Abstract
This study documents the suite of processes associated with source-to-seafloor fluid migration in the Connemara field area on the basis of 3D seismic data, well logs, 2D high-resolution seismic profiles, subbottom profiles, short cores and sidescan sonar data. The combination of datasets yields details about fluid migration pathways in the deep subsurface, in the unlithified shallow subsurface and about the distribution of fluid and gas seeps (pockmarks) at the sea floor. The Connemara field area is characterized by vertical fluid migration pathways (“seismic chimneys” or “gas chimneys”) that extend from the top of the Jurassic sequence, cross-cutting the entire Cretaceous sequence to the Upper Tertiary deposits over a vertical distance of up to 1.5 km. Their localization is mainly structurally controlled to the crest of tilted fault blocks along the main hydrocarbon migration pathways. These chimneys are important conduits for focused vertical fluid/gas flow from the deep to the shallow subsurface. However, gas seeps (pockmarks) at the sea floor are almost randomly distributed, which indicates a change from focused to diffuse fluid/gas migration in shallow, unconsolidated sediment. Where the vertical chimneys reach up to unlithified Eocene to Miocene sands, widespread deformation, interpreted as fluidization, occurs around the main conduit. This deformation affects about 32% of the entire unconsolidated Tertiary section (Late Eocene – Miocene). A Plio-Pleistocene glaciomarine drift with up to five horizons with iceberg ploughmarks seals the Tertiary sands. In the near surface sediments it is observed that gas accumulation occurs preferentially at iceberg ploughmarks. It is inferred that lateral migration at five levels of randomly oriented ploughmarks dispersed gas over larger areas and caused random pockmark distribution at the sea floor, independent from the underlying focused migration pathways. This study demonstrates that fluid flow migration changes from structurally controlled focused flow in the deep consolidated subsurface to diffuse flow, controlled by sediment variability, in the shallow subsurface. This result is relevant to a better understanding of the distribution of seepage-induced features at the seafloor related to focused hydrocarbon migration pathways known from industry data and fluid flow modeling.
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References
Boehm A, Moore JC (2002) Fluidized sandstone intrusions as an indicator of paleostress orientation, Santa Cruz, California. Geofluids 2:147–161
Croker PF, Shannon PM (1987) The evolution and hydrocarbon prospectivity of the Porcupine Basin, offshore Ireland. In: Brooks J, Glennie K (eds) Petroleum Geology of North West Europe. Graham and Trotman, London, pp 633–642
Draganits E, Grasemann B, Schmid HP (2003) Fluidization pipes and spring pits in a Gondwanan barrier-island environment: Groundwater phenomenon, palaeo-seismicity or a combination of both? In: Van Rensbergen P, Hillis RR, Maltman AJ, Morley CK (eds) Subsurface sediment mobilisation vol 216. Geological Society of London Special Publications, pp 109–121
Engelder T, Leftwich JT Jr (1997) A pore-pressure limit in overpressured South Texas oil and gas fields. In: Surdam RC (ed) Seals, traps, and the petroleum system: AAPG Memoir, vol 67, pp 255–267
Games KP (2001) Evidence of shallow gas above the Connemara oil accummulation, Block 26/28, Porcupine Basin. In: Shannon PM, Haughton PDW, Corcoran DV (eds) The Petroleum Exploration of Ireland’s offshore basins. Geological Society, London, Special Publications, vol 188, pp 361–373
Gay A, Lopez M, Cochonat P, Sultan N, Cauquil E, Brigaud F (2003) Sinuous pockmark belt as indicator of a shallow buried turbiditic channel on the lower slope of the Congo basin, West African margin. In: Van Rensbergen P, Hillis RR, Maltman AJ, Morley CK (eds) Subsurface sediment mobilisation. Geological Society of London Special Publications, vol 216, pp 173–189
Haskell N, Nissen S, Hughes M, Grindhaug J, Dhanani S, Heath R, Kantotowicz J, Antrim L, Cubanski M, Nataraj R, Schilly M, Wigger S (1999) Delineation of geologic drilling hazards using 3-D seismic attributes. Lead Edge 18(3):373–382
Heggland R (1997) Detection of gas migration from a deep source by the use of exploration 3D seismic data. Mar Geol 137:41–47
Hurst A, Cartwright J, Duranti D (2003) Fluidization structures produced by upward injection of sand through a sealing lithology. In: Van Rensbergen P, Hillis RR, Maltman AJ, Morley CK (eds) Subsurface sediment mobilisation. Geological Society of London Special Publications, vol 216, pp 123–138
Lewis JC, Byrne T (1996) Deformation and diagenesis in an ancient mud diapir, southwest Japan. Geology 24:303–306
Lisk M, Faiz MM, Bekele EB, Ruble TE (2000) Transient fluid flow in the Timor Sea, Australia: implications for prediction of fault seal integrity. J Geochem Explor 69–70:607–613
MacDonald H, Allen PM, Lovell JPB (1987) Geology of oil accumulation in Block 26/28, Porcupine Basin, offshore Ireland. In: Brooks J, Glennie K (eds) Petroleum Geology of North West Europe. Graham and Trotman, London, pp 643–651
MacLeod MK, Hanson RA, Bell CR, McHugo S (1999) The Alba Field ocean bottom cable seismic survey: Impact on development. Lead Edge 18(11):1306–1312
Maltman AJ, Bolton (2003) How sediments become mobilized. In: Van Rensbergen P, Hillis RR, Maltman AJ, Morley CK (eds) Subsurface sediment mobilisation. Geological Society of London Special Publications, vol 216, pp 9–20
Moore JG, Shannon PM (1995) The Cretaceous succession in the Porcupine Basin, offshore Ireland: facies distribution and hydrocarbon potential. In: Croker PF, Shannon PM (eds) The Petroleum Geology of Ireland’s Offshore Basins. Geological Society of London Special Publications, vol 93, pp 345–370
Revil A (2002) Genesis of mud volcanoes in sedimentary basins: a solitary wave-based mechanism. Geophys Res Lett 29(12):81–84
Roberts SJ, Nunn JA, Cathles L, Cipriani FD (1996) Expulsion of abnormally pressured fluids along faults. J Geophys Res 101:28231–28252
Shannon PM (1991) The development of Irish offshore sedimentary basins. J Geol Soc Lond 148:181–189
Stump BB, Flemings PB (2000) Overpressure and fluid flow in dipping structures of the offshore Gulf of Mexico (E.I. 330 Field). J Geochem Explor 69–70:23–28
Van Rensbergen P, Morley CK, Ang DW, Hoan TQ, Lam NT (1999) Structural evolution of shale diapirs from reactive rise to mud volcanoes at the Baram Delta (offshore Brunei Darussalam). J Geol Soc Lond 156:633–650
Ziegler PA (1982) Geological atlas of Western and Central Europe, Shell Internationale Petroleum maatschappij BV
Acknowledgements
The data for this study were provided by Statoil Ireland Ltd. and by the Petroleum Affairs Division (PAD,DCMNR) in Dublin, Ireland. Part of the mapping and interpretation was carried out by students as part of their research project at Ghent University. PVR is a research fellow of the Foundation of Scientific Research—Flanders. Peter Croker and Roar Heggland reviewed this paper and suggested lot of corrections to the original manuscript.
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Appendices
Appendix 1: Petrophysics, seismic horizons, lithology, and stratigraphy for well 26/28-1
Appendix 2: Petrophysics, seismic horizons, lithology, and stratigraphy for well 26/28-5
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Rensbergen, P.V., Rabaute, A., Colpaert, A. et al. Fluid migration and fluid seepage in the Connemara Field, Porcupine Basin interpreted from industrial 3D seismic and well data combined with high-resolution site survey data. Int J Earth Sci (Geol Rundsch) 96, 185–197 (2007). https://doi.org/10.1007/s00531-005-0021-2
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DOI: https://doi.org/10.1007/s00531-005-0021-2