Liassic Source Rocks from Three Wells from the Sea of Iroise (French Western Approaches) and Dorset (UK) Outcrops: Nature and Modeled Maturity History

  • J. F. Deronzier
  • A. Bruneton
  • J. Mondin
  • A. Mascle
Part of the Special Publication of the European Association of Petroleum Geoscientists book series (3148, volume 4)

Abstract

The first stage of exploration in the Western Approaches and Channel Basins was completed in the middle of the 1980s without any significant results (apart from one oil and one gas condensate show) although 12 wells were drilled in French waters. However, the on­ shore Wytch Farm oil field was developed, and produc­ tion was said to reach about 60000 bopd at the end of 1991. At the same time, the Kinsale Head and Ballycotton gas fields, offshore from southern Ireland, were deve­ loped with reported reserves of 1.4 Tcf and 73 Bcf respec­ tively. Significant amounts of hydrocarbons may thus be present in as yet undiscovered structural or stratigraphic traps. Present studies will benefit from the results of the first wells, as well as from the much improved quality of present seismic data with respect to those available in 1970. It is now also possible to gain a better understanding of the quality, distribution, and maturation history of the potential source rocks, the most widespread and ma­ ture of which are the Liassic black shales. Sections of the­ se shales have been sampled along the classic field expo­ sures of the Dorset coast, and from cuttings in three wells. The Dorset section is immature and the average organic content is 3 %. At Levneg 1 the Liassic section is about 1250 m thick, with the best potential in the Pliensbachian to Hettangian intervals. Present TOCs are low (about 1 %), but these rocks are overmature so that their initial organic content can be estimated to have been in the ran­ ge of at least 2 %. The present depth of these levels and the present heat flow cannot explain this present matura­ tion so that their tectonic history must also be taken into account. The IFP-CGG IS 88 seismic line clearly shows, at this locality, the inversion in Tertiary times of the basin where up to 4000 m of sediment hat accumulated in Me­ sozoic times. The relatively good Liassic source rocks at the Rea-Gwenn and Travank wells are immature and were deposited in a much less subsiding area. They ap­ pear to be more similar to the Dorset section. As for the area south of Wytch Farm, 1-D Matoil modeling shows that the generation of oil or gas stopped at Levneg as soon as the process of inversion was initiated, which im­ plies that, in this case, pre-Tertiary structural traps are more favorable targets than recently inverted structures.

Keywords

Clay Petroleum Hydrocarbon Sandstone sedImentatIOn 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Bénard F, De Charpal O, Mascle A, Trémolières P (1985) Mise en évidence d’une phase de serrage E-W au Crétacé inférieur en Europe de l’Ouest. CRAS Paris 300; II, 15:765–768Google Scholar
  2. Bois Ch, Gabriel O, Sibuet JC (eds) (1991) Les bassins sédimentaires de Mer Celtique et de Manche: apport des profils seismiques SWAT. Etude de la croûte terrestre par sismique profonde; Mer Celtique, Manche et ses Approches occidentales. Profils SWAT et WAM. Mém Soc Géol Fr 159Google Scholar
  3. Butler M, Pullan CP (1990) Tertiary structues and hydrocarbon entrapments in the Weald Basin of southern England. In: Hardman RFP, Brooks J (eds) Tectonics events responsible for Britains oil and gas reserves, Geol Soc Spec Publ 55: 371–392Google Scholar
  4. Chadwick RA (1993) Aspects of basin inversion in southern Britain. J Geol Soc Lond 150: 311–322CrossRefGoogle Scholar
  5. Colley MG. Mc Williams ASF, Myers RC (1981) Geology of the Kinsale Head Gas Field, Celtic Sea. Ireland. In: Petroleum geology of the Continental Shelf of North West Europe. Institute of Petroleum, London, pp 504–510Google Scholar
  6. Cornford Ch, Christie O, Endresen U, Jensen P, Mythr M-B (1987) Source-rock and seep oil maturity in Dorset, southern England. Org Geochem 13; 1-3: 399–409CrossRefGoogle Scholar
  7. Dranfield P, Begg SH, Carter RR (1987) Wytch Farm Oilfield: Reservoir characterization of the Triassic Sherwood Sandstone for input to reservoir simulation studies. In: Brooks J, Glenny KW (eds) Petroleum Geology of NW Europe. Graham & Trotman, London, pp 149–160Google Scholar
  8. Ebukanson EJ, Kinghorn RRF (1985) Kerogen facies in the major Jurassic mudrock formations of Southern England and the implication on the depositional environments of their precursors. J Petrol Geol 8; 4:435–462CrossRefGoogle Scholar
  9. Ebukanson EJ, Kinghorn RRF (1986) Maturity of organic matter in the Jurassic of Southern England and its relation to the burial history of the sediments. J Petrol Geol 9; 3: 259–280CrossRefGoogle Scholar
  10. Espitalié J, Deroo G, Marquis F (1985-1986) La pyrolyse Rock Eval et ses applications. Rev IFP 40, 5: 563–579; 6: 755-784; 41,1:73-89Google Scholar
  11. Evans CDR (1990) The geology of the Western English Channel and its western approaches. BGS, U. K. offshore regional report, London, HMSO, 93 pGoogle Scholar
  12. Foucher JP, Chenet PY, Montadert L, Roux JM (1984) Geothermal measurements during deep sea drilling project leg 80. In: de Graciansky PCh, Poag CW et al. (eds) Initial Reports of the Deep Sea Drilling Project volume LXXX, Washington U. S. Government Printing Office, pp 423–436Google Scholar
  13. Gairaud H, Le Théoff B (1992) Geodynamic evolution of an intracratonic basin: the Paris Basin. EAPG Conf Paris, June 1982, Pap, pp 18–19Google Scholar
  14. Hamblin RJO, Crosby A, Balson PS, Chadwick RA, Penn IE, Arthur MJ (1992) The geology of the English Channel. British Geological Survey, U. K. Offshore Regional Report, London, HMSO, 106ppGoogle Scholar
  15. House M (1989) Geology of the Dorset Coast. Geologist’ Association Guide, the Geologists’ Association, London, 170 ppGoogle Scholar
  16. Jenkins HC, Senior JM (1991) Geological evidence for intra-Ju-rassic faulting in the Wessex Basin and its margins. J Geol Soc Lond 148,2:245–260CrossRefGoogle Scholar
  17. Miles JA, Downes ChJ, Cook SE (1993) The fossile oil seep in Mupe Bay, Dorset: a myth investigated. Mar Pet Geol 10: 58–70CrossRefGoogle Scholar
  18. Penn IE, Chadwick RA, Holloway S, Roberts G, Pharaoh TC, Allsop JM, Hulbert AG, Burns IM (1987) Principal features of hydrocarbon prospectivity of the Wessex-Channel Basin. In: Brooks J, Glenny KW (eds) Petroleum geology of NW Europe, Graham & Trotman, London, pp 109–118Google Scholar
  19. Selley and Stoneley (1987) Petroleum habitat in South Dorset. In: Brooks J, Glenny KW (eds) Petroleum geology of NW Europe. Graham & Trotman, London, pp 139–148Google Scholar
  20. Shannon PM (1991) Tectonic framework and petroleum poten0tial of the Celtic Sea, Ireland. First Break 9:107–122Google Scholar
  21. Stoneley R (1982) The structural development of the Wessex basin. J Geol Soc 139; 4:545–554CrossRefGoogle Scholar
  22. Willis-Richards J (1993) Control on lithospheric strength, fracture opening and fluid movement in SW England. In: Parnell J, Ruffell AH, Moles NR Geofluids ’93, Extended Abstr, pp 128–131Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1994

Authors and Affiliations

  • J. F. Deronzier
  • A. Bruneton
  • J. Mondin
  • A. Mascle

There are no affiliations available

Personalised recommendations