Flow of formation waters in the Cretaceous-Miocene succession of the Llanos Basin, Colombia

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doi: 10.1306/A25FF319-171B-11D7-8645000102C1865D
Authors:Villeges, M. E.; Bachu, Stefan; Ramon, J. C.; Underschultz, J. R.
Author Affiliations:Primary:
Instituto Colombiano del Petroleo, Bucaramanga, Colombia
Alberta Geological Survey, Canada
Volume Title:AAPG Bulletin
Source:AAPG Bulletin, 78(12), p.1843-1862. Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States. ISSN: 0149-1423
Publication Date:1994
Note:In English
Summary:This study presents the hydrogeological characteristics and flow of formation waters in the post-Paleozoic succession of the Llanos basin, a mainly siliciclastic foreland sub-Andean sedimentary basin located in Colombia between the Cordillera Oriental and the Guyana Precambrian shield. The porosity of the sandy formations is generally high, in the range of 16-20% on average, with a trend of decreasing values with depth. Permeabilities are also relatively high, in the 102 and 103 md range. The salinity (total dissolved solids) of formation waters is generally low, in the 10,000-20,000 mg/L range, suggesting that at least some strata in the basin have been flushed by meteoric water. The shaly units in the sedimentary succession are weak aquitards in the eastern and southern parts of the basin, but are strong in the central-western part. The pressure in the basin is close to or slightly subhydrostatic. The underpressuring increases with depth, particularly in the central-western area. The flow of formation waters in the upper units is driven mainly by topography from highs in the southwest to lows in the northeast. Local systems from the foothills and from local topographic highs in the east feed into this flow system. The flow of formation waters in the lower units is driven by topography only in the southern, eastern, and northern parts of the basin. In the central-western part, the flow is downdip toward the thrust-fold belt, driven probably by pore-space rebound induced by erosional unloading, which also is the cause of underpressuring. Hydrocarbons generated in the Cretaceous organic-rich, shaly Gacheta Formation probably have migrated updip and to the north-northeast, driven by buoyancy and entrained by the topography-driven flow of formation waters; however, the downdip flow of formation waters in Cretaceous-Oligocene strata in the central-western part of the basin could have created conditions for hydrodynamic entrapment of hydrocarbons.
Subjects:Basins; Cenozoic; Clastic rocks; Cretaceous; Erosion; Foreland basins; Genesis; Giant fields; Ground water; Hydrodynamics; Mesozoic; Meteoric water; Migration; Movement; Oil and gas fields; Oligocene; Paleogene; Permeability; Petroleum accumulation; Pressure; Sedimentary basins; Sedimentary rocks; Shale; Siliciclastics; Solutes; Structural traps; Tertiary; Traps; Underpressure; Andes; Colombia; Cusiana Field; Eastern Cordillera; Guiana Shield; Llanos; South America; Cano Limon Field; Cupiagua Field; Gacheta Formation; Wells
Record ID:1994049706
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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