The subject matter hereof is related to the subject matter of U.S. Pat. No. 4,061,389 and is directed specifically to the improvement that promotes effective connection of a pull tool to a down hole object or fish and simple and effective disconnection of the pull tool from the article if such is desired.
During drilling operations, well servicing operations and the like, objects may become lost or stuck within a well bore and these objects are typically referred to in the industry as "fish." For example, a section of drill pipe or production tubing might become disconnected from a pipe string and it is then necessary to introduce a pull tool into the well bore, establish connection with the fish and then remove the fish. Many different types of pull tools, grap pling devices, spears, etc. have been developed for the purpose of conducting fishing operations in well bores. It is typical for wire line operations to be utilized for the purpose of introducing a pull tool into the well bore for fishing operations.
In many cases, down hole devices are positioned within casing and tubing strings for the purpose of controlling well operations. In most cases, such down hole devices are equipped with API Standard fishing necks which normally include an undercut shoulder to enable grappling by standard installation and retrieval tools. Quite often the API Standard fishing neck will become corroded or eroded by well conditions to the point that only a stub pipe is exposed without the usual undercut shoulder that is provided on the fishing neck. Connection between a wire line controlled fishing tool and a worn fishing neck may be accomplished by means of an overshot type grappling device generally defined by a collet structure having internal teeth that establish a gripping relation with the worn fishing neck. Although overshot type retrieving tools are successfully utilized in many cases, a common problem with such tools is the inability of the operator to achieve disconnection from the worn fishing neck in the event the tool is unable to accomplish an effective pulling operation. Occasionally, disconnection can be achieved by a substantial jarring or other violent mechanical movement, but, in some cases, disconnection of the pulling tool from the fish is extremely difficult if not impossible. In cases where the pulling tool or wire line is inadequate for the pulling operations that are required, it is necessary that the pulling tool be disconnected from the fish and replaced with a wire line controlled pulling tool of substantially greater pulling capacity. If a light-weight wire line pulling tool is unable to accomplish the pulling operation and becomes firmly fixed to the fish or other object to be pulled, retrieval of the fishing equipment itself obviously compounds the problem and adds materially to the expense of the service operation.
As mentioned above, application of shocks to the pulling tool will sometimes result in disconnection, thereby enabling service personnel to remove the wire line pulling tool and substitute a tool and wire line of substantially heavier gauge. Application of mechanical shocks to the down hole equipment of the well and the wire line tool itself can easily cause failure or excessive wear of one or more of these mechanical components. It is desirable, therefore, to provide down hole service equipment, such as wire line controlled pulling tools, that will effectively become interconnected with down hole objects such as wire line tools, fish, etc., and, in the event disconnection is necessary, will readily become disconnected upon simple mechanical movement of a wire line controlled pulling tool.