• DGF Nyhedsbrev

DGF’s oliegeologisk foredragsrække

Grundvandsmøde torsdag den 18. september 2003
Prækvartære grundvandsmagasiner
Heldagsmøde i Torvehallerne, Vejle

Program:

10.00 Indskrivning (the og kaffe)

10.15 Miocæne grundvandmagasiner i Jylland

• Sedimentologiske og stratigrafiske undersøgelser af de miocæne aflejringssystemer v. Erik Skovbjerg Rasmussen (GEUS)
• Billund deltaet, et nyopdaget grundvandsmagasin i Midtjylland v. Jørgen Fjeldsø Christensen (Ribe Amt)
• Mapping of Tertiary aquifers in Schleswig-Holstein v. Wolfgang Scheer (Landesamt für Natur und Umwelt)
• Kortlægning af basis Miocæn og Odderup Formationen i Jylland (poster) v. Niels Skytte Christensen (Geol. Inst. KU)

12.00 Frokost

13.00 Kalkmagasiner på Sjælland og i Nordjylland

• Kalkmagasiner i Østdanmark set med geofysiske metoder v. Thomas Vangkilde (Rambøll)
• Kortlægning af fersk–saltvandsgrænsen i kalkmagasinerne på Sjælland v. Kurt Klitten (GEUS)
• Simulering af udvikling af fersk-saltvandsgrænsen i kalkmagasinerne på Sjælland v. Flemming Larsen ( DTU)

14.45 Kaffe/the-pause

15.15 Grundvandsstrømning,saltvandsgrænse m.v. i kalkmagasiner

• Eksempler fra det nordlige Jylland v. Karsten Juul (Dansk GeoFysik)
• Grønsandskalken på Sjælland – høj transmissivitet i lukkede kar? v. Niels Philip Jensen (Vestsjællands Amt)

16.30 Afslutning

Praktiske oplysninger

Mødested: Torvehallerne, Kirketorvet 10-16, 7100 Vejle (lige ved stationen)

Pris: DGF-medlemmer 600 kr, studentermedlemmer 400 kr, andre 800 kr. Prisen inkluderer frokost (uden drikkevarer) og kaffe/the

Tilmelding: Flemming Jørgensen, Vejle Amt, Teknik og Miljø, Damhaven 12, 7100 Vejle,
e-mail: fj [at] vejleamt [dot] dk, tlf: 7572 3144 lok. 5124
Husk navn, adresse, tlf.nr og evt. e-mail samt oplysninger om evt. DGF-medlemsskab.
Tilmelding er bindende. Girokort vil blive fremsendt.

Tilmeldingsfrist: 1. september 2003.

Yderligere info: Flemming Jørgensen (se ovenfor) eller Henrik Olsen: 4597 1129, heo [at] cowi [dot] dk

Hent program i pdf-format (134 kB)

Because North Sea chalks are extremely fine grained and have low permeabilities, they typically require 25% or more porosity to be productive hydrocarbon reservoirs. Preservation of such substantial porosity in deeply buried chalks requires unusual conditions because chalks lose pore space rapidly as a result of chemical and physical compaction associated with overburden loading.

Overpressuring is particularly widespread in North Sea chalks as a consequence of rapid rates of sediment accumulation and low permeability of both the chalks and the overlying Tertiary section. Studies indicate that the overpressuring currently seen in many areas has existed for at least 10 million years, in some areas possibly in excess of 30-35 million years. Maintenance of substantial overpressures for such long periods of time is difficult, particularly in areas of substantial tectonic activity (e.g., along faults or on piercement salt domes). Partial or complete loss of overpressures at any stage after their initiation could lead to rapid porosity loss until overpressures were reestablished. Thus, understanding the history of regional and local pore-fluid pressure variations is an important factor in models used to predict porosity variations in chalks of the North Sea Basin.

Geochemical studies, especially fluid-inclusion investigations, of Cretaceous chalks of the Skjold Field in the Danish North Sea have provided insights on episodic variations in fluid compositions, and thus, by inference, into variations in fluid throughput and pore pressure history of that field. Successive generations of calcite cements in fractures from chalks on this salt dome structure show alternations between zones of water- and oil-filled fluid inclusions, sometimes with a corrosion zone between them. Those variations are interpreted to reflect at least two episodes of oil filling and overpressuring of the structure, followed by failure of the seal, with loss of overpressuring and oil charge. Following those pressure dissipation events, calcite cementation under aqueous conditions helped to heal the extensive fractures produced in the chalk. This allowed gradual repressurization and refilling of the structure with hydrocarbons.

Other lines of evidence that support the concept of repeated pressurization-depressurization and the movement of deep basin waters through the field include the presence of oil trapped in low porosity and permeability chalks, extensive alteration of carbon and oxygen isotopic ratios, anomalously high fluid inclusion temperatures, significant dolomite in some horizons, and the presence of celestite in fracture fills.

The presentation will be held in English. Non-DGF members are welcome.

After receiving a B.S. in geology from Yale in 1965, Peter Scholle spent a year on a Fulbright-DAAD fellowship at the University of Munich in Germany, a year at the University of Texas at Austin, and completed a Ph.D. at Princeton in 1970. He has worked for five years for various oil companies (Cities Service, Gulf and Chevron) and consulted for other companies for many years. Nine years were spent with the U. S. Geological Survey in Reston (VA) and Denver (CO). Peter Scholle taught at the University of Texas at Dallas for three years and was Professor of Geology at Southern Methodist University from 1985 to 1999. Peter Scholle is now the Director of the New Mexico Bureau of Geology and Mineral Resources.