Outside the Middle East, onshore fold–thrust belts (FTB) of Tertiary to Recent age contain a significant part of the globally developed petroleum, but far less of the oil and gas remaining undiscovered. Depending on high quality data and on deep drilling, renewed exploration of former failures is commercially attractive, and it will help in exploring the deepwater belts of compression. In FTB with a defined petroleum system, an under-explored trend may be the informally named ‘deep-updip’ or DUD trend. Shale-gas-prone formations in FTB require new exploration strategies, but in the public domain, this type of prospect has not yet been discussed. FTB discoveries require geological insight, persistence and exponentially rising investment. The paper includes examples from the Northern Alps, from the Llanos foothills of Colombia, from Eastern Venezuela and from the Po Valley basin of Italy.
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Onshore fold–thrust belts are commonly perceived as ‘difficult’ places to explore for hydrocarbons and are therefore often avoided. However, these belts host large oil and gas fields and so these barriers to effective exploration mean that substantial unexploited resources may remain. Over time, evaluation techniques have improved. It is possible in certain circumstances to achieve good 3D seismic data. Structural restoration techniques have moved into the 3D domain and increasingly sophisticated palaeo-thermal indicators allow better modelling of burial and uplift evolution of source and reservoirs. Awareness of the influence of pre-thrust structure and stratigraphy and of hybrid thick and thin-skinned deformation styles is augmenting the simplistic geometric models employed in earlier exploration. But progress is a slow, expensive and iterative process. Industry and academia need to collaborate in order to develop and continually improve the necessary understanding of subsurface geometries, reservoir and charge evolution and timing; this publication offers papers on specific techniques, outcrop and field case studies.