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Learn about cementing plug procedure

2018-04-09 16:12:24

After the casing runs into the well, a cementing head is hooked to the top of the wellhead to receive the slurries from the pumps. Plugs are used during cementing operations to help remove dispersed mud and mud sheath from the casing inner diameter and minimize the contamination of cement.


There are two wiper plugs: bottom plug and top plug also known as cementing plugs. The bottom of the plug is pumped ahead of the cement slurry and behind the spacer who wipes any remaining dispersed mud from the inner diameter of the casing as it moves down the string.


The mud inside the casing is important to be removed because it prevents mixing the drilling fluids with the cement slurries. When the bottom plug seats at the float collar, differential pressure ruptures a diaphragm on the plug, allowing cement to flow through, turn the corner at the bottom of the hole or toe end of a horizontal well. It fills the annular space between the casing and the formation.


Top and bottom plugs said as Cementing Plugs are always different colors. The color for bottom plugs and top plugs differs from company to company though. Once the full volume of cement has been pumped, a top plug is dropped and pumped behind the slurry from the inner diameter of the casing and then seats at the float collar. It helps in resting on the bottom cementing plug and causing a pressure increase at the surface indicating that the cement has been displaced.


The pressure on the cement being pumped into the well increases until a diaphragm is broken within the bottom cementing plug. It permits the slurry to flow through it and up the outside of the casing string. After the process of bottom cementing plug, the top cementing plug reaches the bottom cementing plug, the pumps are turned off and the cement is allowed to set.  The time taken for the cement to harden is called thickening time. The thickening time is also counted for the setting wells at deep depths, under high temperature or pressure in corrosive environments and special cements are employed. Both the Cementing Plugs work with the right amount of co-ordination thus, the quality matters a lot.


cement plug


Trouble with Cementing Plugs:


1. If you find out that wiper plugs from different companies have different diaphragm burst ratings, it can be a trouble. Plugs being exposed to the sun and harsh weather conditions are surely a sign of poor quality which leads to a deteriorated and cracked rubber. Burst ratings for the plugs is ranged from 150 to 250 psi.


2. In some cases where heavyweight pipe was used, the diaphragms burst prematurely if not wiped the casing properly to the float shoe. In such cases, the bottom cementing plug was left somewhere up the casing until the top cementing plug arrived and pushed it down. Now, when the remainder of the casing is wiped and the mud from the walls accumulated in the shoe joint or around the casing shoe area and everything gets settled.



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