Los Sistemas Petroleros Devonicos Del Subandino Sur Y Pie De Monte De La Cuenca De Tarija. Bolivia

The charge system of the Tarija Basin involves Devonian sources that have poor to moderate —occasionally good- quality for hydrocarbon generation. Thermal maturity of the source intervals show wide thermal maturity variations from the initial stages of the oil<br>window to very advanced phases of gas generation, depending on the stratigraphic position and geologic setting. Effective expulsion of hydrocarbons is believed to have begun at relatively high levels of thermal maturity (VRE>O.9-1.0%), with prevalence of gassy<br>hydrocarbons. Modeling of hydrocarbon generation of the Devonian source rocks demonstrates that the main episodes of expulsion and charge occurred coupled to the Andean tectonics. A generally low thermal heat flow linked to the Tertiary foreland deposits<br>constrained the maturation process. Main generation areas are related to the synclines in the South Subandean Thrust Belt and two main depocenters in the Santa Cruz and Pilcomayo areas. Preferred migration pathways are interpreted to be the main thrusts and faults. GAE estimations points to low efficiency petroleum systems. The main trapping mechanism is structural, both in the South Subandean and in the Foothills. The predominance of condensate accumulations precludes assessing definite oilsource<br>correlation patterns. Nevertheless, genetic relations were proved for the Eifelian sources. Isotope data, arranged by reservoir and geographic location, is consistent with significant variations in thermal maturity, allowing for distinct kitchens of a same source rock<br>and/or co-sourcing. Three petroleum zones are recognized in the Tarija Basin: Santa Cruz, Pilcomayo (extending up to northern Argentina) and the South Subandean Thrust Belt. In addition to the classical Los Monos-Huamampampa (!), a second petroleum system is proposed with the name Sección Lochkoviano-CarbOnico(.). 2P EUR reserves were allocated to these Devonian systems; yet to find resources were estimated in the range 17.5-56.0 x 1012 cfg. Contributions of a Silurian petroleum system have a hypothetical significance for deep gas in the Subandean Thrust Belt.