A new perspective on sequence stratigraphy of syn-orogenic basins: insights from the Tertiary Piedmont Basin (Italy) and implications for play concepts and reservoir heterogeneity
Massimo Rossi, Jonathan Craig, 2016. "A new perspective on sequence stratigraphy of syn-orogenic basins: insights from the Tertiary Piedmont Basin (Italy) and implications for play concepts and reservoir heterogeneity", The Value of Outcrop Studies in Reducing Subsurface Uncertainty and Risk in Hydrocarbon Exploration and Production, M. Bowman, H. R. Smyth, T. R. Good, S. R. Passey, J. P. P. Hirst, C. J. Jordan
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The Tertiary Piedmont Basin was reshaped as the Apennines progressively overrode the Alpine retroforeland. Nine basin-wide unconformities were followed by abrupt accommodation turnarounds or high-accommodation/high sediment supply intervals. Unusual stratigraphic discontinuities require a different perspective to reconcile allostratigraphy and sequence stratigraphy, highlighting a wider range of tectonically driven discontinuities (subaerial/subaqueous/regressive/transgressive), diachronism of accommodation and sediment–fairway turnarounds, unusual routing to deepwater, and relationships between fourth- and fifth-order sequences. This approach allows innovative play concepts and prediction of reservoir heterogeneity. Steep gradients and high sediment fluxes favour the development of coarse-grained deltas dominated by hyperpycnal processes and large-scale instability/sediment failures, often expressed by retrogressive slump scars, owing to over-steepening generated by drowning unconformities related to orogenic collapse or basin inversion. During increasing-accommodation intervals, subaqueous erosion leaves remnants of drowned deltas forming stratigraphic traps sealed by prodelta-slope muds. The sediments removed feed turbidites, generated during transgressive intervals and deposited at the toe of oversteepened slopes. These may eventually back-fill the slump scar system and show a fining-upward stacking-pattern owing to the re-establishment of the equilibrium profile. Another play concept relies on the combination of onlapping non-marine to marginal marine deposits against fault-bounded basement highs, sealed by marine muds deposited during the subsequent drowning.
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The Value of Outcrop Studies in Reducing Subsurface Uncertainty and Risk in Hydrocarbon Exploration and Production
Field studies over a range of scales have been important in the upstream oil and gas industry for decades. Advances in digital outcrop characterization and data capture, coupled with increased computational capabilities, have resulted in a resurgence in fieldwork; these field studies are required to develop depositional, stratigraphic and structural concepts and provide the data which underpin the current generation of complex, computer generated, 3D subsurface models. These models provide an informed means of benchmarking the subsurface along with a more considered view of subsurface uncertainty and management of the risks identified. The papers in this volume cover safety in the field, frontier basin petroleum system assessment, field appraisal and development including unconventional resources, applications of techniques such as LiDAR and 3D photogrammetry, and uncertainty characterization. The studies were undertaken in diverse locations such as the Faroe Islands, Italy, Algeria, India, the USA and Trinidad; they represent a range of tectonic settings and a wide geological time frame. The spectrum of papers is testament to the value and integral position that fieldwork occupies within the modern hydrocarbon industry.