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Drilling Engineering - Primary Cementing

Petroleum Engineering, Drilling Engineering, Primary Cementing

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Drilling Engineering - Primary Cementing

  1. 1. JAMES A. CRAIG
  2. 2.  Cement Composition  API Classes of Cement  Cement Additives  Density control  Accelerators  Retarders  Viscosity control  Types of Cementing  Cementing Operation  Cementing equipment  Cementing process  Performing a good cementing job
  3. 3.  Cement is made of limestone and clay/or shale mixed in the right proportions  Cement (oxides of Ca, Al, Fe, and Si) is heated in a rotary kiln to between 2,600 oF to 2,800 oF.  The result from the kiln is called Clinker.  Clinker is ground with a controlled amount of gypsum (CaSO4.2H2O) to make Portland cement.  Gypsum retards setting time and increases ultimate strength.
  4. 4. Clinker
  5. 5.  The classes used today are primarily Classes A, C, G, and H.  Classes A, B, and C are used for surface casing job.  Class A is used in some areas because it is very similar to construction cement and can be obtained locally.  Classes A and C are already ground with an accelerator.  Classes G and H are basic cements.  Class G is a finer grind and requires more mix water resulting in a lower density.  Class G is more common around the world.  Classes E and F are used for deep wells under high temperature and pressure.
  6. 6.  Cement additives will be sub-divided into these functional groups:  Density control  Accelerators  Retarders  Viscosity control  Others
  7. 7.  Density of cement should be high enough to prevent the high-pressured formations from entering the well.  Density of cement should not be so high as to cause fracture of the weaker formations.  Density of normal slurry (cement mixed with normal amount of water) is usually too high for formation strength.  It is desirable to lower slurry density by:  Lowering slurry density reduces cost.
  8. 8.  Methods of lowering slurry density:  Increase water/cement ratio  Add low-specific-gravity solids  Effect of high (excess) water/cement ratio:  Increase thickening time  Increase free water  Reduces compressive strength  Lowers resistance to sulfate attack  Increases permeability of the set cement
  9. 9.  Common low-specific-gravity solids in use are:  Bentonite  Diatomaceous earth  Solid hydrocarbons  Pozzolan  Expanded perlite  Bentonite  Most common light-weight additive  Ability to hydrate permits the use of high water concentration.  High amount will reduce cement strength and thickening time.  Cement strength retrogress with at high temperature above 230 oF.
  10. 10.  Diatomaceous earth (Diacel D)  Lower specific gravity than bentonite  Permits higher water/cement ratios without resulting in free water.  Like in bentonite, high amount will reduce cement strength and thickening time.  More expensive than bentonite.  Solid hydrocarbons  Gilsonite (lustrous asphalt) and Kolite (crushed coal)  Almost no effect on slurry thickening time.  Higher cement compressive strengths than other types of low-density solids.
  11. 11.  Pozzolans  Siliceous and aluminous materials that react with lime and water to a form a calcium silicates that possesses cementitious properties.  Natural pozzolans are volcanic ash  Artificial pozzolans include glass, furnace slag and fly ash (residue from chimneys of coal-burning power plants.  Only slight reduction in slurry density is achieved.  Perlite  Volcanic glass bubbles that has sometimes been used in geothermal wells because of its insulating properties.  Considerably more expensive
  12. 12.  If there is need for higher slurry density, additives that are used are:  Hematite  Reddish iron oxide ore (Fe2O3)  Very common because of its high specific gravity (5.02)  Barite  Barium sulfate  For smaller increases in density  Requires more water to keep slurry pumpable  Sand  Additional water not needed to be added to the slurry  Little effect on strength and pumpability of the cement
  13. 13.  Accelerate cement hydration  Decrease thickening time  Applicable for shallow, low-temperature wells.  They are inorganic compounds:  Calcium chloride  Sodium chloride  Gypsum  Little amount is needed. If in excess, it will retard the cement.  In offshore drilling: NaCl, CaCl2, MgCl2in seawater act as accelerators.
  14. 14.  Calcium chloride  Used in concentration of up to 4%  Anhydrous type is preferable because it absorbs moisture less readily  Sodium chloride  Best result is achieved at a concentration of 5%  Saturated type are used in salt formations or reactive shale formations.  Gypsum  Special grade of gypsum hemihydrate cement is mixed with portland cement.  Maximum working temperature is 140 oF for the regular grade, and 180 oF for the high-temperature grade.
  15. 15.  Also called thinners or dispersants  Increase the thickening time of cement  Applicable for deeper, high temperature wells.  Are typically organic compounds  Lignins  Borax  Sodium chloride  Cellulose derivatives
  16. 16.  Lignins  Calcium lignosulfonate  Most common retarder  Very low concentration is needed  Organic acids can be added for high temperature jobs  Borax  Sodium tetraborate decahydrate  Sodium chloride  At high concentrations  Cellulose derivatives  CMHEC (carboxylmethyl hydroxyethyl cellulose)  Commonly used  Works with all portland cements
  17. 17.  High slurry viscosity will:  Increase pump horsepower  Increase annular frictional pressure loss, which may lead to formation fracture.  Common viscosity-control additives are:  Organic deflocculants (e.g. calcium lignosulfonate)  Sodium chloride  Certain long-chain polymers
  18. 18.  Silica flour –to form stronger, more stable, and less permeable cements at high temperature.  Hydrazine–oxygen scavenger to control corrosion.  Radioactive tracer –to determine where cement has been placed.  Nylon–to make cement more impact resistant  Paraformaldehydeand sodium chromate –to counter the contamination effect of organic deflocculants from drilling muds.
  19. 19.  Primary cementing  Casing cementing –cementing of casing to the borehole  Liner cementing –cementing of liner. More complex than casing cementing  Secondary/remedial cementing  Plug cementing –to separate lower section of a well from upper section. Open hole or cased hole.  Squeeze cementing –to plug off abandoned perforation, repair annular leaks, and plug severe lost circulation zones.
  20. 20.  Cementing Equipment  Cementing Process  Performing a Good Cementing Job
  21. 21.  Cement head
  22. 22.  Guide shoe Guides the casing past irregularities in the borehole wall.
  23. 23.  Centralizer They are placed on the outside of the casing to help hold the casing in the center of the hole.
  24. 24.  Float collar Acts as a check valve to prevent cement from backing up into the casing.
  25. 25.  Float shoe Serves the function of both a guide shoe and a float collar when no shoe joints are desired.
  26. 26.  Cement basket Placed on the outside of the casing to help support the weight of the cement slurry at points where porous or weak formations are exposed.
  27. 27.  Bottom plug
  28. 28.  Top plug
  29. 29.  Scratchers Placed on the outside of the casing to help remove mudcake from the borehole walls, either by reciprocating the casing or by rotating the casing.
  30. 30.  Bottom rubber wiper plug is released to minimize cement contamination from drilling fluid.  Spacer fluid (or mud preflush) may be pumped also.  Desired volume of slurry is pumped  Top wiper plug is released  Drilling fluid displaces the top plug down the casing  When bottom plug reaches the float collar, its diaphragm ruptures.  The whole cement slurry has been fully displaced when the top plug bumps the bottom plug.
  31. 31.  Cement excess * Note:care should be taken to ensure cement does not reach the subsea well or mudline.
  32. 32.  Casing centralization  Pipe movement  Drilling fluid condition  Hole condition  Displacement velocity  Spacer fluids  Mud-cement density difference  Directional wells
  33. 33.  Centralization promotes a good cementing job  Centralizers are used to keep the pipe in the center of the hole  For a non-Newtonian fluid when pipe is not well centralized, the velocity on the narrow of the annulus is slower than the velocity on the wide (Popcorn theory).  The point between the centralizers is the hardest to centralize
  34. 34.  The degree of centralization is called % Standoff.  100% -perfectly centralized  0% -pipe touching wall  A minimum standoff of 70% is a good rule-of-thumb () ()%Standoff1100% bcCDRR + =−×−
  35. 35.  Rule of thumb:  1 centralizer per 2 joints in vertical wells.  1 centralizer per 1 joint in directional wells  2 centralizers per 1 joint in high angle or horizontal wells.  Smaller hole clearance will require more centralizers
  36. 36.  Pipe movement is rotation and/or reciprocation.  It increases the displacement efficiency  Drag forces associated with rotation will pull the cement into the narrow side of the annulus.
  37. 37.  Reciprocation has a tendency to break the gel strengths of the mud in the narrow side of the annulus.  The pipe should be reciprocated from the time the pipe reaches bottom until the cement plug bumps.  Pipe sticking may be a problem  Landing the casing if it starts to stick
  38. 38.  Higher viscosity mud is harder to displace  Viscosity of mud can be reduced prior to cementing by adding water (or thinners in a weighted mud).  Move the casing  The thicker the mud, the longer it should take to circulate.
  39. 39.  A clean hole allows the ease of running casing and getting centralizers to bottom.  Washouts are hard to cement  If washouts are a problem, change the mud to try and minimize the washouts.
  40. 40.  Which should be employed: turbulent, laminar or plug flow?
  41. 41.  Laminar flow:  Has the smallest displacement efficiency (75% and less).  Laminar flow gives inadequate cementations and should be avoided when possible since it promotes channeling  Plug flow:  Lowest annular velocity (30 to 90 feet/min, depending upon cement properties).  Very efficient  Limited to cementations of small volumes and where the mud in the hole is of low density.  Can be used when high displacement rate is possible because of ECD or hole size.
  42. 42.  Turbulent flow:  High displacement efficiencies.  Applicable to large volume cementations  Applicable where the mud and cement slurry weight are similar.  Limited in use by excessive bottomhole circulating pressure.  Can be limited by insufficient surface pump horsepower.  Primarily chosen because it requires shortest of all cementation times.
  43. 43.  Cement and mud are not compatible and should be kept separate.  A spacer fluid is used to separate the cement and mud in the annulus.  The spacer fluid should compatible with both cement and the mud  The spacer volume should equal at least 500 ft in the annulus.
  44. 44.  In water based muds (WBM), water is a very good spacer  Water is thin and will easily go into turbulent flow  Compatible with both cement and mud  Cost effective  In weighted muds, spacer may have to be weighted with barite.
  45. 45.  Little effect on displacement efficiency  The cement should be at least 0.5 ppg greater than mud density to prevent movement after the pump stops
  46. 46.  Difficult to get adequate centralization  Cuttings bed  There may be cuttings beds on the bottom of the hole.  They should be removed before cementing.
  47. 47.  Free water  Should be zero to minimize the possibility of a free water channel on the high side of the hole.
  48. 48.  Data:  Casing setting depth, HTVD= 3,000 ft  Average hole size, Dh= 17-1/2 in.  Casing ID, DCID= 12.615 in.  Casing OD, DCOD = 13-3/8 in.  Float collar (from shoe), HFC = 44 ft  Pump factor, Fp= 0.112 bbl/stroke  Casing program:LEAD (or FILLER)TAIL (or NEAT) Density (ppg)13.815.8 Height (ft)2,0001,000 Yield (ft3/sack)1.591.15 Excess volume = 50%
  49. 49. Questions:  How many sacks of LEAD cement will be required?  How many sacks of TAIL cement will be required?  How many barrels of mud will be required to bump plugs?  How many strokes of pump will be required to bump plugs?
  50. 50. 22Annular capacity,C183.35hCODADD− = 2217.513.375183.35− =30.6946 ft/ft= Determine number of sacks of LEAD: Excess# SacksyieldACh××=0.69462,0001.501.59××=1,311 sacks= 2Casing capacity,C183.35CIDCD= 212.615183.35=30.8679 ft/ft= 2Casing capacity,C1,029.4CIDCD= 212.6151,029.4=0.1545 bbl/ft=
  51. 51. Determine number of sacks of TAIL: Excess# Sacks (annular) yieldACh××=0.69461,0001.501.15××=906 sacks= # Sacks (casing) yieldAFCCH×=0.8679441.15×=33 sacks= # Sacks (total) (annular) (casing)=+90633=+939 sacks=
  52. 52. Determine barrels of mud to bump plugs: ()VolumeTVDFCCHHC=−×()3,000440.1545=−×456.7 bbls= Determine number of strokes to bump plugs: Volume# StrokesPF=456.70.112=4,078 strokes=