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1、Equipment
The two stage mechanical cementing collar is a tool for performing the cementing of oil and gas wells in two stages.
The first stage cement is displaced through the bottom of the casing and generally the cementing is displaced to a position in the annulus from the bottom of the casing to a position below the stage cementing collar.
The second stage cement is pumped into the annulus through the stage cementing collar ports, that have been opened to allow this displacement. The opening of the ports is performed mechanically through release of a mechanical device, called a free fall opening device (FFOD).
The free fall opening device is released from the surface, allowed to gravitate into the stage cementing collar, and then pressure is applied to open the cementing ports in the stage cementing collar.
Once the second stage cement has been displaced from inside the casing into the annulus above the stage collar. A closing plug, which has been introduced into the casing on top of the second stage cement, lands in the stage collar, and through the application of internal casing pressure, shears off another set of shears pins, allowing the cementing ports to be closed. And subsequently a locking ring is engaged to permanently close the cementing ports in the stage cementing collar.
After the cement has become hard, a drill bit is lowered into the casing. And any remaining cement, in addition to the plugs that have been used during the operation of the tool, are drilled up and the cuttings are circulated out of the casing and collected at the surface.
This mechanical stage tool is furnished with accessories consisting of shut-off plug、landing collar、free fall opening dart and closing plug. Float equipment of choice may be used below the plug landing baffle. An opening dart is furnished for opening the cementing ports. The tool should not be installed when the casing deviation above or at the tool is 35degree or less. The shut-off baffle is installed in landing collar .
2、Description
2.1 5 Inch Mechanical Stage Cement Collar Parameter
| Size(inch) | 5” |
| Wall thickness(ppf) | 18PPF |
| Grade | P110 |
| Max O.D. (inch) | 5.67 |
| Drill out I.D.(inch) | 4.276 |
| Cement port size(inch)/number | 1 ’’/4 |
| Opening/closing pressure (psi) | 1200/1500 |
| internal pressure(psi) | 12500 |
| External pressure(psi) | 10500 |
| Yield strength(psi) | 130500 |
| Flow rate(Cubic Meters/ per minute) | 1.6 |
| Thread | LTC |
2.2 Two stage Mechanical Stage Cement Collar Structure
2.3 Inspection
Inspect Stage Collar and auxiliary equipment upon arrival at location. Remove stage collar from box and remove plastic covering to inspect.
Check the Stage Collar for signs of damage on the outside diameter and for damaged threads.
Check Free Fall Opening Dart and Closing Plug to verify that they will seat properly in Stage Tool.
Check the First Stage Flexible Plug nose diameter and receiver plate internal bore. Verify that type of release pin that is being used in the cementing head.
If the release pin extends a minimum of 75% the distance across the internal bore of the cement head. And it is at least 40mm in diameter then the first stage plug maybe preloaded . If there is a pressure equalization channel or rod between the lower and middle or upper cement inlet port on the cement head.
If the release pin does not meet these minimum requirements. Or there is no pressure equalization channel or rod. Do not preload the first stage plug as vacuum may cause the plug to be sucked past the release pin.
If unsure, do not load the first stage plug.
If the plug release mechanism is not operable, or the release pin is not sufficient to retain the plug. Or an equalizing channel is not present, do not preload the second stage Closing Plug.
| Tool Size | 5” |
| Opening Pressure | 1200 psi |
| Closing Pressure | 1500psi |
All pressures are based upon pressure to over come the differential pressure at the stage collar at the time of opening and closing of the inner sleeve.
The tensile load resulting from the stage tool closing pressure and /or first plug bump pressure (Casing internal diameter X pressure force) should be added to the casing weight to determine the total load on tool.
3. Procedure
3.1.Install the landing collar with shut-off baffle at desired location in casing string.
3.2.Install the stage tool at desired location in casing string.
3.3.First stage plug maybe preloaded if the cementing head has a plug retainer bar that extends past the centre line of the cementing head. If the cement head retainer bar does not extend past the centre of the cementing head the first stage plug should not be pre-loaded into the head.
3.4.Land casing, circulate hole clean and pump (Do not place tongs on stage tool)
pre-wash as required.
3.5.Mix and pump first stage cement.
3.6.Drop shut-off plug on top of first stage cement. ( Cement lines may be pumped out prior to displacement)
Note:
The shut-off plug and stage tool closing plug can be preloaded in a special stage tool cementing head with positive release indicator.
3.7. Pump pre-calculated amount of displacement fluid, land shut-off plug into baffle, noted by sudden pressure increase. And pressure up to 4mpa over circulating pressure to ensure plug has landed. (The shut-off plug may be pumped through the stage tool at flow rates of .3 – .5 m3/min.)
3.8.Release pressure and check float valves for backflow. With floats holding proceed or if not, wait for cement to set, if possible.
3.9.Drop opening cone and wait for it to free fall to stage tool, approx. 1 minute per 60m. Closing plug may be loaded in head at this time. A normal rate of drop is about five minutes per 300 meters in 1.15 specific gravity fluid. If the fluid has higher specific gravity calculate the percentage increase over 1.15 specific gravity and apply this percentage to the calculated drop time. (Example if the specific gravity is 1.5 then the calculated percentage difference is 30% higher and the calculated dropping rate of bomb would be (100%-30% = 70%) 210 meters per 5 minutes. The use of thicker walled heavier weight casing will also affect the rate of free fall. The opening device dropped in 177.8mm – 32.2 Kg./M will free fall faster than in 52.1 Kg./M. casing.
3.10.Pressure up to 1200psi to open stage tool. When stage tool opens, establish circulation and condition hole. If stage tool fails to open, release pressure, and allow more time for opening cone to reach stage tool, then repeat the pressure build-up. Open stage tool, circulate and condition hole.
3.11.Pump pre-wash as required, mix and pump cement and release closing plug. (Cement lines may be pumped out prior to displacement) Pump pre-calculated amount of displacement fluid to land plug in stage tool. (The closing plug should be landed at a flow rate of approx. .5 m3 per minute).
3.12.When closing plug seats, continue pumping until the pressure indicated below is reached. (greater pressure may be required, however do not exceed the casing burst or surface equipment.)
3.13.Hold pressure for 5 minutes, release pressure and check for backflow.
3.14.If excessive backflow is observed, “run-into” the stage tool with a higher pump rate and/or pressure. Check again for closure.
Note:
If stage tool fails to close, it is recommended that the casing be shut-in at surface until cement sets up.
4、DRILLING RECOMMENDATIONS
PREPARATION:
4.1.Apply Thread Lock on thread of float equipment. The first 3 to 5 joints of casing above the float equipment and the Stage Collar and 1 joint above the Stage Collar. Do Not use an excessive amount of thread lock in the box end of the float equipment or stage tool.
4.2.Pump some cement slurry on top of the first stage and closing plugs to ensure they are embedded in cement. This will prevent the plugs from rotating during drill out.
4.3 Use of a three-cone, long-milled tooth rotary bit is preferred for drilling out the stage collar and plugs. The bit with a configuration for use in medium to soft formations is preferred. Mills bits maybe used, but will have lower penetration rates.
4.4.Do not drill in an automatic mode, use manual control at all times during drill out. The use of a junk basket to catch drilled particles is acceptable and/or a casing scraper if drilling production casing. Reamers and stabilizers installed close to the bit will keep the bit on target.
DRILL OUT
4.5.Drill in the range of 40-60 RPM. Caution: NEVER EXCEED 90 RPM.
4.6.Apply 35-50 Kilograms of drilling weight per millimeter of bit diameter.
4.7.DO NOT SPUD ON TARGET
.Use a pump rate that will circulate cuttings without decreasing bit weight on the target. (A pump rate of .1 liter/second per millimeter of bit diameter is a good starting point.)
4.8.DO NOT USE EXCESSIVE PUMPING RATES.
. Maintain at minimum of 650 PSI per square millimeter of bit surface. Raise and lower the bit occasionally while drilling to clear junk from the bit.
5、Special Warning
5.1 Forbidding use the casing tongs on the stage collar’s body.
5.2 Wrong installation method
5.3 Correct installation method
5.3.1 First, use the chain tongs on the stage collar’s pin end, and then tighten the thread.
5.3.2 Role in the casing tongs on the casing coupling that under the stage collar. Hydraulic tongs clamp the casing up the stage collar. Then tighten the thread by the Hydraulic tongs.
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