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.

A method includes drilling a borehole in a seafloor with a drill bit coupled to an end of a drill string extended from a drilling rig, emitting seismic energy from the drill bit as the drill bit advances to extend the borehole, deploying a plurality of autonomous underwater vehicles (AUVs) on the seafloor in a first geometry relative to the borehole, each AUV including a seismic receiver, and receiving the seismic energy emitted from the drill bit with the seismic receiver of each AUV.

A method includes drilling a borehole in a seafloor with a drill bit coupled to an end of a drill string extended from a drilling rig, emitting seismic energy from the drill bit as the drill bit advances to extend the borehole, deploying a plurality of autonomous underwater vehicles (AUVs) on the seafloor in a first geometry relative to the borehole, each AUV including a seismic receiver, and receiving the seismic energy emitted from the drill bit with the seismic receiver of each AUV.

Embodiments related to addition of a variable mass load to the shell of a marine vibrator to compensate for air spring effects. An embodiment provides a marine vibrator, comprising: an outer shell; a driver disposed at least partially within the outer shell and coupled thereto; and a mass load coupled to an exterior surface of the outer shell; wherein the marine vibrator has a resonance frequency selectable based at least in part on the mass load.

Embodiments related to addition of a variable mass load to the shell of a marine vibrator to compensate for air spring effects. An embodiment provides a marine vibrator, comprising: an outer shell; a driver disposed at least partially within the outer shell and coupled thereto; and a mass load coupled to an exterior surface of the outer shell; wherein the marine vibrator has a resonance frequency selectable based at least in part on the mass load.

A system includes a mobile vehicle including a geolocator and an active acoustic source configured to generate acoustic wave energy directed toward a fiber optic network that includes one or more fiber optic cables and a distributed acoustic sensing (DAS) interrogator communicably coupled to the one or more fiber optic cables; and a control system. The control system is configured to perform operations including acquiring a signal from the DAS interrogator in response to the acoustic wave energy generated from the active acoustic energy source during movement of the mobile vehicle on or above the terranean surface; determining a geolocation of the mobile vehicle from the geolocator during or subsequent to acquisition of the signal from the DAS interrogator; and determining a location of the at least one fiber optic cable based on the determined geolocation of the mobile vehicle during acquisition of the signal from the DAS interrogator.

A system includes a mobile vehicle including a geolocator and an active acoustic source configured to generate acoustic wave energy directed toward a fiber optic network that includes one or more fiber optic cables and a distributed acoustic sensing (DAS) interrogator communicably coupled to the one or more fiber optic cables; and a control system. The control system is configured to perform operations including acquiring a signal from the DAS interrogator in response to the acoustic wave energy generated from the active acoustic energy source during movement of the mobile vehicle on or above the terranean surface; determining a geolocation of the mobile vehicle from the geolocator during or subsequent to acquisition of the signal from the DAS interrogator; and determining a location of the at least one fiber optic cable based on the determined geolocation of the mobile vehicle during acquisition of the signal from the DAS interrogator.

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.

Method, source array and source element that generate seismic waves. The source element includes an enclosure having an opening covered by a piston; a local supply accumulator fluidly communicating with an interior of the enclosure, a pressure of the fluid inside the local supply accumulator being larger than a pressure of the fluid inside the enclosure; a local supply valve located between the local supply accumulator and the enclosure and configured to control a flow of the fluid from the local supply accumulator to the interior of the enclosure; and a controller configured to control the local supply valve such that the pressure inside the enclosure does not fall below a first preset value based upon an ambient pressure of the enclosure while seismic waves are generated.

Method, source array and source element that generate seismic waves. The source element includes an enclosure having an opening covered by a piston; a local supply accumulator fluidly communicating with an interior of the enclosure, a pressure of the fluid inside the local supply accumulator being larger than a pressure of the fluid inside the enclosure; a local supply valve located between the local supply accumulator and the enclosure and configured to control a flow of the fluid from the local supply accumulator to the interior of the enclosure; and a controller configured to control the local supply valve such that the pressure inside the enclosure does not fall below a first preset value based upon an ambient pressure of the enclosure while seismic waves are generated.