Lithic reservoir diagenesis of Cretaceous Carmopolis MemberSergipe-Alagoas basin, Brazil

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

OSTI ID:6681793

Souza, R S ^[1]

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1. Petrobras/Cenpes, Diger, Rio de Janeiro (Brazil)

The Lower Cretaceous sandstones and conglomerates of the Carmopolis Member are important oil reservoirs in the Sergipe-Alagoas basin, northeastern Brazil. The reservoirs are lithic phyllarenites, rich in schist, phyllite, and slate fragments. This composition is seldom seen in oil reservoirs because the mechanical compaction and deformation of such constituents usually eliminates most of the porosity at the beginning of diagenesis. This apparent anomaly was analyzed in detail. The diagenetic history comprises an eogenetic stage, influence by hypersaline lacustrine brines, and a compaction mesogenetic stage. The sequence of diagenetic processes was (1) mechanical infiltration of clays; (2) precipitation of early poikilotopic dolomite or calcite/aragonite rims; (3) mechanical compaction; (4) quartz and feldspar overgrowths; (5) cementation and grain replacement by ferroan calcite; (6) generation of secondary dissolution porosity; (7) reactivation of mechanical compaction; (8) cementation and grain replacement by late ferroan dolomite/ankerite; (9) second stage of porosity generation; and (10) precipitation of kaolinite, quartz, chlorite-smectite clays and sulfides. The quantitative analysis of reservoirs ranging from 180 to 2,200 m depth has shown that mechanical compaction was, as expected, the main process of porosity destruction. Compaction affected mostly the beds lacking early dolomite cementation, where lithic micaceous fragments were deformed and squeezed into the pore spaces. Early dolomite was essential to support the mechanically unstable lithoclasts against increasing overburden, preserving the potential porosity and permeability. This interpretation was confirmed by experimental analysis of porosity and permeability reduction under confining pressures of 500, 1,000, and 2,000 psi, developed in samples with variable lithoclasts and dolomite contents.

• OSTI ID: 6681793
• 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
BRAZIL
PETROLEUM DEPOSITS
RESERVOIR ROCK
CALCITE
CHLORITE MINERALS
CONGLOMERATES
CRETACEOUS PERIOD
DIAGENESIS
FELDSPARS
KAOLINITE
PERMEABILITY
POROSITY
QUARTZ
SANDSTONES
SEDIMENTARY BASINS
SMECTITE
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHALCOGENIDES
CLAYS
DEVELOPING COUNTRIES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
LATIN AMERICA
MESOZOIC ERA
MINERAL RESOURCES
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SOUTH AMERICA
020200* - Petroleum- Reserves
Geology
& Exploration
580000 - Geosciences