Faults and Fractures of Polideformed Folds in the Llanos Foothills, Colombia

Alberto Ortiz-Fernandez¹, Oswaldo Ordoñez², and Mauricio Valencia^2
1 Instituto Colombiano del Petroleo Ecopetrol, Piedecuesta, Colombia
² Universidad Nacional de Colombia Sede Medellin, Medellín (Antioquia), Colombia

Overimposed fractured systems present in an oil producer polideformed fold were scaled and characterized in a sector of the Llanos Foothills in Colombia using cores, image logs and outcrop information. The use of microfractures to quantify and develop mechanical-deformed folds led to prediction of more relevant attributes in hydraulic conductivity. This study identifies and characterizes three main fracture families coming from same number of main tectonic events, most of them open today and present in core and outcrop information available.

Close correlation was found between fractured zones, productive units and facies type. Anisotropy of rocks was confirmed by high values of subcritical index (SCI) indicating clustering tendency of fracture distribution. Fracture modelling shows complex relationships between fracture propagation, fracture intensity and fracture aperture, altough last parameter is still poor understood due to tools limitations (UBI log scale, coring, exhumation fractures in outcrops).

Description of different aspects of fracture types like geometry, slickensides and fillings led to conclusions about fracture history related to hydrocarbon placement. No matter matrix controls oil production, fractures and faults are responsible for high but short productive rates, showing that caution must be used in reservoir depletion if plans are for maximum depletion instead of short term high production. The combination of several tools permits a fine tuning of fracture characterization and suggest that this type of traps in the foothills area are dominantly gas apron with significant amounts of ligth oil that should be produced as an extra bonus.