Temporal constraints on the growth and decay of large‐scale mobilized mud masses and implications for fluid flow mapping in sedimentary basins

Abstract

Seismic‐stratigraphic analysis of the Cretaceous to succession of the Uer Terrace, North Sea seabed Basin, Norway, demonstrates that the Upper Oligocene succession has undergone large‐scale mobilization of mudstone‐dominated units due to the upward migration of water and associated hydrocarbons into the interval, which is in some way linked to a period of gas expulsion from adjacent deep basins. Seismic‐stratigraphic analysis of units overlying the mobilized zones indicates they created positive seafloor topography during the Late Miocene implying gaseous fluids were expelled at the seabed. Loading by the overlying Pliocene succession caused the mobilized mud masses to deflate and resulted in the formation of low‐relief, fault‐bounded craters. The results of this study have implications for understanding the location and timing of fluid flow in sedimentary basins.

Evaluation of internal geometries within the Miocene Utsira Formation to establish the geological concept of observed CO2 responses on 4D seismic in the Sleipner area, North Sea

“…the MMU). Three main types of structural deformation have been described: (i) Polygonal faulting (Cartwright, 1994;Shoulders et al, 2007); (ii) Sand injection (Larsen, 1994;Cosgrove & Hillier, 2000;Shoulders & Cartwright, 2004;Briedis et al, 2007;Shoulders et al, 2007) and (iii) Sediment mobilization (Løseth et al 2003;Jackson & Stoddart, 2005;and Jackson, 2007).…”

“…An analysis into the features of the Upper Hordaland Group in the Norwegian sector of the Viking Graben is not unique and the sedimentary, structural and seismic characteristics have been covered by a variety of authors (e.g. Løseth et al, 2003;Jackson & Stoddart, 2005;Jackson, 2005). It is however important to detail its specific features here, in the region of the Sleipner Øst field and CO 2 injection point, due to their influence on the structure and stratigraphy of the Utsira Formation.…”

“…In seismic the Middle Miocene unconformity (Top Hordaland Group/Base Utsira Formation) is an uneven interface with pronounced circular and irregular shaped mounds that can protrude over 100 meters above mean level of the surrounding, more-or-less flat lying surface ( Figure 4.9 (a)). These soft sedimentary deformation features are an abundant feature of the top surface of the Upper Hordaland Group throughout the Viking Graben and have been interpreted as the product of mud-volcanism (Fyfe et al, 2003), mobilized mud masses (Løseth et al, 2003;Jackson & Stoddart, 2005;Jackson, 2007), and sand injection (Løseth et al, 2003) in other areas of the Viking Graben. Overlying the unconformity is the sand-rich Utsira Formation, which contains seismic reflection events that terminate by either onlap or downlap onto the uneven morphology of the unconformity.…”

“…During the hiatus, or during polygonal fault formation/reactivation it is likely that gas sourced from deeper basinal sediments in the oil/gas generative window and leaking hydrocarbon traps flowed vertically through the polygonal faults, which acted as conduits for subsurface fluid migration (Cosgrove & Hillier, 2000). Evidence for this process comes from sand-injectites found within Tertiary basin fill at c. 2000-2200ms TWT (Figure 4.2) that manifest themselves as V-Brights in seismic; and 'gas chimneys' observed in seismic by Løseth (2003); Jackson & Stoddart (2005); and Jackson (2002), that emanate from deep, underlying structural hydrocarbon traps upwards into the Cenozoic basin fill in other parts of the Viking Graben. Gas flowed vertically along fault planes and charged the poorly consolidated Skade Formation sandstones.…”

Application of three-dimensional seismic data to documenting the scale, geometry and distribution of soft-sediment features in sedimentary basins: an example from the Lomre Terrace, offshore Norway

“…lc; see full discussion by Jackson & Stoddart 2005). Based on their chaotic seismic expression, mudstone-dominated lithology and location above interpreted fluid flow conduits, the chaotic reflection packages are interpreted as the seismic expression of zones of mud which became mobilized and highly deformed in response to gas and water migrating through the poorly consolidated, mudstone-dominated succession (LCseth et al 2003;Jackson & Stoddart 2005).…”