TY - JOUR
T1 - 25-Norhopanes
T2 - Formation during biodegradation of petroleum in the subsurface
AU - Bennett, Barry
AU - Fustic, Milovan
AU - Farrimond, Paul
AU - Huang, Haiping
AU - Larter, Stephen R.
N1 - Funding Information:
The authors thank the Bacchus I sponsors (BP, Chevron, ConocoPhillips, ExxonMobil, ENI E&P Division, Enterprise Oil, JNOC, Norsk Hydro, Petrobras, Shell, TotalFinaElf) for providing financial support. Encana are thanked for providing sample material from the Athabasca-2 well. The Alberta Ingenuity Centre for In-Situ Energy is also thanked for support (Milovan Fustic, PhD student). The authors acknowledge that much of the work was carried out at the NRG (Newcastle University) prior to re-locating to Calgary (Barry Bennett, Steve Larter, Huang Haiping) and Bideford (Paul Farrimond). We are also grateful to Drs. Mike Moldowan and Ken Peters for constructive reviews.
PY - 2006/7
Y1 - 2006/7
N2 - Quantitative data from petroleum systems in China (Liaohe basin) and Canada (Athabasca tar sands) support the theory that 25-norhopanes are produced during biodegradation of petroleum in the subsurface. Within a single oil column, both case histories showed increasing severity of degradation, indicated by destruction of hopanes and production of 25-norhopanes downward to the oil-water contact. In the Athabasca samples between the [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, New Jersey, p. 363] scale of biodegradation levels 5-9, concentrations of C28 20S triaromatic steroids and other biodegradation-resistant compounds increased by 35%, reflecting a concentration effect as a consequence of removal of more degradable compounds. Over the same interval, the concentrations of C28 17α 25-norhopane and C29 17α 25-norhopane increased by an order of magnitude, thus requiring that the balance be met by their net production during degradation. A detailed molecular investigation of the Athabasca bitumen revealed that C30 17α hopane degrades faster than C29 17α hopane, whilst the rate of formation of both C29 17α 25-norhopane and C28 17α 25-norhopane are similar, complicating a straightforward interpretation of demethylation of hopanes to form 25-norhopanes. Hopane degradation in the Athabasca tar sand may also occur without the production of 25-norhopanes. The results show that even within a single petroleum accumulation, a number of mechanisms control changes in the abundance and composition of hopanes and 25-norhopanes.
AB - Quantitative data from petroleum systems in China (Liaohe basin) and Canada (Athabasca tar sands) support the theory that 25-norhopanes are produced during biodegradation of petroleum in the subsurface. Within a single oil column, both case histories showed increasing severity of degradation, indicated by destruction of hopanes and production of 25-norhopanes downward to the oil-water contact. In the Athabasca samples between the [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, New Jersey, p. 363] scale of biodegradation levels 5-9, concentrations of C28 20S triaromatic steroids and other biodegradation-resistant compounds increased by 35%, reflecting a concentration effect as a consequence of removal of more degradable compounds. Over the same interval, the concentrations of C28 17α 25-norhopane and C29 17α 25-norhopane increased by an order of magnitude, thus requiring that the balance be met by their net production during degradation. A detailed molecular investigation of the Athabasca bitumen revealed that C30 17α hopane degrades faster than C29 17α hopane, whilst the rate of formation of both C29 17α 25-norhopane and C28 17α 25-norhopane are similar, complicating a straightforward interpretation of demethylation of hopanes to form 25-norhopanes. Hopane degradation in the Athabasca tar sand may also occur without the production of 25-norhopanes. The results show that even within a single petroleum accumulation, a number of mechanisms control changes in the abundance and composition of hopanes and 25-norhopanes.
UR - http://www.scopus.com/inward/record.url?scp=33745000091&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33745000091&partnerID=8YFLogxK
U2 - 10.1016/j.orggeochem.2006.03.003
DO - 10.1016/j.orggeochem.2006.03.003
M3 - Article
AN - SCOPUS:33745000091
SN - 0146-6380
VL - 37
SP - 787
EP - 797
JO - Organic Geochemistry
JF - Organic Geochemistry
IS - 7
ER -