Modelling the influence of tectonic compression on the in situ stress field with implications for seal integrity: the Haltenbanken area, offshore mid-Norway
T. Skar, F. Beekman, 2003. "Modelling the influence of tectonic compression on the in situ stress field with implications for seal integrity: the Haltenbanken area, offshore mid-Norway", New Insights into Structural Interpretation and Modelling, D. A. Nieuwland
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Exploration for hydrocarbons in overpressured domains is often considered high risk because of the possibility of seal failure and fluid leakage due to natural hydraulic fracturing. Several of the wells drilled in highly overpressured reservoirs on Haltenbanken, offshore mid-Norway, have proved to be devoid of hydrocarbons suggesting that ineffective seals are the cause of exploration failure. However, recent petroleum discoveries within this area demonstrate that fluid pressure is not the ultimate control on entrapment of hydrocarbons. We investigate the way in which far-field tectonic compression may have influenced the in situ stress conditions on Haltenbanken, and assess whether tectonic stresses also may facilitate local fracturing of the seal by reducing the retention capacity (minimum horizontal stress-fluid pressure).
We have approached the problem by applying a finite element model. The elasto-plastic model assumes two-dimensional plane-strain and is constrained from geological and geophysical data. The results show that: (1) contrasts in the rock’s mechanical properties across discontinuities (e.g. sediment interfaces) cause rapid shifts in stress magnitudes; (2) the differences in stress magnitudes across such discontinuities can be subdued or enhanced under increased horizontal compression; and (3) structurally controlled variations in vertical displacements produce local concentrations of highs and lows in the stress field. The combined result of these three factors is that the magnitude of horizontal stress may vary quite considerably within spatially restricted areas. The implication of these predictions in terms of hydrocarbon preservation potential in highly overpressured regions is that rapid shifts in minimum horizontal stress magnitudes can reduce the retention capacity and therefore facilitate natural hydraulic fracturing.
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New Insights into Structural Interpretation and Modelling
This title has arisen from the Geological Society of London conference of the same name. Since the publication of the predecessor of this book (‘Modern insights into structural interpretation, validation and modelling’, SP99, 1996, edited by Buchanan & Nieuwland) much progress has been made. This has been primarily thanks to the continuously increasing computing speed and computer memory capacity, which has positively affected all fields in structural interpretation, seismics and modelling, directly or indirectly.
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