Asphaltenes

Susan Garner, PhD

RD&E Group Leader

October 22, 2015

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What Are Asphaltenes?

� What causes them?

� Where can they occur?

� Types of treatment

� Mitigation Strategy

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Asphaltenes• Asphaltenes are defined as the heavy components of crude oil that are insoluble in non-polar solvents such as hexanes but soluble in aromatic solvents such as toluene

• Structure (no exact composition)– large complex aromatic structures that contain carbon, hydrogen, oxygen, sulfur, nitrogen, and possibly metals(nickel and vanadium)

Proposed Structure of an Asphaltene Molecule from a Venezuelan Crude

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S

COOH

R

R

CH3

S

CH3

NH

CH 3

R

RESINS

R

S

CH 3

R

CH 3

CH3

CH3

R

CH3

R

AROMATICS

R

R

COOH

R

CH3

R

R

CH3

RCH3

SATURATES

CH3

CH3

CH3

CH3

CH3

ASPHALTENES

CH3

CH3

O

NH

NH

CH3

CH3

S

S CH3

CH3R

CH3R

CH3

CH3

CH3

Crude Oil Compound Class Separation• Petroleum contains millions of different molecules

• Petroleum maybe considered a stabilized colloidal or

nano dispersion

• Attractive and dispersive forces govern the stability of

the oil, or the potential for the solute to precipitate

• A number of factors may cause precipitation and

other production problems

S S SS A A A S

S A R R R A SS A R A A R A SS A R A A R A SS A R R R A SS A A A S

S S S

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Asphaltene Destabilization

Potential Asphaltene Aggregation Pathway

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DEPOSITION ZONES

Wellbore

Wellhead

Flow lines

Separator

Modified from: Jianxin Wang (2000), P & Sc Group, New Mexico Tech.

Near wellbore region

� Problems Associated with Asphaltene Deposition� Formation Damage

� Plugged flow-lines and equipment, chokes, separators, pumps, etc.

� Reduced effectiveness of surface equipment

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Precipitation vs. Deposition

Precipitation- Separation of a solid phase out of the liquid phase. • Function of thermodynamic variables such as composition, pressure and temperature• Adverse rheological effects and/or fouling

Deposition- formation and growth of a layer of solid precipitant on a surface

• Function of flow-hydrodynamics, geometry and surface and particle interactions• Major mechanism for blockages in flowlines and wellbores

• Precipitation is necessary but not a guarantee for deposition

• Co-deposition of other species such as wax

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Causes of Asphaltene Issues

� Pressure and temperature change

� The chemical composition of the crude changes

� A mechanical change takes place

� Asphaltenes come in contact with acid

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Pressure and Temperature

� Pressure and temperature changes can alter the delicate equilibrium between the resins and asphaltenes

� Pressure effect are usually more severe, especially when the pressure drops below asphaltene precipitation point

� Asphaltene precipitation occurs in flowlines and separators where the pressure and temperature changes are the greatest

http://flowassurance.blog.com/flow-assurance-topics/

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Chemical Changes

� Mixing of crudes – can upset the balance between resin and asphaltenes

� Miscible floods – tend to be nonpolar (CO2, C4-C6) and can strip the stabilizing agents away from asphaltenes

� Release of gases – as a result of a drop in pressure below the crude bubble point (highest content of dissolved gas in oil)

� Gas lift – injected gas changes the chemical composition of the crude

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Mechanical Changes

� SHEAR� Since the resins in the crude are

in a loosely associated equilibrium with the asphaltenes, they can be physically stripped from the asphaltenes resulting in flocculation

� ESP- Electric Submersible Pump

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Contact with acid

� Acids and asphaltic oils are incompatible

� Great care must be given to asphaltic crudes during well completion and stimulation

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Identification of Field Deposits

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Resolving Asphaltene and Paraffin Deposition

� Remediation – the deposits must be removed in a safe, cost-effective manner� Mechanical: pigs, physical removal

(cutting)

� Chemical: solvent/dispersants

� Thermal for Paraffin: heated vessels, pipe in pipe technology, hot oil or water treatment

Things to keep in mind while doing thermal remediation for paraffin

- Deposits can have melting points ranging from 160˚F to 220˚F.

- Deposits can have softening points ranging from 120˚F to 170˚F.

- Contact time

� Control – the root cause of the problem must be addressed and treatment implemented before deposition occurs� Process or operational changes

� Chemical treatment: dispersants, inhibitors, combination products

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Chemical Types

� Solvents

- Used for dissolving organic deposits off formation, tubing and flowlines

- Typically have high aromatic content for asphaltenes

- Aromatic/aliphatic for paraffin

- Recirculation of well allows for more effective treatment

- Solvents are more effective with heat

- Large volumes

15 minutes

1 hour

4 hours

24 hours

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Chemical Types� Dispersants

- Break larger deposits into smaller particles which can be carried through the system

- Dispersants do not prevent asphaltene flocculation or wax crystallization but can prevent deposition

- Surface active agents that can work in the presence of water by water-wetting the paraffin particles, keeping them from reuniting or depositing on flowlines

- Dispersants are surface active and may contribute to the stabilization of water-in-oil emulsions and to oil-in-water carryover

- Works alone or in conjunction with solvents or inhibitors

Deposit

Shear Dislodges Deposit Particles

Particles Stabilized by Dispersants

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Chemical Types

Untreated Asphaltenes Treated Asphaltenes

Inhibitor

� Asphaltene Inhibitors

- Inhibitors are polymeric resinous material that stabilize the asphaltenes and prevent destabilization, agglomeration and flocculation

- Forms a strong association with asphaltene moieties

- Preventive treatment and it is recommended that asphaltene inhibitors be added to the system before the asphaltenes begin to flocculate

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Best Practices When Using Chemicals

DO

� Select the right chemistry for your application

� Measure a baseline prior to initiating chemical program

� Monitor performance over time to adjust to change in production and/or temperature

� Apply the chemical in the correct spot in the system

DON’T

� Mix chemistries with other chemistries without validation from vendors

� Use inhibitors in batch treatment

Monitoring Program

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Monitoring� Onboard ADT / Turbiscan testing

� Routine sample collection and evaluation� SARA, HTGC, ADT, etc.

� Platform monitoring,� Bridles, valves, sensors, grid out etc.

� Routine program assessment and optimization.

� Sub-sea monitoring� ∆T — insulations due to asphaltene deposition

� ∆P — continuous friction losses monitoring

� Skin — every time a well is shut in

� Pigging frequency / returns — closer analysis can illustrate settlingvs. deposition

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Monitoring

Detection of residual AI from field samples(Nalco Champion proprietary method)

Risk Mitigation

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Our Approach for Risk Mitigation

� Risk Assessment

� Pre-Production

� Oil analysis

� Characteristics of the field

� Product Selection

� Performance screening of potential chemical solutions

� Characterization

� Comparison to Global Database

� Product synthesis and formulation

� Field Readiness

� SurFlo Plus Certification (HP Viscosity, Thermal Stability, Material Compatibility, Emulsion tendency)

� Water quality

� Asset Specific

Characterize

Field Readiness

Product Selection

Risk Assessment

Reliable Solution

Risk Assessment

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Wang, Creek, Buckley; SPE Applied Technology

Workshop, Abu Dhabi, UAE, Feb. 9-12, 2009

ASIST Modeling-Identifying Asphaltene Onset

� ASIST determines onset of asphaltene instability using a series of liquid n-alkanes

� Titrate STO with n-alkanes and observe flocculation with microscopy to determine onset of precipitation

� Measure refractive index oil/n-alkane mixture at onset

� Onset RI has linear correlation to n-alkane molar volume to power of ½ (Vp1/2).

� Stability of asphaltene in live oil sample under reservoir conditions can be estimated using PVT and compositional data for the reservoir fluid and stability of STO

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ASIST Prediction

GOM – A GOM – B

No AOP detected AOP at 4300 psia

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SARA Analysis

SaturatesAromatics

Resins

Asphaltenes

Oil Composition (wt%)

SAT ARO RES ASPH

69.0 23.9 6.9 0.8

Asphaltene Stability Index = ���������������������

��!�����"#��!$�

• > 0.9 = unstable

• 0.7 – 0.9 = potential problems

• < 0.7 = stable

ASI = 2.3

Product Selection

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Comprehensive Evaluation of

Product Performance

� Risk Assessment and Characterization findings are incorporated to determine the key factors involved with asphaltene related risk specific to the asset

� A test matrix is designed to capture these factors and best mimic your operating conditions

� Potential Asphatlene Control products progress through the performance screening process to identify the most suitable solution

Coupon Deposition Test

Precipitation Tests

Rocking Cell

HT Turbiscan

Potential inhibitor

candidates

Stable and reliable product

Field Readiness

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Field Readiness

� Ensuring that the risk mitigation planned is applicable for your situation and will not contribute to or exacerbate another treatment program

� Considerations � Emulsion tendency

� Foaming tendency

� Water quality

� Viscosity

� Operational impacts

� Other production chemicalapplications

Stability

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Summary� Asphaltenes are defined as the heavy components of crude

oil that are insoluble in non-polar solvents such as hexanes but soluble in aromatic solvents such as toluene� Precipitation- Separation of a solid phase out of the liquid phase.

� Deposition- formation and growth of a layer of solid precipitant on a surface

- Precipitation is necessary but not a guarantee for deposition

� Causes for asphaltene destabilization � Pressure and temperature change

� The chemical composition of the crude changes

� A mechanical change takes place

� Asphaltenes come in contact with acid

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Summary

Characterize

Field Readiness

Product Selection

Risk Assessment

Reliable Solution

Coupon Deposition Test

Precipitation Tests

Rocking Cell

HT Turbiscan

Potential inhibitor

candidates

Stable and reliable product

Questions???Comments….