Reservoir architecture model of the Nieuwerkerk Formation (Early Cretaceous, West Netherlands Basin): diachronous development of sand-prone fluvial deposits

Abstract

The sand-prone fluvial Delft Sandstone Member of the Nieuwerkerk Formation is the main target for geothermal exploitation in the West Netherlands Basin. Uncertainty reduction in the modelling of permeability heterogeneity and connectivity of the sandstone reservoir units is of prime importance in the low-profit geothermal energy market. Lithostratigraphic correlation of the Delft Sandstone Member dates back to the 1970s, and considers the fluvial deposits as Valanginian (140–134 Ma) in age and synchronously deposited throughout the basin.Analysis of newly-acquired palynological data, in combination with well-log correlation and seismic interpretation, enabled the construction of a sequence-stratigraphic framework for the Nieuwerkerk Formation, in which the fluvial sandstones were deposited in a much wider age range than previously believed, from Late Ryazanian to Valanginian (142–134 Ma). The depocentre of fluvial deposition shifted in time from NE to SW across the width of the basin. This diachronous development resulted in a discontinuous spatial arrangement of fluvial sandstones. The new reservoir architecture model will aid in the well placement of geothermal doublets and the assessment of interference risk of adjacent geothermal projects.

Geology of the Upper Jurassic to Lower Cretaceous geothermal aquifers in the West Netherlands Basin – an overview

“…The Upper Cretaceous sediments are therefore more homogeneous in thickness, wedging towards the basin margins (Fig. 2;Den Hartog Jager, 1996;Vondrak et al, 2018). The palaeo-coastline transgressed from the northwest boundary of the WNB in the Ryazanian to the northwest boundary of the Roer Valley Graben in Hauterivian times, which is reflected by increasingly marine sedimentation covering the terrestrial syn-tectonic strata (Den Hartog Jager, 1996;Herngreen and Wong, 2007;Jeremiah et al, 2010;Vejbbaek et al, 2010).…”

“…Palynological and lithofacies analysis indicates that the siliciclastic Delft Sst Mbr succession formed in a relatively humid, lower-coastal-plain meandering-river depositional environment (Donselaar et al, 2015;Vondrak et al, 2018). Variability in net-togross and sandstone stacking patterns in the Nieuwerkerk Formation is the result of relative base-level fluctuations by differential movement along extensional faults in combination with rising sea level.…”

“…The sedimentary architecture of such a depositional setting is a sand-prone unit with high vertical and lateral continuity caused by erosional truncation of the underlying floodplain mudstone and fine-grained upper parts of the underlying sandstone. These sand-prone units have c.40-60% net-to-gross and are characterised by stacked multi-storey sandstone bodies with minor mudstone intervals (Vondrak et al, 2018). 2) Low net-to-gross intervals were formed during a high rate of accommodation increase, which favoured the preservation of floodplain fines, and consist of interbedded claystone, siltstone and coal layers with minor thin sandstone intercalations.…”

“…Initially, the marine sandstones of the Vlieland Formation were the main target. However, interest shifted rapidly to the Delft Sandstone Member (Delft Sst Mbr) of the underlying Nieuwerkerk Formation because of its higher temperature, permeability and thickness (Donselaar et al, 2015;Willems et al, 2017c;Vondrak et al, 2018). Recently the deeper Alblasserdam Member (Alblasserdam Mbr) of the Nieuwerkerk Formation has been targeted, and ongoing exploration aims for a combined development of both stratigraphic intervals.…”

New insights on subsurface energy resources in the Southern North Sea Basin area

“…Following on from hydrocarbon exploration experience, the Vlieland Sandstone Formation of the Rijnland Group was the primary target initially, with the deeper Schieland Group being a secondary target. However, geothermal wells drilled in synclines, contrary to anticlinal conventional oil and gas wells, found that the Schieland Group sandstones in the lows are thicker and have higher permeabilities than the pre-drill expectation (Willems et al 2017;Vondrak et al 2018). Presently, the Schieland Group sandstones, especially the Delft Sandstone Member, are the primary target for geothermal exploration with better reservoir characteristics and hotter than the overlying Vlieland Sandstone Formation sandstones.…”