Improved methods of providing acoustic source signals for seismic surveying, wherein a plurality of signals can be easily separated from one another after data acquisition, wherein the source signals are not sweep based.

A seismic source includes a base plate having a bottom surface contacting a surface of the ground. The coupler is connectable to the bottom surface of the base plate and projects downward from the base plate. The coupler contain soil under the base plate during operation. Another seismic source includes a base plate and at least one contact member. The base plate has an upper surface engaging the seismic source, a lower surface configured to contact a soil surface. The contact member projects from the lower surface and has a planar bottom surface with a surface area less than a surface area of the base plate lower surface.

Methods for generating boreholes used for generating geothermal energy or other purposes include forming the borehole by accelerating a projectile into contact with geologic material. Interaction between the projectile and the geologic material generates an acoustic signal, such as vibrations within the formation, that is detected using acoustic sensors along a drilling conduit, at the surface, or within a separate borehole. Characteristics of the geologic material, such as hardness, porosity, or the presence of fractures, may be determined based on characteristics of the acoustic signal. The direction in which the borehole is extended may be modified based on the characteristics of the geologic material, such as to create a borehole that intersects one or more fractures for generation of geothermal energy.

Processes and systems described herein are directed to performing marine surveys with marine vibrators that emit orthogonal coded pseudo-random sweeps. In one aspect, coded pseudo-random signals are generated based on coded pseudo-random sequences. The coded pseudo-random sequences are used to activate the marine vibrators in a body of water above a subterranean formation. The activated marine vibrators generate orthogonal coded pseudo-random sweeps. A wavefield emitted from the subterranean formation in response to the orthogonal coded pseudo-random sweeps is detected at receivers located in a body of water. Seismic signals generated by the receivers may be cross-correlated with a signature of one of the orthogonal coded pseudo-random sweeps to obtain seismic data with incoherent residual noise.

A survey method includes generating a first amplitude modulation signal by amplitude-modulating a carrier wave repeating the same pattern at a predetermined cycle in each of a plurality of vibrators with a modulation signal whose cycle is 1/m times the predetermined period and is different for each of the vibrators, transmitting the seismic wave based on the first amplitude modulation signal, generating a second amplitude modulation signal in one or more receivers, the second amplitude modulation signal being identical to the first amplitude modulation signal generated by any one of the seismic vibrators, generating a reception signal in each of the one or more receivers by receiving a synthetic seismic wave in which the seismic waves generated by the seismic vibrators are synthesized, calculating a correlation value between the reception signal and the second amplitude modulation signal, and analyzing characteristics of the medium on the basis of the correlation value.

Methods of designing seismic survey and acquisition of seismic data with reduced noise using equally or optimally irregularly spaced sources or receivers are described. Specifically, prime number ratios for the station to line spacing is used to prevent harmonic leakage and other noise contaminations in the acquired seismic data.

Methods and systems for characterizing fractures in a subterranean formation are provided. The method includes introducing an encapsulated explosive unit into a casing located in a wellbore within the subterranean formation and maintaining the encapsulated explosive unit in a stage of the casing. The method also includes detonating the encapsulated explosive unit within the stage to generate a pressure wave that passes through a group of perforations and into the fractures and measuring a reflected pressure wave using a pressure sensor coupled to the bridge plug to produce a pressure measurement. The method further includes converting the pressure measurement into an acoustic signal correlated with the pressure measurement by an acoustic signal generator contained in the bridge plug and transmitting the acoustic signal to apply acoustic pressure on a fiber optic cable coupled to an exterior surface of the casing.

Methods and systems for characterizing fractures in a subterranean formation are provided. The method includes introducing an encapsulated explosive unit into a casing located in a wellbore within the subterranean formation and maintaining the encapsulated explosive unit in a stage of the casing. The method also includes detonating the encapsulated explosive unit within the stage to generate a pressure wave that passes through a group of perforations and into the fractures and measuring a reflected pressure wave using a pressure sensor coupled to the bridge plug to produce a pressure measurement. The method further includes converting the pressure measurement into an acoustic signal correlated with the pressure measurement by an acoustic signal generator contained in the bridge plug and transmitting the acoustic signal to apply acoustic pressure on a fiber optic cable coupled to an exterior surface of the casing.

Embodiments relate to relate to marine vibrators that incorporate one or more piston plates that act on the surrounding water to produce acoustic energy. An example marine vibrator may comprise: a containment housing; a piston plate; a fixture coupled to the containment housing; a mechanical spring element coupled to the piston plate and the fixture; a driver disposed in the marine vibrator, wherein the driver is coupled to the piston plate and the fixture; and a container coupled to the piston plate, wherein the container is configured to hold a variable mass load; wherein the marine vibrator has a resonance frequency selectable based at least in part on the variable mass load.

Embodiments relate to relate to marine vibrators that incorporate one or more piston plates that act on the surrounding water to produce acoustic energy. An example marine vibrator may comprise: a containment housing; a piston plate; a fixture coupled to the containment housing; a mechanical spring element coupled to the piston plate and the fixture; a driver disposed in the marine vibrator, wherein the driver is coupled to the piston plate and the fixture; and a container coupled to the piston plate, wherein the container is configured to hold a variable mass load; wherein the marine vibrator has a resonance frequency selectable based at least in part on the variable mass load.