A method of removing material from a target is described. The method comprises the steps of providing a tool, the tool having at least one propellant source; pressurising the tool to a pressure higher than the environmental pressure; igniting at least one of the propellant source(s) to form a combustion zone; and directing combustion products generated at the combustion zone along at least one tool flow path. The tool flow path(s) is selectively openable or closable, such that upon exiting the tool flow path(s) the combustion products interact with a target, the interaction causing material to be removed from the target.

A rotary actuator assembly can include a fluid motor with a rotor that displaces with hypocyclic precessional motion within a stator in response to fluid flow through the fluid motor, and a gear reducer section including an input gear that is fixed relative to the rotor and displaces with the hypocyclic precessional motion relative to an output gear. Another rotary actuator assembly can include a fluid motor with a rotor having a central longitudinal axis that rotates about a central longitudinal axis of a stator, and a gear reducer section including an input gear that rotates with the rotor and displaces relative to an output gear, and the input gear having the same central longitudinal axis as the rotor. A well system can include at least two fluid motors, and fluid flow through one fluid motor causes rotation of the other fluid motor in the well.

A tool for cleaning out the lower end of a cased wellbore having an installed production string. The tool is lowered down the production string until it projects from an end of the production string and into the wellbore. High pressure fluid is then sprayed from the tool’s fluid openings into nearby portions of the wellbore. Once cleaning operations are complete, the tool is carried back to the ground surface using subterranean fluid pressure.

A tool for cleaning out the lower end of a cased wellbore having an installed production string. The tool is lowered down the production string until it projects from an end of the production string and into the wellbore. High pressure fluid is then sprayed from the tool’s fluid openings into nearby portions of the wellbore. Once cleaning operations are complete, the tool is carried back to the ground surface using subterranean fluid pressure.

A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A method and apparatus for casing recovery in which a clean-up of the inside of the outer casing above the inner casing is performed on the same trip in the wellbore as cutting and pulling a section of the inner casing. A bottom hole assembly including a spear, a casing cutter and at least one clean-up tool is described. An embodiment of a clean-up tool being a jetting sub which can jet fluid radially to wash the outer casing and selectively allow fluid to pass through the sub at different pressures is described. The jetting sub can be used to control operation of other tools in the bottom hole assembly such as the casing cutter and a hydraulic jack.

A method and apparatus for casing recovery in which a clean-up of the inside of the outer casing above the inner casing is performed on the same trip in the wellbore as cutting and pulling a section of the inner casing. A bottom hole assembly including a spear, a casing cutter and at least one clean-up tool is described. An embodiment of a clean-up tool being a jetting sub which can jet fluid radially to wash the outer casing and selectively allow fluid to pass through the sub at different pressures is described. The jetting sub can be used to control operation of other tools in the bottom hole assembly such as the casing cutter and a hydraulic jack.

A method of positioning a bottom hole assembly in a wellbore includes lowering the bottom hole assembly into the wellbore. The bottom hole assembly has a whipstock, a downhole tool, and a cleaning tool having a cleaning element. The method also includes cleaning at least a portion of a wall of the wellbore using the cleaning tool, and activating the downhole tool to engage the cleaned portion of the wall.

A variety of methods, systems, and compositions are disclosed, including, in one embodiment, a method of servicing a borehole including providing a borehole servicing fluid in a borehole penetrating a subterranean formation, wherein the borehole servicing fluid includes a nucleophilic organic molecule and an electrophile. The method further may include reacting the nucleophilic organic molecule and the electrophile to generate at least an acidic species. The method further may include contacting an acid-soluble component in the subterranean formation with the acidic species such that the acidic species degrades the acid-soluble component.

A variety of methods, systems, and compositions are disclosed, including, in one embodiment, a method of servicing a borehole including providing a borehole servicing fluid in a borehole penetrating a subterranean formation, wherein the borehole servicing fluid includes a nucleophilic organic molecule and an electrophile. The method further may include reacting the nucleophilic organic molecule and the electrophile to generate at least an acidic species. The method further may include contacting an acid-soluble component in the subterranean formation with the acidic species such that the acidic species degrades the acid-soluble component.