Development and application of a low-solid Development and application of a low-solid oil based perforation fluid to maximize well oil based perforation fluid to maximize well productivityproductivity

Anne-Mette Mathisen,Anne-Mette Mathisen,Eva Alterås, Morten StenhaugEva Alterås, Morten Stenhaug

Aberdeen 20. - 21.03.2002Aberdeen 20. - 21.03.2002

Outline of the presentationOutline of the presentation

The case

Field description

Well design

Revision of the perforation fluid

Investigation and development of new perforation fluids

Perforation of well A-23H - result and operational experience

Conclusion

The case....The case....

Some of the long horizontal wells in the Visund field has shown considerably lower well productivity than expected

Detailed work to understand the mechanisms which influenced the productivity of these wells, and to identify methods to improve productivity were initiated

Strategies for completion, perforation and completion fluid were given highest priority

The Visund Field The Visund Field North Sea, Norwegian sectorNorth Sea, Norwegian sector

Snorre A/B

VisundVigdis

Tordis

Bergen

Florø

Stavanger

The Visund DevelopmentThe Visund Development

Subsea development - water depth : 335 m

Semisubmersible production, drilling and living quarters platform

23 wells, 13 horizontal producers including 2 satellite wells

Platform located above subsea completed wells with flexible risersbetween the wellheads and the platform

Production strategy based on both water and gas injection

Capacities :

Oil production : 16000 Sm3/dGas production: 10 - 13 M Sm3/dWater production : 18000 Sm3/d

Visund developmentVisund development

The Visund ReservoirThe Visund Reservoir

Sandstone of the Jurassic Statfjord, Amundsen and Brent groups

Heavily segmented by faults with varying sealing properties

Saturated and undersaturated oil, with various composition and pressure within different reservoir segments

Medium to high initial reservoir pressure:

Pres : 430 - 460 barTres : 114 - 118 deg. C

Visund - Well location map

0 1 2 3 4 5Kilometer

N

B-2H

B-1AH

A-11H

A-9H

A-10AH

B-1H

BRENT N2

BRENT N1BRENT S1

STATFJORD/AMUNDSEN

A-1AH

A-7H

A-2HA-1BH

A-23H

A-5H

A-8HA-3H

A-5CHOil - Statfjord and Amundsen

Gas -Brent

Oil -BrentA-5AH

A-25H

A-5DH

Visund Nord

N3

Original Well designOriginal Well design

1000 - 2000 m horizontal section drilled with OBM

Perforated liner

12 spf, low debris, deep penetrating zinc charges

Overbalanced perforation in CaBr2/CaCl2-based kill pill

7" tubing, down hole pressure and temperature gauge

Immediate clean up

Welltype : Oil ProducerRKB Kværner subsea Xmas tree

0m

MSL 29mALL DEPTHS FROM RKB

Seabed @ 364m RKB7", 32#, Tubing

TRSCSSV TSM 7.5 @ 425m (top item) Perforation From (m MD) To (m MD) Length perf.(m)7" liner

30" shoe @ 451m 7" liner 7" liner

7 5/8", 39#, Tubing

18 5/8" shoe @ 1487m MD

13 3/8" shoe @ 3500m MD

Calculated TOC - 3900m MD

NaCl Brine 1.10 s.g. Pressure Gauge Carrier @ 4250m MD

SBRM Packer @ 4300m MD2 Way Seals

SABL-3 Packer @ 4350m MDNo Seals

Flexlock Liner Hanger w/ZXP Packer, TOL @ 4400m MD

Halliburton Communication Cplg. 10 3/4" shoe @ 4500m MD(shear pin)

TD @ 6470m MD

OCRE FBIV @ 4375m MD

General Completion Schematics

Well 34/8-A-23H

Well Sketch : 23 Oct 00

Geological cross-section along the wellpath, well 34/8-A-23 HGeological cross-section along the wellpath, well 34/8-A-23 H

-3050

-3000

-2950

-2900

-2850

-3050

-3000

-2950

-2900

-2850

3000 3500 4000 4500 5000

3000 3500 4000 4500 5000

Stat1_1

Stat1_2

Stat1_3

Stat1_4

Stat2_1

Stat2_2Stat2_3

Am1_1

Am1_2

0 100 200 300 400 500

Meter

TD @ 6147m MD

TD @ 6616m MDDown 1

Up 1

Down 2

Perforated intervals

Scope of work :

" Well productivity for the next producers to be significantly improved relative to previous wells"

Reevaluation of the completion strategy

Reevaluation of perforation strategy

Reevaluation of completion fluid strategy

Improvement of well productivityImprovement of well productivity

Criteria for selection of perforation fluidCriteria for selection of perforation fluid

Compatibility with formation rock

Compatibility with formation water

Compatibility with packer fluid

Particle content for fluid loss control

Cost

Criteria for selection of perforation fluidsCriteria for selection of perforation fluids

Reservoir pressure of 430 bar requires 1.65 s.g fluid density

Available brines with sufficient density:

CaCl2/CaBr2 < 1.71 s.g

KCOOH/CsCOOH < 2.20 s.g( ZnBr < 2.30 s.g )

Review of CaClReview of CaCl22/CaBr/CaBr22 as perforation fluidas perforation fluid

Compatibility with formation rockFormation damage tests showed 30 % reduction in permeability

Formates showed only 10 % impairment

Compatibility with formation waterRisk of CaCO3 precipitation due to high content of HCO3-

Formates entirely compatible

Compatibility with perforation chargesLow debris zinc charges used due to long horizontal perforation interval and the need for effective cleanup

Formation of ZnO powder during detonation in the vicinity of water

Possible formation of cement material due to further reaction with Ca-ions in the brine

Theory:

Zn + H2O => ZnO + H2

Zn + 2H2O => Zn(OH)2 + H2

Zn + CaCl2 + 2H2O => ZnCl2 + Ca(OH)2 + H2

xZn(OH)2 + yZnCl2 +zH2O => 2Zn(x+y)(OH)xCly(H20)z

Ref. SPE58758

Review of CaClReview of CaCl22/CaBr/CaBr22 as perforation fluidas perforation fluid

Review of CaCl2/CaBr2 as killpillReview of CaCl2/CaBr2 as killpill

In-house laboratory work verified the behavior of zincpowder in Ca-based brines.

Review of CaClReview of CaCl22/CaBr/CaBr22 as perforation fluidas perforation fluid

Perforation in oil based mud ???

Low content of water => reduced reaction with Zn-charges

Good fluid loss controlOil as continuos phases => reduced relative permeability effectsImproved clean up of the toe of the well due to low viscosity

Operational preferable due to high potential for time and cost saving

1.65 s.g OBM => extreme amounts of solids and potential for particle settling and plugging of perforation tunnels

High risk of reduced productivity

#2*@31 mm #4@whole length

Wel

lbor

e

Form

atio

n

#3@56mm

* Differential Pressure Transducer.

Investigations to qualify a new perforation fluidInvestigations to qualify a new perforation fluid

Study initiated with MI Norge to investigate the effect of different perforation fluids

Core flood tests to evaluate formation damage potential of water based andoil based perforation fluids and the impact of zinc perforation debris

Conventional brines (1.26 s.g NaCl, 1.38 s.g CaCl2, 1.55 s.g CaBr2, ), 1.55 s.g OBM and a new 1.65 s.g invert emulsion system with CsCOOH

Ref. SPE 73709MI Norge, SPE Formation damage Conference Lafayette, Feb. 2002

Investigations to qualify a new perforation fluidInvestigations to qualify a new perforation fluid

Core flooded with 1.26 s.g NaCl with perforation debris

Core flooded with 1.55 s.gOBM with perforation debris

Ref.: SPE73709

Investigations to qualify a new perforation fluidInvestigations to qualify a new perforation fluid

Conclusion from the core flood tests

Particle content in the perforation fluid effect the perforation clean up efficiency

Water based fluids show a chemical reaction with perforation debris that increase the fluid loss

Ref. SPE73709

Revised criteria for selection of perforation fluidRevised criteria for selection of perforation fluid

Low impairment of permeability

Entirely compatible with formation water

Low content of water to reduce reaction with perforation debris

Low content of particles to improve cleanup of perforation tunnels

Oil as continuos phase to reduce relative permeability effects

Low viscosity to increase cleanup efficiency at the toe of the well

Less emphasis on cost

New perforation fluid for well A-23HNew perforation fluid for well A-23H

Low solid oil based perforation fluid (LS OBM)

Density 1.65 s.g Oil to water ratio of 40/60

CsCOOH as internal phase

Minimum content of CaCO3 particles (60-90 g/l)

Particle size distribution optimized against permeability

Perforation of well A-23HPerforation of well A-23H

The well was perforated in June 2001 in the newly developed LS OBM-fluid and with a revised perforation strategy.

Operational problemsHigh losses to formation after perforation

Pumped additional kill pill based on CsCOOH-brine to cure losses

Investigations concluded that the circulation port failed during displacement and the upper part of the well was most likely perforated in clear brine

Same type of fluid based on CaCl2 used on Oseberg later on => no operational problems

Production of well A-23HProduction of well A-23H

Production controlled by maximum drawdown to reduce risk of sand production

Production rate after clean up: 7700 Sm3/D

Productivity 3-4 times higher than in previous comparable wells.

ConclusionConclusion

Improved productivity of well A-23H is the result of total consignment to the problem, where completion, perforation and fluid strategies are the most important items

Use of a new low solid oil based perforation fluid is regarded as being successful, and is an important contribution to improved well productivity