The SPE Foundation through member donations and a contribution from Offshore Europe

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1 Primary funding is provided by The SPE Foundation through member donations and a contribution from Offshore Europe The Society is grateful to those companies that allow their professionals to serve as lecturers Additional support provided by AIME Society of Petroleum Engineers Distinguished Lecturer Program

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3 Origin and Behaviour of Oil Asphaltenes Integration of Disciplines Artur Stankiewicz Society of Petroleum Engineers Distinguished Lecturer Program

4 Acknowledgments The data and supporting examples are primarily based on the research and field application that took place at various Shell locations. Author is grateful to Shell and Schlumberger for permission of presenting this material to the SPE audience. Cooperating service companies, scientific institutions and all who, over the years, worked with me on the R&D and implementation of technologies in the area of asphaltenes. 4

5 Outline Introduction into the World of Asphaltenes Setting the scene Basic facts and definitions Origin of asphaltenes (source and changes in geological time) Few remarks on asphaltene structure & analytical techniques Theory of the oils critical range Fluid properties and live oil behaviour Stock tank liquid screens Live oil behaviour and screens Examples of diversity in the world of asphaltenes and implications Field application Conclusions 5

6 Asphaltenes why do we care? Asphaltenes precipitated in the production system (reservoir wellbore tubing pipeline topside facilities) may lead to their deposition = reduced or shut-in production Topside facilities Pipes blocked due to asphaltenes (photo courtesy of alco)

7 Pressure (psia) Asphaltenes one of many solid phases encountered in production systems Wax 1 Reservoir Hydrate 8 6 Asphaltenes 4 2 Flow line Temperature ( C) Asphaltenes Waxes Hydrates Diamondoids Inorganic Scales Sulfur Asphaltenes when unstable typically precipitate at higher T and P than other solids After John Ratulowski 7

8 Asphaltenes deposition how? Composition Changes Instability due to commingling of incompatible fluids Carryover & blending with LG fouls gas side equipment Gas lift mandrills foul Injection gas can cause reservoir impairment, wellbore deposition, and fouling of pumps Pressure Changes ear-perforation reservoir impairment Deposits in wellbores & flowlines cause excessive pressure drop & additional plugging Precipitated solids accumulate in low energy regions

9 ASPHALTEES are defined as the material that precipitates out of crude oil or reservoir rock extract on the addition of excess light alkanes Asphaltenes in Oil [wt. %] Pentane Asphaltenes % C n of n-alkane Heptane Decane Precipitant type IMPLICATIOS: It is a solubility class = OT well defined molecule Various analytical procedures prevent standardization 9

10 Asphaltene Content of Unstable Oils ~ Asphaltene problems are localized, <1% of total world production Some countries have serious challenges (e.g., Venezuela, Kuwait) 1

11 Asphaltenes an Engineering Domain, but Can t we just all get along? Main Technical Areas: Prediction (Deposition Potential) Prevention (Monitoring & Control) Inhibition (Chemical treatment) Remediation (Recovery & Removal) Majority of issues are driven by fluids phase behaviour, production scenarios, topside separation or the Enhanced Oil Recovery processes. Geochemistry brings a fresh view on nature s diversity a global asphaltene molecule does OT exist influenced by source rock type and oil generation/expulsion/migration processes. 11

12 Geochemical and Engineering-View on Asphaltenes H S S OH OH S After Steve Larter & Eugene Frolov RG Petroleum Group S H H Modified from Pelet et al., 1986 Saturate Aromatic Resin Asphaltene S A R A Simple solubility model can explain asphaltene stability 12

13 atural Processes that can Affect Asphaltene Stability in Crude Oil Oil Composition Asphaltene Content/Stability Source Rock Secondary Processes (in reservoir) Kerogen Composition Thermal Maturity (t & T) Gas Washing (late gas charge) Hybridization (mixing) Biodegradation (bacteria) 13

14 Where They Come From? Source Rock Kerogen Types and Origin Lacustrine Shales Type I Lagoonal shales and coals Type III Flood Plain Coals Marine deltaic and open marine settings Type II 14

15 Maturity and its Importance A rock with sufficient organic matter of suitable chemical composition to generate and expel hydrocarbons at appropriate maturity levels is called a source rock Thermal degradation of kerogen (burial, T ) breakdown and release of hydrocarbons Maturity = structural simplification 15

16 Origin and Maturity Affects Structure and Behaviour (T, from bio- to geomacromolecule) H H H H H H V- H S H S H H H V- H S HS S HS H H H H H H H S H S S HS H 16

17 Asphaltenes General Trends With maturity (irrespective of their source origin): Molecular ratios H/C, O/C, /C and S/C Molecular weight (size) Metals (e.g., i, V) Sulfur % IMPLICATIO: Pitch Lake Trinidad Oils in the specific maturity range show increased potential for asphaltene precipitation low maturity, heavy and biodegraded oils, and high maturity condensates are generally stable 17

18 Oil Asphaltene Content [wt. %] Oil Asphaltene Content and the Oil Gravity as Indicators of Maturity Approx. Region of Fluids with Asphaltene Problems Primary fluids only West Africa Venezuela orth Sea Canada Middle East Italy GOM Oil Gravity [API] 18

19 Fluid Instability wrt Asphaltene Precipitation Maturity Controlling Fluid Stability thus Asphaltene Precipitation Hypothesis Critical Range OTE: atural processes and production scenarios can affect asphaltenes behaviour Low Maturity Fluids (Heavier) High Maturity Fluids (Condensates) Maturity increase Maturity indicators: e.g. API increase, Asphaltene % decrease 19

20 Saturate / Aromatic Compositional Asphaltene Stability Screens Unstable Marginal Stable Colloidal instability index Critical asphaltene to resin ratio SARA plot (shown) Unstable Stable Asphaltene / Resin Stankiewicz et al., 22 2

21 Transmitted Power Dead Oil Titration Tests Discrete or continuous titration Detection Visual Spot test Light scattering Does not contain effect of gas Stable FPA Floc Point Analyzer Unstable P-Value Heptane TC Floc Point Computer Titrator Volume of Titrant eat Oil Oil + 1 ml of Hexadecane P = 1.5 Detector 2 mw IR Laser Magnetic Stirrer 21

22 High p&t System to Evaluate Asphaltene Behaviour in Live Oil eat oil Oil with asphaltenes DBR Solids Detection System (Light Transmittance) 22

23 Example of on-problematic Fluid from Venezuelan Well Power of Transmitted Light (mw) Water-like Droplets Water-like Droplets Pres P SAT ~ 193 psi Pressure (psig) on-problematic = no deposition observed Problematic = deposition in the wellbore observed 23

24 Example of Problematic Fluid from Venezuelan Well Power of Transmitted Light (mw) 1mm 1mm Pres 1mm P OAP ~ 35 psi 1mm 1mm P SAT ~ 186 psi Pressure (psig) Information that can be used to optimize operations 24

25 H/C of Asphaltenes Example of Variation in Molecular Composition of Asphaltenes VE S GOM World MW~ MW~1 MW~22 MW based on GPC (SEC) S/C 25

26 Particle Count Variations in Flocc Size is Critical Venezuelan Oil (deposition problems) orth Sea Oil (no deposition observed) psi psi psi psi psi psi psi psi Size [mm] -15 Depressurization experiments at reservoir T 26

27 Oil/Asphaltene Molecular Composition vs Activity of Field Chemicals Venezuelan Oil Asphaltenes = 5 % API = 32 Sulfur oil = 1.4 % Different Chemical Inhibitors A B C D orth Sea Oil Asphaltene = 1 % API = 38.5 Sulfur oil =.11 % The same chemical react differently with different asphaltenes 27

28 Pressure (psia) Variations in PVT Behavior Venezuela type asphaltenes orth Sea type asphaltenes L & Asph & Wax Phases Temperature ( C) Liquid Phase L & Asph Phases L & V & Asph Phases L & V L & Asph & Wax Phases Liquid Phase L & V & Asph Phases L & V L & Asph Phases Temperature ( C) Asph Stability Bubble point Asph Stability Regions of asphaltenes instability After: Ting et al, Petrophase Trondheim, 24 28

29 Example of Carbonate Reservoir API S% Asphaltene Content Problem ranking 1 Heavy deposition 4 o deposition 5 meters Heavier fluids without asphaltene deposition Lighter fluids with asphaltene challenges

30 Conclusions Molecular composition of asphaltenes varies and depends on factors such as source rocks and maturity an average asphaltene structure does not exist. Knowledge of physical/chemical properties of oil and its asphaltenes may be successfully used for prediction of their behavior ahead of production best practices: Routine measurements of fluid property for each new well or reservoir Comprehensive database of fluid properties for each field (existing and new) Constant calibration of empirical observations against field experience Integrated approach and cooperation of various disciplines 3

31 Food for thought Asphaltene deposition problems to date are confined to specific areas and relatively light fluids, however: Increased focus on the EOR/IOR unravels new potential challenges in the area of precipitation/deposition of previously stable hydrocarbon fluids. An integrated approach and cooperation of engineers and geoscientists (e.g. geochemists) is necessary to understand oil asphaltene behavior and its influence on fluid properties. 31