Cement Plugs Oilfield Glossary

Cement Plugs

Cement Plugs Oilfield Glossary
The main functions of cement plugs are,below
 Separate mud from cement
 Wipe the casing from mud before cement is pumped and then wipe casing from the cement -
.film after the complete volume of cement is pumped
.Prevent over-displacement of cement -
.Give surface indication that cement placement is complete -
.Allow the casing to be pressure tested -
In effect, the cement plugs act as barriers between mud and cement providing
 physical separation between the two fluids. Bad cement jobs, especially around the casing shoe, result from cement contaminated with mud

Stop Collars

The stop collar serves as a stop to any cementing aid that is attached to the outside of the
.casing. It is available in various designs for standard and slim hole clearance

 Multi-Stage Collar

A multi-stage collar (or DV tool) is used to allow the casing to be cemented in two stages to
prevent weak formations being subjected to excessive hydrostatic pressure of long cement
columns.The tool is actually a small section of casing with the same strength properties as
the remaining string. The tool has two internal sleeves and openings which are covered by
the  lower  sleeve,  Figure  below The  lower  sleeve  is  opened  by  dropping  a  bomb  which
 pushes the sleeve down and uncovers the holes
. This allows the cement to be pumped through the
casing and the holes in the stage collar and placed around the casing. When the required
volume of cement is pumped, the holes are closed by dropping a closing plug which pushes
.an upper sleeve downward to cover the holes in the stage collar

:Multi-stage cementing is used to

. Reduce total pumping pressure or pumping time - 
. Reduce total hydrostatic pressure of cement on weak formations or on casing - 
. Allow selective cementing of formations within the open hole - 

Scratchers

Scratchers are designed to clean mud-filter cake off the wall of the wellbore when the casing
is  reciprocated  or  rotated.  Reinforcement  of  the  cement  sheath  is  an  added  advantage  of
scratchers. Scratchers should always be used when thick mudfilter cake is suspected on the
walls  of  the  hole.  The  scratchers  help  remove  filter  cake  and  prepare  the  formation  for
bonding with the cement. In combination with centralizers and pipe reciprocation, scratchers
help ensure the success of primary cementing jobs

with my best wishes

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