current source electrode is disposed on the sonde. All the electrodes are adapted to make electrical contact with the pipe. The apparatus includes a digital voltage measuring circuit controllably coupled to selected ones of the voltage measurement electrodes.

Abstract: An electromagnetic induction logging method is disclosed. The method includes measuring electromagnetic induction response in earth formations surrounding a wellbore. The measuring is performed on an electrically conductive sonde support. The measured response is deconvolved with respect to a response of an instrument not having an electrically conductive sonde support.

Abstract: An electromagnetic induction logging instrument is disclosed, which includes an electrically conductive support. At least one magnetic dipole transmitter antenna is disposed on the support. At least one magnetic dipole receiver antenna is disposed on the support and is axially spaced apart from the position of the transmitter antenna. The instrument includes a magnetically permeable shield disposed between the support and the transmitter and receiver. The shield extends substantially the distance between the transmitter and receiver. A measurement while drilling instrument is also disclosed, including an electrically conductive collar, at least one transmitter antenna disposed at a selected position on the collar and at least one receiver antenna disposed on the collar axially spaced apart from the transmitter antenna. A magnetically permeable shield is disposed between the collar, and the transmitter and receiver, and extends substantially the distance between the transmitter and receiver.

Abstract: A method is disclosed for monitoring a reservoir. The method includes making a first set of electromagnetic measurements at locations along the Earth's surface, making a first measurement from at least one sensor disposed proximate the reservoir in a wellbore and determining an initial Earth model from the first electromagnetic and first sensor measurements. The initial Earth model include a fluid contact. At selected times, the sensor and electromagnetic measurements are repeated and a spatial distribution of the fluid contact is determined from the repeated measurements.

Abstract: A method is disclosed for generating an image of earth formations penetrated by a wellbore. The method includes generating an initial model of the earth formations using formation resistivity measured by a direct current signal. A response to the initial model of an instrument used to make the direct current resistivity measurements is calculated. The calculated response is compared to the measurements of resistivity. The model is adjusted, and the calculating and comparing are repeated until a difference between the calculated response and measurements reaches a minimum. The adjusted model is refined based on resistivity measurements made using an electromagnetic measuring instrument, and the refined model is constrained using acoustic velocity measurements.

Abstract: A method is disclosed for generating an image of earth formations penetrated by a wellbore. The method includes generating an initial model of the earth formations using formation resistivity measured by a direct current signal. A response to the initial model of an instrument used to make the direct current resistivity measurements is calculated. The calculated response is compared to the measurements of resistivity. The model is adjusted, and the calculating and comparing are repeated until a difference between the calculated response and measurements reaches a minimum. The adjusted model is refined based on resistivity measurements made using an electromagnetic measuring instrument, and the refined model is constrained using acoustic velocity measurements.