A system and techniques for detecting near-subsurface voids in the earth use a controlled source electromagnetic transmitter and a plurality of controlled source electromagnetic receivers. Signals received by the plurality of controlled source electromagnetic receivers corresponding to signals generated by the controlled source electromagnetic transmitter are analyzed. Bi-static doublets detected in the received signals are used to identify the location of the near-subsurface voids.

Disclosed are methods and apparatus for electromagnetic surveying using dynamically-selected source waveforms. In accordance with an embodiment of the invention, a source waveform is adapted by dynamically selecting a source waveform from the set of pre-calculated waveform sequences. The dynamic selection of the source waveform may depend on a measured background noise level. Other embodiments, aspects, and features are also disclosed.

A vertical bipole source in a borehole generates a vertical bipole flow. The vertical bipole flow generates mutually orthogonal time-domain B-field data. Magnetic receivers at a surface location receive the time-domain B-field data and determine elements of a hydrocarbon reservoir using a 3D EM inversion technique. The vertical bipole source may extend into the borehole or be a virtual bipole source located at a surface location above a reservoir.

There is described apparatus for orienting at least one electromagnetic field sensor, a related receiver unit and method of use. The apparatus has an orientation detector having an output which is dependent upon an orientation of the electromagnetic field sensor, an actuator and a controller which is arranged in communication with the orientation detector and the actuator, the controller being configured to be operable to generate at least one instruction for operating the actuator for moving the electromagnetic field sensor into a predefined orientation, in dependence upon the output from the orientation detector.

A method for collecting and processing the tensor artificial-source electromagnetic signal data and a device thereof; the method comprising the steps of: step S1: determining an electric field polarization direction in a measuring area, and arranging electromagnetic field sensors according to the electric field polarization direction in the measuring area, step S2: respectively collecting artificial-source electromagnetic field signals and natural-field-source electromagnetic field signals, step S3: respectively Fourier-transforming the collected electromagnetic field signals, thereby obtaining the electromagnetic field values corresponding to the artificial source, and the collected electromagnetic field signals corresponding to n groups of natural sources, step S4: calculating to obtain the underground tensor impedances according to the electromagnetic field values corresponding to the artificial source and the electromagnetic field signals corresponding to n groups of natural sources that are obtained based on the least square method, step S5.

A calibration method includes determining calibration standards for a reference tool including a reference transmitter and a reference receiver. First and second calibration factors are measured to match a receiver on an electromagnetic measurement tool (the tool to be calibrated) to the reference receiver and to match a transmitter on the electromagnetic measurement tool to the reference transmitter. The electromagnetic measurement tool is deployed in a subterranean wellbore and used to make electromagnetic measurements therein. The measured first and second calibration factors and at least one of the calibration standards are applied to at least one of the electromagnetic measurements to compute a gain calibrated electromagnetic measurement.

A method for collecting and processing the tensor artificial-source electromagnetic signal data and a device thereof; the method comprising the steps of: step S1: determining an electric field polarization direction in a measuring area, and arranging electromagnetic field sensors according to the electric field polarization direction in the measuring area, step S2: respectively collecting artificial-source electromagnetic field signals and natural-field-source electromagnetic field signals, step S3: respectively Fourier-transforming the collected electromagnetic field signals, thereby obtaining the electromagnetic field values corresponding to the artificial source, and the collected electromagnetic field signals corresponding to n groups of natural sources, step S4: calculating to obtain the underground tensor impedances according to the electromagnetic field values corresponding to the artificial source and the electromagnetic field signals corresponding to n groups of natural sources that are obtained based on the least square method, step S5:

Disclosed is a three-dimensional directional transient electromagnetic advanced detection device, wherein the CPU and the bus communication end of the transient electromagnetic transmitting module are both connected to the system bus, the signal output end of the transient electromagnetic transmitting module is connected to the transient electromagnetic transmitting coil outside the borehole to be detected, the signal input end of the electromagnetic signal receiving module is connected to the signal output ends of the three-dimensional magnetic field sensor and the one-dimensional Z-directional electric field sensor, the signal output end of the electromagnetic signal receiving module is connected to the electromagnetic signal input end of the SCM, the communication end of the first memory is connected to the data storage end of the SCM, the communication end of the three-dimensional electronic compass is connected to the compass signal communication end of the SCM, the host data communication of the SCM is connected to the second optical cable port of the local host through the first optical cable port and the optical cable. The device can detect harmful geological bodies such as aquifer and water-conducting channels and make a intensive and effective detection forecast.

Disclosed is a three-dimensional digital virtual imaging device for stratigraphic texture of borehole core, wherein the probe depth counting pulley is mounted on the lifting wire frame, the output shaft of the motor is configured to drive the reel to rotate, and one end of the cable is connected to the cable transfer node of the retractable reel, the signal input end of the borehole imaging trajectory measuring probe of the on-site imaging host is electrically connected to one end of the cable through the cable transfer node of the retractable reel, the cable is wound on the retractable reel, a retractable line is controlled by the retractable reel, the cable is extended and retracted on the probe depth counting pulley, the probe depth counting pulley records the length of the retractable line of the cable, the depth feedback signal output end of the depth counting pulley is connected to the depth feedback signal input end of the on-site imaging host, the motor control signal output end of the on-site imaging host is connected to the control signal input end of the motor, and the signal output end of the borehole imaging trajectory measuring probe is connected to the other end of the cable. It can automatically generate borehole video, two-dimensional digital virtual borehole core image and 3D borehole trajectory in real time.

A system for near-surface geophysical subsurface imaging for detecting and characterizing subsurface heterogeneities comprises an instrument that outputs probing electromagnetic signals through a ground surface that interact and are affected by scattered signals of acoustic waves that travel through the ground surface and further senses vibrational modes of a subsurface below the ground surface; an imaging device that dynamically generates a time sequence of images of properties of the acoustic waves and maps elastic wave fields of the acoustic waves; and a processor that analyzes dynamic multi-wave data of the images to quantify spatial variations in the mechanical and viscoelastic properties of the subsurface.