Intertek performs complete tar formation (tar-mats) and tar distribution studies, including study design, sample analysis, data interpretation and prediction of tar distributions. Westport experts perform numerous oil quality distribution studies, including studies of tar occurrence and distribution, on a global basis. The tar study determines the origin of the tar. Testing includes the analysis of the tar and the analysis of lighter hydrocarbons in the area, with assessment of geologic conditions at the locations of occurrence.

Tar and related geochemical analysis include:

• Whole oil, tar and saturated fraction gas chromatography
• SARA separation and quantification of oil and tar
• Elemental analysis of tar
• Chemical composition of gas samples
• Isotopic composition of methane through butanes in gas samples
• Stable isotope analysis of the whole oil and SARA fractions

The geochemical data is interpreted in the structural and geologic context to determine the cause of tar formation. Understanding the origin and distribution of heavy, high-viscosity hydrocarbons in an area of petroleum exploration or production can be critical to minimizing production cost.

Tar studies help operators better understand:

• The mechanism of formation of the tar
• Locations and intervals with conditions favorable for tar formation
• Production processes that might cause tar precipitation during production (such as gas injection, pressure reduction, etc.)

Helping Operators make decisions that minimize the effect of tar on production cost:

• Minimizing drilling in tar-rich areas
• Avoiding completing tar zones
• Employing production practices that do not cause tar formation

Asphalt-rich or heavy oil can form and accumulate within geologic systems by a number of different processes:

• Migration and emplacement of immature asphalt-rich bitumen
• Precipitation of asphaltenes from oil
• Biodegradation of oil
• Water-washing of oil
• Phase separation of oil
• Gravity segregation of oil
• Evaporation of light ends from oil
• Thermal alteration of oil or bitumen

These processes operate individually or jointly to produce heavy hydrocarbons. High-viscosity, wax-rich deposits can be formed from residue of high-wax oils. These wax-rich deposits can have the general appearance of tar and can present production problems.

Exploration and Production Tar Study:

Analysis of the heavy oil and examination of the petroleum system helps Intertek clients understand the origin and distribution of the heavy oil (tar). A tar study can lead to reliable prediction of specific occurrences of the tar prior to drilling.

Tar studies require geochemical analysis of heavy and lighter hydrocarbons from the area and evaluation of the geochemical data in the total geologic context. A tar study determines the origin (formation) of the tar. The tar study then determines the necessary and sufficient conditions for the formation and accumulation of the tar. Finally, the study delineates specific locations where the conditions are met and tar is expected.

After tar origination is determined, a tar study determines tconditions for formation of the tar, defining conditions of temperature, pressure, water contact, gas infusion, seal breach, geologic uplift, etc. that are necessary for formation of the tar. Finally, once the tar formation conditions are defined, the study focuses on defining locations in the study area that may meet the tar formation criteria and assigning probabilities or risk of encountering tar at those locations. Contact Intertek for more information on how tar formation studies can directly benefit your exploration and production projects.