An explosive system for fracturing an underground geologic formation adjacent to a wellbore can comprise a plurality of explosive units comprising an explosive material contained within the casing, and detonation control modules electrically coupled to the plurality of explosive units and configured to cause a power pulse to be transmitted to at least one detonator of at least one of the plurality of explosive units for detonation of the explosive material. The explosive units are configured to be positioned within a wellbore in spaced apart positions relative to one another along a string with the detonation control modules positioned adjacent to the plurality of explosive units in the wellbore, such that the axial positions of the explosive units relative to the wellbore are at least partially based on geologic properties of the geologic formation adjacent the wellbore.

An arrangement has an opto-pyrotechnic initiator, at least one laser, and an optical fibre, via which the laser radiation of the laser is guided to the opto-pyrotechnic initiator. Also disclosed is a method for improving the safety of such an opto-pyrotechnic initiator. At least one optical filter element having power-dependent or intensity-dependent transmission or reflection is arranged in the beam path of the laser radiation between the laser and the initiating impingement location of the laser radiation in the initiator. The filter element and the beam guidance for the laser radiation are selected such that for a laser power of the laser, that is intended to effect an initiation, the filter element has a higher transmission or reflection or can be switched to a higher transmission or reflection than for a lower laser power by application of an optical or electronic signal that is independent of the laser radiation.

An arrangement has an opto-pyrotechnic initiator, at least one laser, and an optical fibre, via which the laser radiation of the laser is guided to the opto-pyrotechnic initiator. Also disclosed is a method for improving the safety of such an opto-pyrotechnic initiator. At least one optical filter element having power-dependent or intensity-dependent transmission or reflection is arranged in the beam path of the laser radiation between the laser and the initiating impingement location of the laser radiation in the initiator. The filter element and the beam guidance for the laser radiation are selected such that for a laser power of the laser, that is intended to effect an initiation, the filter element has a higher transmission or reflection or can be switched to a higher transmission or reflection than for a lower laser power by application of an optical or electronic signal that is independent of the laser radiation.

An explosive assembly includes a first explosive unit having a first longitudinal end portion having a first mechanical coupling feature, a second explosive unit having a second longitudinal end portion having a second mechanical coupling feature, and a tubular connector having a first end portion mechanically coupled to the first mechanical coupling feature and a second end portion mechanically coupled to the second mechanical coupling feature, such that the first explosive unit, the connector, and the second explosive unit are connected together end-to-end along a common longitudinal axis. Each explosive unit can contain a high explosive material and a detonator, and the connector can comprise a detonation control module electrically coupled to the detonators and configured to detonate the explosive units.

An explosive assembly includes a first explosive unit having a first longitudinal end portion having a first mechanical coupling feature, a second explosive unit having a second longitudinal end portion having a second mechanical coupling feature, and a tubular connector having a first end portion mechanically coupled to the first mechanical coupling feature and a second end portion mechanically coupled to the second mechanical coupling feature, such that the first explosive unit, the connector, and the second explosive unit are connected together end-to-end along a common longitudinal axis. Each explosive unit can contain a high explosive material and a detonator, and the connector can comprise a detonation control module electrically coupled to the detonators and configured to detonate the explosive units.

An initiator apparatus (IA) for blasting, the apparatus including: a magnetic receiver for receiving a magnetic communication signal through the ground by detection of a magnetic field; a controller, in electrical communication with the magnetic receiver, for processing the magnetic communication signal to determine a command for blasting; and a light source in electrical communication with the controller for generating a light beam to initiate a light-sensitive explosive (LSE) in accordance with the command.

An initiator apparatus (IA) for blasting, the apparatus including: a magnetic receiver for receiving a magnetic communication signal through the ground by detection of a magnetic field; a controller, in electrical communication with the magnetic receiver, for processing the magnetic communication signal to determine a command for blasting; and a light source in electrical communication with the controller for generating a light beam to initiate a light-sensitive explosive (LSE) in accordance with the command.

An optical initiator of a pyrotechnic charge, including: a body including a cavity, which contains the pyrotechnic charge and a mechanism for igniting the charge by absorption of a laser radiation, the ignition mechanism being placed in contact with the charge; a laser radiation source; an optical fiber for transporting laser radiation from the source to the ignition mechanism. The ignition mechanism includes a metal plate and the metal plate and the laser radiation source are configured for a laser radiation issuing from the laser radiation source to be absorbed by the metal plate and converted into thermal energy, so that thermal conduction of the thermal energy from the metal plate to the pyrotechnic charge causes the ignition of the pyrotechnic charge. The metal plate can include perforations arranged periodically.

An optical initiator of a pyrotechnic charge, including: a body including a cavity, which contains the pyrotechnic charge and a mechanism for igniting the charge by absorption of a laser radiation, the ignition mechanism being placed in contact with the charge; a laser radiation source; an optical fiber for transporting laser radiation from the source to the ignition mechanism. The ignition mechanism includes a metal plate and the metal plate and the laser radiation source are configured for a laser radiation issuing from the laser radiation source to be absorbed by the metal plate and converted into thermal energy, so that thermal conduction of the thermal energy from the metal plate to the pyrotechnic charge causes the ignition of the pyrotechnic charge. The metal plate can include perforations arranged periodically.

In accordance with embodiments of the present disclosure, systems and methods for triggering detonation of a perforating gun via optical signals are provided. An improved laser firing head may be used with an optical cable (e.g., fiber optic cable) run through the wellbore to trigger detonation of a perforating gun in response to an optical signal. The laser firing head may be activated, and the perforating gun fired, upon the application of an optical signal output from the surface and transmitted through the optical cable. The disclosed system using the laser firing head with the optical cable may be impervious to electrical interference, since the laser firing head may only fire the perforating gun when a properly modulated laser or light source is directed down the optical cable for a specific period of time.