Casing is mandatory in the drilling operations as it has a lot of casing functions as to prevent cave-in of unconsolidated formations, isolate problem zones and many more. As mentioned before in the our casing design guide that selection of casing depends on many factors. Here in this article, we shall learn every thing about the drilling best practice for casing running procedures, tools & equipment. In other word, you will lean how casing is run in the hole and you can use it in your rig floor program.
Casing Running Procedures
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- First Check The Casing And Cementing Check List
- After open hole log, a tripping pipe to bottom is recommended to condition the hole and mud. The Mud Engineer shall check and, if necessary, adjust the mud properties. Plastic viscosity, yield strength and weight shall be kept as low as possible.
- There is a difference between the driller’s and logging depths, strapping in or out of the Drill String shall be considered.
- Check the weather forecast to ensure conditions be such as to allow safe operations.
- Replace the upper pipe rams with the correct size of rams for the casing to be run. A pressure test of the bonnet and rams seals shall be performed when the pipe rams are changed. Remember Blowout preventer may be required for any Well Control issue.
- Retrieve the wear bushing.
- Do not lay down the Bottom Hole Assembly BHA unless unavoidable. Before running 7″ casing, break-out BHA and 5″ Drill Pipe. After the Casing Cementing Job, while waiting on cement lay down the BHA and 5″ DP.
- From the caliper log determine the correct volume of slurry, spacers. Centralization Pattern to be used.
- Verify that the differential pressure between the slurry and mud does not exceed the Casing Collapse Rating. Also make sure that the density of slurry and the planned top of cement do not cause losses of circulation and/or gas migration while waiting on cement.
- The Company Drilling and Completion Supervisor, Company Drilling Engineer (if on site) and Cementing Operator shall conduct individually, calculations for the cementing job prior to running the casing. The figures/calculations shall be compared in order to ascertain final cement, volumes, etc.
- Calculate the Maximum Allowable Overpull while running casing same as for the Drill String.
- Landing joints are to be inspected and selected to avoid interference with wellhead. The coupling must be minimum a 2m from casing hanging point.
- Do not start running the casing without the Cementing Operator being on site. The operator will start the unit pumps and check for system malfunctions.
- Check the length of elevator links several days in advance for fitness with casing running tools & equipment i.e. spider, circulating/cementing heads, circulating casing packer.
- Install Centralizers as per the Drilling Program its installation pattern when the casing is on the pipe rack, in order to avoid time wasting during casing running
- Check shoe and collar integrity.
- Test the sealing adapter 30″-20″ shoe for perfect fit.
- Record initial pit levels to establish a reference volume in order to detect any abnormal condition while running the casing.
- Arrange an appropriate length of high pressure flexible hose for casing string circulating down and/or reciprocating.
- Centre the travelling block with the rotary table to facilitate casing running and hanging.
- Check subs, crossovers, stage collar, ECIP for correct threads, dimensions, etc.
- Visual inspect the casing internal surface on the pipe rack to ensure that all joints are free from foreign matter.
- Before commencing of the casing running procedures & its job, the Toolpusher, Driller, Cementing Operator, Mud Engineer and Mud Logging Operator shall be fully informed of the Casing Cementing Job Procedure and given the following data:
- Total amount of lead and tail cement slurries.
- Volumes, density and composition of spacers.
- Calculated top of tail and lead slurries based on hole conditions.
- Desired density of lead and tail slurries.
- Required amount of mixing water for both slurries (fresh or sea water to be duly noted by all concerned).
- Total amount of cement to be used.
- Required volumes of additives for both slurries.
- Estimated setting time of the cement.
- Internal volume of casing from top to float collar and number of rig pump strokes to bump the plugs.
- Volume of casing from float collar to float shoe and number of rig pump strokes for over displacement only.
- Maximum allowable displacement rate compatible with the MAASP (How to Calculate MAASP).
Casing Running Procedures
- A circulation sub, fitting the casing thread, equipped with a WECO connection, shall be readily available on rig floor at all times during casing running.
- The most forgotten casing running procedures is to pick up the shoe joint and remove the blank thread protector at V-door. Lower the joint through the rotary and visually verify for back flow. Fill the joint with mud, then pick up to check for flow through.
- Generally a float collar shall be run two joints above the shoe in 13 3/8″ and 9 5/8″ casing and three joints above a 7″ shoe, 30″ conductor casing pipe, after drilling of 36″ hole, and 20″ surface casing shall be cemented using a Drill Pipe inner string with a sealing sleeve adapter.
- Use a thread lock compound on all the connections on and below the float collar (or landing collar).
- Pick up the collar joint and remove the blank thread protector at the V-door. Make up the joint and fill with mud. Pick up and check the shoe and collar for flow through.
- After casing running 6 joints, make up the circulating head and test the float equipment pumping at the maximum displacement rate. Record pressure losses due to collar and shoe at various flow rates.
- When running Buttress casing, make up the first 10 joint connections to the reference triangle (do not consider the joints between shoe and collar since the torque transmission factor of thread lock compound is not the same value as casing dope). Record the average torque required for these first joints and use it for the remaining part of the string. The torque value shall then be checked every 10-20 joints and adjusted, if necessary.
- When a casing running procedures for other threads, the make up torque should be in accordance with the manufacturer’s specifications.
- Rotary slips with safety clamp and side door elevators may be used up to a weight equal to 60% of the rating for the elevators. Beyond this weight, use slip power elevator and spider.
Note: Slip power elevator and spider shall always be used when running casing in open hole
- Stop the block before setting the spider and then slowly slack off pipe weight to minimize pipe slippage, notching or crushing.
- The maximum casing running procedures speed should be calculated for the well specific mud properties and formation integrity. As a rule of thumb, running speed should never exceed 0.6m/sec. (20sec/joint) inside casing and 0.3m/sec. (40sec/joint) in open hole.
Note : For 7″ casing the running speed shall not exceed 0.2m/sec. (1 joint every minute).
- Inform the Driller that speed variation is a cause of surge and possible mud loss, so it is particularly important to run the casing in as smooth a manner as possible.
- Fill up the casing after every joint and completely every 10 joints. If running a casing liner (One of Types Of Casing), fill up the running string at each stand.
- While running the casing compare the actual string weight and pit level, with theoretical values previously plotted, in order to detect any possible abnormal condition.
- Intermediate circulation is generally not necessary, however it may be advisable under the following circumstances:
- When the weight indicator shows excessive dragging or a tendency to stick.
- When an excessive amount of mud cake, cuttings or shale is expected.
- When it is anticipated that returns will be lost if excessively high pump pressure is required to break circulation at bottom.
- At the previous casing shoe. Circulation should start at a very low pump rate increasing gradually to the maximum displacement rate. Record the circulating pressures at the various rates.
- When installing a production casing string it is recommended to place a short joint near the pay zone to aid in checking depths with casing collar locator (CCL) during later logging operations.
- During casing running, plot the casing weight and pit levels on the graph (described earlier) and compare them with the theoretical values previously plotted to detect any possible abnormal condition.
- At the previous casing shoe depth fill up the string completely and circulate the volume inside the casing. Check levels and start circulation at a very low pump rate increasing gradually up to the maximum allowable displacement rate. Record the circulating pressures at the various flow rates.
- Space out the casing string in order to have the cementing head at a convenient height. On the other hand, ensure that the last casing collar is not across the hanging point.
- With the casing at TD circulate the total hole volume, following the procedure in step 19.
- During circulation, check the levels and any bottom cushion. At the end of circulation, record the pressure with the estimated displacement rate.
- During the final circulation and the following cementing job phases, hang the casing on the travelling block and do not leave it on the rotary table clamp.
Note : In particular instances the ‘Post Plug’ technique should be used in order to reciprocate the casing string.
Casing Operations With A Top Drive
- With the introduction of 500 tons bails and adequately rated swivel, the Top Drive is rated at 500 tons for casing operations. Longer bails (132” or 144”) must be used to allow clearance for the casing elevator under the torque wrench in the pipe handler.
- Also clearance for the cementing head must be taken into consideration when determining casing bails length. By attaching a short piece of hose to the saver sub in the pipe handler, the casing can be filled while lowering by using the remotely controlled kellycock to start and stop the calculated filling flow. If desired, casing can be run conventionally using the block and hook by swinging the Top Drive aside. Very long bails must be used to prevent the block from contacting the Top Drive dolly.
- It is recommended to prepare landing/circulating heads (4 1/2″ If Box connections) connected directly to top drive for 13 3/8″, 9 5/8″ and 7″ casing, in order to facilitate circulating down, casing reciprocation, casing retrieve with circulation, etc.
- Circulating Casing Packers compatible with top drive systems are available in the market (i.e. Weatherford, PBL, CTC, TAM, etc.).