FISHING AND IT`S IMPORTANCE IN OIL FIELD INDUSTRY EPISODE 4
Last sessions we discussed the fishing tools from the view of retrieving some small junk parts But today we are going to start a new topic that is how to retrieve a part of tubing, or how To release a stuck pipes …etc.
Pipe Recover Methods – Overview
Stuck pipe is a subject no oil company or drilling contractor really likes to Discuss. This condition has existed since man first started drilling wells and Will probably continue to exist as long as drilling and workovers are in Progress. Pipe can get stuck even when all preventive measures have been Taken. Recovering stuck pipe is an expensive, discouraging, and time Consuming operation that requires special tools and services. One of the services used for recovering stuck pipe is wire line pipe Recovery. Wire line pipe recovery work has become a technical, scientific Service that requires specialized, competent and highly trained personnel. Typically, a free point and back-off or cut is used to recover the portion of Pipe that is free to allow fishing operations to proceed on the stuck portion Of the pipe.
There are several methods of separating pipe in the well bore including:
– Back offs
– Chemical cutters
– Jet cutters
– Severing tools
– Mechanical cutters.
While the wire line man will be the one determining the stuck point, making back offs, and using the chemical and jet cutters and severing tool, you will need to understand these operations in order to supervise the process. You are ultimately responsible for any fishing operation.
The method and the tool that you use will depend on the:
– Value of fish
– Location of the fish
– Type of fish
– Conditions in the hole.
First of all, what is stuck point?
The stuck point is the point at which all pipe below is stuck and all pipe above is free. The stuck point is also referred to as the free point, the ESP (estimated stuck point), and the EFP (estimated free point).
What is the purpose of determining the stuck point?
The determination of the stuck point will allow you to either back-off or cut and remove that portion of the fish that is free. While the formulas used to determine the stuck point only give an approximation of the location, you will be able to determine the correct tool sizes to use based on the section of the string that is stuck. For example, if the pipe is stuck at the BHA, you will need to use larger tools to fish with than if the pipe is stuck further up in the work string.
How to calculate it?
There are several formulas that may be used to determine the estimated freepoint for stuck pipe, including:
– Stretch formula
– Tapered string formula.
How to measure the stretch?
Both formulas listed above require a stretch measurement. In general, the smaller the stretch in the work string, the shallower the stuck point. Use the procedure below to measure stretch.
1- Pick up the weight of the drill string and mark the pipe at the top of the rotary.
2- Pull an over pull, which will vary as conditions dictate.
3- Mark the pipe a second time level with the rotary.
4- Measure the distance between the two marks. This distance in inches is the stretch in the drill string.
Feet of Free Pipe = (1,000,000 x Inches of Stretch)/ (K x Pounds of Over Pull)
For collared pipe: K = 1.4 ¸ Weight of the Pipe Per Foot.
For integral joint tubing or drill pipe: K = 1.5 ¸ Weight of the Pipe Per Foot
1- STRETCH FORMULA
The following example problem will help you to understand the stretch formula:
The packer is set at 8,000’ and you are using 2-3/8 EUE N80 tubing. The string weight is 37,600 (therefore, the weight per foot is 37,600/8,000 = 4.7). The maximum pull is 57,600 lbs (20,000 lbs. of which is over-pull). The stretch length is 48”.