Formation damage is an impairment to a reservoir caused by wellbore fluids. This happens when drilling and during workover operations. This is typically the result of an invasion by a foreign fluid into a reservoir rock. Operational changes are necessary to minimize the amount of formation damage that occurs. When formation damage does occur, it becomes necessary to use a pulling unit.

Saturation Changes

One reason for formation damage is saturation changes. When mud filtrate enters the reservoir, this changes the water saturation and can lead to a reduction in production. High fluid loss can lead to an increase in water saturation, which can also lead to a decrease in rock permeability. 

Solids Plugging

Solids plugging is another problem for a wellbore. The reservoir rock pore spaces can become plugged by fine solids found in the mud filtrate or in the solids that have been dislodged by the rock matrix. 

Clay-Particle Swelling

Clay-particle swelling is a problem when drilling into sandstone that has water-sensitive clay. Freshwater invades the reservoir rock and causes the clay to swell. This restricts or blocks throat areas.

Using a Pulling Unit

The pulling unit removes the casing and other components that are inside the wellbore. It removes the drilling rods that are found inside the wellbore. The wellbore can show signs of internal damage in various ways, such as there being a leak or a sudden drop in pressure.

Benefits of Using Pulling Units 

When taking formation damage into account and using pulling units, you can dramatically improve the productivity of a well. The wellbore might be experiencing production problems, and you will not be able to correct the problem by any other means.

Types of Pulling Units

The type of pulling unit used to perform repairs can vary depending on the use of the unit. Some units are vertical and telescope upward after they are connected to the instruments in the wellbore. Others are shaped like a wheel and are attached to a pump system.

What each has in common is that it is designed to pull out the well or pumping system while eliminating the need to dig, which would destroy the surface and also be more expensive. Fortunately, pulling systems are portable and can be moved to the location where they will be used. They are often mounted to the back of a truck so that they can be easier to move. 

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