Cementing

Primary Cementing as a one important operation during drilling. This slide is included fundamental of cementing which helps to petroleum and civil engineering

1. Primary Cementing Design and Development of Oil and Gas Fields Sadeq Rajabi 1

2. 2 Agenda The Manufacture of Cement Classes and Types of Cement Hydration of Cement Properties of Oil Well Cement Introduction Cement Slurry Additives

3. Introduction Function of Cement Cement slurry is to carry all of the additives Support the casing The cement must adequately isolate the intervals of interest Prevent the movement of fluids from one formation to another Protect the casing from corrosive fluids in the formations 3

4. Manufacturing of cement Cements are made from limestone (CaCo3) or other high calcium carbonate materials and clay or shale. Some iron and aluminum oxides may be added if not present in sufficient quantity in the clay or shale. These materials are finely ground and mixed, then heated to 2600 – 2800°F in a rotary kiln. The resulting clinker is then ground with a controlled amount of gypsum (Ca2SO4·2H2O) to form Portland Cement. 4

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6. Bulk Cementing Bulk Plant is where cement oil well a nd additives blend together Then transported and delivered in bulk cement tanker (instead of in bags) to the job site Cementing unit mixer is used for mix w ater, dry powder and special chemical to make liquid slurry 6

7. Classification Of Portland Cement American Society for Testing and Material (ASTM): Construction cement American Petroleum Institute (API): Oil well cement Classification According to Resistance of Sulfate Ordinary (O) Moderate Sulfate Resistance ( MSR) High Sulfate Resistance (HSR) 7

8. Typical Composition of Portland Cement Compounds API CLASS C3S C2S C3A C4AF FINENESS ( sq cm/gram) Depth (Ft) Temperature (F) Resistance Sulfate A Portland 53 24 8 8 1500 – 1900 0 – 6000 80-170 Ordinary class B Portland 47 32 3 12 1500 – 1900 0 – 6000 80-170 HSR or MSR C Accelerated 58 16 8 8 2000 – 2400 0 – 6000 80-170 HSR or MSR D &E&F Retarded 26 54 2 12 1100 – 1500 6000 –14000 10000–16000 170-290 230-320 HSR or MSR Only in HSR G Basic 52 32 3 12 1400 – 1600 ALL depths 200 HSR or MSR H Basic 52 32 3 12 1400 – 1600 ALL depths 200 HSR or MSR 8 Chemical Name Notation Chemical Formula Tricalcium Silicate C3S 3Cao.Sio2 Dicalcium Silicate C2S 2Cao.Sio2 Tricalcium Alminium C3A 3Cao.Al2O3 Tetracalcium Alminiumflouride C4AF 4Cao.Al2O3.Fe2O3

9. Class A,B,C Construction Cement cheaper Shallow depths B can resist to sulphate more than A C can harden quickly due to the high concentration of C3S Class D, E, F Oil well Slow Set Cement expensive retarded cement due to coarser grind, takes more time to set deep wells at high level of temperatures and pressures Class G, H Oil well Basic Cement can be used with wide range G most common type of cement Class J Used in deep and hot well 9 API Classification WCR = 0.46 – 0.56 WCR = 0.38 WCR = 0.44 – 0.38

10. Non-API Classification Pozmix cement result of mixing Portland cement with pozzolan and bentonite used for shallow wells due to its light weight lightweight but durable cement less expensive than most other types Gypsum Cement formed by mixing Portland cement and gypsum used for remedial jobs; it can develop a high early strength It is very appropriate for sealing off lost circulation zones Diesel oil cement mixture of one of the basic cement classes (A, B, G, H), diesel oil or kerosene and a surfactant only set in the presence of water have unlimited setting times used to seal off water producing zones 10

11. Hydration of Cement Chemical reaction between cement and water is referred as hydration. The hydration rate for cement is also highly dependent on the cement particle size and the temperature by the slurry during setting . Hydration is reaction of cement with water to form the binding material (C_S_H gel) In presence of water, Silicates (C2S and C3S) and Aluminates (C3A and C4AF) form product of hydration which in time produce a firm solid and hard mass (the hydrated cement paste) 11

12. Tricalcium Silicate hydrates rapidly and form earlier strength Produce more amount heat during hydration process Calcium Silicates Hydrate Dicalcium Silicate hydrates slowly and it is responsible for progressive strength Produce less amount heat during hydration process Calcium Hydroxide ( Portlandite ) 12 2(3CaO.Sio2) + 6 H2O → 3CaO.2SiO.3H2O+3Ca(OH)2 2(2CaO.Sio2 ) + 4 H2O → 3CaO.2SiO.3H2O+3Ca(OH)2

13. Ca (OH)2 reacts with Sulfates to form calcium sulfate and causes the deterioration (Sulfate attack) Tricalcium Aluminum hydrates rapidly Produce large amount heat during hydration process Calcium Aluminum Hydrate Tetracalcium Aluminum fluoride hydrates show higher resistance to sulfate attack 13 3Cao.Al2O3 + H2O → 3CaO.Al2O3.6H2O 4Cao.Al2O3.Fe2O3 + H2O → 3CaO.2SiO.6H2O+CaO.Fe2O3.H2O

14. In general, the relative hydration rate follows the sequence : The process of hydration could take several days or even weeks at low temperatures. However , at high temperatures , maximum strength is attained after a few hours . The development of compressive strength is primarily dictated by the two major cement components, C3S and C2S. C3S is the constituent primarily responsible for the development of early (1 to 28 days) compressive strength, C2S is responsible for the development of later (28 + day) compressive strength . 14 C3A > C3S > C4AF > C2S

15. GENERAL PROPERTIES OF OIL WELL CEMENTS Viscosity Thickening time Density Yield Fluid loss Free water Compressive Strength 15

16. VISCOSITY The viscosity of cement is normally 40-75 funnel seconds . is controlled by the amount of water added to the cement. Only 25% water by weight of cement is required for hydration, but more water is added to provide for pumpability A low viscosity cement will have better displacement properties at higher flow rates while a high viscosity cement may have better displacement properties at lower flow rates 16

17. Newtonian fluids Power law fluids Bingham fluids where, 𝜏 shear stress 𝜏𝑦 Yield Point 𝜇𝑝 Plastic Viscosity 𝛾 Shear rate Cements are non-Newtonian fluids. The cement gets thinner as the shear rate increases The Bingham Plastic and the Power Law Models can be used to describe the viscosity of cement (Power Law Model is more accurate) 17 𝜏 = 𝜇 𝛾 𝜏 = 𝐾𝛾 𝑛 𝜏 = 𝜏 𝑦 + 𝜇 𝑝 𝛾

18. API Recommended Test: Rotational Viscometer If relationship is linear (Bingham plastic model) then following formulas can be used: Plastic Viscosity (PV) = D600 - D300 (centipoise) Yield Point (YP) = D300 - PV 18

19. THICKENING TIME The thickening time of a cement slurry is the time during which the cement slurry can be pumped and displaced into the annulus From 20 minutes to days but g enerally 2 - 3 hours thickening time is enough If the operation is delayed whilst waiting on the cement to set and develop this compressive strength the drilling rig is said to be “waiting on cement” (WOC) 19

20. Increasing pressure will shorten thickening time Thickening times can be reduced by adding accelerators such as calcium chloride 20

21. Retarders are added to cement to increase thickening time extenders added to the cement to reduce density will increase thickening time Adding more mix water will increase thickening time API Recommended Test: Consistometer 21

22. Where, T is the torque on the paddle in g-cm Bc is the slurry consistency in API consistency units Thickening time is assessed by using a consistometer that plots the consistency of a slurry over time The end of the thickening time is considered to be 50 or 70 Bc for most applications 22

23. DENSITY 23 less than 8.33 ppg to 20 ppg Slurry densities need to be varied to prevent lost circulation or to control abnormal formation pressures. Too much water will increase thickening time and reduce the strength of the cement. The density can be decreased by adding extenders such as pozzolans and bentonite The extenders require more mix water Density can be increased by adding weight material such as barite and hematite cement slurries generally have a much higher density than the drilling fluid API Recommended Test: Mud balance

24. YIELD The yield is the volume of cement mixture created per sack of initial cement. Depending upon the additives for densified cement 0.90 ft3 per sack to 4.70 ft3 per sack for a pozzolan , cement and bentonite mix 24 API CLASS WATER (gals/ sk ) DENSITY ( ppg ) YIELD (ft3/ sk ) A 5.2 15.6 1.18 B 5.2 15.6 1.18 C 6.3 14.8 1.32 D 4.3 16.4 1.06 E 4.3 16.4 1.06 G 5 15.8 1.15 H 4.3 16.4 1.06

25. FLUID LOSS Usually, bentonite or high molecular weight polymers are added to the cement to reduce the fluid loss The recommended API fluid loss ranges 50 to 250 ml for liners 50 to 200 ml for squeeze cementing No control to 100 ml for a typical casing job The fluid loss be kept below 150 ml when annular gas flow is a problem API Recommended Test: Filtration Rate 25

26. FREE WATER Free water is caused by the separation of the mix water and cement solids . In deviated and horizontal wells, the separated mix water will migrate to the high side of the hole and cause a channel . High free water content is also often a sign of an unstable slurry with settling problems . Free water problems will be enhanced by long thickening times which often occurs at the topmost part of the hole. Also , it can cause a lack of cement sheet protection on the casing and corrosion problems over time leading to holes in the casing. Addition of fluid loss additives or 0.1% to 0.2% bentonite will reduce the free water content to near zero. 26

27. COMPRESSIVE STRENGTH When cement sets, it develops a compressive strength over time. Above 3,000 psi, there is very little change in compressive strength as the pressure increases. The compressive strength will be near the maximum within 72 hours. Extenders and using more mix water will decrease the ultimate compressive strength At the same temperature, accelerated cements will attain a higher compressive strength quicker than neat cements and retarded cements. 27

28. For most oil field applications, a compressive strength of 500 psi is sufficient At high temperatures, cement can suffer from strength retrogression which is a loss in compressive strength with time Above 230°F : a considerable decrease in CS and increase in permeability Addition of 35 to 40 percent silica flour will inhibit strength retrogression API Recommended Test : Strength test machine 28 SILICA FLOUR % COMPRESSIVE STRENGTH (3 days) COMPRESSIVE STRENGTH (7days) 545 425 40 11,025 10,010

29. Effects of Temperature on Compressive Strength Test Temperature °F Compressive Strength psi 12 Hours Compressive Strength psi 24 Hours 70 1090 2250 80 1301 2705 90 1408 2842 100 1490 3100 105 1520 3450 29

30. In the model equations, all possible models (logarithmic, power, linear, exponential) among others were tested based on high multiple correlation coefficient R 2 For 12 Hours For 24 Hours Where CS is the compressive strength in psi, T is the temperature in o F 30 CS = 1397.432 + 1466605/ T 1.5 - 1.4E–07 / T 2 R 2 =0.999 CS = 3423.949+1336778/ T 1.5 - 1.7E–07 / T 2 R 2 =0.980

31. Effect of slurry weight on compressive strength Slurry Weight Kg/L 1.96 1.98 2 Compressive Strength Psi 12 Hours No Strength No Strength No Strength 24 Hours 600 600 600 48 Hours 600 700 950 72 Hours 1750 2250 2500 1 Week (168 Hours) 3000 4500 6000 31

32. Where a, b and c are constants and CS is the compressive strength in psi, t is the compressive strength time in hrs . The constants a, b and c are assumed to be functions of slurry weight ( Sw ) Where S W is slurry weight in kg/l 32 CS = a + b t 0.5 + c / t 0.5 R 2 = 0.999 a = 84126.25 - 11167 S W 3 R 2 = 0.995 b= -8791.66 + 1200.551 S W 3 R 2 = 0.999 c = -188777 + 24656.6 S W 3 R 2 = 0.990

33. CEMENT ADDITIVES Cement additives can be used to : • vary the slurry density • change the compressive strength • accelerate or retard the setting time • control filtration and fluid loss • reduce slurry viscosity • adjust thickening time Adding an extender to the cement can increase yield, but it can also increase viscosity and thickening time and reduce density, filtration and compressive strength. 33

34. Cement Slurry The cement slurry which is used in the above operations is made up from: cement powder; water; and chemical additives. 34 Cement Slurry Accelerators CaCI2 NaCI Mud contaminants Diesel NaOH Heavy weight material Barite Haemitite Extenders Bentonite Pozzolan Friction reducers (dispersants ) Polymers Calcium ligno sulphonate Fluid loss additives Organic polymers CMHEC Retarders Calcium lignosulphonateCMHEC Saturated salt solution

35. BOGUE CALCULATION API uses the following equations for calculating the weight percent of the four main minerals in Portland cement clinker from the weight percent of the oxides present 35 C 3 S = 4.0710CaO - 7.6024SiO 2 - 1.4297Fe 2 O 3 - 6.7187Al 2 O 3 C 2 S = 8.6024SiO 2 + 1.0785Fe 2 O 3 + 5.0683Al 2 O 3 - 3.0710CaO C 3 A = 2.6504Al 2 O 3 - 1.6920Fe 2 O 3 C 4 AF = 3.0432Fe 2 O 3 Oxide Weight Percent Lime ( CaO ) 65.6 Silica ( SiO 2 ) 22.2 Alumina ( Al 2 O 3 ) 5.8 Ferric Oxide ( Fe 2 O 3 ) 2.8 C 3 S = 50.16% C 2 S = 25.89% C 3 A = 10.64% C 4 AF = 8.51%

36. DENSITY CONTROL Normal slurry density for neat cement ranges from 14.8 to16.4 ppg Decreasing the density may be required when lost circulation is a problem . High pore pressures may require increasing the density of the cement. Lightweight additives or extenders reduce the slurry density. The excess water increases thickening time and free water and decreases compressive strength 36

37. Bentonite Due to the large surface area, bentonite requires considerable water to be pumped. Increasing the overall water content of the slurry reduces the weight . In addition to reducing slurry density and cost per unit volume of cement, free water separation, fluid loss and thickening time (at higher concentrations ). 37 1.3 gallons of water for every 2% bentonite in a sack

38. While it will increase yield, slurry viscosity; above a concentration of 10% by weight, dispersants must be added to the slurry . Bentonite will promote strength retrogression above 230°F. 38

39. Pozzolan Pozzolans are siliceous material which will react with lime and water This compound contributes nothing to strength Silica combines with the free lime to form Calcium Monosilicate , a cementatious compound. The result is a cement with less tendency to retrogress in strength. 39

40. There are two types of pozzolans : Natural pozzolans are of volcanic origin and are commonly termed volcanic ash. Artificial Pozzolans include glass, furnace slag, and a residue collected from chimneys of coal burning power plants called "fly ash". Pozzolans will increase slurry volumes, decrease slurry density and provides resistance to attack by corrosive fluids. It will also help to counteract strength retrogression but will not eliminate it. 40 Artificial Natural

41. Gilsonite and Kolite Gilsonite and Kolite can be used for density reduction, though they are more often used for lost circulation material in cement . Gilsonite is a black lustrous asphalt Kolite is crushed coal 41 GILSONITE ( lbs / sk ) WATER (gals/ sk ) DENSITY ( lbs /gal) YIELD (cu ft / sk ) 10 15 25 50 5.0 5.4 5.6 6.0 7.0 15.8 14.7 14.3 13.6 12.4 1.15 1.36 1.46 1.66 2.17

42. Nitrogen Nitrogen can be used to reduce slurry density in foamed cement Common slurry densities range from 4 to 11 ppg . Higher placement pressures require larger volumes of nitrogen since nitrogen is a compressible fluid . The density of a foamed cement will change with depth if the nitrogen to cement ratios are kept constant 42

43. The density can be increased by using weight material such as Barite Ilmenite Hematite Sand Salt Barite and sand are the most common weight materials used with sand being the least expensive. 43 MATERIALS SPESIFIC GRAVITY GRIND (MESH) MAXIMUM DENSITY(PPG) EXTRA WATER NEEDED EFFECT COMPRESSIVE STRENGTH Ottawa Sand 2.63 20-100 18 None None Barite 4.25 325 19 20% Reduce Coarse Barite 4 16-80 20 None None Hematite 5.02 40-200 20 2% None Ilmenite 4.45 30-200 20 None None Dispersant --- --- 17.5 None Increase Salt --- --- 18 --- Reduce

44. ACCELERATORS Accelerators are used to shorten thickening time Most inorganic materials are accelerators and organic materials are retarders . Accelerators are especially important in shallow wells where temperatures are low and therefore the slurry may take a long time to set. Calcium Chloride is the most popular accelerator. Normal concentrations are 2 to 4 %. Sodium Chloride is inconsistent in its application. At low concentrations, salt is an accelerator; whereas at high concentrations, it is a retarder . In the mid range, it depends upon the temperature and the class of cement used 44 Calcium Chloride CaCl2 Sodium Chloride NaCl S eawater

45. Sea water has a sodium chloride content of 20,000 to 30,000 ppm. Salt is always an accelerator in sea water Other accelerators are ammonium chloride ( NH 4 Cl) , gypsum, and sodium silicate . 45

46. RETARDERS Retarders increase the thickening time of cement slurries One common retarder is CMHEC ( carboxymethyl hydroxyethyl cellulose ) CMHEC is always a retarder and never an accelerator . It is effective to temperatures up to at least 450°F. The degree of retardation is directly proportional to the amount used 46 CMHEC Calcium Lignosulfonate Sodium chloride NaCl

47. Calcium Lignosulfonate is a retarder. Some grades are only effective to 165°F; whereas, other grades are effective to 300°F. When used in low concentrations, lignosulfonates are effective retarders; however in high concentrations, they will act as accelerators depending upon the grade. They are more economical than CMHEC. Sodium chloride in high concentrations (above 120,000 ppm) is a retarder Other retarders are borax and most fluid loss additives . 47

48. FLUID LOSS ADDITIVES Using long chain polymers as fluid loss agents such as FLAC, CMHEC, and CHEMAD-1 . Calcium chloride in combination with most fluid loss additives can cause the cement to flash set. Sodium chloride adversely affects the fluid loss properties of cement slurries . Good fluid loss additives should not affect the density, yield, water requirements , or compressive strength of the cement. FRICTION REDUCERS Friction reducers are dispersants used to lower the yield point of the slurry Typical friction reducers are organic acids, lignosulfonate , alkyl aryl sulfonate , polyphosphate , and salt . Many friction reducers act as retarders . 48

49. LOST CIRCULATION MATERIAL Gilsonite , kolite , perlite and walnut hulls are granular materials. Granular materials are best for bridging across fractures. Since they have a lower specific gravity than portland cement, granular lost circulation materials will reduce the density of the slurry . In most cases, they will reduce the compressive strength of the cement. 49 Granular Laminated Fibrous

50. Accelerator Retarder Extender Water Requirement Ineffective Ineffective High Viscosity Relatively Decrease Decrease Increase Thickening Time Decrease Increase Decrease Compressive Strength Relatively Increase Relatively Decrease Decrease Fluid Loss Relatively Decrease Decrease Decrease 50 The laminated material used mostly in cement is cellophane flake Cellophane flakes have very little effect on cement properties except to reduce compressive strength. Fibrous materials used for lost circulation in drilling mud, they are seldom used with cement

51. Refrences Directional and Horizontal Drilling Manual By Richard S. Carden Well cementing By Erik B.Nelson Drilling Engineering Heriot-Watt University By John Ford Modeling of Compressive Strength of Cement Slurry By Joel O. F University of Port Harcourt, NIGERIA 51

52. THANK YOU 52