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08 A Cementing

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  • 1. Cementing Cementing • Objectives • Primary and remedial placement techniques • Applicable tools • Job Sequences • Slurry composition • Job design calculations • Required slurry testing
  • 2. Cement Job Planning 1. Identify purpose for placing cement a) Primary - casing, liner, or tieback b) Remedial – sidetrack or abandonment 2. Identify wellbore parameters a) Pressure b) Temperature c) Fluid types d) Formations 3. Determine TOC, and cement density and volume a) Coverage b) Fracture limitations 4. Downhole equipment tools and procedures 5. Communicate job details to Service Company Primary Cementing Definition- Primary cementing is the process of effectively displacing the drilling fluid and placement of cement slurry(s) to form a continuous and competent cement sheath within the wellbore annulus, while maintaining well control.
  • 3. Primary Cementing: Objectives • Support – Tension – Lateral – buckling, pressures • Isolation – From Surface – Cross flow between zones • Compliance – Government requirements – Company requirements Isolation • Isolation between zones • Isolation to surface • For the life of the well Aquifer – Production Isolation – Environmental – Well Control Gas Sand
  • 4. Intermediate Objectives Objective Action Remove mud / debris Hole condition, centralizers, spacers/washes, from area to be cemented flow rate, wiper plugs, pipe movement Maintain control of the Calculate hydrostatic pressure effects of fluid wellbore columns, Monitor and control U-tube effect Deliver slurry volume with Choose cement type and additives for performance properties needed density, rheology, filtration, yield, required for job compressive strength, etc. Calculate cement volume required. Design job for best placement. Primary Cementing Technique and Issues • Prepare wellbore for casing and cementing operation – Clean cuttings and debris out of hole – Condition mud for easy removal • Run casing string with appropriate tools for the job – Float equipment, stage tool, liner hanger – Centralizers, external casing packer, liner top packer • Mix a dry cement blend on surface with mix water – Cement – Additives – Mix water • Pump it into place in liquid form from the surface – Mud Removal – Cement coverage – Timing • Allow the cement to hydrate and harden in place – Time – Temperature
  • 5. Running the Casing • Pull wear bushing. • Confirm unobstructed access from v-door to rotary table. • Rig up casing handling tools – spider, elevator, tongs, hydraulic power, torque turn, fill up line. • Pick up / make up shoe joints. Test floats. • Run in hole. Continue running casing, filling as required. Add centralizers. Float Equipment • Float Shoe • Float Collar • Acts as check valve • Prevents cement back flow into casing • Typically run in pairs • Available in differential fill design • All components drillable
  • 6. Float Equipment Valve Operation Centralizer Types Bow Type Subs Solid Type • Welded bow • Spiralizer • Turbolizer • Shorty spiral • Spiral Bow • Straight • Rigid Bow
  • 7. Wiper Plugs Purpose - to mechanically separate fluids (drilling fluids, washes, spacers, cement, displacement fluid) within the drill pipe or casing during cementing operations • Bottom Plug • Top Plug Job Types – Conventional Casing
  • 8. Job Types – Inner String Casing Job Types – Liner
  • 9. Wiper Plugs – Ahead of Spacers or Behind? Uncontaminated Slurry in “Wiped” casing behind plug Uncontaminated Spacer and Slurry in “Wiped” casing behind plug Spacer ahead of plug “Film” of Drilling Drilling Fluid Fluid not wiped from casing ID Inner String Stab-in Adapters Latch-In Screw-In Tag-In • Provides hydraulic seal between inner string bore and float equipment. • Piston effect tries to disengage seals during cementing. • Inner string handling tools use false rotary mounted on casing.
  • 10. Stage Cementing Tools • Also available in hydraulically actuated opening sleeve. • Closing plug is pumped down as wiper plug after slurry. • Both plugs are drillable. External Casing Packer (ECP) / Stage Tool
  • 11. Casing Flotation for ERD • Trapped air pocket above shoe creates buoyant force. • This reduces drag due to normal force and allows casing to slide longer distances at high angle. • One time conversion to normal circulation mode. Well Security and Control • Fracture Gradients • Formation Pressures • Hydrostatic Pressures • Equivalent Circulating Density (ECD) • “U” Tubing, Cement “Free Fall”
  • 12. U-Tubing and Cement Free Fall • Cement slurry density inside pipe is greater than the density of the fluid in the annulus, so it will fall to seek an equilibrium. • With a closed system this will tend to pull a vacuum at the wellhead. • How fast will it fall? Depends on density differential and friction factor. Hold back pressure if needed. • Modeling with cementing simulator Key Points • When cement is a liquid, it transmits hydraulic pressure like other fluids • When cement is a solid, it is resistant to hydraulic or gas pressures. • During the transition phase from a liquid to a solid, cement loses the ability to transmit hydraulic pressure but is not yet able to resist hydraulic or gas pressures
  • 13. Volume Calculations • Capacity – annular, between pipe and pipe or pipe and hole – internal, within a pipe or hole • Cement Volume – annular volumes – pipe or hole volume – % Excess, accounts for actual hole size being greater than gauge • Displacement Volume Annular Volume To calculate the annular volume between casing and hole equation is: CapacityAN x length = volume 12-1/4” ID of Hole Capacity in bbl/ft = ((ID2 - OD2) x 0.0009713) (12.252 – 9.6252) x 0.0009713 = 9-5/8” OD = 0.0558 bbl/ft of pipe 2500 ft 0.0558 bbl/ft x 2,500 ft = 139.5 bbl
  • 14. Casing Volume To calculate the internal volume of a casing the equation is: CapacityIN x length = volume 8.677 “ ID Capacity in bbl/ft = ID2 x 0.0009713 = bbl/ft 8.6772 x 0.0009713 = 0.0731 bbl/ft 126 ft 0.0731 bbl/ft x 126 ft. = 9.2 bbl Volume Calculations Volume of Cement = Cased Hole Volume VCH = CCH x LCH Cased Hole volume + Open Hole Volume Open Hole Volume VOH = COH x LOH x Ef + Shoe Joint Volume Shoe Joint Volume VShoe Joint= CCasingx LShoe Joint
  • 15. 72lb 13-3/8” Casing 12.341” ID Cased Hole Volume CCH x LCH = VCH 47lb 9-5/8” Casing 0.058 bbl/ft x 500 ft = 8.677” ID 29 bbls TOC @ 1000 ft 1500 ft 12-1/4” Hole Open Hole Volume COH x LOH = VOH Shoe Joint Volume 0.0558 bbl/ft x 2500 ft CCasingx LShoe Jt = VShoe Jt = 139.5 bbls + Excess 0.0731 bbl/ft x 126 ft = 9.2 bbls 126 ft 4000 ft % Excess Calculation % Excess is used to compensate for hole size being over gauge size. Generally use standard recommendations for % excess in open hole, unless there is caliper data available or it is otherwise agreed upon to use a different value. Open Volume including Excess = ((% Excess ÷ 100) + 1) x Volume For 100% excess this means 2x the calculated volume. For 50 % excess its 1.5x the calculated volume.
  • 16. Recommended % Excess for Open Hole % Excess with % Excess with Depth (feet) WBM OBM 0 – 4,000 100 50 4,000 – 8,000 75 25 8,000 – 10,000 50 15 10,000 – 18,000 35 15 Greater than 25 15 18,000 Volume of Cement = Open Hole volume 279 bbls TOC @ 1000 ft + + Cased Hole Volume 29 bbls 1500 ft + + Shoe Joint Volume 9.2 bbls = 317.2 bbls 126 ft 4000 ft
  • 17. Displacement Volume 8.677 “ ID Equation for the Volume of casing is: Capacity x length = bbls Capacity = ID2 x 0.0009713 = bbl/ft (8.677)2 x 0.0009713 = 0.0731 bbl/ft 3,874 ft Length = Sfc. to Float Collar @ 3,874 ft Volume = 0.0731 bbl/ft x 3,874 ft. = 283.2 bbls To determine the % excess for an enlarged hole diameter. % Excess = ([(ID22 - OD2) / (ID12 - OD2)] -1) x 100 % Excess = ((14.752 – 9.6252) / (12.252 – 9.6252) -1) x 100 = 118 % ID1 = gauge hole diameter, in. (12.25 in this case) ID2 = enlarged hole diameter from caliper, in. (14.75 in this case) OD = casing size, in. (9.625 in this case)
  • 18. Summary of Calculations Phydrostatic = MWppg x .052 x TVDft Fluid Column Height in ft = MWppg = Pressurepsi ÷ .052 ÷ TVDft Volume in bbls ÷ Capacity bbl/ft TVDft = Pressurepsi ÷ .052 ÷ MWppg Volume Excess = Calculated Volume x %Excess / 100 Gradientpsi/ft = MWppg x .052 Gradientpsi/ft = Pressurepsi ÷ TVDft Volume including Excess = ((%Excess / 100)+1) x Calculated Vol MWppg = Gradientpsi/ ft ÷ .052 Deq = SQRT((% excess /100+1) x ID2 )- Capacitybbl/ft = (OD2 x % excess /100)) Hole Diameter2 x 0.0009713 Annular Capacitybbl/ft = %Excess = ((ID22-OD2) / (ID12-OD2)-1)x100 (Hole diameter2 - Pipe Diameter2) x 0.0009713 Casing ID = SQRT[OD2 - (Cwt x 0.3692)] Or Annular Capacitybbl/ft = (Hole diameter2 - Pipe Diameter2) / 1029.4 Cement Slurry Properties • Density (ppg) • Yield (ft3/sack) • Rheology (PV, YP) • Free Water (%) • Solids Settling • Fluid Loss (cc) • Thickening Time (hh:mm to 100 Bc) • Transition Time (hh:mm) • Compressive Strength (psi)
  • 19. Thickening Time • Thickening Time is dependent upon: 1.Temperature 2.Water content 100 3.Additives 120 F 80 4.Cement type 150 F 60 5.Pressure Bc 40 20 ↑ Temperature 0 10 20 30 40 50 60 70 80 90 100 110 ↓ Thickening Time Time Thickening Time • What Thickening Time is: – It is a dynamic laboratory simulation conducted under standard conditions and procedures – It provides an estimate of time in which cement slurry remains pumpable
  • 20. Thickening Time • What Thickening Time is not: – It is not an exact simulation of wellbore conditions – It is not a measurement of cement setting – It is not the amount of time the cement will remain pumpable if there are any unplanned shutdown periods during the job Thickening Time Time that is assumed to be available for placing cement – Mixing and pumping: volume / rate = time – Batch Blending = time – Displacement: volume / rate = time – Safety Factor = time Static times that are not adequately accounted for in the Thickening Time test – Planned Interruptions = static time – Unplanned Interruptions = static time
  • 21. Transition Time Definition: Time between which a cement slurry behaves as a liquid and behaves as a solid – Liquid - fully transmits hydraulic force – Solid - resistant to any hydraulic force During this transition time the cement develops gel strength and loses its ability to transmit hydraulic force. Transition Time • Generally accepted gel strength values – Initial Set = 100 lb/100ft2 for initial set Final Set = 500 lb/100ft2 Transition Time = time from 100 lb/100ft2 to 500 lb/100ft2 • The initial set value is now more often referred to as the critical static gel strength. This value can and should be calculated. • The 500 lb/100ft2 value is a rule-of-thumb, useful for comparison purposes .
  • 22. Cementing Materials • Cement – API – Construction • Water – Fresh – Sea • Additives – Generic – Proprietary Oilwell Cement: Applications Class Typical Use North America, Limited to local regions of manufacture when A conditions require moderate to high sulfate resistance. North America, Conductor and Surface casing jobs when B special properties are not required. Conductor and Surface jobs, when conditions require high C early strength. G International, standard for oilwell cement. H Most common cement for Gulf Coast operations.
  • 23. Water • Fresh water, Drill Water – Standard for API specification test – Typical for land operations – “City” or potable water should be used. Water from a stream, lake, bayou or irrigation ditch may contain organic compounds which will interfere with the cement performance. • Sea Water – Typical for offshore operations. – Tends to accelerate so often the switch is made to fresh water. • Brackish water – Can be used but must monitor quality. Oilwell Cement: Units • 1 sack of cement weighs 94 lbs • 1 sack = 1 cubic foot • Regardless of whether it is in bulk form or sack the standard unit of measure is the “sack”, and one sack = 94 pounds. • Bulk # of sacks x 94lb/sk = pounds of cement Pounds of cement / 94lb/sk = # of sacks
  • 24. Oilwell Cement: Water requirement Compressive Strength 6,000 Hydration Standard Water Water Settling 2,000 Not Pumpable Pumpable 30 40 50 Water Content % Cement Hydration • Tricalcium Aluminate in the cement grain begins to interact with the water. • A layer of Calcium Silicate Hydrate forms over the grain, causing osmotic pressure to increase as water diffuses inside the grain. • Calcium Silicate Hydrate fibrils form and grow and interlink between grains, thereby increasing strength and decreasing permeability. From Schlumberger
  • 25. Water Requirement for API Cements Type of Cement Water Requirement API Class C 6.3 gal/94-lb sack or 56% API Class A 5.2 gal/94-lb sack or 46% API Class G 5.0 gal/94-lb sack or 44% API Class H 4.3 gal/94-lb sack or 38% Cement Additives • Definition: A cement additive is any material added to cement for the purpose of modifying the physical or chemical properties of the cement slurry or the set cement. • Physical forms of additives are: – Dry powder, granules and flakes. – Liquids and liquid emulsions.
  • 26. Cement Additives What properties of the cement slurry or set cement can be controlled by additives? – Density – Transition Time – Rheology – Compressive Strength – Free water – Strength Retrogression – Solids settling – Expansion – Fluid loss – Bond Strength – Thickening time Cement Additives: Categories • Extenders - ↑ Yield, ↓ Cost, ↓ Density • Weighting Agents - ↑ Density, Maintain well control • Fluid Loss Control - ↓ Dehydration • Accelerators - ↓ Thickening time • Retarders - ↑ Thickening time • Dispersants - ↓ Viscosity • Lost Circulation - ↓ Slurry loss to formation • Strength Retrogression Preventatives - ↓ CS Loss • Gas Control - ↓ Transition time • Anti-foam - ↓ Air entrainment
  • 27. Cement Additives: Inconsistencies • Salt accelerates at concentration below 10%, but at concentrations above 10% it retards • Some Fluid Loss additives viscosify, but others disperse • Most retarders disperse, but some viscosify • Dispersants almost always retard, but at low temperatures they can accelerate Cement Additives: Inconsistencies • High temperatures require high concentration of retarder, but in some cases excessive retarder decreases pump time • With slurry designs containing large amounts of additives, 5 or more, the synergistic effects often overcome the primary effects
  • 28. Cement Additives: Units of Addition • Dry – bwoc, by weight of cement – lb/sk, pound per sack of cement – bwow, by weight of water Example: 1% bwoc = 1 x 94 / 100 = 0.94 lbs • Liquid – gps or gal/sk, gallon per sack of cement – gphs, gallon per hundred sacks of cement Slurry Design Cement Slurry design consists of determining the optimum mix of Cement, Water and Additives to provide the required properties for placement and long term performance of the cement sheath. • Design Concepts • General Designs • Basic Requirements • Special Conditions
  • 29. Design Concepts • Designs should be simple – Minimum additives – Easier to take from lab to field • Designs should be consistent – Same blends, similar additive • Designs should be flexible – Not sensitive to minor fluctuations in additive concentration or well conditions • Designs must meet requirements Wellbore Conditions vs Slurry Properties Parameters Properties Pore and fracture pressures - Density Lost circulation Temperatures, BHST, BHCT - Thickening Time Hole and casing geometries - Rheology Formation properties - Fluid Loss Mud Properties - Compatibility Cement Fill - Volume, Yield
  • 30. Lead, Tail and Single Slurries • Lead Slurries – Extended, higher yield per sack, lighter weight – Lower cost, lower performance • Tail Slurries – Mixed at normal density – Optimized properties • Single Slurries – One slurry at one density Slurry Design Guidelines • When there is oil or synthetic mud in the hole – Must test compatibilities • Across salt zones – – Cement slurry must be salt tolerant • For temperatures greater than 250° F – Silica sand or flour must be added
  • 31. Slurry Design Priorities 1. Density 2. Thickening Time 3. Mixability 4. Rheology 5. Fluid Loss Control 6. Compressive Strength 7. Free Fluid and Settling Slurry Design: General Requirements Density + 1.0 ppg > drilling fluid density + 0.5 ppg > spacer density < Equivalent Circulating Density (ECD) to fracture formation Thickening Time Job time plus safety factor, one hour plus Production / gas control - right angle set
  • 32. Slurry Design: General Requirements Rheology Conductor / Surface - mixable and pumpable, thixotropic for lost circulation Intermediate PV < 150, YP < 40 Production PV < 100, YP < 20 Fluid Loss Surface < 500cc/30min Intermediate < 250 cc/30min Production < 100 cc/30min Gas Control < 50 cc/30min Slurry Design: General Requirements Compressive Strength 8 hours maximum for WOC, 500 psi 24 hr, 1000 psi Perforating, 1500 to 2000 psi Free Water Surface strings < 1.0 Deviated wellbores 0% Production strings 0%
  • 33. Conductor and Intermediate Production Deep Production SLURRY Surface Casings Casings and Casings and Liners and for PROPERTIES Drilling Liners Liners Gas Control + 1 lb/gal > drilling fluid density DENSITY < Equivalent Circulating Density (ECD) to fracture formation Job time plus at least one hour for safety factor THICKENING TIME For Production casings or for gas control, the TT chart should display a right angle set (transition from 40 to 100 Bc less than 15 minutes) FREE WATER < 1.0% < 0.5 % 0% 0% FLUID LOSS NA < 250 < 100 < 50 RHEOLOGY < 150 < 150 < 100 < 100 PV YP < 50 < 40 < 25 < 20 Compressive Strength < 12 <8 <8 <8 WOC (hrs to 500psi) 1,000 2,000 2,000 2,000 24 hr Thickening Time When specifying Thickening Time requirement: • Calculate, Do Not Estimate – Temperature. Use simulators as necessary. – Time to mix and pump lead and tail. Time to drop plugs. Displacement time. Safety factor • Evaluate risks – TT must be long enough to insure placement. – Excessive TT increases the risk of well control problems and poor isolation • Remember lab test is a dynamic test
  • 34. Densified Slurries • Cement Slurry density be increased by using less water through the use of dispersants to maintain rheological properties • Class G cements can be mixed at up to 16.5 ppg and Class H cements can be mixed at up to 17.2 ppg. • Hematite common weighting agent. Remedial Cementing • Squeeze - The placement of a cement slurry, under pressure, against a permeable formation causing the slurry to dehydrate and create a cement seal across the formation face. – Repair a primary cement job or casing leak – Add height to cement column to produce upper zones – Eliminate water from the hydrocarbon zone – Reduce the producing gas:oil ratio – Seal the annulus of a liner top or casing shoe – Plug zone(s) in a multi-zone injector or production well • Balanced Plug - The placement of a cement slurry, under normal circulation, to provide isolation between the lower and upper portion of the wellbore. – Sidetrack – Plug back – Abandonment
  • 35. Spacers for Plugs • Separate mud and cement with an adequate volume of spacer or wash • WBM: Chemical wash or spacer • SBM: add surfactant to water wet surfaces • Volume of spacer/wash ahead to be equivalent to 500ft of annular fill • Spacer behind at volume calculated to balance • Always calculate the loss in hydrostatic pressure when using water or base oil/synthetic ahead of a cement plug assuming gauge hole Plug Cement Volume • Use a caliper log to determine the cement volumes and where to set the plug • Set plug in a near gauge section of the hole • If no caliper, use the recommended excess • Actual excess should account for knowledge of the particular area and hole conditions Hole Size (in) % Excess (WBM) % Excess (SBM) 30-26 200 - 24-30 100 - 14-3/4 – 17-1/2 50 20 12-1/4 30 20 6 – 8-1/2 30 20
  • 36. USI CBL comparison Cement USI CBL Heavy, medium, good bond Very light, good bond De-bonded, dry microannulus Liquid microannulus Mud Layer Mud Channel Contaminated Gas Channel Good interpretation Ambiguous Very ambiguous or not detectable Acknowledgements • Thanks to Unocal for their assistance in the preparation of this material • Many of the casing tool examples are from Davis-Lynch company. • Many of the casing handling tool examples are from Varco and BJ as provided by Weatherford.
  • 37. Notes: __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________
  • 38. Notes: __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________