Cementing is very critical step of well construction. Bad cement job can lead to bad situations as well control, low productivity, gas channeling in annulus, etc. Therefore personnel in oilfield should learn and understand this topic. It is quite hard to find very good vdo training in the topic of oil well cementing but we finally find it. This VDO training is very excellent because it teaches all the basic with animations which absolutely helps learners fully understand this topic. Additionally, we add full VDO transcript so it will help some people who cannot catch all the wording in the VDO training. Please feel free to add comments and/or suggestions and we wish you would enjoy learning from this post.
Full VDO Transcript
Here is an overview of casing cemented in a well called primary cementing. The cement’s main jobs are to completely isolate or totally seal off all the oil, gas and water zones from the well bore and to bond the casing firmly to the wall of the whole. Here the crew has drilled the well to the casing point, the depth at which they will set and cement casing. The driller circulates drilling mud to clean the hole and to make sure the mud is in good condition. Then the crew pulls the drill string out of the hole. The next step in primary cementing is for the casing crew to run the casing into the well, one joint at the time. Notice at the bottom of the casing, the guide shoe and float collar. Also notice the centralizers and scratchers. The guide shoe guides the first joint of casing into the well bore. A valve in the float color lets the crew float the casing into the well to lessen the load on the rig’s hoisting system.
Centralizers keep the casing off the wall of the hole to ensure a good cement job and scratchers remove wall cake to ensure a good cement bond to the wall of the hole. The cementing crew next readies the cementing unit, the cementing unit Is a mixes water, dry cement and special additives to the cement to make a liquid cement slurry. A high-pressure cement pumping unit moves the slurry down the casing. To get the cement slurry down the casing, the cementing crew makes up a cementing head also called a plug retainer on the top joint of the casing suspended in their rig’s elevator. The cementing head as an inlet for the cement slurry from the cement pump. Slurry enters the head at the connection on the side. The valves on the head allow the crew to control the point at which it is slurry enters the head. From the cementing head, the slurry goes into the casing. The head also holds special plugs called wiper plugs. The wiper plug retainers keep the wiper plugs in the head until the crew releases them to allow the plugs to be pumped down the casing. The fluid inlet allows the crew to pump mud, water, or a special displacement fluid, the cement that pushes the fluid into the annulus. This head holds two wiper plugs; a bottom wiper plug and a top wiper plug.
The bottom plug goes into the casing first. It wipes mud off the inside of the casing and separates the mud from the cement. The top plug follows the last of the cement into the casing. It wipes cement off the inside of the casing and separates cement from the displacement fluids.
Often, the wiper plugs are identified by different colors to avoid confusion. The bottom plug is usually red or orange. It has a diaphragm that breaks with the problem gets to the bottom of the casing string so the cement can pass through the plug. The top plug is usually black.
Cement pump pressure moves the cement slurry to the cementing head where a crew member releases the bottom wiper plug. Slurry pushes the bottom plug down the casing until it seeps the float collar. When the club seeps, continued pump pressure on the slurry ruptures a diaphragm on the bottom of the plug. This allows cement slurry to go out the guide shoe and into the annulus. When a calculated amount of cement slurry has been pumped, a crew member releases to the top wiper plug.
Displacement fluid forces in the top wiper plug down the casing until it seeps into the float collar on the top of the bottom plug. Because of the top plug is solid, pump pressure rises when the club seeps. A sharp rise in pump pressure signals the pump operator to shut down the pump. The float valve holds the cement in place not allowing it to U-tube back into the casing once it is displaced into the annulus. The cementing job is complete. Depending on hole conditions and the type of cement used, the cement slurry hardens or sets up firmly, generally within 12 to 24 hours.