28
high acidic oil (Oldenburg et al. 2017). These compositional changes have strong
impact on the physical and chemical properties of the oil and influence the transport, interfacial, and corrosion properties. More details on in-reservoir oil biodegradation can be found in Chap. 9.
3.1.2 Macondo Well Oil Molecular Characteristics
The Macondo well (MW) petroleum expelled into the Gulf of Mexico after the
explosion on the Deepwater Horizon rig in 2010 was a mixture of oil and gas.
Reddy et al. (2012) sampled directly above the Macondo well during the blowout
and determined a gas-to-oil ratio of 1600 standard cubic feet per petroleum barrel.
Valentine et al. (2010) and Reddy et al. (2012) both reported the gas being composed of mainly methane (87.5% and 82.5%, respectively) and smaller amounts of
ethane (abundance just above 8%) and propane (around 5%). Reddy et al. (2012)
assessed the Macondo oil as a light oil (API gravity 40° with a density of 820 g L
−1
),
whereas Daling et al. (2014) reported that the oil collected through the riser insertion tube tool (RITT) on the Discoverer Enterprise on May 22, 2010, had a density
of 833 kg m
−3
, a pour point of −27 °C, and interfacial tension of 20 mN m
−1
. The
initial viscosity of the Macondo oil was evaluated to be 3.9 cP at 32 °C (Daling et al.
2014). A maturity assessment of the MW oil based on the relative distribution of
compound groups of the pyrrolic N1 heteroatom class, namely, DBE 9 (alkylated
carbazoles), DBE 12, and DBE 15 (alkylated benzo- and dibenzocarboazoles,
respectively) as established by Oldenburg et al. (2014) indicates a maturity level of
0.9% vitrinite reflectance equivalent (%Re) for the MW oil (Fig. 3.1).
Liquid chromatography (TLC-SARA) measurements revealed that the nonbiodegraded MW oil is dominated by saturated hydrocarbons (74%), followed by
aromatic hydrocarbons (16%) with the non-hydrocarbon (polar) fraction containing
10% (Reddy et al. 2012). The authors reported that the GC-MS amenable MW oil
composition (C5 to C38 saturated and aromatic hydrocarbons) is predominated by
branched alkanes (26%), followed by cycloalkanes (16%) and n-alkanes (15%).
Aromatic species such as alkylbenzenes and indenes (9%) and polycyclic aromatic
hydrocarbons (4%) are less abundant (Reddy et al. 2012). The GC-MS amenable
content of polar oil constituents is 10% (e.g., dibenzothiophenes) with sulfur and
nitrogen elemental abundances of the MW oil assessed as 0.4% each. As only a very
small percentage of the non-hydrocarbon (polar) fraction is GC-amenable due to the
high boiling point of those heteroatom-containing oil species, Fourier-transform ion
cyclotron resonance mass spectrometry (FTICR-MS) is the analytical instrument of
choice to study this oil fraction. McKenna et al. (2013) characterized more than
30,000 acidic, basic, and nonpolar unique neutral elemental compositions for the
MW crude oil. Figure 3.2 shows the compound class distribution of the NIST SRM
2779 Macondo oil measured in electrospray-positive (ESI-P) and electrospraynegative (ESI-N) ion mode as well as in atmospheric pressure photoionization in
T. B. P. Oldenburg et al.
high acidic oil (Oldenburg et al. 2017). These compositional changes have strong
impact on the physical and chemical properties of the oil and influence the transport, interfacial, and corrosion properties. More details on in-reservoir oil biodegradation can be found in Chap. 9.
3.1.2 Macondo Well Oil Molecular Characteristics
The Macondo well (MW) petroleum expelled into the Gulf of Mexico after the
explosion on the Deepwater Horizon rig in 2010 was a mixture of oil and gas.
Reddy et al. (2012) sampled directly above the Macondo well during the blowout
and determined a gas-to-oil ratio of 1600 standard cubic feet per petroleum barrel.
Valentine et al. (2010) and Reddy et al. (2012) both reported the gas being composed of mainly methane (87.5% and 82.5%, respectively) and smaller amounts of
ethane (abundance just above 8%) and propane (around 5%). Reddy et al. (2012)
assessed the Macondo oil as a light oil (API gravity 40° with a density of 820 g L
−1
),
whereas Daling et al. (2014) reported that the oil collected through the riser insertion tube tool (RITT) on the Discoverer Enterprise on May 22, 2010, had a density
of 833 kg m
−3
, a pour point of −27 °C, and interfacial tension of 20 mN m
−1
. The
initial viscosity of the Macondo oil was evaluated to be 3.9 cP at 32 °C (Daling et al.
2014). A maturity assessment of the MW oil based on the relative distribution of
compound groups of the pyrrolic N1 heteroatom class, namely, DBE 9 (alkylated
carbazoles), DBE 12, and DBE 15 (alkylated benzo- and dibenzocarboazoles,
respectively) as established by Oldenburg et al. (2014) indicates a maturity level of
0.9% vitrinite reflectance equivalent (%Re) for the MW oil (Fig. 3.1).
Liquid chromatography (TLC-SARA) measurements revealed that the nonbiodegraded MW oil is dominated by saturated hydrocarbons (74%), followed by
aromatic hydrocarbons (16%) with the non-hydrocarbon (polar) fraction containing
10% (Reddy et al. 2012). The authors reported that the GC-MS amenable MW oil
composition (C5 to C38 saturated and aromatic hydrocarbons) is predominated by
branched alkanes (26%), followed by cycloalkanes (16%) and n-alkanes (15%).
Aromatic species such as alkylbenzenes and indenes (9%) and polycyclic aromatic
hydrocarbons (4%) are less abundant (Reddy et al. 2012). The GC-MS amenable
content of polar oil constituents is 10% (e.g., dibenzothiophenes) with sulfur and
nitrogen elemental abundances of the MW oil assessed as 0.4% each. As only a very
small percentage of the non-hydrocarbon (polar) fraction is GC-amenable due to the
high boiling point of those heteroatom-containing oil species, Fourier-transform ion
cyclotron resonance mass spectrometry (FTICR-MS) is the analytical instrument of
choice to study this oil fraction. McKenna et al. (2013) characterized more than
30,000 acidic, basic, and nonpolar unique neutral elemental compositions for the
MW crude oil. Figure 3.2 shows the compound class distribution of the NIST SRM
2779 Macondo oil measured in electrospray-positive (ESI-P) and electrospraynegative (ESI-N) ion mode as well as in atmospheric pressure photoionization in
T. B. P. Oldenburg et al.