Causes and methods of freeing differential pipe stuck

Methods and procedures for freeing stuck differential pipe.
There are several methods and procedures for freeing differential pipe stuck when sticking pipe occur. The first available and the most effective method is freeing stuck pipe mechanically. Freeing Stuck Pipe Mechanically. Jarring is the process of impacting the stuck part of the drill string with a high force impulse. Drilling jars can be hydraulic or mechanical and with double (up-down) operating feature to impart a larger impact force toward stuck part of drill string. Jarring operation should be started soon after the pipe became stuck, as the chance of successfully releasing the pipe decreases over time since the contact area between the pipe and the filter cake increases. While jarring down, additional torque might be used for maximum efficiency. In general, jarring should be stopped if it is ineffective within the first few hours. The only exception is if large volumes of spotting fluids are displaced in the annulus to the stuck area.
Freeing Stuck Pipe with Spotting Fluids. In the majority of cases, some type of spotting fluid is mixed while the jarring process. If the initial jarring is ineffective in freeing the pipe, to accelerate process the drilling fluid in the annulus at the stuck area must be displaced by a different fluid and the technique known as spotting. Spotting fluids contribute to the freeing process by lubricating the pipe-cake contact area. Determining the depth of the stuck zone is a critical step in this process. Surveys can be conducted, but such operations take quite a long time. In most vertical wells the pipe-stretch method is the convenient technique to define stuck point. Its accuracy is also sufficient, and several m³ of spotting fluid can be pumped while the method is being implemented. By applying overpull on the stuck pipe and measuring the pipe-stretch with different loads stuck point can be calculated easily. Usually, the cause of unsuccessful freeing procedures is the insufficient volumes of spotting fluids. The lessons learned shows that, spotting pretty enough fluid to reach all exposed permeable zones and with a volume remain in the drill pipe to establish annular movement at predetermined period may improve the freeing process. After spotting, the required time for releasing pipe depend on the mud-displacement efficiency, mud properties, differential pressure, pipe-to-hole geometry as well as length of contact area.