The use of palaeo-thermo-barometers and coupled thermal, fluid flow and pore-fluid pressure modelling for hydrocarbon and reservoir prediction in fold and thrust belts
F. Roure, P. Andriessen, J. P. Callot, J. L. Faure, H. Ferket, E. Gonzales, N. Guilhaumou, O. Lacombe, J. Malandain, W. Sassi, F. Schneider, R. Swennen, N. Vilasi, 2010. "The use of palaeo-thermo-barometers and coupled thermal, fluid flow and pore-fluid pressure modelling for hydrocarbon and reservoir prediction in fold and thrust belts", Hydrocarbons in Contractional Belts, G. P. Goffey, J. Craig, T. Needham, R. Scott
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Basin modelling tools are now more efficient to reconstruct palinspastic structural cross sections and compute the history of temperature, pore-fluid pressure and fluid flow circulations in complex structural settings. In many cases and especially in areas where limited erosion occurred, the use of well logs, bottom hole temperatures (BHT) and palaeo-thermometers such as vitrinite reflectance (Ro) and Rock-Eval (Tmax) data is usually sufficient to calibrate the heat flow and geothermal gradients across a section. However, in the foothills domains erosion is a dominant process, challenging the reconstruction of reservoir rocks palaeo-burial and the corresponding calibration of their past thermal evolution. Often it is not possible to derive a single solution for palaeo-burial and palaeo-thermal gradient estimates in the foothills, if based solely on maturity ranks of the organic matter.
Alternative methods are then required to narrow down the error bars in palaeo-burial estimates, and to secure more realistic predictions of hydrocarbon generation. Apatite fission tracks (AFT) can provide access to time–temperature paths and absolute ages for the crossing of the 120 °C isotherm and timing of the unroofing. Hydrocarbon-bearing fluid inclusions, when developing contemporaneously with aqueous inclusions, can provide a direct access to the pore-fluid temperature and pressure of cemented fractures or reservoir at the time of cementation and hydrocarbon trapping, on line with the tectonic evolution. Further attempts are also currently made to use calcite twins for constraining reservoir burial and palaeo-stress conditions during the main deformational episodes. Ultimately, the use of magnetic properties and petrographical measurements can also document the impact of tectonic stresses during the evolution of the layer parallel shortening (LPS).
The methodology integrating these complementary constraints will be illustrated using reference case studies from Albania, sub-Andean basins in Colombia and Venezuela, segments of the North American Cordillera in Mexico and in the Canadian Rockies, as well as from the Middle East.
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Hydrocarbons in Contractional Belts
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.