squeeze cementing

Squeeze Cementing

Squeeze Definition

The placement of a cement slurry under pressure against a permeable formation causing the slurry to dehydrate and create a cementitious seal across the formation face.

Reasons ForSqueeze Cementing

Repair primary cement job Channels Voids due to losses

Shut-off produced water Shut-off produced gas Repair casing leaks Abandon depleted zones Selective shut-off for water

injection Seal lost circulation zone Shut off fluid migration

Squeeze SlurryDesign

Considerations: Viscosity Thickening time Compressive strength Fluid loss control

Squeeze pressure Slurry volume

Primary Concerns

Squeeze Purpose Formation Types Establishing an Injection Rate Method of Squeezing Slurry Design Laboratory Testing Slurry Placement Reasons for Failure

Good Habits

Pre-Job Meeting Review Procedures Discuss Potential Problems Establish alternative Procedure

Good Record Keeping Pressure Times Densities, Rates and Volumes

Cement SlurryViscosity

Low viscosity. Entry into small fractures and

small cracks Slurries using dispersants

preferred High viscosity

Useful for cementing large voids (vugs)

Will not flow into narrow restrictions unless high pressure applied

High gel strength restricts movement of the slurry

Laboratory Testing

Thickening Time Always use Hesitation Squeeze

Schedule Simulate Batch Mixing Monitor Gelling Tendencies Monitor Settling Tendencies Modify API Schedule for Actual

Down Hole Conditions Continue Hesitation until Slurry

Sets

Laboratory Testing

Fluid Loss Use Test Procedure in BJ Lab

Manual Heat Slurry From Ambient

Above 200°F Condition in Pressurized

Consistometer or use Stirring Fluid Loss Cell

Thickening Time

Required job time plus reversal of excess cement

Temperature and pressure Higher than in primary cementing Use API squeeze schedules for

testing Shallow wells

Short times (2 - 3 hours) Use of accelerators

Deep wells and hesitation squeezes Long times (up to hours)

Compressive Strength

High compressive strength Withstand shocks from running

tools, drilling etc. To prevent cracking during re-

perforation Partially dehydrated cement

(filter cake) Will develop sufficient strength Not of primary concern

Fluid Loss Control

Low pressure squeeze Cement to fill all voids Minimum node build up

Important with permeable formations Very low permeability

200 ml/30 minutes Low / medium permeability

100 to 200 ml/30 minutes High permeability (>100 md)

25 to 100 ml/30 minutes

Fluid Loss Control (cont.)

High pressure squeeze Medium to high permeability

200 to 500 ml/30 minutes Fractured limestones, cement

travels large distance from wellbore, re-perforation difficult: High fluid loss rate

300 to 800 ml/30 minutes Lost circulation material beneficial Lead and tail (hesitate)

Lead 300 to 800 ml/ 30 min Tail <300 ml/30 minutes

CementNode

PrimaryCement

Formation

DehydratedCement

Casing

CementNodes

FLUID LOSS(P = 1,000 psi)

800 ml / 30 min

150 ml / 30 min

50 ml / 30 min

15 ml / 30 min6 inchCasing

Cement Node Formation

Rate Of Filter Cake Build Up

Permeability of the formation Low = slow leak off High = fast leak off

Differential pressure applied Time over which pressure is

applied Slurry fluid loss control

Low = slow dehydration

High = fast dehydration Low permeability and fluid loss can

give excessive job times High permeability and fluid loss

can cause bridges

Rate of Filter Cake Build Up (cont.)

For a constant differential pressure applied Rate of cement filter cake growth

for a 30 md formation is approximately twice that for a 300 md formation

For a given cement slurry, the time taken to form a filter cake of given thickness will double for a ten fold decrease in formation permeability

Filter Cake Permeability

Lower fluid loss = lower cake permeability = less solids filtered out of slurry

Fluid Loss Time to Form Permeability

(API) 2.0 in. Cake

Neat cement < 30 sec. ± 5.0 md300 cc < 4 min. ± 0.5 md25 cc > 4 hours ± 0.05 md

Filter cake growth is indirectly proportional to the cake's permeability

Filter Cake Permeability (cont.)

Squeeze pressure Increasing squeeze pressure

does not reduce the permeability of the filter cake

Flow of filtrate through a filter cake is proportional to the permeability of that cake Darcy's law

Flow rate through filter cake of given permeability is proportional to the differential pressure

Cement Slurry Volume

Dependent upon length of interval to be squeezed

For job convenience 10 to 20 barrels are prepared

Volume for high pressure squeezes should be minimized Fracture at low pump rate Keep pressure below fracture

propagation pressure

Cement Slurry Volume (cont.)

Rules of thumb: Cement volume should not

exceed capacity of treating string Use two sacks of cement per foot

of perforations If injection rate after break down

is 2.0 bpm or more: Minimum volume 100 sacks

If injection rate after break down is less than 2.0 bpm: Minimum volume 50 sacks

Planning

Establish Two-Rate Fluid Injection Profile

Determine Fracture Gradient Determine BHSqT Determine Top of Existing

Cement Determine Formation Pore

Pressure

Planning - Cont.

Determine Formation Fluid Characteristics

Calculate Hydrostatic Pressure Differential

Review Completion Records

“Gather Data Before Designing a Cement Slurry”

Injectivity

Viscosity must be manageable Channel repair may require

small cement particle sizes

Injection Testing

Use water, chemical flush or weak acid

Used to ensure all perforations are open

Helps to estimate slurry injection rate

Helps to estimate pressure for performing squeeze

Helps to estimate cement volume required

If injection is not achieved, an acid perforation wash should be performed under matrix conditions

Establishing An Injection

Pump at a Constant Slow Rate Increase rate to Obtain

Desired Cement Placement Rate

“Remember not to Exceed Fracture Gradient !”

Why Establish Injection Rate

To determine if and at what rate “BELOW THE FRACTURE GRADIENT” fluid can be placed against the formation.

Two Rate Injection

Lowest Rate at which the Formation will take Fluid

Minimum Rate needed to Displace Cement to the First Hesitation Always Establish with Clear Fluid Avoid using Mud

Variable

Affects Rate Choice

Thickening Time Packer Depth Slurry Volume Depth Workstring Size Casing Size

When Fracture Pressure Is

Unavoidable ! REMEMBER

You Will Damage the Formation You Will Increase the Difficulty of

getting a Satisfactory Job

The Key is to“BE CONSERVATIVE”

Proper Execution

High Injection Rate - Low Pump Pressure

High Pump Pressure - Low Injection Rates

Types OfInjection Rates

Loose Injection Rates High Rates Low Pressures

Tight Injection Rates Low Rates High Pressures

6 to 8 BPM0 - 200 PSI

0.25 - 0.5 BPM3500 - 4000 PSI

Loose Injection Tight Injection

Injection Rates And Pressures

Injection Rate Profile

From Chevron DTC

Caution

“ High injection rates with high pressures”

Almost Never Acceptable! Yields highly fractured formations

that require a large volume of cement slurry, before actually obtaining a squeeze.

Reasons For Failure

Non-Determination of Injection Rate

Slurry Design and Testing Slurry Placement Problems

Squeeze Cementing Methods

Principal methods: Squeeze packers Cement retainers Bradenhead

Modes of operation: Low pressure High pressure

Job procedures: Running squeeze Hesitation squeeze

Packer or RetainerSetting Depth

Determine from CBL Using tail pipe:

Minimum distance from top perforation is limited by tail pipe length

Do not set tool too close to top perforation: Communication in annulus above tool

can collapse casing Do not set packer too high (running

squeeze): Minimize contamination with mud or

other fluids Minimum 30 ft 75 feet above top

perforation

Retrievable Packers

Compression or tension set packers are used for squeeze cementing

Packer should have by-pass valve to: Allow fluid circulation when running in

hole Clean tool after job Allow reversing of excess cement slurry Prevent swabbing

Flexible, can set and release many times

Can run in tandem with retrievable bridge plugs Place sand on top of bridge plug

Viscous Pill

Mud

Mud

Packer

Spacer

Viscous Pill

Cement

Squeeze Through A Packer Balanced Plug

Method Spot viscous pill Pull to top of pill Spot cement and spacer as balanced plug Under displace (1 to 2 barrels) to ensure

flow out of the drill pipe

Mud

Mud

Viscous Pill

Cement

Mud

Packer

Spacer

Squeeze Through A Packer Balanced Plug

Method Pull out above top of cement (500 ft) Set the packer and squeeze cement When squeeze complete, unset the packer Reverse circulate any excess cement and

spacer out of hole

DrillableCement Retainer

Prevent back flow where no cement dehydration is expected (circulating squeeze into channels)

Used where high differential pressure may disturb the filter cake

Where communication with upper perforated zone makes use of packers risky

Multiple zones, isolates lower zone Allow further squeeze operations without

waiting on cement. Can be set closer to the perforations (Less

fluid injected ahead)

Mud

Mud

Retainer

Running Squeeze Method Through A

Cement Retainer Run in hole with retainer on wireline or

drill pipe Set retainer If wireline set, run in hole with drill pipe If run on drill pipe sting out from retainer

Viscous Pill

Mud

Mud

Cement

Retainer

Spacer

Running Squeeze Method Through A Cement

Retainer (cont.)

Circulate cement down to bottom of drill pipe

Sting into the retainer and squeeze cement

Cement

Viscous Pill

Mud

Mud

Cement

Retainer

Running Squeeze Method Through A Cement

Retainer (cont.)

Sting out from retainer and reverse circulate excess cement and spacer

Pull out of hole

Bullhead Squeeze Method

Casing Pump500 - 1000 psi


Cement

DisplacementFluid

Mud orDisplacementFluid

Pump cement with packer Set

Displace Mud into Formation

Hold Annulus Pressure

Apply Squeeze Pressure

Spotting Method


Sting out of tool Spot cement Stab with Packer Apply Casing Pressure Displace Cement Apply Squeeze Pressure

Bradenhead Squeeze Technique

Used when low pressure squeezing is practiced

Used where casing and surface equipment have sufficient burst resistance to withstand squeeze pressures

This is the most popular method due to its simplicity

Bradenhead Method

Spot Cement Pull Work String Close Annulus Apply Squeeze Pressure

Coiled Tubing Operations

(Through Tubing Squeezes)

Advantages Time Savings Cost Savings Pumping Flexibility Fluid Placement Reduced Formation Damage Safety

Coiled Tubing Applications

Well Stimulation Wireline and Production

Logging Perforating Squeeze Cementing Fill Cleanup Sand Consolidation

Cement Requirements for Coiled Tubing

Squeeze Fluid Loss

< 60 and > 30 cc’s/30 min. Compressive Strength

1000 psi in 12 Hrs. Thickening Time

6 - 8 Hours at BHTT Free Water

Zero cc’s at 45° Angle

Cement Requirements for Coiled Tubing

Squeeze (cont.) Rheologies

@ R.T. PV; 200 to 350 YP; 70 to 130

@ BHTT PV; 70 to 130 YP; 10 to 25

Nodes 0.75 to 1 inch Firm Cake

Mud Placement

Placement of Mud Pull Nozzle Up while

Pumping, to MaintainMud-Brine Interface10 - 15’ Above Nozzle

Pump 1 BBL. Excess

Locate Top of Mud Fluid Pac the Well Wash Out

Contaminated Mud Identify Top of Mud

Viscous Pill

Perforations

Brine Fluid

Cement Placementand Squeeze

Circulate in Cement Pull Nozzle Up while Pumping

Cement, to Maintain Cmt/MudInterface 100’ Above Nozzle

Cement Volume from Evaluation Log

Pull Nozzle Above Cement Close Annulus and Squeeze Squeeze Pressure at 1500 to

2000 psi above Reservoir Pressure and Hold for

40 Minutes

Viscous PillCement

Perforations

Fresh WaterBrine Fluid

ContaminatingThe Cement Pump contaminant and Lower the Nozzle to Displace 1 BBL of Cement per BBL of Contaminant

Contaminate 50’ into MudPull Nozzle up and Pump Contaminant at a Rate of 1 BBL per 2 - 3 BBL of Previously Contaminated Cement

Contaminant

Cement / Contaminant(50/50)

Dehydrated CementNodes

Mud / Contaminant(50/50)

DehydratedCement nodes

Mud, CementandContaminant

Viscous Pill

Reversing Out

Contaminated Cement to be Reversed out the Following Day or After Cement has Set

Jet with Fresh Water While Going Down 50’ Below the Original Mud Top

Reverse out and Pull Nozzle at a Rate to Circulate out 1 BBL per BBL pumped

Repeat Reverse out 2 more Times or Until Returns Cleanup

Evaluate with CET, Repeat if Necessary

If OK, Reperforate and Test

Low Pressure Squeeze Cementing

Bottom hole treating pressure maintained below fracture pressure

Aim to fill perforations and connected cavities with dehydrated cement

Cement volume is small Hydrostatic control is required to prevent

formation breakdown Use safety factor of 500 psi Low pump rates

Friction pressure is negligible Perforations must be clean and free of

mud or solids Cement nodes should be small

High PressureSqueeze Cementing

Bottom hole treating pressure is higher than fracture pressure

Fractures created at or close to perforations

Fluid ahead of cement is displaced into fracture

Cement slurry fills the fracture and any voids or connecting channels

Further applied pressure dehydrates the cement against fracture walls

When final squeeze pressure is applied all channels should be filled with cement filter cake

Extreme Losses

Sodium Silicate Pre-Flush (Flow-Guard) Pump CaCl Pad Pump Fresh Water Pad Pump Flow-Guard Pump Fresh Water Pad Pump Cement Design

One Possible Situation for “Neat” Cement Low fluid loss = good frac!

Use Caution with Sodium Silicate Across Pay Interval

Running Squeeze

Misconceptions Formation Locks-up at High Rates Final Squeeze Pressure Must be

Obtained at the Rate Induced During Injection

Better Term “Walking” or “Creeping”

More Applicable for Low Permeability Formations

Always Know the Location of the Cement Know the P between Cement &

Wellbore face

When To High Pressure Squeeze

Where voids and channels cement behind casing are not connected to the perforations

Where small cracks or micro-annuli allow passage of gas but will not take cement Application of Ultra Fine cements

Perforations are plugged or debris ahead of cement cannot be removed

High Pressure Squeezes (cont.)

Extent of the induced fracture is a function of pump rate

Slurry volume is dependent upon pump rate: High rate = large fracture Large fractures = large volumes

Minimum volumes should be used to allow perforation past cement where required

Drilling mud or low fluid loss fluids should not be pumped ahead

Use weak acid or water as a pre-flush

Related Fracture Theory

Location and orientation of created fracture cannot be controlled

Fractures occur in plane perpendicular to direction of least resistance

In most wells overburden is the principle stress, vertical fractures result. Fracturing pressure is less than

overburden In shallow wells (< 3000 ft)

horizontal fractures can occur Fracturing pressure is greater than

overburden

H2

H1

PF Over-burden

High Pressure Squeeze Fracture

Orientation Where fracture pressure is less

than over-burden pressure

PrimaryCement

CementFilter Cake Mud

Filtrate

Filtrate

Mud

VerticalFracture

DehydratedCement

Casing

Running Squeeze

Cement slurry pumped continuously until final squeeze pressure is achieved This may be above fracture pressure

When pumping is stopped, final squeeze pressure is maintained and monitored

Pressure drop due to filtrate leak off should be re-applied up to final squeeze pressure

Repeat procedure as necessary until pressure remains steady for several minutes

Volumes are large 10 to 100 barrels

Hesitation Squeeze

Only practical method for small volumes Intermittent application of pressure at low

rates 0.25 to 0.5 bpm

Each application of pressure is separated by a period of shut-down to allow for filtrate leak-off 10 to 20 minutes

Initial leak-off is high As cake builds up and applied pressure

increases, leak-off slows down As several hesitations are applied, the

difference between initial pressure and final pressure becomes smaller

2,400

2,000

1,600

1,200

800

400

00 20 40 60 80 100 120 140 160

Surf

ace

Pres

sure

, psi

Time, minutes

A

B C D

Hesitation Squeeze Pressure Behavior

A = Slurry mix-water leaks off B = No slurry mix-water filtrates

therefore squeeze is complete C = Pressure is bled off D = Final pressure test

Hesitation Squeeze Profile Loose Injection Rate

1 2 3 4

1000

2000

0

PRES

SUR

E

TIME in HOURS

Pump as slow as possible( 1/4 to 1/2 BPM )

Chevron DTC

Hesitation Squeeze ProfileTight Injection Rate

2000

1000

0 1 2TIME in HOURS

PRES

SUR

E

( 1/4 to 1/2 BPM )

Chevron DTC

Best Results

“Always Plan for a Hesitation Squeeze, But be prepared for a Running Squeeze”

CFL Two Slurry Method

Conventional Method Lead Slurry: Fluid Loss < 100 cc’s Tail Slurry: No Fluid Loss Control

Modified Method(Chevron DTC)

Lead Slurry: Mod. Fluid Loss - 300 to 500 cc’s

Tail Slurry: Fluid Loss < 100 cc’s More Specifics to follow...

CFL Slurry DesignModified Method

(Chevron DTC) Loose Injection

Lead Slurry Fluid Loss 300 to 500 cc’s Thickening Time

1 to 2.5 hours Free Water & Comp. Strength - N/A

Tail Slurry Fluid Loss < 100 cc’s Thickening Time

3 - 5 hours (Hesitation Schedule)

Free Water & Comp. Strength - N/A

Modified Method

Loose Injection Tight Injection

CFL Two Slurry Method LWL Single Slurry Method

Lead : 500. . . . . . 300 . . . . . 200. . . . . . . N.A. Tail : < 100. . . . . . .100 . . . . 100 . . . . . . . 100

Fluid Loss Control

Chevron DTC

Calculating Pressure to Reverse-Out

Always know what pressures are required to reverse-out.

Step 1: Calculate Differential Fluid Gradient, psi/ft

15.6 ppg x 0.052 = 0.8112 psi/ft ( Cement )10.0 ppg x 0.052 = 0.5200 psi/ft ( Comp Fluid )

0.2912 psi/ft Step II: Determine Tubing Fill

Factor, ft/bbl (decimal book) 2-3/8” 4.7 lbs/ft tubing = 258.65 ft/bbl of fill

Step III: Calculate Pressure to Reverse-Out, psi/bbl

ex: 258.65 ft/bbl x 0.2912 psi/ft = 75.3 psi/bbl**Multiple psi/bbl by the barrels

of slurry left in the tubing

Hesitation Squeeze

Final squeeze is achieved when the leak-off becomes negligible

For loose, permeable formations a first hesitation period of up to 30 minutes is not unreasonable

For tight low permeability formations a short first hesitation period of ± 5 minutes is sufficient

Hesitation Squeeze

(Chevron DTC)

Always Test on Hesitation Schedule

Hesitation Time Dictated by Pressure Build-up

Be Patient Use CFL Slurry Know the Location of the

Cement Never Over-Displace Determine Final Squeeze

Pressure from Injection Profile

Misconceptions of Squeeze Cementing

Cement slurry enters formation pore spaces

All perforations are open High pressure squeezes

create horizontal pancake High final pressure is required

to assure success Final squeeze pressure must

equal future working pressure

GeneralRecommendations

Ensure hole is junk free Ensure perforations are open

Acid wash if necessary Low pressure squeeze where

possible Use low fluid loss cement Cement volume should not exceed

string volume High final squeeze pressure is not

essential Batch mix cement Allow adequate time for cement to

set based on compressive strength data