Meteoric diagenesis and porosity enhancement in Fluvio-Deltaic reservoir facies: B-6 sands, Maracaibo Basin Venezuela
- Intevep S.A., Caracas (Venezuela)
The Eocene northwest-southeast-trending fault-bounded reservoirs reveal a systematic diagenetic evolution due to changing physical and chemical conditions related to an Oligocene uplift, separating an Eocene and a subordinate Miocene phase of subsidence. Compaction, cementation, and dissolution during Eocene subsidence reduced original porosity to about 20%. The Oligocene uplift created abundant secondary porosity, raising the total porosity to around 30%, especially near the truncated erosion surface on the northwest. Here, abundant lamellar porosity is characteristic. Intense leaching action by undersaturated meteoric CO{sub 2}-charged waters may be responsible for the regenerated porosity. The sandstones immediately below the unconformity surface show the best reservoir quality. Leaching of monocrystalline and polycrystalline quartz, feldspar, rock fragments, and clays has produced a highly porous and permeable diagenetic quartzarenite. Porosity and permeability decrease systematically southeastward as the vertical distance from the unconformity surface increases. Labile grains largely persist, and compaction and cementation (calcite, silica, and clays) reduce the reservoir quality. A patchily welded texture observed in the southeast may be due to silica cement originated from grain dissolution near the unconformity surface on the northwest. Presence of highly degraded crudes lends additional support to the influence of meteoric waters on these reservoirs. Similar processes of silica dissolution through the action of acidic meteoric water presently occur in extensive outcrops of Precambrian karstic quartzarenites in Venezuela. These tropical analogs support the efficacy of freshwater flushing mechanism and consequent enhancement of reservoir quality in the Eocene sequence.
- OSTI ID:
- 7091397
- Report Number(s):
- CONF-900605--
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Vol. 74:5; ISSN AABUD; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
Similar Records
Misoa formation sandstone diagenesis, blocks III and V, Maracaibo Basin, Venezuela
Porosity enhancements at unconformities and their implications
Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
ALKALINE EARTH METAL COMPOUNDS
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CENOZOIC ERA
DEVELOPING COUNTRIES
DIAGENESIS
DISSOLUTION
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
LATIN AMERICA
MINERAL RESOURCES
MINERALS
OXYGEN COMPOUNDS
PETROLEUM DEPOSITS
POROSITY
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SOUTH AMERICA
TERTIARY PERIOD
VENEZUELA