Evaluation of Structural Uncertainty as a Tool to Minimize Risk in Exploration, Ramos Field, Andean Foothills, Argentina

Fernandez, Oscar¹, Martin Iribarne², Emilia Muzzio², Alfredo Disalvo³, Clare Bond⁴, Gustavo Vergani³ (1) Midland Valley, Golden, CO (2) Pluspetrol SA, Buenos Aires, Argentina (3) Pluspetrol S.A, Buenos Aires, Argentina (4) Midland Valley, Glasgow, United Kingdom

Structural uncertainty is a frequent obstacle in exploration in fold and thrust belt provinces. Defining a single and unambiguous structural model in areas of poor seismic coverage is nearly impossible. However, exploration teams in these areas most frequently work with a single structural hypothesis at a time, carrying uncertainty in the interpretation as a secondary parameter. In this paper we present a case where three completely different valid alternative structural interpretations are proposed for one same dataset. The structure worked on is the Ramos field in the Andean foothills in northwestern Argentina. The surface expression of this anticline is only minimally linked to the subsurface productive structure, and therefore surface geology is of limited value. Furthermore, the available 2D seismic lines are of poor quality. However, well and dipmeter data are abundant and serial 2D MT profiles provide additional constraints.

Various alternative interpretations were proposed for the structure, out of which the 3 more coherent with the regional setting were developed in detail: a duplex structure, a duplex structure transporting a fault-propagation fold, and a relatively simple fault-propagation fold. These interpretations were propagated laterally over the structure to ensure their 3D validity and balanced along 2D transects. The result is a set of interpretations that represent a spectrum of possible solutions that greatly enhances the evaluation of the risk in drilling new prospects. Based on the differences and likenesses between the interpretations, areas where the structural solutions converge can be defined as those of lower risk for future drilling.