Shallow gas accumulations and fluid flow in the vicinity of the Goliat field, SW Barents Sea

Abstract

This thesis focuses on the Goliat area located in the Hammerfest Basin, SW Barents Sea. The overall aim of this study is to increase the understanding of fluid flow processes between deeper thermogenic sources, and shallow gas accumulations. Indications of an active fluid flow system has been observed throughout the southwestern Barents Sea. Much of the fluid flow from deep hydrocarbon reservoirs has been associated with the denudation history of the Barents Sea. Well-known fluid flow features like pipes or pockmarks appear on seismic images and multibeam bathymetry data and provide evidence for fluid migration. A single seismic data set from the Goliat field area, provided by Eni Norge, has been interpreted for possible indications of fluid flow features and shallow gas accumulation. This study focusses mostly on the sedimentary formations above the Base Cretaceous Unconformity (BCU). Two main sets of faults are categorized: deep-seated faults extending downwards from the BCU and into the Permian strata, and shallow faults affecting the Kolmule and Torsk Formations. Within the shallow faults, two different sets of polygonal faults are interpreted. One polygonal fault system affecting only a small interval within the lower Kolmule Formation, and the other is a set of reactivated polygonal faults affecting both the Kolmule and Tosk Formations. As the SW Barents Sea has undergone several phases of uplift and erosion, different sets of faults have been active at different times. The change and orientation of lithospheric stress causes different sets of faults to be open as potential fluid migration pathways. This makes it possible for fluids to migrate and accumulate at different stratigraphic levels in the subsurface. Pockmarks and fluid flow features above the upper regional unconformity (URU) implies an active fluid flow system after the Plio-Pleistocene glaciation. Amplitude anomalies are often associated with the presence of free gas in the subsurface. The presence and distribution of amplitude anomalies in this work indicates that there is a relation between the deeper-lying hydrocarbon reservoirs and both deep-seated and shallow faults. The observation of pockmarks on the seafloor increases the possibility of free gas to be present in the area.