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Book Chapter

Geochemical Evidence for Two Stages of Hydrocarbon Emplacement and the Origin of Solid Bitumen in the Giant Tengiz Field, Kazakhstan

By
J. L. Warner
J. L. Warner
Chevron Petroleum Technology Company, Richmond, Virginia, U.S.A.
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D. K. Baskin
D. K. Baskin
Chevron Petroleum Technology Company, Richmond, Virginia, U.S.A.
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R. J. Hwang
R. J. Hwang
Chevron Petroleum Technology Company, Richmond, Virginia, U.S.A.
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R. M. K. Carlson
R. M. K. Carlson
Chevron Petroleum Technology Company, Richmond, Virginia, U.S.A.
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M. E. Clark
M. E. Clark
Tengizchevroil, Kazakhstan
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Published:
January 01, 2007

Abstract

Tengiz is a giant oil field on the northeastern coast of the Caspian Sea in Kazakhstan that produces a high-gravity, hydrogen sulfate (H2S)-rich oil from a reservoir containing abundant solid bitumen. Several lines of geochemical and petrographic evidence suggest there were at least two stages of petroleum migration into the Tengiz reservoir, both generated off structure from a marine source rock. The initial charge gave rise to solid bitumen, perhaps by a de-asphaltening process. Bitumen formation was followed by a period of hydrothermal activity, which thermally matured the bitumen to an insoluble pyrobitumen, produced bitumen-freepores, precipitated calcite on the bitumen, and mineralized parts of the Tengiz flank. Finally, a second petroleum charge, most likely from the same source at higher maturity, accompanied by a significant in-flux of H2S arising from thermochemical sulfate reduction (TSR) deep in the basin, filled Tengiz with its present-day oil.

The Tengiz reservoir consists of Carboniferous and Devonian limestones with mostly grainstone and packstone textures that define an isolated mound with a central platform and surrounding flank. Do-lomitization and silicification are sparse; cements are sparry calcite. The reservoir is divided into unit 1 (∼3950-4500 m; ∼12,959-14,763 ft), unit 2 (∼4500-5100 m; ∼14,763-16,732 ft), and unit 3 (∼5100 to >5600 m; ∼16,732 to >18,372 ft). Porosity average is 7% bivolume (BV) (range 0-20%). Where solid bitumen is abundant, it typically occupies 3% BV (range 0-15%), but bitumen occupies less than 1% BV in large parts of the reservoir. Bitumen is commonly encapsulated with calcite cement. Typically production preferentially enters boreholes from a few meter-thick intervals. Top reservoir temperature is 105°C, and initial pressure is 11,500 psi (79.2 MPa).

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Contents

AAPG Studies in Geology

Oil and Gas of the Greater Caspian Area

Pinar O. Yilmaz
Pinar O. Yilmaz
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Gary H. Isaksen
Gary H. Isaksen
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American Association of Petroleum Geologists
Volume
55
ISBN electronic:
9781629810348
Publication date:
January 01, 2007

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