Consequences of Water Level Drops for Soft Sediment Deformation and Vertical Fluid Leakage
- PDF / 2,056,267 Bytes
- 30 Pages / 439.37 x 666.142 pts Page_size
- 36 Downloads / 139 Views
Consequences of Water Level Drops for Soft Sediment Deformation and Vertical Fluid Leakage Christian Hermanrud · Jon Marius Venstad · Joe Cartwright · Lars Rennan · Kristine Hermanrud · Hege M. Nordgård Bolås
Received: 1 March 2012 / Accepted: 20 November 2012 / Published online: 9 January 2013 © International Association for Mathematical Geosciences 2012
Abstract Both water level drops and erosion have previously been suggested as causes of fluid overpressures in the subsurface. Quantification of the relevance of these processes to supra-lithostatic fluid pressure formation with a wide selection of input parameters is lacking, and thus desired. The magnitudes and drop times that are required for water level drops to result in supra-lithostatic pore pressures in a variety of situations are calculated. Situations with pore fluids consisting of water, water with dissolved methane, water with a gas hydrate layer and dissolved methane in the underlying sediments, and water with dissolved methane, a gas hydrate layer, and free gas accumulation below the hydrate layer are separately addressed. The overpressure formation from reservoir gas expansion is also simulated. The simulation results demonstrate that high fluid overpressures can develop in a rock as a response to a water level drop without the presence of gas, provided that the rock has a sufficiently low compressibility. The contribution to fluid overpressuring is however dramatically increased if the pore water is saturated with methane prior to the water level drop, and is further amplified by the presence of gas hydrates and free gas accumulations beneath such hydrates. Gas expansion in reservoirs should be expected to significantly increase the fluid overpressures in shallow, sealed pressure compartments that C. Hermanrud () · L. Rennan · K. Hermanrud · H.M. Nordgård Bolås Statoil Petroleum, Postboks 7005, Trondheim, Norway e-mail: [email protected] C. Hermanrud Department of Earth Science, University of Bergen, Allegt. 41, 5007 Bergen, Norway J.M. Venstad Department of Petroleum Technology and Applied Geophysics, Norwegian Technical University, S.P. Andersens vei 15, 7491 Trondheim, Norway J. Cartwright Department of Earth Sciences, Oxford University, South Parks Road, Oxford OX1 3AN, UK
2
Math Geosci (2013) 45:1–30
experience erosion or water level drops, even if the water level drop duration exceeds one million years. Enough relationships between the calculated overpressure formation and the main controlling factors are provided in order to enable readers to make inferences about a variety of geological settings. Analyses of simulation results prompt us to suggest that pockmarks are likely to be triggered by gas expansion in vertical fluid migration pathways, that the giant craters at the seabed west of Albatross South in the Barents Sea result from hydrate dissociation, and that overpressure build-up due to gas expansion has contributed to reservoir overpressuring in many eroded basins, including the Hammerfest Basin in the Barents Sea. Keywords Water l
Data Loading...
