Mechanically infiltrated clays: recognition and influence in fluvial reservoirs of Reconcavo basin, Brazil
Fluvial sandstones and conglomerates of the Sergi Formation (Jurassic) are the main reservoirs of the Reconcavo basin in northeastern Brazil. These reservoirs contain significant amounts of interstitial detrital clays resulting from early diagenetic mechanical infiltration. The infiltration developed under arid/semiarid conditions, where the lowered water table allowed muddy waters of episodic runoff to infiltrate through the coarse alluvium. The main clay concentrations occurred in the upper phreatic zone and in proximity to sources of influent seepage. It is difficult to identify infiltrated clays in ancient sedimentary rocks due to a lack of well-established petrographic criteria. In this work, a series of petrographic criteria is proposed to recognize these clays in clastic reservoirs. These criteria include the anisophachous coatings of tangentially accreted lamellae and the geometric patterns developed due to shrinkage. The infiltrated clays are among the main controls of reservoir properties, and the horizons of maximum clay concentration are the main internal barriers in most Sergi reservoirs. In general, infiltrated clays damage reservoir quality by creating macroheterogeneities and microheterogeneities, by decreasing recovery efficiency and permeability, and by increasing water saturation. Also, they can cause formation damage either by their swelling properties or through the migration of loose particles left by shrinkage. As demonstrated in the Sergi Formation, infiltrated clays must be adequately identified for the definition of proper procedures for drilling, completion, reservoir development, and EOR programs.
- Research Organization:
- Petrobras, Rio de Janeiro (Brazil)
- OSTI ID:
- 6017520
- Report Number(s):
- CONF-890404-
- Journal Information:
- AAPG Bull.; (United States), Journal Name: AAPG Bull.; (United States) Vol. 73:3; ISSN AABUD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
BRAZIL
CLAYS
CONGLOMERATES
DEVELOPING COUNTRIES
ENERGY SOURCES
ENHANCED RECOVERY
FOSSIL FUELS
FUELS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
JURASSIC PERIOD
LATIN AMERICA
MESOZOIC ERA
MINERAL RESOURCES
PERMEABILITY
PETROLEUM
PETROLEUM DEPOSITS
POROSITY
RECOVERY
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SOUTH AMERICA