Time-lapse cross-hole electrical resistivity tomography (CHERT) for monitoring seawater intrusion dynamics in a Mediterranean aquifer

Surface electrical resistivity tomography (ERT) is a widely used tool to study seawater intrusion (SWI). It is noninvasive and offers a high spatial coverage at a low cost, but its imaging capabilities are strongly affected by decreasing resolution with depth. We conjecture that the use of CHERT (cross-hole ERT) can partly overcome these resolution limitations since the electrodes are placed at depth, which implies that the model resolution does not decrease at the depths of interest. The objective of this study is to test the CHERT for imaging the SWI and monitoring its dynamics at the Argentona site, a well-instrumented field site of a coastal alluvial aquifer located 40 km NE of Barcelona. To do so, we installed permanent electrodes around boreholes attached to the PVC pipes to perform time-lapse monitoring of the SWI on a transect perpendicular to the coastline. After 2 years of monitoring, we observe variability of SWI at different timescales: (1) natural seasonal variations and aquifer salinization that we attribute to long-term drought and (2) short-term fluctuations due to sea storms or flooding in the nearby stream during heavy rain events. The spatial imaging of bulk electrical conductivity allows us to explain non-monotonic salinity profiles in open boreholes (step-wise profiles really reflect the presence of freshwater at depth). By comparing CHERT results with traditional in situ measurements such as electrical conductivity of water samples and bulk electrical conductivity from induction logs, we conclude that CHERT is a reliable and cost-effective imaging tool for monitoring SWI dynamics

Heletz experimental site overview, characterization and data analysis for CO2 injection and geological storage

International audienceThis paper provides an overview of the site characterization work at the Heletz site, in preparation to scientifically motivated CO2 injection experiments. The outcomes are geological and hydrogeological models with associated medium properties and baseline conditions. The work has consisted on first re-analyzing the existing data base from ∼40 wells from the previous oil exploration studies, based on which a 3-dimensional structural model was constructed along with first estimates of the properties. The CO2 injection site is located on the saline edges of the Heletz depleted oil field. Two new deep (>1600 m) wells were drilled within the injection site and from these wells a detailed characterization program was carried out, including coring, core analyses, fluid sampling, geophysical logging, seismic survey, in situ hydraulic testing and measurement of the baseline pressure and temperature. The results are presented and discussed in terms of characteristics of the reservoir and cap-rock, the mineralogy, water composition and other baseline conditions, porosity, permeability, capillary pressure and relative permeability. Special emphasis is given to petrophysical properties of the reservoir and the seal, such as comparing the estimates determined by different methods, looking at their geostatistical distributions as well as changes in them when exposed to CO2

Costa Rica Rift hole deepened and logged

During Leg 111 of the Ocean Drilling Program, scientists on the drilling vessel JOIDES Resolution studied crustal structure and hydrothermal processes in the eastern equatorial Pacific. Leg 111 spent 43 days on its primary objective, deepening and logging Hole 5048, a deep reference hole in 5.9-million-year-old crust 200 km south of the spreading axis of the Costa Rica Rift. Even before Leg 111 , Hole 5048 was the deepest hole drilled into the oceanic crust, penetrating 274.5 m of sediments and 1,075.5 m of pillow lavas and sheeted dikes to a total depth of 1,350 m below sea floor (mbsf). Leg 111 deepened the hole by 212.3 m to a total depth of 1,562.3 mbsf (1,287.8 m into basement), and completed a highly successful suite of geophysical logs and experiments, including sampling of borehole waters

Mechanisms of NK Cell-Macrophage Bacillus anthracis Crosstalk: A Balance between Stimulation by Spores and Differential Disruption by Toxins

NK cells are important immune effectors for preventing microbial invasion and dissemination, through natural cytotoxicity and cytokine secretion. Bacillus anthracis spores can efficiently drive IFN-γ production by NK cells. The present study provides insights into the mechanisms of cytokine and cellular signaling that underlie the process of NK-cell activation by B. anthracis and the bacterial strategies to subvert and evade this response. Infection with non-toxigenic encapsulated B. anthracis induced recruitment of NK cells and macrophages into the mouse draining lymph node. Production of edema (ET) or lethal (LT) toxin during infection impaired this cellular recruitment. NK cell depletion led to accelerated systemic bacterial dissemination. IFN-γ production by NK cells in response to B. anthracis spores was: i) contact-dependent through RAE-1-NKG2D interaction with macrophages; ii) IL-12, IL-18, and IL-15-dependent, where IL-12 played a key role and regulated both NK cell and macrophage activation; and iii) required IL-18 for only an initial short time window. B. anthracis toxins subverted both NK cell essential functions. ET and LT disrupted IFN-γ production through different mechanisms. LT acted both on macrophages and NK cells, whereas ET mainly affected macrophages and did not alter NK cell capacity of IFN-γ secretion. In contrast, ET and LT inhibited the natural cytotoxicity function of NK cells, both in vitro and in vivo. The subverting action of ET thus led to dissociation in NK cell function and blocked natural cytotoxicity without affecting IFN-γ secretion. The high efficiency of this process stresses the impact that this toxin may exert in anthrax pathogenesis, and highlights a potential usefulness for controlling excessive cytotoxic responses in immunopathological diseases. Our findings therefore exemplify the delicate balance between bacterial stimulation and evasion strategies. This highlights the potential implication of the crosstalk between host innate defences and B. anthracis in initial anthrax control mechanisms

The Alpine Fault Hangingwall Viewed From Within: Structural Analysis of Ultrasonic Image Logs in the DFDP-2B Borehole, New Zealand

International audienceUltrasonic image logs acquired in the DFDP‐2B borehole yield the first continuous, subsurface description of the transition from schist to mylonite in the hangingwall of the Alpine Fault, New Zealand, to a depth of 818 m below surface. Three feature sets are delineated. One set, comprising foliation and foliation‐parallel veins and fractures, has a constant orientation. The average dip direction of 145° is subparallel to the dip direction of the Alpine Fault, and the average dip magnitude of 60° is similar to nearby outcrop observations of foliation in the Alpine mylonites that occur immediately above the Alpine Fault. We suggest that this foliation orientation is similar to the Alpine Fault plane at ∼1 km depth in the Whataroa valley. The other two auxiliary feature sets are interpreted as joints based on their morphology and orientation. Subvertical joints with NW‐SE (137°) strike occurring dominantly above ∼500 m are interpreted as being formed during the exhumation and unloading of the Alpine Fault's hangingwall. Gently dipping joints, predominantly observed below ∼500 m, are interpreted as inherited hydrofractures exhumed from their depth of formation. These three fracture sets, combined with subsidiary brecciated fault zones, define the fluid pathways and anisotropic permeability directions. In addition, high topographic relief, which perturbs the stress tensor, likely enhances the slip potential and thus permeability of subvertical fractures below the ridges, and of gently dipping fractures below the valleys. Thus, DFDP‐2B borehole observations support the inference of a large zone of enhanced permeability in the hangingwall of the Alpine Fault

Accretion, structure and hydrology of intermediate spreading-rate oceanic crust from drillhole experiments and seafloor observations

Downhole measurements recorded in the context of the Ocean Drilling Program in Hole 504B, the deepest hole drilled yet into the oceanic crust, are analyzed in terms of accretion processes of the upper oceanic crust at intermediate spreading-rate. The upper part of the crust is found to support the non steady-state models of crustal accretion developed from seafloor observations (Kappel and Ryan, 1986; Gente, 1987). The continuous and vertical nature of borehole measurements provides stratigraphic and structural data that cannot be obtained solely from seafloor studies and, in turn, these models define a framework to analyze the structural, hydrological, and mineralogical observations made in the hole over the past decade.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43190/1/11001_2005_Article_BF01204282.pd

Petrologic description and values of resistivity, CEC, and porosity of samples from ODP Hole 111-504B (Table 1)

The resistivity, porosity, and cation exchange capacity of 36 basaltic samples recovered in Hole 504B during four DSDP and ODP legs have been measured in the laboratory at room temperature and atmospheric pressure. The presence of chlorites and particularly smectites as alteration products of basalt phases is reflected by high values of cation exchange capacity (CEC). Whereas the massive units of Layers 2A and 2B are defined by high and uniform CEC values, the more fractured and altered pillows are characterized in the entire hole by even higher values of CEC and a large variability. The lowest CEC values, measured for the massive units of Layer 2C, are due to changes of basalt alteration fades with depth and the related decreasing abundance of smectites with increasing depth in the oceanic crust. The porosity and the apparent formation factor (computed from resistivity measurements made with a fluid salinity similar to that of seawater) are related by an inverse power law similar to Archie's formula, with m close to 1.0 and a as large as 9.1. A review of the literature shows that such a low m value equates to current conduction in cracks and microcracks present throughout the rock. The presence of these microstructures reflects the extensional regime under which the rock formed at the ridge axis, and they were conserved by precipitation of clay minerals attributable to intense hydrothermal circulation. The comparison of these results to similar studies of mid-ocean ridge basalt physical properties indicates that m tends to increase to values close to 2.0 with age. Such values are, in fact, similar to those found for sedimentary rocks and probably reflect an increased tortuosity of the conducting pore space with increasing age. An inverse relationship also relates CEC and apparent formation factor, indicating that surface conduction of clay minerals plays an important role during downhole electrical experiments. This provides a plausible key to the paradox of low permeability and high apparent porosity obtained from comparing the in-situ experiments conducted in Hole 504B

(Table 1) Paleomagnetic of ODP Leg 126 sites

A paleomagnetic study was made on the deep-marine sediments and volcanic rocks drilled by Ocean Drilling Program Leg 126 in the Izu-Bonin forearc region (Sites 787, 792, and 793). This study evaluates the sense and amount of the tectonic drift and rotation associated with the evolution of the Philippine Sea Plate and the Izu-Bonin Arc. Alternating-field and thermal demagnetization experiments show that most of the samples have stable remanence and are suitable for paleomagnetic studies. Paleomagnetic declinations were recovered by two methods of core orientation, one of which uses a secondary viscous magnetization vector of each specimen as an orientation standard, and the other of which is based on the data of downhole microresistivity measurement obtained by using a formation microscanner. Oligocene to early Miocene samples show 10° to 14° shallower paleolatitudes than those of the present. Middle Miocene to early Oligocene samples show progressive clockwise deflections (up to ~80°) in declination with time. These results suggest large northward drift and clockwise rotation of the Izu-Bonin forearc region since early Oligocene time. Considering previous paleomagnetic results from the other regions in the Philippine Sea, this motion may reflect large clockwise rotation of the whole Philippine Sea Plate over the past 40 m.y

Resistivity, porosity, grain density and CEC for samples of ODP Hole 118-735B

The resistivity, porosity, and cation exchange capacity of 29 gabbroic samples recovered in Hole 735B during Leg 118 of the Ocean Drilling Program (ODP) were measured in the laboratory at room temperature and atmospheric pressure. The samples of lithologic Units IV and VI containing iron and titanium oxides have the highest electrical conductivity and the largest grain density sampled in Hole 735B. The fresh samples are the most resistive of the data set, and the tectonized samples (either due to plastic or brittle deformation) have intermediate values. Cation exchange capacity and electrical resistivity measurements performed at four different fluid salinities indicate that surface conduction mechanisms can be ignored for in-situ measurements of electrical resistivity at Site 735. The main conduction mechanisms for electrical current consequently are reduced to (1) electrolytic conduction in the pore space and (2) electronic conduction in metallic grains of the matrix in the presence of Fe-Ti oxides. In the last case, matrix conduction might become the dominant conduction mechanism, which explains the low resistivity values recorded in situ with the dual laterolog in lithologic Unit IV and in the lower part of the hole. The conduction equation is then written as follows: Co = [(Cw/FF) + Coxides], and the low m value obtained when relating porosity to formation factor with FF = (8.04) phi**-1.08, which suggests that the conducting pore space of gabbros is similar to that of mid-ocean ridge basalts (MORB), that is, mainly constituted of cracks and microcracks, as elsewhere observed in thin sections