Diagenesis and reservoir characterization of the Cretaceous-Tertiary sequence, eastern Venezuela

Conference · Tue May 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6858124

Aquado, B; Ghosh, S; Isea, A ^[1]

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1. Intevep, S.A., Caracas (Venezeula)

The giant El Furrial field Maturin subbasin is the most important oil field discovered in Venezuela in the last three decades. The average oil column has a thickness of 400 m and the reservoirs consist of essentially sandy siliciclastic sediments of nearshore-shallow marine origin. The oil's API gravity ranges from light to extra heavy and occurs in a stratified manner in the reservoirs. A total of 1,080 m of core from the producing sequence was studied through x-ray diffraction scanning electron microscopy, and petrography. This data, along with petrophysical measurements, show a clear differentiation between the Upper Cretaceous and the Oligocene reservoirs. The Upper Cretaceous reservoirs are characterized by relatively fine and uniform grain size, subarkosic composition with common volcanic rock fragments, high degree of chemical and mechanical compaction highly illitic mixed-layer I/S assemblage with less than 10% expandable layers, and ubiquitous baroque dolomite. Additionally, porosity and permeability values are persistently low. Clearly, the Cretaceous sediments are diagenetically mature and may indicate diagenetic transformation at greater depths or under a different thermal regime. In contrast the coarser grained Oligocene reservoirs of quartz arenitic composition show a lesser diagenetic overprint, and greater porosity and permeability. Porosity is dominantly secondary due to cement and grain (mostly quartz) dissolution, as well as tectonically induced grain fracturing. Common kaolinite and minor amounts of I/S with up to 20% of expandable layers attest to a lower diagenetic regime than in the Cretaceous reservoirs.

• OSTI ID: 6858124
• Report Number(s): CONF-900605-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
58 GEOSCIENCES
PETROLEUM DEPOSITS
RESERVOIR ROCK
DIAGENESIS
VENEZUELA
CRETACEOUS PERIOD
KAOLINITE
MATURATION
PETROGRAPHY
POROSITY
SCANNING ELECTRON MICROSCOPY
TERTIARY PERIOD
X-RAY DIFFRACTION
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CENOZOIC ERA
COHERENT SCATTERING
DEVELOPING COUNTRIES
DIFFRACTION
ELECTRON MICROSCOPY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
LATIN AMERICA
MESOZOIC ERA
MICROSCOPY
MINERAL RESOURCES
MINERALS
OXYGEN COMPOUNDS
RESOURCES
SCATTERING
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOUTH AMERICA
020200* - Petroleum- Reserves
Geology
& Exploration
580000 - Geosciences