Abstract: A jar provided with an adjustable preload has a housing defining an anvil surface and a mandrel, movable relative to the housing under an applied load, defining a hammer surface to impact the anvil surface. A trigger mechanism for releasing the mandrel to cause the hammer surface to impact the anvil surface includes a trigger sleeve axially positioned with the housing and a collet that engages the mandrel during application of a load to the mandrel. The collet releases the mandrel to cause the hammer surface to impact the anvil surface upon being moved into registration with the trigger sleeve against the resistance of a biasing spring disposed within the housing. The preload is adjusted by an adjustment mechanism carried by the housing and coupled to the biasing spring. The adjustment mechanism includes an adjustment mandrel disposed between an end of the upper housing section and an end of the lower housing section. The adjustment mandrel is axially movable relative to the upper and lower housing sections.

Abstract: A downhole tool is provided that creates balancing forces that allow a tool such as ajar to continue to function when intrusion of gas into the fluid chamber of the jar occurs to cause gas pressure in the jar to exceed hydrostatic pressure. The excess pressure is balanced by forming an area acted on by the gas pressure equal to the cross-sectional area of the mandrel, such that the forces on the mandrel are equal and opposite.

Abstract: Method and apparatus are provided for pumping operations that may be used to form perforations in the casing of a well, clean perforations and drill drain holes through perforations. A plunger is placed in a reference perforation and the pumping operations may be performed through a nozzle at a known location with respect to the reference perforation. The nozzle may be attached to a flexible hose to drill a drain hole or may be inserted in a body on the bottom of a tubing string. Addition apparatus and method are provided to insure that the plunger or plungers are maintained in a reference perforation or perforations when pumping operations are carried out through tubing.