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The upper Eocene La Paz Formation is the primary petroleum reservoir in the Provincia Field, located in the eastern foothills of the northern Middle Magdalena Valley Basin, Colombia. The average thickness of the La Paz reservoir is 800 feet in the Provincia field. A facies analysis of this unit was conducted using 332 feet of core, which were calibrated with well logs, core petrophysical data, and used for well log facies associations predictions in six wells. Four facies associations are recognized and represent deposition in braided trunk channel, minor channel (distributary or crevasse), crevasse splay and floodplain subenvironments. The minor channel and crevasse splay deposits comprise avulsion deposits. The avulsion deposits are volumetrically important and comprise nearly half of the reservoir (49.1%). Recognition of significant avulsion deposits in this study suggests that channel avulsion and preservation of thick avulsion sequences may be common in braided stream settings and are not exclusively characteristic of meandering systems.

The best reservoir facies in the La Paz Formation are subarkosic sandstones (porosity 16.7%, permeability 409.2 md), deposited in braided trunk channels and comprise 30.6% of the total reservoir thickness. Sandstone facies in the avulsion deposits have poor reservoir quality (porosity 12.9%, permeability 29 md) and act as fluid flow retardants (or lateral plugs). Floodplain deposits comprising 20.3% of the reservoir are impermeable and are the main vertical barriers.

Based on the depositional model, a 2-D reservoir zonation was constructed for the La Paz reservoir. Six flow units were defined, ranging from 50 to 140 feet in thickness, each separated by floodplain deposits. Within the flow units, interbedded avulsion deposits and trunk channel deposits produce high reservoir heterogeneity. Understanding all of the depositional elements in this type of fluvial system has helped to create realistic reservoir characterization that could be applied to reservoir simulation models.

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