Scientific Analysis Laboratories (SAL)

Spill Source Identification The Future for Oil Analysis

David Smith, Technical Director

Scientific Analysis Laboratories Ltd

dsmith@salltd.co.uk

The project

The project:To determine if oil residues in sediment & water samples are derived from two nearby oil pipes.

- Firstly to distinguish if there are differences between the two potential sources, - Secondly to correlate the environmental samples to either source.- Thirdly to try to age the spills in time.

Help & Hindrance

The two oil pipelines are from the same source regionOils from different wells within the same field can have markedly different properties.Oils in pipelines often represent 'blends' of different crude oils. Both the physical and chemical properties can differ from the original crude.Oil from an individual well can vary with depth of the reservoir, and the year of production.Oil from years apart will almost certainly be different.

Analysis to be carried out

● Whole oil gas chromatography● API gravity● Stable Carbon Isotope analysis● Biomarker analysis● Pristane / Phytane ratio

Oil 50API gravity = 39.89 (SG 0.8256) pr/ph = 1.97

Oil 51API gravity = 38.23 (SG 0.8337) pr/ph = 2.37

Rating the oils as 'light oils'

Whole oil fingerprints are similar but not identical.

Pristane / Phytane

Pristane / PhytanePr/ph used to define the source of oils :

<1 = derived from carbonate source rock (often high in Sulphur)

1-3 indicate marine oils

>3 none marine oils

Oils 50 & 51 are sufficiently close to show they derive from similar but NOT identical sources

Pr/ph can also be influenced by maturity, indicating oil 51 is more mature than oil 50

Whole oil Chromatogram – Oil 50

Whole Oil Chromatogram Oil 51

Whole oil comparison

Gasoline Range Chromatogram – Oil 50

Gasoline Range Chromatogram Oil 51

Gasoline Range comparison .

MaturityThe biggest difference between the oils is in their preservation state. Oil 50 has visibly less normal alkanes than oil 51This is reflected in the Pr/nC17 and Ph/nC18 ratios, the higher values for the 50 oil indicating that this oil has suffered more secondary alteration than the 51 oil.

This secondary alteration is in the form of water washing. The effect of water washing (which is often but not always accompanied by biodegradation) is to remove the more water soluble hydrocarbons

This is highlighted by an examination of the distribution of the gasoline (C4-C7) range hydrocarbons in each of the oils. the more water soluble aromatics benzene and toluene are present in reduced concentrations in the 50 oil compared to the 51 oil.

Oil Maturity from Gasoline Data

Oil Preservation Plot From Gasoline Data

Biomarkers

Biomarker analysis performed on the oils (and sediment extracts) concentrated on hydrocarbon classes that would yield information on the source and maturity of the oils. The two most commonly used groups of hydrocarbons are steranes (monitored by the main mass fragmentation ion m/z 217)hopanes (m/z 191).

The distribution of the principal steranes containing between 27 and 29 carbon atoms provide information regarding source input (marine vs. non-marine organic matter) and maturity of the oil whilst certain hopanes provide crucial information regarding the source of the oil. Some are highly source specific markers and are indicative of regions

Both oils share near identical biomarker profiles (next slides) and various biomarker ratios (next table) and plots (next slides) indicate the oils to be from the same source at the same level of maturity.

Hopane (m/z) 191 for Oil 50 & 51

Hopane (m/z) 191 for Oil 50 & 51

Key Biomarker ratios for Oils 50 & 51

Source parameters

parameter

Oil 50 Oil 51

Sterane/hopane ratio 0.41 0.28

C28/C29 sterane ratio 0.89 0.86

Oleanane index 0.42 0.48

δ13C-value -27.35 -27.38

Ts/Tm ratio 0.80 0.83

C29ααα20S/20S+20R sterane ratio 0.35 0.35

Sterane Plot for Oils 50 & 51

Stable Carbon Isotope analysisTo be compatible with the sediment extract data, stable carbon isotope analysis was performed on the combined saturate and aromatic fractions of the oils rather than on the whole oil or isolated fractions from the oils.

The δ13C values of -27.35 and -27.38‰ are near identical indicating that, despite suffering some secondary alteration post generation, the oils share the same source .

Biodegredation

Because the aliphatic (saturate) hydrocarbons would be preferentially lost over the aromatics (the bacteria consumes n-alkanes first) then the ratio of the saturate hydrocarbons to the aromatic hydrocarbons (S/A) should be a measure of the degree of degradation suffered. Tables (seen latter) present TPH yields, S/A ratios and the Oleanane index for the high impact samples from areas Spill 1& 2. The S/A values fall within the narrow range of 1.77-2.27

The concentration data is also interesting as the highest concentrations of hydrocarbons are observed in the shallowest of the spill 1 & 2 samples suggesting that there has been insufficient time for (a) degradation of the surface oil and (b) penetration of the oil with depth.

Biodegredation #2

This crude is a water wet oil. This means that in the reservoir the oil is in contact with water.Most susceptible are the alkanes, followed by the acyclic isoprenoids then the alkylated benzenes (1ring first followed by 2 ring, etc.). Next come the hopanes with the 17αhopanes being lost preferentially to the other hopanes. The steranes are next to be lost followed by the diasteranes. Most resistant to loss are the compounds gammacerane and oleanane. The oleanane index (the ratio defined by oleanane/oleanane+17α C30 hopane) is considered to be a measure of the level of degradation suffered by the spilled hydrocarbons.

Biodegredation #3

Biodegredation #4

Evaporation

Environmental Fate

What we expect to see............ Accepting that the oils may represent blends of oils from different wells/reservoirs and are not oils from a single reservoir that has no barriers to production then the range for the oleanane index is between 0.42 and 0.48

Thus by monitoring the oleanane index for the sediment extracts it is possible to assess the level of degradation of the sediment extracts compared to the oil.

Similarly the stable carbon isotope value of the combined aliphatic and aromatic fraction of the sediment extracts should provide us with a correlation parameter, correlating the sediment extracts with each other and the oils. With increasing biodegradation the C12 isotope is lost preferentially to the C13 isotope so one should see the degraded samples being isotopically heavier than the unaltered oil.

Spill area #1SAL No TPH

Yield (ppm)

GC S/A Ol index δ13C(‰)

379059-32 23163 UCM 1.77 0.49 -27.42

379059-33 359 UCM 2.23 0.49 -27.47

379059-34 722 UCM 1.8 0.49 -27.17

379059-35 1968 UCM 0.49 0.48 -27.44

379059-36 6888 UCM 2.86 0.48 -27.29

379059-37 310 UCM 1.98 0.48 Ts

Observations on spill area #1

Observations: Oil in sediment is moderately degraded (no alkanes/acyclic isoporenoids). Oleanane index and stable carbon isotope values very similar to oil in pipelines biomarkers unaffected. High surface concentrations with suggest spill has not been significantly degraded .

Origin of oil similar to that of Light crude.

Oil 50

Oil 51

379059-032

Spill area #2SAL No TPH

Yield (ppm)

GC S/A Ol index

δ13C(‰)

379059-26 52863 UCM 2.14 0.51 -27.50

379059-27 2559 UCM 1.82 0.56 -27.48

379059-28 1210 UCM 1.99 0.48 -27.30

379059-29 128121 AI 2.15 0.47 -27.56

379059-30 19108 AI 2.27 0.50 -27.48

379059-31 7950 AI 1.77 0.50 -27.53

Observations on spill area #2

Observations:

Oil in sediment is moderately degraded (no alkanes minor acyclic isoporenoids). Oleanane index and stable carbon isotope values very similar to oil in pipelines biomarkers unaffected. High surface concentrations

Origin of oil similar to that of Light crude.

379059-026

379059-029

379059-030

Spill area #3SAL No TPH

Yield (ppm)

GC S/A Ol index δ13C(‰)

379059-44 911 Trace 2.02 0.51 -27.53

379059-45 457 Trace 2.07 0.51 -26.23

379059-46 456 Trace 5 0.50 -26.88

Observations on spill area #3

Observations: More degraded oil than in spill areas 1& 2 suggesting older spillMuch lower concentrations.

Biomarker data indicates contamination from Light crude

Answers to questions 1&2

(a) Could the spills be attributed to an oil spill date or do any of the sites indicate that spilled oil was prior to the expected leak date

(b) Can the hydrocarbons be ‘aged’

In all of the analysed samples the level of biodegradation suffered by the spills has precluded age dating based on the various published methods. This is because the n-alkanes and the acyclic isoprenoids (used for age dating) have, in the majority of cases, been lost to biodegradation.

The rates of biodegradation for these oils are more than likely very high with 50% of the native oil being lost through evaporation and dissolution within 24 hours of the spill. Consequently spilled oil can be almost completely consumed through the action of bacteria within a very short period of time, weeks or months rather than years. This makes it impossible to tell whether spilled hydrocarbons are due to an specific event in time or a more recent event.

Answer to Question 3(c) Can the hydrocarbons in the sediment be correlated to the oils in the pipelines.

Biomarker analyses (targeting the steranes and hopanes) and stable carbon isotope analyses performed on oils taken from the two pipelines indicate that the oils derive from the same oil source at the same level of organic maturity.The oils do have separate post generation histories suggesting that the oils do not come from the same well or the same reservoir.The biomarker data for the oils extracted from the sediments indicate that these hydrocarbons correlate to the oils in the pipeline the only differences being related to different levels of biodegradation or extreme low concentration of the biomarkers in the sediments.

The Future for Oil Analysis ?The Aliphatic Aromatic splits provide only so much detail in the chromatogram, without having to go to slow 'expensive' alternatives.Such as biomarkers, whole oil and isotope ratio MS

What if we could acquire chromatographic patterns that are multidimensional, and look at a chromatographic landscapes visualised in 3 dimensions that would be better for pattern matching:

443743-017

Aliphatic only

Ali / Aro Std

Diesel

438161-001

432682-060

Thank You

Any Questions ?