Rig Site Tips: Running Casing Procedures and Instructions



Running the Casing in the wellbore is an important issue when drilling an oil and gas well. An oil and gas well is drilled in sections from the surface to the production zone. It is not possible to drill the well in one section due to the difference in formations properties. Each section of formation, after being drilled, has to be sealed off by running a steel pipe called casing (Click Here). The annular space between the casing and the borehole is filled with cement (Click Here).

Casing Running Preparations

Many points have to be performed accurately to make sure the success of running the casing. Missing some details can lead to many problems and affect the overall performance of the operations. 
Prior to running the casing the well has to be conditioned. The tight spots have to be eliminated by performing a short trip before pulling the drill string. The driller has to work on the intervals where he notices high torque and does not continue running to bottom till getting stable torque on those intervals. In the case of highly deviated wells, where the severe dog legs become an obstacle to run the casing, a semi-packed hole BHA has to be run to soften these intervals (For Tripping Instructions Click Here). Also, the drilling mud has to be conditioned by reducing the plastic viscosity and yield point because the mud in this case is no longer used to carry cutting. The surge effect is reduced and the risk of losses is minimized by decreasing the yield point.

Fig 01- Casing on Rack
The casing joints and accessories have to be prepared while drilling is carried on. The casing joints have to be measured and drifted. The threads have to be checked and cleaned. 
According to standards, for casing smaller than 8 5/8'' the mandrel length of the drift has to be 6'' and for casing larger than 9 5/8'' the mandrel has to be 12''. The Outer diameter OD and the length of the drift itself should be checked prior to the job.
The crew which is going to prepare the casing should remove the protectors and carefully insert the drift from the box without damaging the thread or seal area. They have to make sure to do not free-fall out of the pin end to avoid damaging the threads. Any pipe which fails to drift should be marked on the body and not used in the operation. 
The casing joints should be cleaned and this can be performed by blowing compressed air through the joints in order to remove any debris. The threads have to be cleaned and free from dirt. They should be kept dry and protected with clean protectors. The threads can be cleaned using steam jet and followed by an air blast to dry them effectively. Diesel should not be used to clean the threads because it can attracts debris and encapsulated them between thread roots which can make them difficult to be removed. 
The casing joints have to be measured twice to remove any doubts. The joints which are not used for any reason like fail to drift or damaged threads have to be laid out from the casing rack. After measuring and double checking the measures, the casing is numbered to prepare the casing tally which includes joint number, buoyed string weight, metal displacement, the position of centralizers, crossovers and any other accessories, it has to include also the cumulative length and the final depth of any joints when landing the casing shoe on bottom. 
The total number of joints should be noted including the pup joints and the damaged joints. In case of facing problems when running casing like impossibility of reaching the bottom, the crew has to be sure of the depth of landing by counting the remain joints on surface.

Fig 02- Example of Casing Tally

The casing shoe and float collar should be checked. The main thing to be sure about is the type threads of these two parts of the casing string. If the thread is not like the one of the casing joints, cross over are expected to be used in the shoe track to adapt the threads. The casing shoe normally has to be made up on the first joint and protected from debris which can affect the float in it. The two joints which are chosen for the shoe track should be the tallest ones to gain few barrels just in case of not getting the pressure bump when circulating the cement.

Fig 03- Float Collar, Guide Shoe and Float Shoe
 
Casing running equipment are also very important for the success of the job. They have to be on site on time, checked and prepared. The overall condition of the power tongs have to be checked, in particular the dies. The tong specifically should have torque output tested up to the maximum anticipated for the job. The side door and spider elevators have to get the right lifting capacity. 

Casing Running Procedures and Instructions 

After cleaning and preparing the rig floor, the first joint with casing shoe made up on it is picked up. The casing joints have to be transferred carefully to catwalk. Installing the Klampon protector can be used to protect the pin end of the joint. 
The shoe track is composed of the casing shoe, two casing joints and float shoe. The shoe track components should be made up using pipe lock compound. The pipe lock has to be put on the pin part. The float collar pin is stabbed in the second joint carefully and made up using the chain tong, then the next join pin is stub in the float collar and made up using the power tong. The pipe lock is used to avoid backing off the casing shoe and float collar while drilling them with the next BHA. 
The casing shoe and the float collar should be tested, the shoe track is filled with mud (Click Here) then lifted at least 30 ft above the rotary table, then lowered again, the level into the shoe track should decrease and the floats should not allow the back flow. In the case when the floats fail, make the circulating head and circulate to remove any debris which can affect the floats, then re-test again.
The next joints are doped with casing thread compound to all boxes and seal areas. The dope is applied when the joint is in the V door not when the joint is on the rotary. Extra joints should be on site, cleaned, calibrated and measured which can be used when damaging joints. 
Safety clamps or single joints elevator is used above the slips before removing the elevator to avoid losing the casing into the well. They are used till getting the weight of 25000 lbs. 
For buttress couplings, the casing is made up to more or less than 3/8 inch from the base of the triangle. Make up several joints to triangle, then use that average torque to make up the remaining joints. The coupling can be warm up but should not get hot, if this is the case may be it indicates the over-torquing or galling. The connection should be made up with the high gear of the power tong, then low gear is engaged prior to shouldering.
Fill each joint with mud and monitor the correct amount of mud returned to the mud pit while running in the hole to record any losses or gain (Click Here).
Change to spider elevator before running in the open hole
Fig 04- Side Door and Spider Elevators 
Wash down at least the last joint of casing to avoid plugging the casing shoe. When tagging the bottom of the hole, count the joints remain at the surface including the damaged ones and make sure that this is the right depth of the bottom. If it is ok, space out the casing string to avoid getting the coupling into the last casing spool. Expect pup joints on rig site to use them when spacing out. Rig up and make up the cementing head, line up and then circulate at least 120 % of the casing string capacity and prepare for the cementing job. 

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