SPE 106712Case Study from 12 Successful Years of High Temperature

Fracturing in Bach Ho Field Offshore Vietnam

S. Jain, A. Prestridge, P. Dellorusso, N. C. Nghi

Schlumberger

D.D. Lam, V.Q. Hung

Viestsovpetro

SPE 106712

OUTLINEOUTLINE

• Introduction

• Reservoir Description

• Vessel Set-up

• Design, Execution, Evaluation

• Results & Discussion

• Conclusion

SPE 106712

IntroductionIntroduction

• Bach Ho field is located in the South China Sea, close to

Vung-Tau, Vietnam

• Field has 215 wells with an average seawater depth of 165 ft

• Production is from the Miocene, Oligocene and the Basement

formations

• Drilling practices and other damage mechanisms restrict

most wells from producing to their potential

SPE 106712

IntroductionIntroduction

• Propped fracturing is conducted in Oligocene whereas both

acidizing and fracturing have been tried in the Basement.

• High temperatures (>275oF), closure stress (>8,000 psi) and

operating from a vessel makes the execution of fracturing

treatments challenging.

SPE 106712

Reservoir DescriptionReservoir Description

• Average well depth - 12,500 ft

• Average porosity - 13 to 17%

• Permeability - 0.1 to 20 mD

• Water saturation - 10 to 15 %

• Presence of Migratory Clays

SPE 106712

Damage MechanismsDamage Mechanisms

• Completion Fluid

• Drilling Mud System

• Perforating Strategy

• Faulty Completion Practices

• Migratory Clays

Equipment SetEquipment Set--upup

Rental for vesselsranges from $10,000to $30,000/day

Equipment tailoredto enable faster rig-up/rig-down

Vessel put togetherfor fracturing o/p in8 days and thedemobilization wascompleted in only 2 days

Storage tanks

Lab. & Monitoring unit

Proppant Silo’s

POD

Coflexip hose

Pumps

SPE 106712

Design ConsiderationsDesign Considerations

• Fracturing Fluid - Zirconate C/S-Linked

Polymeric Fluid

• Rheology - 110 cP at 170 sec-1 and 300°F

• Proppant - High Strength Proppant

• Fluid loss - 0.003 to 0.007 ft/min1/2

• Polymer Clean-up - Combination of encapsulated

and live breaker

SPE 106712

ExecutionExecution

• Diagnostic Tests

Wellbore Fill-up and Breakdown

Step-down

Step-Rate

Equilibrium

Calibration Test

• Main Fracture Treatment

SPE 106712

Treatment ParametersTreatment Parameters

• Treatment Rate - 20-25 bpm

• Proppant Concentration - 8-9 PPA

• Proppant Quantity - 60k to 80k lbs

• Diagnostic Tests - ~250 bbl (Linear)

~500 bbl (C/S)

• Treatment Volume - ~1500 bbls

• Pad Percentage - 40 to 75 %

SPE 106712

Case Study (Well A)Case Study (Well A)

• Target zone - Oligocene

• Total Vertical Depth (TVD) - 12,100 ft

• Perforation interval - 160 ft

• Shot density - 6 spf

• Permeability - 6 mD

• Porosity - 14%.

SPE 106712

Well A - Production History

0

200

400

600

800

1000

1200

1400

1600

Nov-04 Feb-05 May-05 Sep-05 Dec-05 Mar-06 Jul-06

Time

Oil

Prod

uctio

n (B

OPD

)

1400 bopd(naturally producing)

130 bopd(gas-lift)

Production History

SPE 106712

0 15.0 30.0 45.00

2000.00

4000.00

6000.00

0

10.0

20.0

30.0

Treating Pressure (JobData)Slurry Rate (JobData)Proppant Conc (JobData)

Treating Pressure

Time (min)

Pres

sure

(psi)

+

Step-Rate

Equilibrium Test

CalibrationInjection

CalibrationDecline

Diagnostic TestsDiagnostic Tests

SPE 106712

0 6 12 18 246000

6400

6800

7200

7600

Rate - bbl/min

Botto

m H

ole P

ress

ure -

psi

L1-S

L1-E

L2-S

L2-E

StepStep--Rate AnalysisRate Analysis

Frac. Extension Pressure

Estimated Closure Pr.

SPE 1067120 0.5 1.0 1.5

6000

6200

6400

6600

6800

7000

0

500

1000

1500

2000

2500Pre ssure De riva tive (dP /dG)Supe rposition De riva tive (GdP /dG)

G Function

Pres

sure

- ps

idP/dG

& G

dP/dG

Pc

ISIPL1-S

L1-E

L2-S

L2-E

Decline AnalysisDecline Analysis

Closure Pressure

SPE 106712

Treatment Redesign

• Closure Pressure - 6600 psi

• Leak-off Coefficient - 0.006 ft/min1/2

• Fluid Efficiency - 12%

• Pad Percentage - 75%

SPE 106712

Fracturing TreatmentFracturing Treatment

Abnormal Treating Pr.

7.0 47.0 87.00

2000.00

4000.00

6000.00

8000.00

10000.00

0

5.0

10.0

15.0

20.0

25.0Treating Pressure Backup (JobData)Slurry Rate (JobData)Proppant Conc (JobData)

Treating Pressure

Time (min)

Pre

ssur

e (p

si) R

ate (bbl/min)

+

+

Proppant Stages

Abnormal Treating Pr.

SPE 106712

Fracture Conductivity

SPE 106712

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 10 20 30 40 50 60 70 80 90 100

Prop

ped

Widt

h - i

n

Fracture Half-Length - ft

0

2000

4000

6000

8000

10000

12000

Conductivity (Kfw) - md.ft

Propped Width (ACL) Conductivity - Kfw

Fracture Width vs. Half-Length

SPE 106712

Well A - Production History

0

200

400

600

800

1000

1200

1400

1600

Nov-04 Feb-05 May-05 Sep-05 Dec-05 Mar-06 Jul-06 Oct-06 Jan-07

Time

Oil

Prod

uctio

n (B

OPD

)

Post Frac. Production460 bopd

Pre Frac. Production130 bopd

Production History

SPE 106712

Abnormal Treating Pressures

• Higher Surface pressure at the start of the main treatment

• Undesirable due to high HHP and surface treating pressure limitations

• Poroelasticity and stress concentration expected as possible reasons 7.0 47.0

0

2000.00

4000.00

6000.00

8000.00

10000.00

Treating Pressure BaSlurry Rate (JobData)Proppant Conc (JobD

Treating Pressure

Time (min)

Pres

sure

(psi

)

+

3500

psi

SPE 106712

Abnormal Treating Pressures

• Increase in closure pressure as a result of increasing reservoir pressure

• Large relatively clean zones, combined with the fact that the treating pressures decreased within few minutes of the start of the treatment does not support poroelasticity as a possible factor

• Alteration in magnitude andorientation of the in-situ stress field locally, can be about twice the effective stress.

• Crosslinked gel filter cake seals the fracture face in the near well-bore region, hence pressure must exceed the stress concentration effect before a fracture can be initiated

ppVH αασυ

υσ +−−

= )(1

Poroelasticity Stress Concentration

SPE 106712

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

A1 A2 A3 A4 A5 A6 A7Well Name

Prod

uctiv

ity In

dex

(bbl

/day

/psi

) Pre-Frac PIPost Frac PI

Pre/Post Job PI Comparison

SPE 106712

0

100

200

300

400

500

600

A1 A2 A3 A4 A5 A6 A7Well Name

lb/ft

of p

ropp

ant p

umpe

d

0

10

20

30

40

50

60

Rat

io o

f PI

lbs of prop. pumped / Net HeightRatio of PI increase (normalized)

Quantity of Proppant/ft vs. PI Increase

SPE 106712

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10Well Name

PI (b

bl/d

ay/p

si)

Pre Treatment PI

Post Treatment PI

Acid & Propped Frac.

Acid Fracturing

Acidizing

Comparison of PI for treatments in Basement

SPE 106712

ConclusionsConclusions

• Fracturing successfully implemented in the White Tiger

field with over 60 treatments performed at a success

rate greater than 85%.

• Average increase in Productivity Index of 5 times

• Propped fracturing has been successfully implemented in

Oligocene whereas high leak-off in the basement limits

its application in the latter.

SPE 106712

ConclusionsConclusions

• Abnormally high surface pressures observed in the start of the treatment can be attributed to stress concentration effects

• Higher volume of proppant pumped / feet of net height results in higher PI thus indicating that bigger jobs can improve NPV

• Acidizing results in improved productivity in the basement but successfully executing propped fracturing jobs with reasonable proppant volumes will result in improved Productivity Index.

SPE 106712

Questions ?

SPE 106712Case Study from 12 Successful Years of High Temperature

Fracturing in Bach Ho Field Offshore Vietnam

S. Jain, A. Prestridge, P. Dellorusso, N. C. Nghi

Schlumberger

D.D. Lam, V.Q. Hung

Viestsovpetro