Controls on halogen concentrations in sedimentary formation waters

AbstractChlorine is the most abundant halogen in sedimentary formation waters with concentrations from &lt;100 to &gt;250000 mg/l. Bromine is the second most abundant halogen at &lt;1 mg/l to &gt;6000 mg/l with iodine from &lt;0.1 mg/l to &gt;100 mg/l and fluorine from &lt;0.1 mg/l to 30 mg/l. Chlorine and bromine show a strong systematic covariation suggesting that they are subject to the same controlling mechanisms. Fluorine only shows relatively high concentrations at elevated chlorine and bromine concentrations showing that fluorine, chlorine and bromine are possibly controlled by the same processes. Iodine does not correlate with any of the other halogens indicating that unique processes control iodine.Key geological parameters that influence chlorine and bromine (and possibly fluorine) concentrations are the presence of salt in a basin, the age of the reservoir unit and the kerogen-type within the main hydrocarbon source rock in a basin. The presence of salt in a basin shows that sea water was evaporated to halite saturation producing connate waters with high concentrations of chlorine and bromine. The presence of salt also leads to high salinity waters through water-salt interaction during burial and diagenesis. Tertiary reservoirs typically have much lower chlorine and bromine concentrations than Mesozoic or Palaeozoic reservoirs. The age of the reservoir unit may simply reflect the different amounts of time available for formation water to interact with salt. The dominance of type II marine kerogen in a basin leads to higher bromine concentrations. This may reflect the dominance of a marine influence in a basin which is more likely to lead to salt deposition than terrestrial depositional environments. Iodine concentrations are independent of all these parameters. Other geological parameters such as depth of burial, temperature, basin forming mechanism and reservoir lithology have no influence upon halogen concentrations.Key processes that affect halogen concentrations are sea water evaporation and dilution, water—salt interaction and input from organic sources. Chlorine and bromine data lie close to the experimentally-derived sea water evaporation trend showing that sea water evaporation may be an important general control on halogens. Sea water dilution is probably responsible for most low salinity formation water chlorine and bromine concentrations for the same reason. Sea water dilution can occur either by meteoric invasion during burial, or following uplift and erosion, or by diagenetic dehydration reactions. Water can interact with salt in a variety of ways: halite dissolution by congruent processes, halite recrystallization by incongruent processes, sylvite dissolution or recrystallization and halite fluid inclusion rupture. Halite dissolution will lead to high chlorine and relatively low bromine waters because halite contains little bromine. In contrast, halite recrystallization will lead to bromine-enhanced waters because NaBr dissolves preferentially to NaCl. The occurrence of dissolution or recrystallization will depend on the water rock ratio, greater volumes of water will lead to more dissolution and waters with higher Cl/Br ratios. Sylvite is usually rich in bromine so dissolution will lead to bromine-enhanced waters. Primary aqueous inclusions in halite contain high bromine concentrations so that rupture, during deformation or recrystallization, will lead to bromine-enhanced formation water. A combination of these processes are responsible for the very limited range of Cl/Br ratios although congruent halite dissolution must have a limited role due to the absence of waters with high Cl/Br ratios.Iodine is strongly concentrated in organic materials in the marine environment; oils and organic rich-source rocks have high I/Cl and I/Br ratios relative to sea water or evaporated sea water. All formation waters are enriched in iodine relative to sea water implying that there has been input from organic matter or interaction with oil. However, hydrocarbon source rock type in a basin has no discernible effect upon iodine concentrations.</jats:p

Groundwater compartmentalisation: a water table height and geochemical analysis of the structural controls on the subdivision of a major aquifer, the Sherwood Sandstone, Merseyside, UK

International audienceCompartmentalisation, the subdivision of an aquifer into discrete and relatively isolated units, may be of critical importance for the protection of groundwater although it has been largely ignored in the groundwater literature. The Lower Triassic Sherwood Sandstone, in north west of England, UK, may be a good example of an aquifer that has been compartmentalised by numerous high angle faults with displacements of up to 300 m. The study was initiated to assess the local groundwater flow, the extent of seawater invasion and the controls on recharge in the aquifer and to try to understand whether the aquifer is broken into discrete compartments. Maps and schematic cross-sections of groundwater heads for the years 1993, and 2002 were prepared to trace any structural controls on the groundwater heads across the area. Studying the contour maps and cross sections revealed that: 1) there are substantial differences in groundwater head across some of the NNW-SSE trending faults implying that groundwater flow is strongly limited by faults, 2) an anticline in the east of the area acts as a groundwater divide and 3) the groundwater head seems to follow the topography in some places, although steep changes in groundwater head occur across faults showing that they locally control the groundwater head. The aquifer was thus provisionally subdivided into several hydrogeological sub-basins based on groundwater head patterns and the occurrence of major structural features (faults and a fold). Using groundwater geochemistry data, contour maps of chloride and sulphate concentration largely support the structural sub-division of the area into hydrogeological sub-basins. Scrutiny of groundwater geochemical data, averaged for each sub-basin, confirmed the degree of compartmentalisation and the occurrence of sealed faults. The variation of the geochemical composition of the groundwater not only relates to the different, localised geochemical processes and seawater intrusion but also relates to compartmentalisation due to faulting. Faults have limited the degree of mixing between the groundwater types thus retaining the specific characteristics of each sub-basin. Highly localised seawater intrusion is mainly controlled by low permeability fault close to the Irish Sea and Mersey estuary. There is effectively no invasion of seawater beyond the faults that lie closest to the coastline. Freshwater recharge to the aquifer seems to be highly localised and mainly occurs by vertical percolation of rain and surface water rather than whole aquifer-scale groundwater flow. This study provides a detailed understanding of the groundwater flow processes in Liverpool as an example of methods can be applied to groundwater management elsewhere

A nonlinear cointegration approach with applications to structural health monitoring

One major obstacle to the implementation of structural health monitoring (SHM) is the effect of operational and environmental variabilities, which may corrupt the signal of structural degradation. Recently, an approach inspired from the community of econometrics, called cointegration, has been employed to eliminate the adverse influence from operational and environmental changes and still maintain sensitivity to structural damage. However, the linear nature of cointegration may limit its application when confronting nonlinear relations between system responses. This paper proposes a nonlinear cointegration method based on Gaussian process regression (GPR); the method is constructed under the Engle-Granger framework, and tests for unit root processes are conducted both before and after the GPR is applied. The proposed approach is examined with real engineering data from the monitoring of the Z24 Bridge

High-performance thermionic converter Quarterly progress report, 13 Nov. 1965 - 13 Feb. 1966

Stability and optimization parameters of cesium vapor thermionic converters studied in high performance long life equipment fabrication projec

Groundwater compartmentalisation: a geochemical analysis of the structural controls on the subdivision of a major aquifer, the Sherwood Sandstone, Merseyside, UK

International audienceThe study was initiated to assess the local groundwater flow, the extent of seawater invasion and the controls on recharge in the aquifer and to try to understand whether the aquifer is broken into discrete compartments. The study area is located in the northwest of England and encompasses the urban area of Liverpool and surrounding countryside and extends east-west from Liverpool to Widnes and as far north as Formby. The Irish Sea marks the western margin of the area while the Mersey estuary defines the southern margin. The Triassic sandstone in this area has been, and remains, an important aquifer although industrialisation and groundwater exploitation have led to significant water quality problems. Maps of water table for the years 1993, 1997, 2000 and 2002 and schematic cross-sections of the water table height along the faults were prepared to trace any effect of these faults on water table height across. Studying the water table maps and cross sections revealed that: 1) there are substantial differences in water table height across some of the NNW-SSE trending faults implying that groundwater flow is strongly limited by fault, 2) an anticline in the east of the area acts as a groundwater divide and 3) the water table seems to follow the topography in some places, although steep changes in water table occur across faults showings that they locally control the water table elevation. The aquifer was thus provisionally subdivided into several hydrogeological sub-basins based on water table height patterns and the occurrence of major structural features (faults and a fold). Using groundwater geochemistry data, contour maps of chloride and sulphate concentration largely support the structural sub-division of the area into hydrogeological sub-basins. Scrutiny of groundwater geochemical data, averaged for each sub-basin, confirmed the degree of compartmentalisation and the occurrence of sealed faults. The variation of the geochemical composition of the groundwater not only relates to the different, localised geochemical processes and seawater intrusion but also relate to compartmentalisation due to faulting. Faults have limited the degree of mixing between the groundwater types thus retaining the specific characteristics of each sub-basin. Highly localised seawater intrusion is mainly controlled by low permeability fault close to the Irish Sea and Mersey estuary. There is no effectively no invasion of seawater beyond the faults that lie closest to the coastline. Freshwater recharge to the aquifer must be highly localised and will mainly occur by vertical percolation of rain and surface water rather than whole aquifer-scale groundwater flow

Satellite data interpretation of causes and controls on groundwater-seawater flow directions, Merseyside, UK: implications for assessing saline intrusions

International audienceGroundwater in the Triassic Sherwood Sandstone aquifer, Liverpool, UK, has locally elevated chloride concentrations (~4000 mg/l) in parts of the coastal region although there is freshwater right up to the coast line in other areas. The aquifer is cut my numerous faults with vertical displacements of as much 300 m. SPOT satellite data have been used for the Merseyside area of Liverpool. The satellite data revealed and confirmed the location of some of the main faults since the fault zones of the aquifer have low permeability (due to grain crushing, cataclasis, and clay smearing). Where fault zones outcrop at the surface, below the well-developed regolith, there is locally elevated soil water and thus anomalous vegetation patterns in comparison to unfaulted and highly porous aquifer. The ability to identify fault zones by this satellite-based method strongly suggests that they are at least partially sealing, sub-vertical features in the aquifer. Digitally enhanced and processed satellite data were used to define the relative proportions of sand and clay in the near-coastal (inter-tidal) part of the Mersey estuary. Sand-dominated sediment has higher pixel values in comparison with clay deposits in the near infrared spectral region (NIR). Where open and weathered fault rocks crop out at the surface near the intertidal zone, water movement in these potential surface water conduits is limited where the intertidal zone is clay-dominated since clay will plug the conduit. Where these weathered and open fault-rocks crop out against sand-dominated parts of the coastline, fresh water outflux into the seawater has been imaged using the satellite data. Furthermore, the high and low chloride concentration parts of the aquifer are separated by major, sub-vertical fault zones and have allowed a very steep water table gradient to remain in the aquifer

Animal-sediment interactions: the effect of ingestion and excretion by worms on mineralogy

International audienceBy controlled experiments that simulate marine depositional environments, it is shown that accelerated weathering and clay mineral authigenesis occur during the combined process of ingestion, digestion and excretion of fine-grained sediment by two species of annelid worms. Previously characterized synthetic mud was created using finely ground, low-grade metamorphic slate (temperature approximately 300°C) containing highly crystalline chlorite and muscovite. This was added to experiment and control tanks along with clean, wind-blown sand. Faecal casts were collected at regular intervals from the experimental tanks and, less frequently, from the control tanks. Over a period of many months the synthetic mud (slate) proved to be unchanged in the control tanks, but was significantly different in faecal casts from the experimental tanks that contained the worms Arenicola marina and Lumbricus terrestris. Chlorite was preferentially destroyed during digestion in the gut of A. marina. Both chlorite and muscovite underwent XRD peak broadening with a skew developing towards higher lattice spacing, characteristic of smectite formation. A neoformed Fe-Mg-rich clay mineral (possibly berthierine) and as-yet undefined clay minerals with very high d-spacing were detected in both A. marina and L. terrestris cast samples. We postulate that a combination of the low pH and bacteria-rich microenvironment in the guts of annelid worms may radically accelerate mineral dissolution and clay mineral precipitation processes during digestion. These results show that macrobiotic activity significantly accelerates weathering and mineral degradation as well as mineral authigenesis. The combined processes of sediment ingestion and digestion thus lead to early diagenetic growth of clay minerals in clastic sediments

Damage and repair classification in reinforced concrete beams using frequency domain data

This research aims at developing a new vibration-based damage classification technique that can efficiently be applied to a real-time large data. Statistical pattern recognition paradigm is relevant to perform a reliable site-location damage diagnosis system. By adopting such paradigm, the finite element and other inverse models with their intensive computations, corrections and inherent inaccuracies can be avoided. In this research, a two-stage combination between principal component analysis and Karhunen-Loéve transformation (also known as canonical correlation analysis) was proposed as a statistical-based damage classification technique. Vibration measurements from frequency domain were tested as possible damage-sensitive features. The performance of the proposed system was tested and verified on real vibration measurements collected from five laboratory-scale reinforced concrete beams modelled with various ranges of defects. The results of the system helped in distinguishing between normal and damaged patterns in structural vibration data. Most importantly, the system further dissected reasonably each main damage group into subgroups according to their severity of damage. Its efficiency was conclusively proved on data from both frequency response functions and response-only functions. The outcomes of this two-stage system showed a realistic detection and classification and outperform results from the principal component analysis-only. The success of this classification model is substantially tenable because the observed clusters come from well-controlled and known state conditions