Well Cementing

Courtesy: Halliburton

Well Cementing Khalil Rahman Principal Geomechanics Specialist Baker RDS, Perth, Australia Email: [email protected] Tel: 92150617

Cementing Overview •

Primary Cementing (casings & Plugs)

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Secondary (Remedial) Cementing

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Gas Migration

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Mud Displacement

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Casing Equipment

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Cementing Equipment

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Cement Types

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Cement Additives

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Cement Design

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Cement Testing

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Cement Evaluation

Why Primary Cementing? •

Zonal Isolation – Prevents fluids migration from one zone to another zone

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Supporting/Reinforcing Casing – Increased strength against high pressure operations such as fracturing

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Casing Protection

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Well Integrity

– A barrier against corrosive environment – No loose hanging of csings/liners

Single Stage Primary Cementing

Primary Plug Cementing Applications:

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Two Plugs: Bottom & Top

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Maximum cement/mud separation

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Bottom plug wipes mud sheath off inside casing surface

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Top plug gives surface indication when cement placement is complete

• Zonal Isolation • Sidetrack • Lost circulation • Abandonment

– Pressure rise at the surface

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Failure in Cement Plugs

Squeeze Cementing - Bradenhead

Hard to get cement on the upper side due to gravity

Often gas bubbles creates fluid flow channel.

Squeeze Cementing – With Packer

Gas Migration Through Cement • • • •

Gas Migration Through Cement

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Pressure loss in cement column causes the loss of overbalance in high pressure zones first Fluid loss continues in other low pressure zones (still overbalance) Meanwhile gas enters wellbore and percolates up annulus in high pressured zones.

Gas Migration Through Cement Permanent channel left after cement sets

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Cement slurry placed Slurry behaves as a fluid Transmits fluid hydrostatic pressure Filtrate loss causes pressure loss

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Time-Dependent Fluid Loss & Gas Migration

Mud Removal/Displacement • The number 1 cause of a poor quality primary cement job is poor mud removal

Mud Displacement Efficiency

Techniques for Efficient Mud Removal • Mud conditioning • Centralisation • Pipe movement • Mechanical aids

Displacement Efficiency = Cement Area/Annular Area

• Fluid velocity • Spacers and Flushes

Mud Removal - Centralisation Centralisation of casing is critical for mud displacement and complete zonal isolation

Mud Removal – Pipe Movement • Rotation and reciprocation of the pipe fitted with centralizer and scratchers can help remove gelled mud, mud cake and keep casing centred.

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Mud Removal - Circulation

Mud Removal – Mechanical Aids • Mechanical aids can improve mud removal

Mud Removal – Flow Regime

Mud Removal – Effect of Static Time

Spacers & Flushers

Spacers & Flushes •

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Fluid compatibility Fluid separation Mud displacement Rheology Solid suspension Rate

Typical cement spacer components – Freshwater – Viscosifying agent (well specific rheology design) – Weighting agent – Surfactant for SBM/OBM use

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Flushes – Base oil or freshwater with surfactant – Reactive flushes – Flowcheck

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Spacers trains – Ideal for highly deviated wells – Thin fluid thins mud and dislodges cuttings in turbulance – Viscous fluid carries solids and erodes gelled mud

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Casing Equipment

Casing Equipment

• Floating equipment • Cement plugs • Cement head/plug containers • Inner strings • Centralisers

Float Equipment

Casing Equipment – Floating Shoes

• Provides casing buoyancy • Prevents re-entry of cement • Guides casing into hole • Provides landing seats for cementing plugs

Cementing Plugs

Casing Equipment - Centralisers

• Removes mud sheath to help prevent contamination or wet shoe joints • Separate cements from mud • Prevents over-diplacement of cement • Allows pressure testing of casing prior to drillout • Provides surface indication that displacement is complete • Non-rotating (as shown) or standard

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Innerstring Cementing • Reduce displacement volume and therefore reduces job time • Reduce drill-out time • Safety (prevent handling large plugs) • Availability and cost of large plugs & cementing • Prevents channelling in large casing • Prevents casing collapse by applying pressure to casing/tubing annulus

Cementing Equipment • Bulk storage & delivery system • Steady flow bin • Cement mixing and pumping unit • Monitoring package • Liquid additive system/mix tank

Cementing Equipment - Onshore

Offshore Cementing Unit

Cementing Equipment – Liquid Additive System (LAS)

Cement Mixing System

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Cement Types

Cement Additives

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Class A: General purpose construction grade (Type GP) – Low temperature < 170 deg F (<=6000 ft deep)

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Class B: Low temperature sulphate resistant (Type SR; <=6000 ft deep)

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Class C: Low temperature – high early strength (<=6000 ft deep)

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Class D: Moderate temperature & pressure (6000 – 10000 ft deep)

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Class E: High temperatures & pressures (10000 – 14000 ft deep)

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Class F: Extremely HTHP (10000 – 16000 ft deep)

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Class G & H: Basic well cement – surface to 8000 ft deep – accelerators and retarders for wide temp. range

Cement Additives (cont..) • Heavy Weight Additive – Increase slurry density to control formation pressure

• Accelerators – Shorten initial thickening time and accelerate compressive strength development

• Retarders – Slow cement hydration allowing for safe placement

• Fluid loss additives – Lower filtrate loss during and after placement

• Dispersant – Lower rheology and increase rate for turbulent flow

• Light weight additive – Lower cement density and hydrostatic pressure for low frac gradients and more economic slurries

Cementing Design Criteria • • • • • • • • • •

Bottomhole temperature and pressure Weight/composition of drilling fluid Fracture pressure and pore pressure Hole size MD/TVD Casing size/weight/grade Casing equipment Volume of cement required Job time requirements Slurry mix methods / parameters

• Defoamers – Prevent and release entrained air while mixing

• Gas Control Additives – Prevent gas migration during setting

• Silica Flour – Typically use 35% above 230 deg F for high temperature retrogression

• Thixotropic Additives – For lost circulation, is thin while pumping and gels rapidly when static

• Lost Circulation Materials – Various additives to control lost circulation See in your course reader about 20 additives for different function

Cement Testing • Common lab tests for cement slurries – Thickening time – UCA or compressive strength – Rheology – Fluid loss – Free water – Static gel strength

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Thickening Time Chart

UCA Chart

Cement Evaluation – CBL & CAST

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