Seismic stratigraphy of Dinantian carbonates in the southern Netherlands and northern Belgium

Abstract

Due to their potential as a petroleum or geothermal system, the Dinantian carbonates of the Netherlands have recently attracted renewed interest because of the identified presence of excellent reservoir properties. This notion contrasts with the general assumption that these carbonates are tight. Therefore, in order to give the current knowledge state, this paper re-examines the sparse publicly available well and seismic data and literature to assess the distribution and reservoir properties of the Dinantian carbonates.Dinantian carbonate deposition occurred throughout the study area (southern onshore and offshore of the Netherlands and northern Belgium), which is situated on the northern margin of the London-Brabant Massif, progressively onlapping the latter structure. This study confirms the presence of three carbonate facies types in the study area: a Tournaisian low-gradient carbonate ramp system, succeeded by a succession in which the carbonate ramp system evolved to a rimmed shelf setting. Subsidence of the northern margin of the London-Brabant Massif resulted in a landward shift of the shallow-marine facies belts, while the formation of normal faults resulted in a 'staircase'-shaped shallow-water platform-slope-basin profile, associated with large-scale resedimentation processes. After deposition, the limestone deposits were frequently exhumed and reburied. A first period of regional exhumation occurred at the end of the Dinantian, which seems to be associated with porosity-enhancing meteoric karstification, possibly limited to the palaeo-shelf edge. The most intense alterations seem to be present as a deep leached horizon below the Cretaceous unconformity at the top of the Dinantian sequences. In addition, clear evidence for hydrothermal fluid migration is found locally, enhancing reservoir properties at some places while occluding porosity at others. The timing of these phases of hydrothermal fluid circulation is poorly understood.Whereas in the United Kingdom hydrocarbons have been produced from karstified Dinantian carbonates, this petroleum play has received little attention in the Netherlands. This paper shows that, also for the Netherlands, a karstic reservoir probably existed before the start of hydrocarbon generation from the onlapping basal Namurian shales. The hydrocarbon prospectivity of these sediments, however, is primarily controlled by the presence of both a karst-related reservoir and migration routes from a decent-quality source rock. Two geothermal projects producing from this reservoir in the southern onshore Netherlands have shown the potential of the Dinantian carbonates for ultra-deep geothermal projects. To conclude, the findings presented herein are relevant for studies of the hydrocarbon prospectivity and studies of the geothermal potential of Dinantian carbonates in the Dutch on-and offshore.

Characterizing carbonate reservoir fracturing from borehole data – A case study of the Viséan in northern Belgium

“…Carboniferous carbonates (black dots), the possible outlines of the carbonate ramp/shelf (dashed black line and blue fill). Modified after: Bless et al (1983), Muchez & Langenaeker (1993), Geluk et al (2007), Kombrink et al (2008), Van Hulten (2012 and Reijmer et al (2017). 'Heibaart' refers to the multiple wells drilled by Distrigaz (Fluxys) at Heibaart/Loenhout, of which DZH1 is one.…”

Fracture characteristics of Lower Carboniferous carbonates in northern Belgium based on FMI log analyses

“…1; Bless et al, 1981;Langenaeker, 2000;Laenen et al 2004;McCann, 2008;Deckers et al, 2019). Some of the normal faults were already active during the Devonian and/or early Carboniferous (Muchez & Langenaeker, 1993;Reijmer et al, 2017). Indications of pre-Cretaceous reverse fault movements were found near the Belgian mining area, c.30 km southeast of the MOL-GT-01 borehole (Deckers et al, 2019).…”

“…Core material, cuttings and geophysical well logs of the three boreholes provide valuable information on the Lower Carboniferous carbonates in the Campine-Brabant Basin. The primary porosity of the limestones and dolostones is generally very low, in the order of a few per cent with exceptional peaks up to 10-20% (Vandenberghe et al, 2000;Piessens et al, 2008;Reijmer et al, 2017). Therefore, fractures are of major importance for reservoir permeability.…”

Palynological indications for Silurian – earliest Devonian age strata in the Netherlands

“…However, the age of the sediments straddling the interval between the metamorphic basement and the conspicuous Lower Carboniferous platform and ramp limestones of the Zeeland Formation (see e.g. Reijmer et al, 2017) remains elusive.…”