Production System: Packer
This post is an elaboration of the "Petroleum Production System" slide which I share in my previous post [CLICK HERE]. This explanation will fit the best if you want to present the "Petroleum Production System" slide at page 12
The main purposes of Packers in a well are to
provide structural (anchor the tubing to casing) and sealing purpose. From The
isolation and structural functions can be detailed as:
- To isolate the annulus between well and tubing so it will provide sufficient barriers or to prevent the corrosion of the well casing corrosion. The important part for the sealing is large, cylindrical rubber elements around the packer. In situations where the sealed pressure is very high (above 5,000 psi), metal rings are used on either side of the elements to prevent the rubber from extruding.
- A packer will isolate different production zones for zonal isolation. Sometimes, we could produce different fluid from different layers just by using one well. The fluid produced from a layer can be a problem if mixed with fluid from other layer, since the properties are different and there’s a possibility it will create plugging scale or solid.
- Isolate gravel and sand.
- Isolation capability from any fluid from the bottom fluid, e.g. straddle packers. It is usually used by the geologist if they miss the payzone (drill too deep) and want to do drill stem test.
A packer without a seal is called an anchor. They
have various applications:
- Prevent tubing movement. In a well which has lost its natural energy, an artificial lift should be used. Artificial lift such as sucker rod pump will make a lot of movement of the tubing, and the tubing need anchor to prevent movement
- It may also reduce associated stresses of the tubing and transfer the load to the casing.
After a logging has been done, a packer will be run
in the casing on production tubing or wireline. Packer will be run into
borehole until the determined depth is reached. The slip and rubber must be
expanded to contact the casing. There are various methods to expand the rubber
and slip. By mechanical set, slip and rubber will expand because of rotation or
upward /downward motion on the tubing. However, in completions, they are often
hydraulically set, which will use fluid pressure to drive the cone behind the
slips
The packer could be either permanent or
retrievable. The choice will depend on the future plan of the well. The
permanent packers are lower in costs and greater in sealing, but they need to
be milled to be removed. When the well is planned to be intervened in near
future, maybe recompletion or artificial lift, a retrievable packer must be
used. Even though retrievable packers generally lower sealing and gripping capabilities,
but after removal and subsequent servicing, they can be reused.
Packers are also used in Drill Stem Test. There are
3 types of packers used in Drill Stem Test:
- Straddle packer. The straddle packer requires two inflatable packers that are set by rotating the surface pipe. It is usually used to isolate the bottom and upper zone of payzone if the geologist misses the payzone when drilling.
- Standard packer. This is used more often than other methods. The packer is placed above the pay zone. Sometimes the company uses two packers above payzone in case one packer doesn’t hold. Rerunning the test will be more expensive than investing on two packers.
- Cone packer. Sometimes the well is drilled just above the payzone, then drill the core from the payzone with core bit, which is smaller in size. In that case, Drill Stem Test can be done by using cone packer. Put weight on the packer and it will seal the area over the core hole. Too make sure a good seal, a standard packer coan be used above the cone packer.
(source: Davenport, B. Handbook of Drilling Practices, Gulf Publishing Company:1984)
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