Practice and analysis of mechanical principles for the down hole exiting of the sliding block spear

On the basis of sliding block spear application experiences for many years, according to stress analysis on the sliding block and spear rod in fishing situation, the functional relation formula between the acting force of the fish cavity wall to the sliding block and the pull of drilling tools to fishing spear is presented. And the functional relation formula between the torque caused by the tangential friction of the fish cavity wall to the sliding block and the pull of drilling tools to fishing spear is also obtained when back-off or spear exiting. Through the above analysis, we come to the conclusion that the pressure and tangential friction of the fish cavity wall to the sliding block could be decreased by reducing the spear tension followed by downsizing of the static friction torque which illustrates the mechanical principles for the down hole exiting of the sliding block spear. This paper gives a brief introduction of the method and proposal on the down hole exiting about sliding block spear.