Henrik Nygaard Hansen

• Alain, Lucie; Eide, Christian Haug; Hansen, Henrik Nygaard; Scotti, Agustin Arguello; Shukla, Monika & Oftedal, Bjørn Terje [Show all 8 contributors for this article] (2026). Sedimentological controls on the distribution and geometry of chlorite-coated intervals in deeply buried tide-influenced sandstones, Tilje Formation, Norwegian Continental Shelf. Sedimentology. ISSN 0037-0746. doi: 10.1111/sed.70095. Full text in Research Archive
• Hansen, Henrik Nygaard; Haile, Beyene Girma; Müller, Reidar & Jahren, Jens (2022). New direction for regional reservoir quality prediction using machine learning - Example from the Stø Formation, SW Barents Sea, Norway. Journal of Petroleum Science and Engineering. ISSN 0920-4105. 220. doi: 10.1016/j.petrol.2022.111149. Full text in Research Archive Show summary

  Recently, the petroleum industry has focused on deeply buried reservoir discoveries and exploring potential CO2 storage sites close to existing infrastructure to increase the life span of already operating installations to save time and cost. It is therefore essential for the petroleum industry to find an innovative approach that exploits the existing core- and well log data to be successful in their endeavor of effectively characterizing and predicting reservoir quality. Continuous data sources (e.g. wireline logs) have a huge potential compared with expensive, time inefficient and sporadic data from cores in determining reservoir quality for use in a regional context. However, whereas core analysis offers in-depth knowledge about rock properties and diagenetic processes, continuous data sources can be difficult to interpret without a formation-specific framework. Here, we demonstrated how the pre-existing core data could be effectively used by integrating petrographic- and facies data with a pure predictive machine learning (ML) based porosity predictor. The inclusion of detailed core analysis is important for determining which reservoir parameter(s) that should be modeled and for the interpretation of model outputs. By applying this methodology, a framework for deducing lithological and diagenetic attributes can be established to aid reservoir quality delineation from wireline logs that can be used in frontier areas. With the ML porosity model, a Random Forest Regressor, the square of the correlation was 0.84 between predicted- and helium porosity test data over a large dataset consisting of 38 wells within the Stø Formation across the SW Barents Sea. By integrating the continuous ML porosity logs and core data, it was possible to differentiate three distinct bed types on wireline log responses within the Stø Formation. Particularly, the relationship between Gamma ray (GR) and porosity was effective in separating high porosity clean sand-, low porosity cemented clean sand and more clay and silt rich intervals. Additionally, in the P-wave velocity (VP) - density domain, separation of high porosity clean sand- and heavily cemented low porosity clean sand intervals were possible. The results also show that the ML derived porosity curves coincide with previously published and independent facies data from a selection of the wells included in the study. This demonstrates the applicability of the model in the region, because the Stø Formation has been described to exhibit similar lithological- and mineralogical properties over large parts of the Western Barents Sea area. Even though, continuous porosity data could be estimated from other sources like VP, neutron or density logs, this would generally require matrix and fluid information. This study demonstrated the effectiveness of the ML model in generating continuous porosity logs that are useful for characterizing and predicting reservoir properties in new wells. This methodology offers a workflow for exploiting already acquired core and well log data for frontier exploration that can be adapted to other formations and exploration scenarios worldwide.

• Haile, Beyene Girma; Hansen, Henrik Nygaard; Aagaard, Per & Jahren, Jens (2022). How do chlorite coatings form on quartz surface? Journal of Petroleum Science and Engineering. ISSN 0920-4105. 215. doi: 10.1016/j.petrol.2022.110682. Full text in Research Archive Show summary

  Chlorite-coats on quartz surfaces are ubiquitous in various sedimentary environments. Chlorite-coats shield the surface of quartz from quartz cement overgrowths, thus preserving anomalously high porosity in deeply buried sandstone reservoirs. The inhibition of the quartz cement implies that the chlorite-coats on the surface of quartz grains can significantly influence the physicochemical behavior of the quartz grains. Therefore, failure to notice the initial thin microscale coatings forming during deposition can have serious consequences for modeling several geochemical reactions occurring at liquid-solid interfaces. Despite this huge implication, the fundamental mechanisms involved in chlorite-coat formation is not well understood. Here we present an experimental study to determine the parameters that control chlorite-coat formation on the surface of quartz grains. The batch experiments were conducted in a concoction of quartz and chlorite under different conditions of ionic strength, pH, and presence of humic acid (HA), iron- (Fe) and aluminum (Al) oxides). HA, Fe- and Al oxides are suggested to aid the emplacement of chlorite-coat precursors. At pH 7, the quartz–chlorite and quartz–chlorite–Fe/Al-oxides mixing experiments performed in saline and non-saline solution result in equal chlorite-coat coverages, suggesting neither salinity nor Fe and Al-oxides explain the mechanisms of chlorite-coat formation. At pH 5 and 9, however the chlorite-coat coverage was superior only in saline solution, indicating differences in coat coverage may be caused by variable electrokinetic charge distribution due to the distribution and transport of dissolved salt. The chlorite-coat barely formed in experiments that contain HA in quartz–chlorite mixtures regardless of ionic strength and pH. Against a long-standing notion, the presence of organic matter cannot necessarily be prerequisites for binding chlorite on the surface of quartz grains. The dynamic interactions between solution chemistry and surface chemistry of solid phases (quartz, chlorite, HA, Fe and Al oxides) can result in changing the electrokinetic properties in a region near the solid phases and at mineral-solution interfaces. We therefore propose that the electrokinetic response that arises in heterogeneous systems may explain the mechanisms of chlorite-coat formation.

• Løvstad, Kristoffer; Hansen, Henrik Nygaard & Jahren, Jens Sigurd (2021). The porosity preserving effect of basin wide illitic coating in deeply buried sandstone intervals of the lower Jurassic Stø Formation, Barents Sea. Marine and Petroleum Geology. ISSN 0264-8172. 137. doi: 10.1016/j.marpetgeo.2021.105498. Full text in Research Archive Show summary

  The Stø Formation contains the main target reservoirs for petroleum exploration in the Norwegian Barents Sea Area, however, the clean sandstones of the Stø Formation can be heavily quartz cemented in areas that have undergone extensive post depositional burial. The Stø Formation in well 7219/8-2 has previously been identified as having porosities well above the expected porosity depth trend due to the porosity preserving effects of illitic grain coating. In this study the Stø Formation in 14 wells with maximum burial depths at top of formation ranging from 2672 to 3623 m have been investigated and several new intervals of the formation show abnormally high porosities relative to the expected burial trend. Thin sections from 4 wells were available and in all of these remnants of grain coating illitic clay was observed in varying amounts, with the effectiveness in reducing quartz cement overgrowth being determined by the continuity of grain coats. This indicates that the degree of grain coating coverage exerts the main control on the porosity of the clean deeply buried parts of the Stø Formation. With increasing burial depths, the porosity difference between intervals with continuous grain coats and intervals with less continuous grain coats becomes ever larger. Intervals observed to have extensive grain coating coverage compact with a significantly reduced rate with increasing burial compared to poorer coated intervals in the chemical compaction domain. The noticeable and consistent difference in the chemical compaction trend between coated- and negligible coated intervals within the Stø Formation could allow for establishment of powerful predictive models without the need for expensive petrographic- or core plug data.

• Hansen, Henrik Nygaard; Løvstad, Kristoffer; Lageat, Gildas; Clerc, Sylvain & Jahren, Jens Sigurd (2021). Chlorite coating patterns and reservoir quality in deep marine depositional systems – Example from the Cretaceous Agat Formation, northern North Sea Norway. Basin Research. ISSN 0950-091X. 33(5), p. 2725–2744. doi: 10.1111/bre.12581. Full text in Research Archive Show summary

  Sediment gravity flows transport large volumes of sand and clay minerals into submarine systems, which store some of the world's major reserves of oil and gas. However, knowledge about grain-coating clay mineral formation and its role in preserving reservoir quality in deep marine settings is poorly documented. Here we present a case study on the Agat Formation, a deep marine deposit interpreted as a series of turbidites, using a multimethod approach including petrographical, petrophysical and sedimentological data. This study investigates the occurrence and origin of chlorite coating and demonstrates how extensive chlorite coating substantially affects reservoir quality. The presence of green marine clay pellets suggests an initial shallow marine origin and sedimentological evidence reveals that the sediments were later remobilized by gravity flows and deposited at their present location. We suggest that the precursor clay coating was emplaced prior to sediment remobilization because of the presence of clay coating on grain contacts and all detrital components, the continuous nature of coating and the lack of clay bridges between the grains. Therefore, the origin of chlorite coating in deep marine environments may be recognized using the characteristic properties of inherited precursor clay coating. Chlorite coating thickness varies between an upper and lower sand unit, with an average of ca. 4.5 µm and ca. 24 µm, respectively. Permeability is significantly reduced in the interval with exceedingly thick chlorite coating but shows only a subtle decrease in helium porosity. This study enlightens the importance of crucially evaluating porosity in sandstones with thick chlorite coating using a multimethod approach. The results from this study can be useful in future exploration endeavours in the area and in other deep marine systems with a similar setting worldwide.

• Hansen, Henrik Nygaard; Løvstad, Kristoffer; Muller, Reidar & Jahren, Jens (2017). Clay coating preserving high porosities in deeply buried intervals of the Stø Formation. Marine and Petroleum Geology. ISSN 0264-8172. 88, p. 648–658. doi: 10.1016/j.marpetgeo.2017.09.011. Full text in Research Archive Show summary

  The Stø Formation is the most important reservoir interval in the Norwegian Barents Sea, however the reservoir quality can be highly affected by the detrimental effects of quartz cement where there have been extensive post depositional burial. Core plug data from well 7219/8-2 in the Southwestern Barents Sea shows abnormally high porosity and permeability values in certain units of the deeply buried and otherwise highly quartz cemented Stø Formation. The amount of quartz cement in the samples is inversely proportional to the porosity. Samples with high and low porosities are similar texturally and mineralogically, but the high porosity samples have a layer of illitic clay coating the majority of the detrital quartz grains. Illitic clay coating present at grain contacts can result in a lowered IGV given they aid in the dissolution of quartz at interfaces, also creating a source of dissolved silica. Clay induced dissolution means that silica saturation is not a limiting factor in quartz cementation in these samples. The results show that the illitic clay coating is capable of limiting the amount of authigenic quartz overgrowth from 20 to 23% in samples with negligible grain coating to 5–11% in the intervals with high coating coverage. The illitic clay coating inhibits quartz overgrowth by limiting the surface area available for nucleation on detrital grains. The Stø Formation comprises mainly shallow marine deposits of highly reworked clean sandstone. Abnormally high porosities appear to be linked to settings where sediments of a more proximal location are preserved without extensive reworking. The grain coating clay is illitic and most likely originates from clay infiltration processes prior to final deposition. The difference in extent of clay coating in similar facies can mostly be correlated with varying amount of post depositional reworking. This study suggests that there is a potential for considerable porosity and permeability to be preserved in deeply buried sandstones in the Barents Sea. This study could be important in the future exploration activity of deeply buried structures in the area.

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• Shukla, Monika; Hansen, Henrik Nygaard; Line, Lina Hedvig & Jahren, Jens (2024). Distribution and prediction of grain coating chlorite in tide-dominated sandstones of Tilje Formation in Halten Terrace area, Norwegian Continental Shelf: Implications for Hydrocarbon exploration. Full text in Research Archive

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