Abstract: A hydraulic drill string jar is powered and actuated by drilling fluid pressure controlled from the earth surface. By selective manipulation of drilling fluid flow, the jar can be conditioned to operate in drilling mode to avoid activation of the jars while normal drilling and fluid flow activities take place. By different fluid flow manipulations, the jar is conditioned to operate in the jarring mode. In the jarring mode, the jars will axially shock the drill string each time the flow rate is reduced below a preselected amount and then increased to a higher preselected amount.

Abstract: A column of drill collars have holes or jets extending radially from the collar bore through the collar wall. A wash pipe extends full length through the bore of the perforated collars, so sized as to leave an annular flow space between the wash pipe and the collar bore wall. A remote control selector valve is situated such as to receive drilling fluid from the upwardly continuing drill string and direct the fluid through the wash pipe to the drill bit for regular drilling, or on cue from the earth surface, direct fluid to the annulus to be expelled through the drill collar perforations to help free stuck pipe or to prevent such sticking.