Being the effect of groundwaters’ geologic agency, present-day physico-chemical characteristics of the sedimentary fill of onshore and offshore Netherlands are indicators of paleo and present-day fluid flow conditions (Chapter 1). Important indicators of periods of active paleo fluid flow in onshore and offshore Netherlands are present-day sediment diagenetic characteristics and characteristics of oil and gas accumulations.
6.1 Overview of indirect indicators derived from published studies
Tables 4 and 5 present an overview of the different types of indirect indicators and the related fluid flow events.
Studies on the genesis of Mississippi Valley-type Pb-Zn deposits (e.g. Muchez et al.
1994, 1995) and the results of modelling studies of elevated (paleo) temperatures (e.g.
Bayer et al. 1995, 1996; Von Winterfeld et al. 1994) are consistent with the existence of large-scale north-flowing topography-induced fluid flow systems originating at the southern and southeastern margin of the Netherlands during different times in geological history (Late Carboniferous – Early Permian; Jurassic – Early Cretaceous;
recent; Table 4). Studies on the diagenetic evolution of the continental sediments of the Slochteren Formation and the Lower Germanic Trias Group during the pre- and early rift stages (Table 5) confirm the existence of topography-induced (indicators 5, 7, 8) and density-induced fluid flow conditions (indicator 9) in the Southern Permian Basin. The data on sediment diagenetic evolution also reflects expulsion of water from poorly permeable units, e.g. by sedimentary loading in the basinal areas (indicator 10) and topography-induced flow from intrabasinal highs during the main syn-rift period (indicator 11), and are indicative of focussed fluid flow along faults during the periods of increased tectonic activity (indicator 10).
Indicator Fluid flow event Timing Source
1. Composition of fluid – Meteoric origin mineralising fluids Kimmerian Muchez et al.
inclusions and stable – SE-NW topography-induced flow tect. phases 1994, 1995 isotopes of ferroan calcites – Discharge area Namur syncline
in fractures in Dinantian – Recharge area Ardennes Massif sediments (Belgium,
SW of Maastricht)
2. Pb-Zn mineralisations – Northward topography-induced flow Late Jurassic Lünenschloss of Bleiberg; Numerical – Recharge area Ardennes Massif et al. 1997 modelling fluid flow – Discharge area Variscan front
and heat transport – Focussed flow through fault zones
3. Present-day hydrothermal – Northwestward topography-induced flow Recent Bayer et al. 1995 system Aachen hot springs – Recharge area Rhenish Massif
(Germany); Numerical – Discharge area Variscan front modelling of fluid flow – Focussed flow through fault zones and heat transport
Table 4 Indirect indicators of northward topography-induced flow of groundwater originating at the southern and southeastern margins of the Netherlands during different times in geological history
Indicator
4. Anomalously high coalification Upper Carboniferous Coal Measures near Aachen thrust, Germany, and in SE Netherlands 5. Dolomite, anhydrite and quartz
cements in Slochteren Fm in CBH and NE of TYH; oxygen and strontium isotopic values of dolomite; sulfur isotopic values of anhydrite
6. Kaolin cement, leached K-feldspar in Slochteren Fm (e.g. in BFB)
7. Carbon, oxygen and strontium isotopic composition of dolomite cement in Main Buntsandstein Subgroup (offshore F17, 18; L2, 5, 6, 9)
8. Dolomite and anhydrite cements in Volpriehausen Fm (offshore F15) 9. Halite cements in Detfurth
Sandstone Fm (offshore L2, F15)
10. Illite cements in Slochteren Fm and Lower Germanic Trias Group (BFB, WNB)
11. Illite cements in Upper Rotliegend Group (NE onshore Netherlands;
adjacent to WH);
Reconstructed oxygen isotopic composition diagenetic fluid
12. Stable isotopes groundwater Vlieland Sandstone Fm (WNB)
Fluid flow event
Northward forced fluid flow discharging along thrust fault zone near Aachen
Topography-driven flow of meteoric water from Permian basin margin to basin center
Expulsion acid CO2-rich water from Limburg Group into Slochteren Fm
Flow of meteoric water through Main Buntsandstein Subgroup
Flow of meteoric water through Volpriehausen Fm Downward expulsion of brines from evaporites of Röt Fm into Detfurth Sandstone Fm
– Hydrothermal flow along fault zones
– Expulsion K-rich water from Limburg Group and/or Zechstein Group into Slochteren Fm
Flow of meteoric water through Upper Rotliegend Group; Recharge area TYH Recharge area WH
Flow of meteoric water through Vlieland Sandstone
Lanson et al. 1995, 1996
Rossel 1982 Platt 1993 Gaupp et al. 1993 Purvis and Okkerman 1996
Lepoutre et al. 1996
Dronkert and Remmelts 1993 Lepoutre et al. 1996
Lanson et al.
1995,1996 Lee et al. 1989 Leveille et al. 1997 Clauer et al. 1996 Gaupp et al. 1993 Platt 1993
Table 5 Present-day indirect indicators of fluid flow events based on published sources
Hydrochemical, sediment-diagenetic as well as petroleum geochemical studies provide stong evidence for a period of active meteoric fluid flow through the Lower Cretaceous reservoirs in the West Netherlands Basin and the Broad Fourteens Basin, presumably during Late Cretaceous to Early Tertiary times (indicators 12, 13 and 14). A distinct period of illite cementation in the Upper Rotliegend Group in Northeastern Netherlands occurred during Eocene-Oligocene times (indicator 15). Lee et al. (1989) associate the cementation with a of period of active fluid flow along a nearby fault zone.
Present-day fluid flow conditions in onshore Netherlands include fluid flow and related compaction as induced by recent sediment loading (Table 5, indicator 18:
Kooi et al. 1998, Kooi and De Vries 1998). From the hydrochemical compositions of the groundwater in the west of onshore Netherlands it can be inferred that this water has been expelled from Quaternary sediments, by compaction (Stuyfzand 1993).
13. K-feldspar leaching in Vlieland Sandstone Fm (BFB)
14. Biodegraded oils in Upper Jurassic and Lower Cretaceous reservoirs (BFB, WNB)
15. Illite cements in Upper Rotliegend Group near fault (NE onshore Netherlands)
16. Shallow gas accumulation;
Shallow gas seepage
17. Pockmarks at seabottom Netherlands offshore
18. Current land subsidence (onshore Netherlands)
19. Potclay (onshore Netherlands);
overcompaction
20. Fracture vents and sand boils (onshore Netherlands)
21. Hydraulic heads; chemical compositions groundwater; various groundsurface features
Flushing of Vlieland Sandstone Fm
Flow of oxygen-rich meteoric water through Upper Jurassic and Lower Cretaceous reservoirs
Fluid flow along fault zone
Vertical fluid migration through Pliocene and Quaternary units
Fluids escaping at seabottom
Groundwater flow in Tertiary and Quaternary sediments induced by Late Pleistocene and Holocene sedimentary loading
Expulsion of groundwater due to ice-loading
De Jong and Laker 1992
Roelofsen and De Boer 1991 De Jager et al. 1996 Van Balen et al.
2000 Kooi et al. 1998 Kooi and De Vries 1998 Table 5 (Continued)
The location of oil and gas fields in on- and offshore Netherlands provides additional valuable information on fluid flow conditions and fluid pathways. For example, the widespread occurrence of Posidonia sourced oil fields in the Lower Cretaceous reservoirs in the West Netherlands Basin and the Broad Fourteens Basin (Rondeel et al. 1996) means that there must have been cross-formational flow or along-fault flow of oil through the Werkendam and Brabant Formations and the Upper Jurassic units. The gas fields in reservoirs of the Lower Germanic Trias Group in the Dutch Central North Sea Graben (e.g. F15, L2, Crépieux et al. 1998, Lepoutre et al. 1996) are sourced from Limburg Group coal measures. These gas fields must must have been filled by paleo and/or present-day cross-formational migration through the poorly permeable Zechstein Group and part of the Lower Germanic Trias Group, via permeable fault and fracture zones or salt depletion zones in the Zechstein Group.
Shallow gas accumulations in Pliocene–Pleistocene reservoirs in the offshore blocks A12 and A18 (Wride 1995) and shallow gas seepage along fault systems through Pliocene and Quaternary units in block F3 (Schroot 2001) reveal Quaternary to recent vertical fluid migration in northern offshore Netherlands (indicator 16). A number of pockmarks have been identified on the floor of the Netherlands North Sea (indicator 17: Laban 1999, Schroot and Schüttenhelm 2003). Pockmarks are indicators and recorders of focussed fluid flow (gas or liquid) (Hovland et al. 2002). The fluids escaping through pockmarks may be sourced or driven by changing overpressure conditions at any depth beneath the surface (Hovland et al. 2002).
6.2 Identified periods of active fluid flow
The present-day indicators of fluid flow allowed fluid flow/groundwater flow events in the different rifting stages to be recognised. The identified groundwater flow events are qualitatively related to the different types of driving mechanism as previously determined from geological history (Tables 2 and 3; Tables 4 and 5):
Pre-rift period — Topography of the water table (indicator 5) Early-rift period — Expulsion (sedimentary loading) (indicators 6, 9)
— Topography water table (indicators 1, 7, 8) Main syn-rift period — Tectonic forces (Basins) (indicator 10)
— Topography of the water table (Highs) (indicator 11)
— Topography of the water table (S, SE Netherlands) (indicators 1, 2)
Post-rift period — – – –
Syn-inversion period — Topography of the water table (indicator 12, 13, 14)
— Tectonic forces (indicator 15)
Post-inversion period — Topography of the water table (SE Netherlands) (indicator 3)
— Topography of the water table (indicator 21)
— Sedimentary loading (indicator 18, possibly also 16 and 17)
— Glacial loading (indicator 19)
— Tectonic forces (indicator 20)
Flow of groundwater during the post-rift period induced by sedimentary-loading could not be verified from the available indicators. Publications on petroleum systems infer a phase of oil and gas migration during the post-rift period (e.g. Bodenhausen and Ott 1981, De Jager et al. 1996).