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Tor Austad - One of the best experts on this subject based on the ideXlab platform.
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wettability alteration and improved oil recovery by spontaneous imbibition of seawater into Chalk impact of the potential determining ions ca2 mg2 and so42
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Peimao Zhang, Medad T Tweheyo, Tor AustadAbstract:Abstract Carbonate wettability is dictated by the surface chemistry related to stability of the water film between the oil phase and the rock surface. It has been verified, both in the field and laboratory, that seawater is an excellent injection fluid to enhance the oil recovery from fractured Chalk. The objective of different papers in this series has been to understand the chemistry for improved spontaneous imbibition of seawater into low permeable Chalk at low water wetness. Improved spontaneous imbibition of water will take place if the Chalk becomes more water-wet during the production phase. The potential determining ions present in seawater, Ca2+ and SO42−, have great influence on the surface charge of Chalk, which can modify the wettability during water injection. In the present study, it was verified that Mg2+ is another strong potential determining ion towards Chalk, which can increase the positive surface charge density. At high temperatures, Mg2+ can even substitute Ca2+ from the Chalk surface, and the degree of substitution increased as the temperature increased. The interplay between the three potential determining ions: Ca2+, Mg2+ and SO42− and the Chalk surface with the aim to improve the water wetness of biogenic Chalk, was studied from a spontaneous imbibition point of view. To improve water wetness, SO42− must act together with either Ca2+ or Mg2+. In both cases, the efficiency increased as the temperature increased. The water wetness of Chalk can be improved if some of the carboxylic material adsorbed onto the Chalk surface is displaced. A chemical mechanism discussing the mutual interaction between the potential determining ions and the Chalk surface is proposed.
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Wettability alternation in Chalk 8. Thermally induced spontaneous imbibition of water into oil-wet Chalk at elevated temperatures
Journal of Petroleum Science and Engineering, 2001Co-Authors: Dag Chun Standnes, Eli J. Høgnesen, Tor AustadAbstract:Wettability alternation in Chalk 8. Thermally induced spontaneous imbibition of water into oil-wet Chalk at elevated temperatures
P. Rosier - One of the best experts on this subject based on the ideXlab platform.
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The impact of broadleaved woodland on water resources in lowland UK: III. The results from Black Wood and Bridgets Farm compared with those from other woodland and grassland sites
Hydrology and Earth System Sciences Discussions, 2005Co-Authors: J. Roberts, P. RosierAbstract:In the United Kingdom the planting of broadleaved woodland has led to concerns about the impact on water resources. Comparative studies, typically using soil water measurements, have been established to compare water use of broadleaved woodland and grassland. The diversity of outcomes from these studies makes it difficult to make any consistent prediction of the hydrological impact of afforestation. Most studies have shown greater drying of soils under broadleaved woodland than under grass. However, two studies in a beech wood growing on shallow soils above Chalk at Black Wood, Micheldever, Hampshire showed little overall difference between broadleaved woodland and grass, either in soil water abstraction or in evaporation. Two factors are thought to contribute to the different results from Black Wood. It is known that evaporation can be considerably enhanced at the edges of woodlands or in small areas of woodlands. The studies at Black Wood were made well within a large area of fairly uniform woodland. Other studies in which a difference occurred in soil drying between broadleaved woodland and grass used measurements made in small areas of woodlands or at woodland edges. Another important difference between comparison of woodland at Black Wood and grassland growing nearby, also on shallow soils above Chalk, compared to other broadleaved woodland/grass comparisons, growing on other geologies, is the influence of the Chalk. Although vegetation such as grass (and woodland) does not populate the Chalk profusely with roots, water can be removed from the Chalk by the roots which proliferate at the soil/Chalk interface and which can generate upward water movement within the Chalk. Published work showed that only in a very dry summer did the evaporation from grass growing on shallow soils above Chalk fall below potential. In broadleaved woodland/grass comparisons on non-Chalky soils it is possible that moisture deficits in the soil below the grass may reach critical levels and reduce evaporation below that of the woodland with which it is being compared.
Peter Japsen - One of the best experts on this subject based on the ideXlab platform.
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regional velocity depth anomalies north sea Chalk a record of overpressure and neogene uplift and erosion
AAPG Bulletin, 1998Co-Authors: Peter JapsenAbstract:A normal velocity-depth trend for the Upper Cretaceous-Danian Chalk Group is determined by identifying interval-velocity data that represent maximum burial in areas unaffected by overpressuring; these data are derived from 845 wells throughout the North Sea Basin. Data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths. Positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the North Sea Basin, and reflect regional Neogene uplift and erosion of up to 1 km along the present-day limit of the Chalk. A hiatus at the base of the Quaternary increases in magnitude away from the basin center, where a complete Cenozoic succession is found. This hiatus is consistent in size with the missing section estimated from Chalk velocities when allowance is made for the Quaternary reburial of the Chalk. Negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the Chalk exceed 10 MPa, equivalent to a burial anomaly greater than 1 km relative to the normal trend. The Chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden; therefore, the Chalk is considered to represent a regional aquitard, and the hydrodynamic model of long-distance migration within the Chalk is rejected. The Neogene uplift and erosion of the margins of the North Sea Basin and the rapid, late Cenozoic subsidence of its center fit into a pattern of late Cenozoic vertical movements around the North Atlantic.
Ida Lykke Fabricius - One of the best experts on this subject based on the ideXlab platform.
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New insight into the microtexture of Chalks from NMR analysis.
Marine and Petroleum Geology, 2016Co-Authors: Ophelie Faÿ-gomord, Ida Lykke Fabricius, Jeroen Soete, Konstantina Katika, Serge Galaup, Bruno Caline, Fanny Descamps, Eric Lasseur, Jessica Saïag, Rudy SwennenAbstract:An integrated petrographical and petrophysical study was carried out on a set of 35 outcrop Chalk samples, covering a wide range of lithologies and textures. In this study various Chalk rock-types have been characterized, in terms of microtextures and porous network, by integrating both geological, sediment-petrological and petrophysical data, including porosity, permeability, low-field NMR (Nuclear Magnetic Resonance), MICP and specific surface area (BET) measurements. The data allow an in depth understanding of the NMR signal of Chalks, with a focus on tight Chalks, including all low reservoir quality Chalks independently of their sedimentological and/or diagenetic history. The study aims to develop an NMR-based approach to characterize a broad range of Chalk samples. The provided laboratory low-field NMR Chalk classification can be used as a guide to interpret NMR logging data. Based on the petrographical and petrophysical analysis, 6 groups of samples were identified, each of them characterized by a unique NMR signature: (1) micritic Chalks, (2) grainy Chalks, (3) cemented Chalks, (4) marl-seam Chalks, (5) argillaceous Chalks and (6) silicified Chalk. NMR T2 distributions were linked to pore body size and T2 logarithmic (T2lm) was calculated. It is apparent that tight Chalks, whether their characteristics are sedimentological or diagenetic, yield smaller pore body sizes (T2lm < 20 ms), as well as narrower pore throats (average radius < 150 nm) and lower permeability values (typically below 0.2 mD). Grainy Chalks possess T2 distributions reflecting larger pore sizes (T2lm > 60 ms) and pore throats (average radius > 290 nm) and higher permeabilities (up to 13 mD). The marl-seam Chalk samples yield bimodal T2 distributions, with a first peak related to the micritic matrix pores and a second peak related to intraparticle pores within fossils. For all samples, permeability was inferred from NMR spectra using SDR (Schlumberger Doll Research) model.
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New insight into the microtexture of Chalks from NMR analysis
Marine and Petroleum Geology, 2016Co-Authors: Ophelie Faÿ-gomord, Ida Lykke Fabricius, Jeroen Soete, Konstantina Katika, Serge Galaup, Bruno Caline, Fanny Descamps, Eric Lasseur, Jessica Saïag, Rudy SwennenAbstract:An integrated petrographical and petrophysical study was carried out on a set of 35 outcrop Chalk samples, covering a wide range of lithologies and textures. In this study various Chalk rock-types have been characterized, in terms of microtextures and porous network, by integrating both geological, sediment-petrological and petrophysical data, including porosity, permeability, low-field NMR (Nuclear Magnetic Resonance), MICP and specific surface area (BET) measurements. The data allow an in depth understanding of the NMR signal of Chalks, with a focus on tight Chalks, including all low reservoir quality Chalks independently of their sedimentological and/or diagenetic history. The study aims to develop an NMR-based approach to characterize a broad range of Chalk samples. The provided laboratory low-field NMR Chalk classification can be used as a guide to interpret NMR logging data. Based on the petrographical and petrophysical analysis, 6 groups of samples were identified, each of them characterized by a unique NMR signature: (1) micritic Chalks, (2) grainy Chalks, (3) cemented Chalks, (4) marl-seam Chalks, (5) argillaceous Chalks and (6) silicified Chalk. NMR T2 distributions were linked to pore body size and T2 logarithmic (T2lm) was calculated. It is apparent that tight Chalks, whether their characteristics are sedimentological or diagenetic, yield smaller pore body sizes (T2lm 60 ms) and pore throats (average radius > 290 nm) and higher permeabilities (up to 13 mD). The marl-seam Chalk samples yield bimodal T2 distributions, with a first peak related to the micritic matrix pores and a second peak related to intraparticle pores within fossils. For all samples, permeability was inferred from NMR spectra using SDR (Schlumberger Doll Research) model.
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Porosity and sonic velocity depth trends of Eocene Chalk in Atlantic Ocean: Influence of effective stress and temperature
Journal of Petroleum Science and Engineering, 2014Co-Authors: Ahmed Awadalkarim, Ida Lykke FabriciusAbstract:Abstract We aimed to relate changes in porosity and sonic velocity data, measured on water-saturated Eocene Chalks from 36 Ocean Drilling Program drill sites in the Atlantic Ocean, to vertical effective stress and thermal maturity. We considered only Chalk of Eocene age to avoid possible influence of geological age on Chalk compaction trends. For each depth, vertical effective stresses as defined by Terzaghi and by Biot were calculated. We used bottom-hole temperature data to calculate the time–temperature index of thermal maturity (TTI) as defined by Lopatin. Porosity and compressional wave velocity data were correlated to vertical effective stresses and to TTI. Our porosity data showed a broader porosity trend in the mechanical compaction zone, and the onset of the formation of limestone at a shallower burial depth than the porosity data of the Ontong Java Plateau Chalk show. Our porosity data do not show or at least it is difficult to define a clear pore-stiffening contact cementation trend as the Ontong Java Plateau Chalk. Mechanical compaction is the principal cause of porosity reduction (at shallow depths) in the studied Eocene Chalk, at least down to about 5 MPa Terzaghi׳s effective stress corresponding to a porosity of about 35%. This indicates that mechanical compaction is the principal agent of porosity reduction. Conversely, at deeper levels, porosity reduction is accompanied by a large increase in sonic velocity indicating pore-filling cementation. These deep changes are correlated with TTI. This indicates pore-filling cementation via an activation energy mechanism. We proposed a predictive equation for porosity reduction with burial stress. This equation is relevant for basin analysis and hydrocarbon exploration to predict porosity if sonic velocity data for subsurface Chalk is available.
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Chalk as a Reservoir
74th EAGE Conference and Exhibition - Workshops, 2012Co-Authors: Ida Lykke FabriciusAbstract:Reservoir properties of Chalk depend on the primary sediment composition as well as on subsequent diagenesis and tectonic events. Chalks of the North Sea almost exclusively have mudstone or wackestone texture. Microfossils may have retained their porosity where degree of diagenesis is low, or be partly or fully cemented where diagenesis is more pronounced. It is a Chalk characteristic that permea bility is controlled by the porosity and internal surface of the mud matrix, whereas the larger pores play an insignificant role. Cemented microfossils may take up a significant volume in a wackestone, and the best reservoir properties are typically found in mudstone intervals.
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Engineering properties of Chalk related to diagenetic variations of Upper Cretaceous onshore and offshore Chalk in the North Sea area
Journal of Petroleum Science and Engineering, 2009Co-Authors: M.l. Hjuler, Ida Lykke FabriciusAbstract:Abstract Predicting properties of reservoir Chalk involve testing and modelling of easily obtainable outcrop Chalk. However, variations in onshore and offshore Chalk properties will expectedly occur due to different diagenetic history. Understanding diagenetic mechanisms and their consequences are thus a key issue when reservoir Chalk characterization is based on outcrop Chalk. In Chalk of the Valhall field high pore pressure and hydrocarbon presence have counteracted recrystallization and cementation and preserved high porosity despite a burial depth of c. 3 km. As a consequence inter-particle connections are poorly developed and Valhall Chalk is expectedly geomechanically weak. Similar high porosity and weak consolidation were observed in Danish outcrop Chalk which expectedly will match the Valhall samples geomechanically. In Chalk of the Dan, South Arne and Ekofisk fields recrystallization and cementation features are significantly better developed compared to the Valhall field. Calcite redistribution has strengthened particle contacts and reduced porosity, assumingly providing a geomechanically stronger Chalk. Similar low porosity and well-developed recrystallization and cementation features are found in English Chalk which from a geomechanical point of view may share characteristics with Chalk of the Dan, South Arne and Ekofisk fields. Matrix permeability is related not only to porosity but also to specific surface area of Chalk which is controlled partly by calcite recrystallization partly by type and amount of non-carbonate minerals. In onshore Chalk significant mineralogical differences are reflected in varying specific surface area. In contrast, specific surface area of Upper Cretaceous reservoir Chalk show little variation indicating that care must be taken when choosing an outcrop Chalk as substitute for reservoir Chalk during flooding experiments.
J. Roberts - One of the best experts on this subject based on the ideXlab platform.
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The impact of broadleaved woodland on water resources in lowland UK: III. The results from Black Wood and Bridgets Farm compared with those from other woodland and grassland sites
Hydrology and Earth System Sciences Discussions, 2005Co-Authors: J. Roberts, P. RosierAbstract:In the United Kingdom the planting of broadleaved woodland has led to concerns about the impact on water resources. Comparative studies, typically using soil water measurements, have been established to compare water use of broadleaved woodland and grassland. The diversity of outcomes from these studies makes it difficult to make any consistent prediction of the hydrological impact of afforestation. Most studies have shown greater drying of soils under broadleaved woodland than under grass. However, two studies in a beech wood growing on shallow soils above Chalk at Black Wood, Micheldever, Hampshire showed little overall difference between broadleaved woodland and grass, either in soil water abstraction or in evaporation. Two factors are thought to contribute to the different results from Black Wood. It is known that evaporation can be considerably enhanced at the edges of woodlands or in small areas of woodlands. The studies at Black Wood were made well within a large area of fairly uniform woodland. Other studies in which a difference occurred in soil drying between broadleaved woodland and grass used measurements made in small areas of woodlands or at woodland edges. Another important difference between comparison of woodland at Black Wood and grassland growing nearby, also on shallow soils above Chalk, compared to other broadleaved woodland/grass comparisons, growing on other geologies, is the influence of the Chalk. Although vegetation such as grass (and woodland) does not populate the Chalk profusely with roots, water can be removed from the Chalk by the roots which proliferate at the soil/Chalk interface and which can generate upward water movement within the Chalk. Published work showed that only in a very dry summer did the evaporation from grass growing on shallow soils above Chalk fall below potential. In broadleaved woodland/grass comparisons on non-Chalky soils it is possible that moisture deficits in the soil below the grass may reach critical levels and reduce evaporation below that of the woodland with which it is being compared.