spe #140751 slide presentation

Enhancing Production by Removing Zinc Sulfide Scale

From an Offshore Well: A Case History

Authors: Sandra L. Berry, Joel L. Boles, Amit Singh, Baker Hughes, Imran Hashim, Newfield Exploration

SPE 140751

Presentation Outline

• Scale Mineralogy and Chemistry• Acid Solubility Studies• Oxidizing Agent Treatments• Scale Reprecipitation Study • Well Acid Treatment • Acid Flowback Sample Analysis• Conclusions

Factors That May Affect The Dissolution Rate of the Scale in The

Well Downhole temperature and pressure Pressure changes H2S scavenger concentration and type

Ratio of acid volume to scale weight Scale pre-treatment with oxidizers

Scale Mineralogy and Chemistry

Zinc Sulfide Solids From Bailer Runs

Mineralogy XRD Results

Minerals 1st Run Drive Bailer (10011 ft)

2nd Run Drive Bailer (10011 ft)

3rd Run After Spot 20 Gals 15% HCL Pump Bailer (10011 ft)

Wurtzite(ZnS) Major Major Major

Iron sulfide Minor Minor Minor

Major =>20%

Minor =5-20%

Trace =<5%

Zinc Sulfide Scale Chemistry

Wurtzite

Hexagonal form

Sphalerite

Cubic FormReference: Encyclopedia of Materials: Science and Technology

Acid Solubilities At 150°F With Atmospheric Pressure

Approximately 5.0 grams of scale was placed in 50 mls of each tests acid.

#1-10% HCl + 10 gpt ACI +10 gpt Intensifier + 1 gpt Surface Tension Reducer + 2 gpt Flowback Additive + 26 gpt Acetic Acid + 100 pptg Iron Control #1 + 25 pptg Iron Control #2 + 15 gpt Hydrogen Sulfide Scavenger #2 + 2 gpt Clay Stabilizer

#2-15% HCl #3 -15% HCl + 15 gpt HS #2 # 4 -15% HCL + 15 gpt HS #3

Pounds of Zinc Sulfide Scale Dissolved Per Gallon Of Acid At 150°F For One Hour At

Atmos. Pressure

Pounds Of Zinc Sulfide Dissolved Per Gallon Of Acid

0.34 0.35 0.35

2.27

0.83 0.73 0.79

3.47

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

10% HCl (#1) 10% HCl (#2) 10% HCl (#3) 10% HClTheor.

15% HCl (noHS)

15% HCl + 15gpt HS-2

15% HCl + 15gpt HS-3

15% HClTheor.

Test Acid #

# o

f Z

inc S

ulf

ide D

isso

lved

Acid Solubility Tests With Excess Zinc Sulfide Scale At 150°F/AP and 220°F/1000 psi

Nitrogen Pressure For Two Hours

Second set of solubility tests Excess zinc sulfide scale (45 grams/100 mls acid) Acid blends: 1) 15% HCl with no additives

2)15% HCl + 10 gpt ACI + 10 gpt Intensifier + 5 gpt HS#3 + 50 pptg Iron Control #1

Compare the solubility of 15% HCl with/without additives as well as the effects of pressure on the solubility of zinc sulfide in 15% HCl.

Pounds of Zinc Sulfide Scale Dissolved With Excess Zinc Sulfide Scale Present

Pounds of Zinc Sulfide Dissolved With Excess Zinc Sulfide Scale Present

1.711.9

0.6990.871

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

15% HCl (No Additives)

15% HCl(Additives)

15% HCl (No Additives)

15% HCl(Additives)

Acid Systems With/Without Pressure

#o

f Z

inc

Su

lfid

e D

iss

olv

ed

Pe

r G

all

on

of

Ac

id

220 F with 1000 psi Nitrogen Pressure

150F With Atmospheric Pressure

Zinc Sulfide Scale Solubilities With Excess Acid at 150F/AP and 220°F/1000 psi Nitrogen Pressure

and Varying Concentrations of HS#3

• Third set of tests• 5X excess acid ratio to scale solid• Solubility test at AP and HT/HP Conditions• Varying concentrations of HS#3• Acid blends: #1 15% HCl + 10 gpt ACI + 10 gpt Intensifier + 5 gpt HS#3 + 50 pptg Iron Control Agent.

#2 15% HCl + 10 gpt ACI + 10 gpt Intensifier + 10 gpt HS#3 + 50 pptg Iron Control Agent




Solubility Tests with 5X Excess Acid Versus Previous Solubility Tests

Test #

Conditions Scale to Acid Volume Ratio

% Solubility Efficiency

1 150°F/Atmospheric Conditions 45.0 grams in 100 mls of acid

54.7% Solubility Efficiency

2 220°F/1000 psi nitrogen pressure 45.0 grams in 100 mls of acid


3 150°F/Atmospheric Conditions 4.50 grams in 100 mls


4 220°F/1000 psi nitrogen pressure 4.50 grams in 100 mls of acid


Solubility Tests with 5X Excess Acid and Varying Concentrations of HS-3

Zinc Sulfide Dissolved In 15% HCl Acid Versus Concentration of HS-3 At Atmospheric and HTHP Conditions

00.050.1

0.150.2

0.250.3

0.350.4

5 gptHS-3

10 gptHS-3

15 gptHS-3

50 gptHS-3

100gpt

HS-3

5 gptHS-3

10 gptHS-3

15 gptHS-3

50 gptHS-3

100gpt

HS-3

Concentration Of HS-3 (gpt) in 15% HCl Acid

# o

f Z

inc

Su

lfid

e D

isso

lved

Per

G

allo

n o

f 15

% H

Cl

150F With Atmospheric Pressure

220F With 1000 psi Nitrogen Pressure

Oxidization Agent Studies

Reported to increase acid solubility Oxidization agents treatments

-5% Sodium hypochlorite

-3% Hydrogen peroxide

-Concentrated oxidizer formulation

Treatment reacts for one hour at 150°F Ratio of 22.4 grams of scale with 50 mls

acid Acid : 15% HCl + 10 gpt ACI + 10 gpt

Intensifier + 5 gpt HS#3+ 50 pptg Iron control agent

Acid Solubility of Scale After Treatment With Oxidizing AgentsDissolution Rate of Zinc Sulfide Scale In 15% HCl Acid After

Treatment With Oxidizers

00.5

11.5

22.5

33.5

4

Oxidizer Treatment

#Of

Zin

c S

ulf

ide

Sca

le

Dis

solv

ed P

er G

al. o

f 15

% H

Cl

Aci

d

220F/1000 psi Nitrogen

72F/AtmosphericTheoretical Solubility

Acid Solubility of Zinc Sulfide After Oxidizing Agents

Test # Scale Treatment Test Conditions Acid Treatment Pounds of Zinc Sulfide per Gallon of Acid

% Increase In Acid Solubility Over Untreated Scale

1 5% Sodium Hypochlorite 720FAtmospheric Pressure

15% HCl + Additives 2.235 14.9%

2 3% Hydrogen Peroxide 720FAtmospheric Pressure

15% HCl + Additives 2.335 18.6%

3 Concentrated Oxidizer Formulation #1

720FAtmospheric Pressure

15% HCl + Additives 1.861 0%

4 5% Sodium Hypochlorite 2200F/1000 psi nitrogen pressure

15% HCl + additives 1.158 24.7%

5 3% Hydrogen Peroxide 2200F/1000 psi nitrogen pressure

15% HCl + additives 1.198 27.2%

6 Concentrated Oxidizer Formulation #1

2200F/1000 psi nitrogen pressure

15% HCl + additives 1.086 19.7%

Zinc Sulfide Reprecipitation Tests

Conduct zinc sulfide scale dissolution tests 22.4 grams of scale in 50 mls of 15% HCl Filter solution to collect acid effluent Initial acid effluent pH of 0.35 Aliquots were taken out and pH was adjusted

to 1.0, 2.0, 3.0, 4.0, 5.0 with 0.2N NaOH Fluids were observed for precipitation

HCl Acid Effluent With pH Adjustment By Addition of 0.2 N

NaOH

Concern about maintaining pH of acid solution below 3.0 to prevent reprecipitation in the formation or wellbore.

Well Treatment• Acid scale treatment designed from lab tests to

determine acid strength, additive package, and proper acid to scale ratio

• Recommended acid formulations: 15% HCl Formulation: 15% HCl + 20 gpt Acid Corrosion Inhibitor +

20 gpt Intensifier#1 + 20 gpt Intensifier#2 + 1 gpt Flowback Additive + 50 pptg Iron Control Agent#1 + 25 pptg Iron Control Agent#2 + 10 gpt HS#3 + 2 gpt HS#22 + 0.5 gpt Clay Control

7.5% HCl Formulation: 7.5% HCl + 10 gpt Acid Corrosion Inhibitor + 10 gpt Intensifier#1 + 1 gpt Surface Tension Reducer + 26 gpt Acetic Acid + 10 pptg Iron Control Agent #1 + 50 pptg Iron Control Agent #2 + 25 pptg Iron Control Agent#3 + 10 gpt HS#3 + 2 gpt HS#22 + 2 gpt Clay Control.

Well Treatments

Treatment thru coiled tubing 1st treatment -12 bbls of mixed solvent

(remove hydrocarbons from scale) 2nd treatment -12 bbls of 15% HCl acid

spotted in four stages of 3.0 bbls each across the sliding sleeve, screen and perforation area.

Soaking time of 15 minutes at each stage

Well Treatments Acid circulated from bottoms up Fresh treatment of solvent to remove hydrocarbons

from formation Followed by 53 bbls. of 7.5% acid and 30 bbls. of 5%

KCl with N2 Foam diversion treatment in 3 stages Utilized to dissolve scale from formation pore

throats. Acid flowed back after a 12-hour soak period.

Acid flowback samples of the 15% circulated acid and the 7.5% injected acid were collected and analyzed.

Corrosion inhibitor slugs were pumped ahead of the acid treatment to better protect the coiled tubing string from the stronger 15% HCl acid system.

Treatment Plot For Acid Spot Across Sliding Sleeve, Screen And Perforations

0

5000

10000

We

llH

ea

d (

ps

i)

0

500

1000

1500

2000

N2

Ra

te (

sc

f/m

in)

0

1000

2000

3000

4000

5000

An

nu

lus

(p

si)

0

5

10

Pu

mp

Ra

te (

bp

m)

Start CI SlugStart Solvent

Start 15% HClCI Slug on zone

Start 5% KCl flush

Solvent on zone (cirl)

Solvent (inject)

15% HCl (inject)

15% HCl (1 - cirl)

15% HCl (2 - Cirl)

15% HCl (3 - Cirl)

15% HCl (4 - Cirl)

Circulate out 15% HCl to surface

100 200 240Elapsed Time (min)

Solvent - Acid Soak

Treatment Plot For Acid Spot With N2 Across Formation

0

5000

10000

We

llH

ea

d (

ps

i)

0

500

1000

1500

2000

N2

Ra

te (

sc

f/m

in)

0

1000

2000

3000

4000

5000

An

nu

lus

(p

si)

0

5

10

Pu

mp

Ra

te (

bp

m)

Start Solvent

Start 7.5% HCl - 1

Start KCl/N2 - 1

Solvent on zoneStart 7.5% HCl - 2

Start KCl/N2-2

7.5% HCl - 2 on zone

KCl/N2 - 2 on zoneStart 7.5% HCl - 3

Start KCl slug7.5% HCl - 3 on zone

Start KCl flush

250 300 350 400 450Elapsed Time (min)

Acid / N2 Injection

Acid Flowback Samples

Four acid flowback samples collected 1)Sample #1 –First spot treatment (15% HCl circulated)

2)Sample #2 – First spot treatment (15% HCl circulated)

3)Second Injection Flowback Sample #1(7.5% HCl injected)

4)Second Injection Flowback Sample #2(7.5% HCl injected)

Samples analyzed for elemental composition/physical

characteristics.

Acid Flowback Samples Physical Parameters and Elemental Composition

Parameter 10-28-09 11:30 am

First Spot Treatment

Sample #1 (15% HCl Circulated)

10-28-09 11:35 am First Spot Treatment

Sample #2 (15% HCl Circulated)

10-28-09 11:00 pm

Second Injection Sample #1 (7.5%

HCl Injected)

10-28-09 11:05 pm

Second Injection Sample #2 (7.5% HCl

Injected)

Appearance Black with solids Black with solids Black with solids Black with solids Smell “Rotten egg” odor “Rotten egg” odor “Rotten egg” odor “Rotten egg” odor pH 0.79 0.74 4.9 4.2 % Solvent 20% 30% 5% 5% % Aqueous 80% 70% 95% 95% Elemental (mg/l) Calcium 14,690 546 41 20 Barium ND ND ND ND Magnesium 1,523 311 38 26 Iron 7,224 12,060 366 699 Potassium 8,287 7,422 841 735 Sodium 6,929 6,261 285 269 Boron 10 <10 ND ND Copper ND ND ND ND Manganese 92 66 3 <5 Molybdenum ND ND ND ND Phosphorus 87 39 12 40 Silica 38 37 5 7 Strontium 44 ND ND ND Zinc 3,673 15,358 258 1,079 Aluminum 4,208 97 ND 15 Sulfur 671 606 294 855 Chromium 568 2297 15 127

Conclusions

Solubility of the submitted zinc sulfide is much lower in 15% HCl than the calculated theoretical value.

Increased pressure significantly decreases the solubility of zinc sulfide scale in 15% HCl

Conclusions Solubility tests with 5x the theoretical

amount of 15% HCl acid showed the maximum dissolution of this scale.

Study shows the importance of treating scale with excess acid volume to increase the scale dissolution rate at increased pressure and to ensure the removal of all the scale.

Conclusions Adding HS#3 to the acid enhanced the acid

dissolution rate up to a concentration of 10 gpt . However, above this concentration the scale dissolution rate begins to decline and a secondary precipitation begins to develop in the solution.

Study with pre-treatment of the zinc sulfide scale with an oxidizing agent to try to increase the dissolution rate show that 3% H2O2 was the most effective oxidizing agent.

Conclusions

Laboratory analysis is critical to maximizing the efficiency of zinc sulfide scale removal operations to properly identify scale form and combinations of additives that will best ensure removal.

Questions?

spe #140751 slide presentation

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