Print this pageFluvial Architecture and Reservoir Characterization of the Upper Eocene La Paz Formation, Provincia Field, Middle Magdalena Valley Basin, Colombia
SUAREZ, MARIO A.
The Provincia Field, in the eastern foothills of the Middle Magdalena Valley Basin, Colombia, produces oil and gas from the upper Eocene La Paz Formation, which has an average thickness of 800 ft. A facies analysis of this unit was conducted using 332 ft of core calibrated with well logs, core petrophysic data, and well log facies prediction from 6 wells. The facies associations recognized represent deposition in braided trunk channels fill, minor channels fill (distributary or crevasse channels), crevasse splays, floodplain and levee subenvironments. The crevasse channels and crevasse splays represent avulsion complex deposits that represent 48.2% of the facies associations in the La Paz Formation. This model illustrates that channel avulsion and preservation of thick avulsion sequences are not exclusively characteristic of meandering systems.
The best reservoir fabric in the La Paz Formation (porosity 16.7%, permeability 409.2 md), corresponds to subarkoses deposited by braided trunk channels comprising 30% of the facies associations. The sandy facies in the avulsion complexes have poor reservoir quality (porosity 12.9%, permeability 29 md), acting as fluid retardants or vertical and horizontal plugs. Levees and floodplain deposits comprise 21.8% of the facies associations representing the main vertical barriers.
Based on the depositional model, a 2-D reservoir zonation was made. Six flow units were recognized ranging from 40ft to 125 ft in thickness, separated by levees and floodplain deposits. Within the flow units interbedded avulsion complex deposits produce a high reservoir heterogeneity. Understanding all of the depositional elements in this type of fluvial system, helps to create a more realistic reservoir characterization that can be applied for reservoir simulation models.