Evaluation of the quality, thermal maturity and distribution of potential source rocks in the Danish part of the Norwegian–Danish Basin

Abstract

The quality, thermal maturity and distribution of potential source rocks within the Palaeozoic–Mesozoic succession of the Danish part of the Norwegian-Danish Basin have been evaluated on the basis of screening data from over 4000 samples from the pre-Upper Cretaceous succession in 33 wells. The Lower Palaeozoic in the basin is overmature and the Upper Cretaceous – Cenozoic strata have no petroleum generation potential, but the Toarcian marine shales of the Lower Jurassic Fjerritslev Formation (F-III, F-IV members) and the uppermost Jurassic – lowermost Cretaceous shales of the Frederikshavn Formation may qualify as potential source rocks in parts of the basin. Neither of these potential source rocks has a basinwide distribution; the present occurrence of the Lower Jurassic shales was primarily determined by regional early Middle Jurassic uplift and erosion. The generation potential of these source rocks is highly variable. The F-III and F-IV members show significant lateral changes in generation capacity, the best-developed source rocks occurring in the basin centre. The combined F-III and F-IV members in the Haldager-1, Kvols-1 and Rønde-1 wells contain 'net source-rock' thicknesses (cumulative thickness of intervals with Hydrogen Index (HI)> 200 mg HC/g TOC) of 40 m, 83 m, and 92 m, respectively, displaying average HI values of 294, 369 and 404 mg HC/g TOC. The Mors-1 well contains 123 m of 'net source rock' with an average HI of 221 mg HC/g TOC. Parts of the Frederikshavn Formation possess a petroleum generation potential in the Hyllebjerg-1, Skagen-2, Voldum-1 and Terne-1 wells, the latter well containing a c. 160 m thick highly oil-prone interval with an average HI of 478 mg HC/g TOC and maximum HI values> 500 mg HC/g TOC.The source-rock evaluation suggests that a Mesozoic petroleum system is the most likely in the study area. Two primary plays are possible: (1) the Upper Triassic – lowermost Jurassic Gassum play, and (2) the Middle Jurassic Haldager Sand play. Potential trap structures are widely distributed in the basin, most commonly associated with the flanks of salt diapirs. The plays rely on charge from the Lower Jurassic (Toarcian) or uppermost Jurassic – lowermost Cretaceous shales. Both plays have been tested with negative results, however, and failure is typically attributed to insufficient maturation (burial depth) of the source rocks. This maturation question has been investigated by analysis of vitrinite reflectance data from the study area, corrected for post-Early Cretaceous uplift. A likely depth to the top of the oil window (vitrinite reflectance = 0.6%Ro) is c. 3050–3100 m based on regional coalification curves. The Frederikshavn Formation had not been buried to this depth prior to post-Early Cretaceous exhumation, and the potential source rocks of the formation are thermally immature in terms of hydrocarbon generation. The potential source rocks of the Fjerritslev Formation are generally immature to very early mature. Mature source rocks in the Danish part of the Norwegian–Danish Basin are thus dependent on local, deeper burial to reach the required thermal maturity for oil generation. Such potential kitchen areas with mature Fjerritslev Formation source rocks may occur in the central part of the study area (central–northern Jylland), and a few places offshore. These inferred petroleum kitchens are areally restricted, mainly associated with salt structures and local grabens (such as the Fjerritslev Trough and the Himmerland Graben).

Buried pockmarks on the Top Chalk surface of the Danish North Sea and their potential significance for interpreting palaeocirculation patterns

“…The pockmarks in the study area in the southern Danish Central Graben are located in a hydrocarbon producing area. The possible source rocks that were mature for hydrocarbon generation during the Danian were the Bryne Formation and possibly the Lulu and Lola Formations (Kubala et al, 2003;Petersen et al, 2008). These source rocks covered the southern part of the Danish Central Graben (Figs.…”

“…In the Miocene the Farsund Formation source rock progressed into the light oil / condensate window, and in Pliocene it started to produce gas (Kubala et al, 2003;Andresen et al, 2008). An additional source rock potential was assigned to the Lola Formation (lower Upper Jurassic), the Lulu Formation (upper Middle Jurassic) and the Middle Jurassic Bryne Formation (Kubala et al, 2003;Petersen et al, 2008) (Fig. 3).…”

Review of hydrocarbon potential in East Denmark following 30 years of exploration activities

“…4B). But none of the investigations associated with the licences suggested mature hydrocarbons in rim Thomsen et al (1987) and Petersen et al (2008). synclines around salt structures, nor did they verify filling of structures by migrating hydrocarbons from mature source rocks in the Norwegian sector.…”

“…4B). Based on the available source rock analysis and maturity modelling it appears that only minor amounts of hydrocarbons may have been generated and expelled from Lower Jurassic shales in deep rim synclines around the salt diapirs (Petersen et al 2008).…”

An overview of 20 years’ hydrocarbon exploration studies and findings in the Late Cretaceous-to-Tertiary onshore Central Sarawak, NW Borneo: 1997–2017 in retrospect

“…The high TOC recorded in the analysed source rocks obtained from the Tanjong (68.10 wt%), Nyalau (70 wt%), Balingian (40.34wt%), and Liang (34.83 wt%) is connected with the high concentration of organic matter known to be present in coals. This notwithstanding, coals have been variously reported as functional hydrocarbon source rocks in different basins of the world (Carter and Naish 1998;Petersen and Brekke 2001;Wilkins and George 2002;Petersen et al 2004Petersen et al , 2008aAbdullah and Abolins 2006;Petersen 2006;Petersen and Nytoft 2006;Cardott et al 2015;Carvajal-Ortiz and Gentzis 2015;Daher et al 2015;Uguna et al 2015;Wang et al 2015;Xuanjun et al 2015;Pan et al 2016;Zou 2017), although an additional care should be put into consideration in assessing coals as a petroleum source rock (Sykes and Snowdon 2002). The onshore Sarawak coals have been reported to be rich in nitrogen, sulfur, and oxygen (NSO) compounds Abdullah 2011, 2012a, b;Sia et al 2014) and other potentially hazardous metallic materials that may not only influence the quality (API rating) of generated oil and gas but also pose possible dangers on the environment during production.…”