Depicting fluid escape pipes using 3D and time lapses seismic surveys: the Loyal Field (Scotland, UK) case study

Fluid escape pipes were first documented from 3D seismic data over a decade ago, and have subsequently been identified in many petroliferous basins worldwide (Løset et al., 2009). Understanding their internal architecture and formation mechanism is crucial as they often represent important pathways for vertical fluid flow and secondary hydrocarbon migration in sedimentary basins (Cartwright & Santamarina, 2015). As such they also disclose important information about leakage mechanisms within potential storage reservoirs. Here we propose a detailed seismic interpretation analysis of some fluid escape pipe affecting the overburden Upper Paleogene-Neogene units in the Loyal field. The Loyal field (Scotland, UK) is an oil and gas productive field located in the Quadrant 204 and 205 of the UKCS, 130 km west of Shetlands, on the slope of the Faroe-Shetland Channel. In this field, active since 1998, the extraction of oil and associated gas focused on the upper Paleoene/Eocene structural traps, but fault systems and other leakage structures, such as gas pipes and wipe-out zones, appear to have an important role in the fluid migration across the younger Paleogene-Neogene stratigraphic succession. By means of seismic interpretation and image post-processing mapping techniques, we analysed some full and partial stack seismic survey from a 4D dataset (released by BP) with the aims of characterizing first the main Paleogene-Neogene structural and sedimentary history of the area and then the distribution and geometric characteristic of the fluid escape pipes observed. We also investigated their relation with the major Paleogene fault systems and the surrounding sedimentary features. The analysis indicates that the majority of fluid escape pipes varies in a wide range of 200m –to 1-2 km height with diameter varying between few to hundred meters and are localized in the highest crest of the Loyal field slope basin structure. The fluid escape pipes observed rarely occur in isolation, but are more typically found in clusters in some case exploiting pre-existing faults in most case (the largest) unrelated to any pre-existing features. The root zone seems to be distributed between the Lista/Balder formation and the Mesozoic reservoir currently under production. Near- middle - Far Off-set amplitude analysis of some fluid escape pipe suggest that the fluid are on partly composed by gas. Except one single clear visible example, the upward limit of the seismically visible pipe structures seem to terminate within the subsurface at buried pockmarks or through laterally extensive high amplitude reflections. Løset H., Gading M., Wensaas L. 2009. Hydrocarbon leakage interpreted on seismic data. Marine and Petroleum Geology, 26, 1304-1319. Cartwright J., Santamarina C. 2015. Seismic characteristics of fluid escape pipes in sedimentary basins: Implications for pipe genesis. Marine and Petroleum Geology, 65, 126-140.