General Description
Bowen manufactures the surface jar and is probably the least known of any fishing tool.
I would suggest each one of you visit a Bowen store near you and review all of their tools and be sure to ask about the Surface Jar.
The Surface Jar is a trigger or trip hammer in a sense. It is run above the rotary and can be set on the job to trip at any desired weight.
The Surface Bumper Jar is designed to be installed in the drill string at the surface during fishing operations that require downward jarring impacts against a fish at the point where it is stuck. The stroke of the tool is 48 inches. It is unique, in that, it is used only on the surface to release a stuck fish.
Use
The Surface Bumper jar may be used to great advantage where the downhole drilling, fishing, or washover running string becomes stuck, and a heavy downward force is required to release it. It is often used to free keyseated drill pipe and drill collars, and to initiate abrupt jarring impacts down the string to actuate Drilling Bumper Subs, Bumper Safety Joints, and other similar downhole bumping tools. It is also useful for transmitting very heavy downward forces to release grappling tools such as Overshots or Spears when the grapples or slips have become imbedded in the fish or have become fouled due to repeated and prolonged downhole jarring. In many instances, it has been successfully used where all previous methods have failed.
Construction
Basically, the Surface Bumper Jar consists of a Top Sub, a hexagonal Mandrel Assembly working in a Bowl Assembly, and a Bottom Sub. The length of the stroke is important, since, when using the tool, it is not necessary that the two striking surfaces meet as with conventional downhole jarring tools.
Operation
To run the Surface Jar, you have to plan the string before going in the hole. An example of how and where you would use them would be as such: Suppose you have a drill collar stuck at 5,000 feet and want to jar down with 35,000 lbs. You would start in the hole prepared to latch onto or screw into the fish. When you are far enough in the hole that you have 35,000 lbs. of you work string still out of the hole, you would put in a set of Bumper Jars in the string and continue in the hole. When you have reached the fish and have latched onto it, you put the Surface Jars in the string above the rotary and set them for approximately 40,000 lbs. Then pick up on the string. This will open the Bumper Jar down the hole. When you exceed 40,000 lbs, the Surface jars will trip, allowing the 35,000 lbs. of pipe above the Bumper Jars to fall (suddenly closing the Bumper Jars and putting downward force on the fish below).
I do not recommend extended jarring down on drill pipe, below the point of impact. This will cause the pipe to become fatigued and work in two sometimes creating a worse job than you already have.