primary cementing and secondary cementing
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Primary Cementing And Secondary Cementing
Submitted by Htet Naing Htoo
Participated in The general overview of cementing (Group Presentation) at Trust Training Center
• Primary Cementing is the placement of cement into the
annulus.Zonal isolationSeal off certain zones from other zones
Casing SupportProvide axial support for the surface casing and other casings that may be run later
Casing protectionProvides support and protection against plastic formations and corrosive formation fluids
Borehole SupportProvide support to the borehole for plastic, water-sensitive, or unconsolidated formations.
The Goal of Primary Cementing
Basic cementing procedure
1. Running Casing2. Circulating mud by rig pump3. Pressure testing4. Pumping wash and spacer5. Dropping the bottom plug6. Mixing slurry7. Pumping lead slurry8. Pumping tail slurry9. Dropping the top plug10. Displacing slurries and plugs with fluid11. Checking returns
• The first joint of the casing run into the well has a float or guide shoe attached to the end.
• After the first or second joint, a float collar is
installed. The space between the float collar and the shoe is called a shoe track.
• When the casing string is run to the desired depth, special connections may need to be made just at the wellhead; this process is called nippling up.
Circulating mud by rig pumpMud conditioning is achieved by circulating mud down the casingand taking returns at the annulus
Condition the mud & clean the well
Caution:The mud conditioning must bedesigned with the same attention:poor design can result in channeling
• The high-pressure treating lines running from the cement unit to the well connection must be pressure tested before the cementing process begins
1. Prime the cement unit and lines with water to fill all the lines2. Close the valve at the wellhead, and make sure no one is
near the lines3. Increase the pressure to a predetermined level by having the
unit pump water.4. Hold the pressure for about 5 minutes, and monitor for leaks.
Pumping wash and spacer• A chemical wash or a weighted spacer or both are typically pumped ahead of the cement slurry to act as a buffer between the cement and drilling fluid.
The chemical wash Helps thin and disperse the drilling mud in the wellbore and annulus
A spacerKeep the drilling mud and slurry separated during the displacement
Dropping the bottom plug
Wiper plugs are pumped ahead and behind the cement slurry on primary cement jobs
•Separate slurry from drilling fluids•Wipe the inside walls of the casing•Help provide a positive indication (pressure) that the cement is in place outside the casing
The cement slurry
This process can be done continuously or in a batch procedure The mix fluid (water plus cement additives) can be prepared ahead
of time or mixed on-the-fly using a liquid additive system.
Any required additives
Pumping lead slurry• Lead slurry - a low-density,
high-yield slurry; designed to fill and cover the upper section of the annulus
• It is pumped from the cementing unit through the cement head and into the casing • When the bottom plug reaches the float collar, the plug’s diaphragm ruptures and the wash, spacer, and slurry proceed to the casing shoe.
Pumping the tail slurry
Tail slurry – A higher-density slurry Used to cover the lower section of the annulus up from the bottom of the hole.
Dropping the top plugTop plug• Solid wiper plug• Separate and protect the slurry from contamination by the displacement fluid that will be pumped in the next step.
After the slurry has been pumped into the casing, the top plug is released from the cement head.
Pumping is stopped when the tail slurry has been pumped
The valves on the cement head are set to allow fluid—usually water or spacer—to be pumped to push the top plug out of the cement head.
Displacing slurries and plugs withfluids
• The cement slurries and wiper plugs are pumped down the well using either drilling fluid or another fluid.
• When the bottom wiper plug lands on the float collar, the membrane on top ofthe plug ruptures and the slurry is pumped out of the bottom of the casing and up
into the annulus.
• When the top plug reaches the bottom plug, it is sealed against the bottom plug by a pressure increase
• The float collar contains a check valve
• At the end of a cementing job, check to ensure that the float collar or float shoe is not leaking
• This check is done by allowing fluid to flow back to the cement unit displacement tanks
• If the float collar or shoe is working correctly, 2 to 5 bbl will flow back and then stop
• When a primary cement job objectives have not been achieved, or when the cement or casing has failed over time, it may be necessary to repair the problem.
Squeeze cementing Plug cementing
Cement slurry is forced through holes or splits in the casing to repair a primary cement job or a well problem.
Purposes of squeeze cementing
• Repair improper zonal isolation• Eliminate water intrusion• Repair casing leaks
Repair improper zonal isolation
• The top of the cement may be lower than designed because of losses during the primary job, inaccurate hole volume calculations, or incomplete displacement.
• The solution is to squeeze cement slurry through perforations just above the cement top to extend the cement column length in the annulus.
Eliminate water intrusion• Unwanted water or gas from above or below the producing
zone is plugged off by perforating these zones and squeezing cement slurry through the perforations.
Repair casing leaks
• A packer is run and set above the damaged casing. • Cement slurry is circulated down to the damaged area• The packer is set• The cement slurry squeezed at low pressure in and around
the holes in the casing
Remedial squeeze techniques
The injection of cement slurry into zones at pressures below the fracture pressure of the formation.
To fill perforation cavities or interconnected channels.
Slurry volumes are usually small since slurry is not injected into the formation.
Special precautions must be taken to ensure that the formation is not fractured.
Is used when it is not possible to inject slurry at pressures below the fracture pressure.
Cement is placed by breaking down the formation and injecting cement slurry into the zone.
Slurry volumes are usually relatively high since the created fractures and the perforations, have to be filled with cement slurry.
As a special precaution a wash or weak acid should be pumped ahead of the slurry to minimize the pump rates required to initiate the fractures.
Running squeeze• The continuous pumping of a calculated volume of
slurry until the final squeeze pressure is attained.• This technique could be used during low-pressure or
high-pressure squeeze jobs but usually results in the pumping of large slurry volumes in such cases.
• The intermittent application of pressure at a rate of 0.25 bbl/min to 0.50 bbl/min at 10- to 20-min intervals until the final squeeze pressure is reached.
• Relatively small slurry volumes are used in hesitation jobs compared with those used in running squeeze jobs.• Hesitation time depends on the type of formation, ranging from 5 min in tight formations to 30 min in loose formations.
Sometimes referred to as the poor boy squeeze, does not use a downhole isolation tool.
The entire casing and wellhead is exposed to the final squeeze pressure.
When open perforations exist below the zone, it may be necessary to run a bridge plug to isolate it from the treated zone.
Applicable for shallow depths and long splits in casing
Application• Squeeze tools
Uses either retrievable or drillable downhole tools.
Isolate the upper portion of the casing and wellhead from the cement and squeeze pressures and to improve the control and placement of fluids during squeeze cementing jobs.
Useful in multiple setting operations, such as selective testing and cementing of multiple zones.
Examples of the retrievable tools•DLT packer• PosiTrieve packer•Hurricane packer•Shorty squeeze tool•Retrievable bridge plug.