Imaging through gas‐filled sediments using marine shear‐wave data

Abstract

Marine multicomponent sea‐floor data of excellent quality have been acquired over the Tommeliten Alpha field. The most dominating wave modes are interpreted to be conventional compressional PP-waves and converted PS-waves. The most important geophysical problem associated with the Tommeliten Alpha field is the presence of a gas chimney obscuring the conventional 3-D seismic image of the reservoir zone. The converted PS-waves effectively undershoot the gas chimney, leading to substantially improved images of the reservoir. Subsequent interpretation indicates the Tommeliten Alpha structure is a faulted dome.

Seismic chimneys in the Southern Viking Graben – Implications for palaeo fluid migration and overpressure evolution

“…These observations were confirmed by a shear wave experiment indicating high gas-saturation within a chimney structure at Tommeliten (Granli et al, 1999). This kind of chimney is interpreted to be caused by gas saturated fractures within a low permeable cap rock (Løseth et al, 2009).…”

“…Based on our interpretations, 46 large-scale vertical seismic anomalies are present in the study area. Large scale chimney-like anomalies have so far been described as solitary structures (Gay et al, 2012), in many cases above leaking deep reservoirs (Hovland and Sommerville, 1985;Granli et al, 1999).…”

“…resulting in pipe structures offshore Nigeria (Løseth et al, 2011) or Norway (Bünz et al., 2003), or fluid flow may be continuous and long-lasting, e.g. the chimney structures above the leaking hydrocarbon reservoirs Ekofisk (Hovland and Sommerville, 1985) and Tommeliten (Granli et al, 1999;Arntsen et al, 2007). The terms seismic chimney and pipe are used interchangeably in the literature.…”

Elastic least-squares reverse time migration

“…Similarly, other conventional migration methods can be applied to PP-and PS-wavefields after their separation. Usually, the P-and S-waves can be approximated by the vertical-and horizontal-component data (Granli et al, 1999) or separated by using approximations such as elastic potentials (Etgen, 1988;Zhe and Greenhalgh, 1997;Sun and McMechan, 2001;Stanton and Sacchi, 2014). The separation of P-and S-waves is not always accurate because it will generate crosstalk artifacts between the unseparated wave modes in the migration images (Du et al, 2012).…”

Converted-wave diodic moveout and application in the land gas cloud area

“…PS converted-wave traveltime and velocity difference between positive and negative offset can be observed if the source and detector are interchanged for a converted wave travelling through a gas cloud, which degrades the PS converted wave imaging. Granli et al (1999) fi rst demonstrated the PS convertedwave difference when the data from Tommeliten fi eld was processed. It was named the diodic effect by Thomsen (1999).…”