Tar Mats and Bitumen Deposition; Origins and Properties

Production and Operations Drilling


Tar and bitumen deposition can be upstructure, or at the oil-water contact or various locations in-between. Tar can be impermeable and might or might not be a regional seal. In other cases, tar zones can be highly permeable flowing light oil. Tar can have the rheology of coal, or can flow (or ooze). The origins of this bewildering array of tar properties have been grossly misunderstood in part due to the lack of any thermodynamic treatment of asphaltenes. The recent development of the Flory-Huggins-Zuo equation of state (FHZ EoS) for asphaltenes, with its reliance on the Yen-Mullins model of asphaltenes, has led to a simple, concise form of asphaltene thermodynamics, thereby enabling a 1st-principles approach addressing tar deposition and tar mats. Another prior shortcoming was the lack of reservoir fluid data to enable a robust evaluation of asphaltene thermodynamics. Downhole Fluid Analysis (DFA) is now ubiquitously acquired and provides asphaltene gradients in crude oil with exquisite accuracy. A decade of reservoir studies employing these advances has elucidated a broad array of reservoir fluid geodynamic processes that give rise to asphaltene accumulation and destabilization yielding bitumen deposition and tar mat formation. Wide-ranging data streams support conclusions of the reservoir studies including production data, pressure transient analysis, analytical chemistry, geochemistry, flow assurance analysis, core extracts, mud gas analysis and petrophysics. This new vantage provides an excellent foundation for treating tar and bitumen deposition in virtually all reservoirs.


  • Crude Oil Characterization
  • Petroleum Systems and Trap Filling
  • Reservoir Fluid Geodynamics
  • Tar Mats and Bitumen Deposition
  • Tar Case Studies; DFA with Integration
  • Workflow for Reservoir Tar Analysis

Learning Level

This course is designed to introduce a new understanding of tar and bitumen and to bring novices on these topics up to speed. Principles presented in this course will be accessible to those with only the most basic understanding of crude oil. Nevertheless, asphaltene and tar experts will also benefit. The holistic approach will empower oilfield technologists from beginners to experts and from reservoir technologists to reservoir management.

Course Length

1 Day

Why Attend?

Tar mats and bitumen deposition have significant impact on reservoir concerns including aquifer support and sweep efficiency, location of water injectors, productivity of formations, viscosity gradients and viscous oil at the OWC, mobile bitumen, upstructure tar and bitumen deposition, and asphaltene flow assurance. This course treats all these concerns with a relatively simple, yet comprehensive framework. The link between tar-related issues and ‘reservoir fluid geodynamics’ will be clarified. This course is designed to help technologists assess and mitigate development risks associated with tar, bitumen and asphaltenes in reservoirs.

Who Should Attend

  • Oilfield technologists, especially those on asset teams
  • Petrophysicists
  • Reservoir engineers
  • Geologists and geophysicists
  • PVT and fluid experts
  • Geochemists
  • Research chemists
  • Field engineers


Atet Abdel

Oliver C. Mullins, Scientific Advisor, Schlumberger

 Dr. Oliver C. Mullins has 30 years of experience in the industry and is the primary originator of Downhole Fluid Analysis that is used globally in most WL sampling jobs. His extensive studies led to the Yen-Mullins model of asphaltenes, which has been confirmed repeatedly, recently by high-resolution molecular imaging at IBM Zurich. The development of FHZ EoS for asphaltenes by Drs Freed, Zuo and Mullins enabled quantitative interpretation of reservoir fluid geodynamic processes via DFA data sets. Published reservoir studies from all corners of the globe treat a broad array of reservoir complexities. Dr Mullins has authored a book on DFA, coedited 3 books on asphaltenes, coauthored 13 book chapters, 240 papers and has coinvented 100 US patents and has 10,700 citations on Google Scholar.