Process-Based Modelling of the Brent Delta, Gullfaks Area, Norway

Process-Based Modelling of the Brent Delta, Gullfaks Area, Norway

Koolen, G.J.H.M.

Storms, J.E.A. (mentor)
Walstra, D.J.R. (mentor)

Civil Engineering and Geosciences

Applied Earth Sciences

Applied Geology

2011-07-01

With the use of the process-based geological model Delft3D a base case model is set up to simulate the Brent delta using Gullfaks field conditions as appeared during the Aalenian and Bajocian periods in the Mid-Jurassic. The aim is to visualize and comprehend the morphology and stratigraphy of the base case upon changing both wave conditions and discharge conditions. Wave height and peak period are varied during a first scenario, where discharge and sediment concentration of the river are altered during a second scenario. Nine hydrodynamic and geologically realistic model set-ups were simulated. They represent an outbuilding wave dominated deltaic environment in three dimensions. Within these nine models either the wave height and wave peak period (wave models) or the fluvial discharge and sediment concentration (discharge models) were varied. The wave models with the largest energy, i.e. largest wave height and peak period, show the most assymetrical delta built out towards the wind direction. Sediment is fed to the delta front by distributary channels and further redistributed by longshore currents. Typical wave-dominated lobate structures and an elongated delta built-out are the morphological result. In the low wave energy models the distributaries are concentrated in two channels distributing sediment laterally towards the sides, whereas a more variable distributary channel pattern is encountered in the larger wave energy models. The discharge models feeding the largest amount of sand and clay into the basin show smallest wave influence and most stable formation of the delta front and intertidal-, and supratidal zones. A two way distributary channel system develops from the main fluvial river transporting sediment equally to the deltas sides. Morphologically the delta becomes more river dominated, building out symmetrically and the sedimentation from distributary channels being dominant over wave erosion. The discharge models, having a constant wave climate, show a typical erosional (wave) base with stability or progradation of the delta front and prodelta occurring below this erosional base and erosion of the intertidal-, and supratidal zone above the erosional base. All models typically have an initial mouth bar formation which very rapidly builds out to a sandy stable delta front. Fining upward sequences are the general appearance in abandoned channel fills with relatively more clay content in the lower wave energy models and lower sediment discharge models. Clay is also more abundant in the sediment stack laterally away from the centre delta where sediments are younger. The heterolithic upper part of the channel fill was found to be most susceptible for reworking by waves and (cutting) distributary channels. The cleanest sand stacks were found in the centre delta, in the intertidal zone and delta front. These sand stacks are largest in the larger wave energy models and higher discharge models. The facies description being dependent on three hydrodynamic parameters has partly succeeded. Incorporation of more hydrodynamic or geological parameters could potentially increase the accuracy of facies description.

modelling
Brent
process-based
Norway
Delft3D

http://resolver.tudelft.nl/uuid:bf8dd4d1-07e8-4c84-88ab-8bc711cffc54

2011-09-02

Student theses

master thesis

(c) 2011 Koolen, G.J.H.M.