The disclosure provides a method for extracting gas by fracturing a coal seam through a combination of hydraulic slotting and multi-stage combustion impact wave, comprising first cutting slots in an impact borehole using a hydraulic slotting equipment to perform pressure relief and permeability enhancement on a coal seam and enlarge a N.sub.2 or CO.sub.2 storage space, then injecting a large amount of N.sub.2 or CO.sub.2 into the borehole by means of a high pressure gas cylinder and a pressure reducing valve through a gas injection and extraction pipe, then injecting a certain amount of methane and dry air into a high-temperature and high-pressure combustion chamber by means of the high pressure gas cylinder and the pressure reducing valve, so that the gases are mixed and combusted to form high-temperature and high-pressure impact wave to push a piston to compress the N.sub.2 or CO.sub.2, thereby generating a large number of factures on the coal seam around the impact borehole under guiding action of the slots. The impact wave is repeatedly generated to form a multi-stage impact, and the impact of the next stage is based on the impact of the previous stage, so that the fractures on the coal seam around the borehole are further expanded and run through. After the N.sub.2 or CO.sub.2 is compressed by means of the multi-stage impact, more fracture networks are formed on the coal seam around the borehole under the guiding action of the slots and the fractures, thereby enhancing the borehole-based efficient gas extraction.

Methods and systems for supply of fuel for a turbine-driven fracturing pump system used in hydraulic fracturing may be configured to identify when the supply pressure of primary fuel to a plurality of gas turbine engines of a plurality of hydraulic fracturing units falls below a set point, identify a gas turbine engine of the fleet of hydraulic fracturing units operating on primary fuel with highest amount of secondary fuel available, and to selectively transfer the gas turbine engine operating on primary fuel with the highest amount of secondary fuel from primary fuel operation to secondary fuel operation. Some methods and systems may be configured to transfer all gas turbine engines to secondary fuel operation and individually and/or sequentially restore operation to primary fuel operation and/or to manage primary fuel operation and/or secondary fuel operation for portions of the plurality of gas turbine engines.

An example laser tool is configured to operate within a wellbore of a hydrocarbon-bearing rock formation. The tool includes one or more optical transmission media. The one or more optical transmission media are part of an optical path originating at a laser generator configured to generate a laser beam. The one or more optical transmission media are for passing the laser beam. The tool includes a mono-optic element that is part of the optical path. The mono-optic element is for receiving the laser beam from the one or more optical transmission media and for altering at least one of a geometry or a direction of the laser beam for output to the hydrocarbon-bearing rock formation. The tool also includes one or more sensors to monitor one or more conditions in the wellbore and to output signals based on the one or more conditions.

An example laser tool is configured to operate within a wellbore of a hydrocarbon-bearing rock formation. The tool includes one or more optical transmission media. The one or more optical transmission media are part of an optical path originating at a laser generator configured to generate a laser beam. The one or more optical transmission media are for passing the laser beam. The tool includes a mono-optic element that is part of the optical path. The mono-optic element is for receiving the laser beam from the one or more optical transmission media and for altering at least one of a geometry or a direction of the laser beam for output to the hydrocarbon-bearing rock formation. The tool also includes one or more sensors to monitor one or more conditions in the wellbore and to output signals based on the one or more conditions.

Methods and systems for supply of fuel for a turbine-driven fracturing pump system used in hydraulic fracturing may be configured to identify when the supply pressure of primary fuel to a plurality of gas turbine engines of a plurality of hydraulic fracturing units falls below a set point, identify a gas turbine engine of the fleet of hydraulic fracturing units operating on primary fuel with highest amount of secondary fuel available, and to selectively transfer the gas turbine engine operating on primary fuel with the highest amount of secondary fuel from primary fuel operation to secondary fuel operation. Some methods and systems may be configured to transfer all gas turbine engines to secondary fuel operation and individually and/or sequentially restore operation to primary fuel operation and/or to manage primary fuel operation and/or secondary fuel operation for portions of the plurality of gas turbine engines.

A fracturing system can include a fracturing manifold coupled to a plurality of fracturing trees. The fracturing manifold may include adjustment joints that enable adjustment of the length of the fracturing manifold. The fracturing manifold can also include pivot joints that allow angular displacement of portions of the fracturing manifold with respect to other portions. The adjustment and pivot joints can accommodate spacing and elevation differences between the fracturing trees.

Methods and systems for supply of fuel for a turbine-driven fracturing pump system used in hydraulic fracturing may be configured to identify when the supply pressure of primary fuel to a plurality of gas turbine engines of a plurality of hydraulic fracturing units falls below a set point, identify a gas turbine engine of the fleet of hydraulic fracturing units operating on primary fuel with highest amount of secondary fuel available, and to selectively transfer the gas turbine engine operating on primary fuel with the highest amount of secondary fuel from primary fuel operation to secondary fuel operation. Some methods and systems may be configured to transfer all gas turbine engines to secondary fuel operation and individually and/or sequentially restore operation to primary fuel operation and/or to manage primary fuel operation and/or secondary fuel operation for portions of the plurality of gas turbine engines.

A well tool can include a body and at least one barrier element. The barrier element can include a pyrolytically degradable material that is positionable to block a flow of fluid across the body within a wellbore and to degrade by pyrolysis over time within the wellbore.

A well tool can include a body and at least one barrier element. The barrier element can include a pyrolytically degradable material that is positionable to block a flow of fluid across the body within a wellbore and to degrade by pyrolysis over time within the wellbore.

An energetic charge for propellant fracturing may include a propellant material or a shape of the energetic charge being selected such that a rise time of a deflagration of the energetic charge is determined to be in the propellant fracturing regime. The propellant fracturing regime may be defined by a set of linear equations associated with the rise time for pressure from the deflagration of the energetic charge. The rise time may be calculated based on an equation {dot over ()}=(dP/dt)/E, where {dot over ()} represents a strain rate, dP/dt represents a change in pressure with respect to time, and E is Young's modulus, and where the set of linear equations relate the rise time to a borehole diameter.