Geochemical characteristics of bitumens and seeps from Tanzania

Conference · Fri Mar 01 04:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7170592

Mpanju, F ^[1]; Philp, P ^[2]

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1. Tanzanian Petroleum Development Corp., Dar Es Sallam (Tanzania)
2. Univ. of Oklahoma, Norman (United States)

A number of bitumen extracts from prospective source rocks and oil seeps of potential oil-producing areas in Tanzania have been characterized by a variety of geochemical techniques. The data obtained from this study have provided additional insight into the source rock potential of these areas. However, in this paper it is proposed to discuss in detail the results from two of the more unusual samples in this region, namely Wingayongo and Pemba. The Wingayongo bitumens isolated from an exposed Neocomian-aged sandstone, possibly a paleoreservoir, are almost totally devoid of n-alkanes and steranes and dominated by hopane-type biomarkers with the so-called immature {beta}{beta}-stereochemistry at the C{sub 17} and C{sub 21} positions. There is no typical evidence of biodegradation having occurred leading to the proposal of an unusual source material or maturity history for this sample. The Pemba seep samples were also characterized by relatively high concentrations of hopanes with the immature stereochemistry at the C{sub 17} and C{sub 21} positions and a virtual absence of n-alkanes and steranes. The aromatic fractions contained relatively high concentrations of hopanic acids, with the immature stereochemistry at C{sub 17} and C{sub 21} positions and a virtual absence of n-alkanes and steranes. The aromatic fractions contained relatively high concentrations of hopanic acids, with the immature stereochemistry at C{sub 17} and C{sub 21}. On the basis of these data, it is proposed that the seeps in the Pemba region are not true oil seeps. Rather they are formed as a result of extremely high levels of bacterial activity with the bacteria utilizing natural gas in the region as the substrate. The net result is a material referred to in other areas of the world as paraffin dirt whose occurrence results from extensive microbial activity in the region and not directly from seepage of products having a thermal origin.

• OSTI ID: 7170592
• Report Number(s): CONF-910403--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:3
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
023000* -- Petroleum-- Properties & Composition
58 GEOSCIENCES
580000 -- Geosciences
AFRICA
BITUMENS
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPING COUNTRIES
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOCHEMISTRY
GEOLOGIC DEPOSITS
HYDROCARBONS
MINERAL RESOURCES
ORGANIC COMPOUNDS
ORIGIN
OTHER ORGANIC COMPOUNDS
PETROLEUM
PETROLEUM DEPOSITS
RESOURCES
SEEPS
SOURCE ROCKS
STEREOCHEMISTRY
TANZANIA
TAR