Most of the available knowledge of fluid escape pipes has been inferred from high resolution marine seismic studies.On seismic data fluid escape pipes are recognizable as columnar zones of disrupted reflection continuity, commonlyassociated with amplitude and velocity anomalies, and scattering, attenuation and transmission artifacts (Cartwright, J.& Santamarina, C,2015). Here we propose a detailed analysis of the seismic expression of the internal structure of somepipe rock from the Loyal field. The Loyal field (Scotland, UK) is an oil and gas productive field located in the Quadrant204 and 205 of the UKCS, 130 km west of Shetlands and characterized by siliciclastic turbidite sandstones which werederived from the uplifted Scottish Massif to the southeast. The Paleocene sandstone reservoirs appear to have beendeposited within or associated with a series of channelized submarine slope systems (Leach et al, 1999). In the presentstudy, we examined the fluid escape pipes affecting the upper Paleogene-Neogene overburden units by using RMS andvariance attributes to better characterize the internal architecture and the different fluid pathway migration across themajor units. The internal seismic image of some large pipes (few km height and several hundred meters thick) shows ahighly variable seismic expression vertically along the pipe, from a wide root zone, often badly affected by artifacts, toa narrower disrupted zone with clear convex upwards deformation across sharp inflection points. Most of the fluidescape pipes shows a clear tendency to ‘upbending’ of reflections within the pipe. The upward stratal deformationwould be consistent with non-fluidized and non-erosive localized fluid flow deflecting the main host rocks. Severalpipes are instead characterized by laterally extensive high amplitude reflections (as indicated by RMS attributes) atdifferent height across the pipes suggesting that the migration did not proceed solely by hydrofracturing mechanism butalso through Darcy flow laterally filling porous and permeable rock. In some case the pre-existing Paleogene-Neogenefaults (mostly enucleating above the mounded Lista Formation) acted as potential conduits for the pipes controllingtheir alignment. Most of the large pipe seems instead unrelated to any preexisting structure but rather controlled by theoverpressure in the root zone inducing hydraulic fracturing in the overburden. Due to the lack of isotope and well datathe timing of the fluid escape pipe structure is poorly contrained. However, a diachroneity in pipe clusters can be arguedby the seismic appearance of the pipes termination zones. In some case RMS and variance attribute anomalies rightabove the pipes conduit suggest the pipes seem to reach the actual seabed indicating a relatively recent activity. Most ofthe other cases the pipes seem clearly to intrude the upper Paleogene and Neogene units without penetrating (in avisibile way) through the Neogene countourite drift deposit, suggesting instead a relatively older age.
Seismic characterization of fluid escape pipes internal structures and implication for their genesis: example from the Loyal field (West Shetland, North sea)
MANISCALCO, ROSANNA
2015-01-01
Abstract
Most of the available knowledge of fluid escape pipes has been inferred from high resolution marine seismic studies.On seismic data fluid escape pipes are recognizable as columnar zones of disrupted reflection continuity, commonlyassociated with amplitude and velocity anomalies, and scattering, attenuation and transmission artifacts (Cartwright, J.& Santamarina, C,2015). Here we propose a detailed analysis of the seismic expression of the internal structure of somepipe rock from the Loyal field. The Loyal field (Scotland, UK) is an oil and gas productive field located in the Quadrant204 and 205 of the UKCS, 130 km west of Shetlands and characterized by siliciclastic turbidite sandstones which werederived from the uplifted Scottish Massif to the southeast. The Paleocene sandstone reservoirs appear to have beendeposited within or associated with a series of channelized submarine slope systems (Leach et al, 1999). In the presentstudy, we examined the fluid escape pipes affecting the upper Paleogene-Neogene overburden units by using RMS andvariance attributes to better characterize the internal architecture and the different fluid pathway migration across themajor units. The internal seismic image of some large pipes (few km height and several hundred meters thick) shows ahighly variable seismic expression vertically along the pipe, from a wide root zone, often badly affected by artifacts, toa narrower disrupted zone with clear convex upwards deformation across sharp inflection points. Most of the fluidescape pipes shows a clear tendency to ‘upbending’ of reflections within the pipe. The upward stratal deformationwould be consistent with non-fluidized and non-erosive localized fluid flow deflecting the main host rocks. Severalpipes are instead characterized by laterally extensive high amplitude reflections (as indicated by RMS attributes) atdifferent height across the pipes suggesting that the migration did not proceed solely by hydrofracturing mechanism butalso through Darcy flow laterally filling porous and permeable rock. In some case the pre-existing Paleogene-Neogenefaults (mostly enucleating above the mounded Lista Formation) acted as potential conduits for the pipes controllingtheir alignment. Most of the large pipe seems instead unrelated to any preexisting structure but rather controlled by theoverpressure in the root zone inducing hydraulic fracturing in the overburden. Due to the lack of isotope and well datathe timing of the fluid escape pipe structure is poorly contrained. However, a diachroneity in pipe clusters can be arguedby the seismic appearance of the pipes termination zones. In some case RMS and variance attribute anomalies rightabove the pipes conduit suggest the pipes seem to reach the actual seabed indicating a relatively recent activity. Most ofthe other cases the pipes seem clearly to intrude the upper Paleogene and Neogene units without penetrating (in avisibile way) through the Neogene countourite drift deposit, suggesting instead a relatively older age.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
