Long Term Cement Integrity Long Term Cement Integrity for Tight Gas Wellsfor Tight Gas Wells

in Hungaryin Hungary

11

in Hungaryin Hungary

Roeland Verbakel,Roeland Verbakel,Geomarket Technical Engineer, Geomarket Technical Engineer,

Schlumberger Well IntegritySchlumberger Well Integrity

OutlineOutline

� Introduction to Tight Gas Wells

� Cementing Challenges and Solutions

22

� Case history

� Summary

Introduction Introduction –– Tight Gas Tight Gas ChallengesChallenges

� Tight Gas Environment� Reservoir Pressure >

10,000 psi (69 MPa)

� Static Temp > 170°C

� Depths from 3500 to 6000m

33

6000m

� Commercial production not possible without hydraulic fracturing (tight gas)

� Unique challenges for cementing� Changes in pressure and temperature

� High temperature and pressure

Tight Gas well is a stressful Tight Gas well is a stressful environmentenvironment

Temperature changes in upper

casings during production

44

Pressure changes: drilling, production

Hydraulic stimulation

Well completion/perforation

Stress AnalysisStress Analysis

� Need to be able to analyze the stresses in the wellbore� Young’s modulus� Rock, cement and casing

Compressive strength

55

� Compressive strength� Tensile strength

� Young’s modulus, CS, Poisson's Ratio and thermal expansion play a complex role in durability

Gas MigrationGas Migration

� Formation

� Mud Removal

� Slurry Properties− Density

− Fluid Loss

− Free Water

Static Gel Strength development

66

− Static Gel Strength development

− Porosity

− Shrinkage

− Permeability to gas

High Pressure,High Pressure,High Temperature EnvironmentHigh Temperature Environment

� High density slurry using multi-modal blend design

� High Solid Volume Fraction

� Very low permeability

� Prevent gas migration

77

� Good mixability

� Quality control at each stage of design and execution

Cementing Challenges and Cementing Challenges and SolutionsSolutionsEngineering approachEngineering approach

Tight gas well

SolutionCementing

Challenge

Fracturing

TreatmentStress Analysis

Flexible

Slurry

Analysis

Tool

�Flexible Slurry

88

Treatment

Short term

gas migration

Micro-annulus

High

Mud Weight

Gas Migration

Analysis

Stress Analysis

Hydraulic

Simulations

Gas migration

additives

Expanding

Agent

High density

Slurry

�High Density

Slurry

Case history Case history –– Tight Gas well in Tight Gas well in Pannonian BasinPannonian Basin

� 500 meter x 4 ½’’ Liner in 5 7/8’’ OH

� Gas pressure of formation 10 kpsi (69 Mpa)

0

m

99

(69 Mpa)

� Reservoir temperature 175°C

2000

4000

Well

Hydraulic simulations and fluid Hydraulic simulations and fluid rheologyrheology

2500

.030

00.0

m

0 20 40 60 80 100Time (min)

32

10W

HP

(ps

i) (

x 10

00) Calc. WHP

Calc. Pump Press.

4F

low

Rat

e (b

bl/m

in) Q In

Fluids at 3749 m

600

500

400

300

She

ar S

tres

s (lb

f/100

ft2)

Mud (Model : HERSCHEL_B., Temp : 50 degC, Pres : undefined)DensCRETE (Model : HERSCHEL_B., Temp : 85 degC, Pres : undefined)MUDPUSH WHT (Model : HERSCHEL_B., Temp : 85 degC, Pres : undefined)

Shear Stress Vs Shear RateHierarchical Rheograms

1010

3500

.040

00.0

Fluid Sequence

0 20 40 60 80 100Time (min)

20

Flo

w R

ate

(bbl

/min

) Q InQ Out

0 20 40 60 80 100Time (min)

2118

1512A

nn. P

ress

ure

(lb/g

al)

FracPoreHydrostaticDynamic

Depth = 3749 m 0 0.1 0.2 0.3Shear Rate(1/s) (x 1000)

200

100

0S

hear

Str

ess

(lbf/1

00ft2

)

Results of the cementing Results of the cementing operationoperation

� Logs run 8 days after the cementing operation

� Exchange to completion fluid 6 days after the job (38 MPa difference)

� Log was affected by micro-annulus

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annulus

� Expanding agent was used in slurry to close micro-annulus over time

� During hydraulic fracturing treatment on the well (3 months later), cement showed good isolation

� No remedial work was needed

SummarySummary

1. Tight Gas cementing operations in Pannonian Basin are very challenging

2. Complete portfolio of design tools is utilized for complex cementing design

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cementing design

3. Slurry quality control and assurance (QA/QC) is key to success

4. Correct well construction first time: critical