Task 4: Damage & StimulationTechnical Status May-June 2000

TerraTek, Inc.

Heriot -Watt University

Triangle Engineering

Duke Engineering and Services, Inc.

eFirst Technologies

Gas Research Institute

Advantek, International, Inc

VIPS

Task 4: Status

4.1 Acquisition of Field Data4.1 Acquisition of Field Data

4.2 Quantitative Evaluation4.2 Quantitative Evaluation

4.3 Well Testing Techniques4.3 Well Testing Techniques

4.4 Damage effects and damaging agents

4.4 Damage effects and damaging agents

‘D.P. Format’ (Mar ‘99) on ‘Data CD’ Data list (review 5 soon)

‘Data CD’ (May 00) Technical presentations (‘99-‘00) Stimulation Record listing

Duke working on fall-off review SRT multi-rate spreadsheet (being/

tested reviewed by TT) (Apr ‘00)

(Matrix) Damage Report (May ‘00) Technical presentations (‘99-‘00) Surface systems overview (In

progress)

Pro

ject

Su

bta

sks

Task 4: Status (cont...)

4.5 Review of Mitigation /Stimulation Techniques

4.5 Review of Mitigation /Stimulation Techniques

4.6 Economics of Damage vs.Damage Mitigation vs. Stimulation

4.6 Economics of Damage vs.Damage Mitigation vs. Stimulation

4.7 Guidelines for best practices

4.7 Guidelines for best practices

Stimulation techniques overview (sent to TT mid May)

Problem-solution spreadsheet

Presentation in Stavanger (Feb.’00) Discussed in this workshop

To be derived from proposed Analysis Strategy

Pro

ject

Su

bta

sks

A. Stimulation Philosophy

B. Stimulation Techniques

– Chemical (Acidising) and Mechanical (Fracturing)

– Field Cases

C. Analysis Strategy

Task 4: Presentation Overview

Stimulation Philosophy

Chemical (acidising)•need to know:

– source of damage &– location of damage

–Input from Task 2

• Choice of stimulation fluid– Remove damage (not always acid)– no deleterious effects on formation

Mechanical (Hydraulic Fracturing)– Bypass damage with high permeability fracture

Injection Damage Mechanisms (1)

• Particle Plugging– Solids and oil in the water (also emulsions?)

• Water / Formation Incompatibilities– Fines Migration and Clay Swelling

• Hydrocarbon Effects– Wax / asphaltines deposits & relative permeability

effects

• Scale– Calcium carbonate, calcium sulphate, barium sulphate

etc.

• Corrosion– Generates iron particles (plugging)– Alters tubing friction - increased tubing roughness (&

diameter?)

Injection Damage Mechanisms (2)

• (lack of) Bacterial Control– Biomass and / or “Schmoo”

– Described by Fambrough et al. (SPE 28976), McLelland and others

• Main components of “Schmoo”:– Sand and formation fines in the PW– Hydrocarbon material in the PW (OIW)– Iron sulphide, from the injection system– Production chemicals– Biomass-material

• “Schmoo” prediction requires extensive water quality / surface facility information

PWRI Damage Mechanisms

Damaged zone (mud filtrate,

completion/injectionfluids, etc)

Fines migrati

on

Mud filter cake

Corrosion

Iron solids

plugging

Fractures plugged

with solids from

injection fluid

Organic scalingBacteria growth, plugging, “schmoo”

Inorganic

scaling

Formation pore

plugging•Solid

particlesOil dropletsOily solid particles

Relativepermeabili

tychanges

Formation Damage - Hydrocarbon deposition

R1

R2

Oil droplet larger than pore

throat

Dissolved Oil

Wax Depositio

n

Free Oil

Asphaltene

Deposition ? Emulsifie

d Oil

Schmoo

Stimulation Philosophy

Chemical (acidising)•need to know:

– source of damage &– location of damage

–Input from Task 2

• Choice of stimulation fluid– Remove damage (not always acid)–additives– no deleterious effects on formation

Mechanical (Hydraulic Fracturing)– Bypass damage with high permeability fracture

Maersk - “Field A” water injection system

Stimulation fluid chosen on basis of damage

• Injection system fouling reported (Check-valve pictured)• Deposits mainly Oil and Iron Sulphide• System Cleaned with an acid / surfactant solution

Impairment

Cement (carbonate)

Quartz

Native rock

Pore lining clay

Pore filling clay

Remaining pore space

ACID (HCL/HF)

Secondary reaction products

Thermodynamic equilibrium simulation chose optimum acid formulation, depending on rock/damage mineralogy

- Increased porosity and permeability - Damage removed

Acidising - Acid formulations

Many acid formulations used for matrix acidising:•Hydrochloric Acid (HCl)•Mud Acids•Organic Acids

•Does not removeall damage typese.g. silica

Mud Acid

The damaged well

K

Kd

rd rw

Damaged Zone rd Damaged zone radius

k Virgin rock permeability kd Damaged zone permeability k > kd kacid

Fully acidised zone, all solubleminerals dissolved

kprecip Partically acidised zone with

precipitated acid /rock reactionproducts

kprecip < k > kacid

1. The damaged well

k kd

k

k kd

2. A small acid treatment

3. A large acid treatment

kacid

rd

kacid

kprecip

kprecip

rd

rd

The mud acidising

process

Stimulation of Carbonate Formations

•(Matrix HCl) Acidising of Carbonate formations is different from treatment of sandstones.

•Wormhole formation & (surface) Acid Wash

a) Cased hole

b) Open hole

Potential Damage caused by Stimulation Fluids

• Deconsolidation of the rock matrix

• Fines generation => acid only partly dissolves formation minerals present between the grains.

• Secondary precipitation => blockage of the pores and pore throats (impairment).

• Fluid incompatibilities.

• Acid precipitation of an insoluble sludge

• Surfactants =>

create a (highly) viscous emulsion

• Relative permeability / wettability changes => due to Surfactants

Repetitive Stimulation - Why?

•Options: continuing damage or acid selection

ELF PICTURE

ELF-3 W-1

0.00E+00

2.00E+05

4.00E+05

6.00E+05

8.00E+05

1.00E+06

1.20E+06

1.40E+06

1.60E+06

1.80E+06

0 2,500,000 5,000,000 7,500,000 10,000,000 12,500,000

Cummulative Injection Volume (BBL)

Pre

ssu

re T

erm

(p

si*d

ays)

0

2,500

5,000

7,500

10,000

12,500

15,000

17,500

20,000

22,500

BH

P (p

si)

& I

njec

tion

Rat

e (B

PD

)

HallInj. Pressure "BHP"Injection RatePWAcidification Jun/95Acidification Sep/95Acidification Nov/95Acidification May/96Acidification Oct/96Acidification Nov/96Acidification Aug/97Acidification Dec/98Acidification Apr/99Acidification May/99Acidification Jun/99Acidification Jul/99Acidification Aug/99Acidification Sep/99Acidification Oct/99Acidification Oct/99Acidification Nov/99Acidification Jan/00Acidification Jan/00

HALL PLOT

Acid treatments

Selection of Acid Composition

Repetitive Acidising of Sandstones

•Often shows decreasing success

•Damage Location - Placement techniques

•Stimulation fluid selection

Field Case - Chevron

Repetitive Stimulation in Carbonate Field

Decline Rate decreases after each stimulation

Mechanical Stimulation

No need to identify formation damage type & location

(Careful) choice of frac. chemicals avoids formation damage (also Acid Fracturing)

formation deconsonsolidation not an issue

PW Injection may plug Proppant pack

proppant pack perm >10X that of formation

Damage location controlled by size PW particles (Frac. mouth area limited)

Frac Pac increases “filter area”

This form of damage avoided by Hydraulically Induced Fracturing (no proppant)

Also Specialist applications e.g. initiation of TIF process

Analysis of producedand formation water

characteristics

Formation damagemechanisms

Remedial action

TSS: particle count (ppm)and size distribution (mm)

Formation / pore pluggingcreating filter cakes

•Solid particles•Oil droplets

•Oily solid particles

Emulsions, wax, oil bank(affecting relative perm.)

Other hydrocarbon deposits(schmoo) etc.

Acid stimulationFracture (increase wellbore)

Clean water

Control

Filtration

OIW: Particle count (ppm)and droplet size (mm)

Solvents and/or surfactantsinjection

Separation, solvents,surfactants

Dissolved gases (CO2, O2,H2S etc.)

Corrosion (tubing, surface equipment damages,

causing iron solids plugging)

Bacterial count (CFU/g) Bacterial growth, pluggingCorrosion due to SRB

TDS (ppm)AW / PW compatibility

Temperature

Scale precipitation:CaCO3, CaSO4, BaSO4 etc.

Critical injection velocity(m/s)

Fines migration

Acid stimulation

Biocides

Tubing wash or matrix stimulationFluid depends on scale type

Acid stimulationFracturing

Clean Water

Corrosion inhibitors (Scavengers)

Material selection

Biocides

Scale inhibitorinjection at surface

Adjust flow rate (bpd),Increase pay zone

periodic stabling treatments

Damage - Mitigation - Stimulation “Roadmap”

PWRI Damage Mechanisms

Damaged zone (mud filtrate,

completion/injection fluids, etc)

Fines migrati

on

Mud filter cake

Corrosion

Iron solids

plugging

Fractures plugged

with solids from

injection fluid

Organic scalingBacteria growth, plugging, “schmoo”

Inorganic

scaling

Formation pore

plugging•Solid

particlesOil dropletsOily solid particles

Relativepermeabili

tychanges

PWRI Stimulation Techniques

SurfactantsSurfactants

Solvents /Mutual solvents

Solvents /Mutual solvents

SequesteringAgents

SequesteringAgents

CorrosionInhibitorsCorrosionInhibitors

OrganicAcids

OrganicAcids

Mud AcidMud Acid

HydrochloricAcid (HCl)

HydrochloricAcid (HCl)

Clean water flush(e.g. sea water

injection)

Clean water flush(e.g. sea water

injection)

Frac-PackFrac-Pack

Closed FractureAcidising

(CFA)

Closed FractureAcidising

(CFA)

ThermallyInduced

Fracturing(TIF)

ThermallyInduced

Fracturing(TIF)

Acid-FracAcid-Frac

ProppedHydraulicFracturing

ProppedHydraulicFracturing

Back-flowto clean

perforations

Back-flowto clean

perforations

Stim-gunStim-gun

WaterHammer

Stimulation

WaterHammer

Stimulation

Acidising Other MethodsAdditives Fracturing

HydraulicFracturingHydraulicFracturing

Field data

• Stimulation Data on CD:• ELF- 3• NAM-1• Maersk A-25 & B-03• BP Amoco Prudhoe Bay H-09• PanCanadian Countess

• Experience from 6 companies to be presented by today’s speakers

Field Case - ELF-3 W1

ELF-3 W-1

0.00E+00

2.00E+05

4.00E+05

6.00E+05

8.00E+05

1.00E+06

1.20E+06

1.40E+06

1.60E+06

1.80E+06

0 2,500,000 5,000,000 7,500,000 10,000,000 12,500,000

Cummulative Injection Volume (BBL)

Pre

ssur

e Te

rm (p

si*d

ays)

0

2,500

5,000

7,500

10,000

12,500

15,000

17,500

20,000

22,500

BH

P (p

si)

&

Inje

ctio

n R

ate

(BP

D)

HallInj. Pressure "BHP"Injection RatePWAcidification Jun/95Acidification Sep/95Acidification Nov/95Acidification May/96Acidification Oct/96Acidification Nov/96Acidification Aug/97Acidification Dec/98Acidification Apr/99Acidification May/99Acidification Jun/99Acidification Jul/99Acidification Aug/99Acidification Sep/99Acidification Oct/99Acidification Oct/99Acidification Nov/99Acidification Jan/00Acidification Jan/00

HALL PLOT

Acid treatments

Field Case - ELF-3 W2

ELF3 W-2

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

Dec

-95

Feb-

96

Apr

-96

Jun-

96

Aug

-96

Oct

-96

Dec

-96

Feb-

97

Apr

-97

Jun-

97

Aug

-97

Oct

-97

Dec

-97

Feb-

98

Apr

-98

Jun-

98

Aug

-98

Oct

-98

Dec

-98

Feb-

99

Apr

-99

Jun-

99

Aug

-99

Oct

-99

Dec

-99

Feb-

00

Apr

-00

Date

Inje

ctiv

ity I

ndex

(BPD

/psi

)

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

Bot

tom

hole

Inj

ectio

n Pr

essu

re (p

si)

Inj. Index "II"Inj. Pressure "BHP"PWAcidification Jun/96Acidification Jun/96Acidification Oct/96Acidification Dec/96Acidification Jan/97Acidification Feb/97Acidification Mar/97Acidification Aug/97

Injectivity Index and Pressure vs. Time

Acid treatments

Analysis Strategy (1)

• Review data made available to PWRI project– Developed familiarity with contents– Data profiling to help identify where it is most

relevant– (Very) Basic quality control checks

• Define stimulation success (economics)• For discussion in this workshop

• Two types of analysis possible:– statistical analysis on large data sets– specific example well analysis

• Guidelines & Best Practices

Process of Data cataloguing started

Stimulation Data on CD:

• ELF- 3

• NAM-1

• Maersk A-25 & B-03

• BP Amoco Prudhoe Bay H-09

• PanCanadian Countess

Statistical Analysis

• Countess data set potentially had opportunity for large scale analysis similar to Prudhoe Bay (PEA 23)– 22 wells with stimulation history

• 15 mud acid, 10 HCl acid, 4 propped hydraulic frac

• Visit to Pan Canadian:– Similar stimulations in different wells had

inconsistent performance i.e. treatment successs / failure

erratic– Advised Wellfile data may be inaccurate / or

incomplete

Damage & Stimulation Overview Spreadsheet

Work in progress

C-06-07-018-15

0.00E+00

1.00E+06

2.00E+06

3.00E+06

4.00E+06

5.00E+06

6.00E+06

7.00E+06

8.00E+06

9.00E+06

1.00E+07

1.10E+07

0 2,500,000 5,000,000 7,500,000 10,000,000 12,500,000 15,000,000 17,500,000

Cummulative Injection Volume (BBL)

Pres

sure

Ter

m (p

si*d

ays)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

Inje

ctiv

ity I

ndex

(BPD

/psi

)

HallInjec. IndexPWPWAcid Squeeze May/76stimulation ?Jet, Re-perf May/96

HALL PLOT

Acid squeeze, Re-Perf.

31-May-76

Jet, Re-Perf. 17-May-96

stimulation treatment ?

Treatment Analysis Template

Formation

Sandstone Carbonate

Hard Soft Hard Soft

Injection regime

Matrix (task 2) Fracture Naturally fractured

Work in progress

Action Plan•List & profile project stimulation data

•Identify gap’s between well categories & project data

•Identify any areas where data is “missing” &

•Propose data sets for “hi-grading”

• produce “stimulation CD” {July}

•Analyse data

•Complete evaluation of collected Published literature:

PWRI: mainly Prudhoe Bay & Carbonate formations Sea Water: all types

•Generation of best practices by linking donated data, reports, published literature etc.