Physical modelling of chemical compaction, overpressure development, hydraulic fracturing and thrust detachments in organic-rich source rock

International audienceGeological evidence for overpressure is common worldwide, especially in petroleum-rich sedimentary basins. As a result of an increasing emphasis on unconventional resources, new data are becoming available for source rocks. Abnormally high values of pore fluid pressure are especially common within mature source rock, probably as a result of chemical compaction and increases in volume during hydrocarbon generation. To investigate processes of chemical compaction, overpressure development and hydraulic fracturing, we have developed new techniques of physical modelling in a closed system. During the early stages of our work, we built and deformed models in a small rectangular box (40 40 10 cm), which rested on an electric flatbed heater; but more recently, in order to accommodate large amounts of horizontal shortening, we used a wider box (77 75 10 cm). Models consisted of horizontal layers of two materials: (1) a mixture of equal initial volumes of silica powder and beeswax micro-spheres, representing source rock, and (2) pure silica powder, representing overburden. By submerging these materials in water, we avoided the high surface tensions, which otherwise develop within pores containing both air and liquids. Also we were able to measure pore fluid pressure in a model well. During heating, the basal temperature of the model surpassed the melting point of beeswax (w62 C), reaching a maximum of 90 C. To investigate tectonic contexts of compression or extension, we used a piston to apply horizontal displacements. In experiments where the piston was static, rapid melting led to vertical compaction of the source layer, under the weight of overburden, and to high fluid overpressure (lithostatic or greater). Crosssections of the models, after cooling, revealed that molten wax had migrated through pore space and into open hydraulic fractures (sills). Most of these sills were horizontal and their roofs bulged upwards, as far as the free surface, presumably in response to internal overpressure and loss of strength of the mixture.We also found that sills were less numerous towards the sides of the box, presumably as a result of boundary effects. In other experiments, in which the piston moved inward, causing compression of the model, sills also formed. However, these were thicker than in static models and some of them were subject to folding or faulting. For experiments, in which we imposed some horizontal shortening, before the wax had started to melt, fore-thrusts and back-thrusts developed across all of the layers near the piston, producing a high-angle prism. In contrast, as soon as the wax melted, overpressure developed within the source layer and a basal detachment appeared beneath it. As a result, thin-skinned thrusts propagated further into the model, producing a low-angle prism. In some experiments, bodies of wax formed imbricate zones within the source layer. Thus, in these experiments, it was the transformation, from solid wax to liquid wax, which led to chemical compaction, overpressure development and hydraulic fracturing, all within a closed system. According to the measurements of overpressure, load transfer was the main mechanism, but volume changes also contributed, producing supra-lithostatic overpressure and therefore tensile failure of the mixture

Développement d'un modèle de simulation d'une épidémie foliaire tropicale à l'échelle de la plante: cas des cercosporioses du bananier

Les cercosporioses du bananier dues à Mycosphaerella fijiensis (agent de la maladie des raies noires (MRN) ou cercosporiose noire) et M. musicola (agent de la maladie de Sigatoka (MS) ou cercosporiose jaune) sont considérées comme les maladies foliaires les plus graves pour les productions bananières. Ces pathogènes sont présents dans la majorité des zones de cultures bananières intertropicales. Le contrôle de ces maladies indispensable pour l'exportation des fruits, consiste actuellement en des applications fréquentes de fongicides par voie aérienne, méthode néfaste pour l'environnement. Un modèle de simulation des cercosporioses a été conçu pour approfondir les connaissances du pathosystème et tester de nouvelles méthodes de lutte, en particulier l'utilisation de variétés résistantes. Un modèle mécaniste de simulation des cercosporioses en temps discret est en cours de développement. Il décrit, sans spatialisation et en conditions climatiques optimales, le développement de la maladie sur un bananier représentatif d'une parcelle pendant un cycle de culture. Ce modèle permettra d'évaluer l'efficacité de différentes composantes de résistance partielle dans le contrôle des cercosporioses et d'étudier la compétition entre les 2 espèces fongiques en cas d'invasion de la MRN (contexte parasitaire actuel en Martinique). Il se décompose en deux sous-modèles, le premier simulant la croissance du bananier, le second simulant la propagation de l'épidémie. Le sous modèle " croissance de la plante " est appréhendé de manière déterministe alors que le sous modèle " propagation de la maladie " est lui stochastique. Ce dernier décrit le fonctionnement du pathogène sur son hôte: contamination, reproduction asexuée (production de conidies), rencontre de lésions, reproduction sexuée (production d'ascospores), dispersion des spores. Les données disponibles pour calibrer le modèle ont été recueillies au Cameroun (MRN) et aux Antilles (MRN et MS) en conditions naturelles d'infestation et en conditions contrôlées (croissance des lésions, nombre de spores émises par lésion). L'estimation des paramètres de ce second sous-modèle a été réalisée dans un cadre Bayésien par le biais de techniques MCMC (Markov Chain of Monte Carlo). On obtient alors une distribution à posteriori de l'ensemble des paramètres du modèle ainsi qu'une distribution a postériori de la variance résiduelle. L'inférence des paramètres et les résultats des premières simulations seront présentés et discutés. (Résumé d'auteur

Time scales of regional circulation of saline fluids in continental aquifers (Armorican massif, Western France)

International audienceIn recent decades, saline fluids have been sampled worldwide at great depths in continental basements. Although some of them have been attributed to marine transgressions the mechanisms allowing their circulation is not understood. In this paper, we describe the horizontal and vertical distribution of moderately saline fluids (60 to 1400 mg L−1) sampled at depths ranging from 41 to 200 m in aquifers at the regional scale of the Armorican Massif (northwestern France). The horizontal and vertical distributions of high chloride concentrations are in good agreement with both the altitudinal and vertical limits and succession of the three major transgressions between the Mio-Pliocene and Pleistocene ages. The mean chloride concentration for each transgression area is exponentially related to the time spanned until present. It defines the potential laws of leaching of marine waters by fresh meteoric waters. The results of the Armorican aquifers provide the first observed constraints for the time scales of seawater circulation in the continental basement and the subsequent leaching by fresh meteoric waters. The general trend of increasing chloride concentration with depth and the time frame for the flushing process provide useful information to develop conceptual models of the paleo-functionning of Armorican aquifers

A 3D CFD model of the interstitial fluid pressure and drug distribution in heterogeneous tumor nodules during intraperitoneal chemotherapy

Although intraperitoneal chemotherapy (IPC) has evolved into an established treatment modality for patients with peritoneal metastasis (PM), drug penetration into tumor nodules remains limited. Drug transport during IPC is a complex process that depends on a large number of different parameters (e.g. drug, dose, tumor size, tumor pressure, tumor vascularization). Mathematical modeling allows for a better understanding of the processes that underlie drug transport and the relative importance of the parameters influencing it. In this work, we expanded our previously developed 3D Computational Fluid Dynamics (CFD) model of the drug mass transport in idealized tumor nodules during IP chemotherapy to include realistic tumor geometries and spatially varying vascular properties. DCE-MRI imaging made it possible to distinguish between tumorous tissues, healthy surrounding tissues and necrotic zones based on differences in the vascular properties. We found that the resulting interstitial pressure profiles within tumors were highly dependent on the irregular geometries and different zones. The tumor-specific cisplatin penetration depths ranged from 0.32 mm to 0.50 mm. In this work, we found that the positive relationship between tumor size and IFP does not longer hold in the presence of zones with different vascular properties, while we did observe a positive relationship between the percentage of viable tumor tissue and the maximal IFP. Our findings highlight the importance of incorporating both the irregular tumor geometries and different vascular zones in CFD models of IPC

Event-based MILP models for resource-constrained project scheduling problems

International audienceIn this paper we make a comparative study of several mixed integer linear programming (MILP) formulations for resource-constrained project scheduling problems (RCPSPs). First, we present three discrete and continuous time MILP formulations issued from the literature. Second, instead of relying on the traditional discretization of the time horizon, we propose two original MILP formulations for the RCPSP based on the concept of event : the Start/End formulation and the On/Off formulation. These formulations present the advantage of involving fewer variables than the formulations indexed by time. Because the variables of this type of formulations are not function of the time horizon, we have a better capacity to deal with instances of very large scheduling horizon. We also illustrate our contribution with a series of tests on various types of instances with the three MILP formulations issued from the literature together with our two new formulations, and we draw some conclusions on their use

The interaction between lipid derivatives of colchicine and tubulin: Consequences of the interaction of the alkaloid with lipid membranes

AbstractColchicine is a potent antimitotic poison which is well known to prevent microtubule assembly by binding tubulin very tightly. Colchicine also possesses anti-inflammatory properties which are not well understood yet. Here we show that colchicine tightly interacts with lipid layers. The physical and biological properties of three different lipid derivatives of colchicine are investigated parallel to those of membrane lipids in the presence of colchicine. Upon insertion in the fatty alkyl chains, colchicine rigidifies the lipid monolayers in a fluid phase and fluidifies rigid monolayers. Similarly X-ray diffraction data show that lecithin–water phases are destabilized by colchicine. In addition, an unexpectedly drastic enhancement of the photoisomerization rate of colchicine into lumicolchicine in the lipid environment is observed and further supports insertion of the alkaloid in membranes. Finally the interaction of colchicine with lipids makes the drug inaccessible to tubulin. The possible in vivo significance of these results is discussed

NMR resonance assignments of NarE, a putative ADP-ribosylating toxin from Neisseria meningitidis

NarE is a 16 kDa protein identified from Neisseria meningitidis, one of the bacterial pathogens responsible for meningitis. NarE belongs to the ADP-ribosyltransferase family and catalyses the transfer of ADP-ribose moieties to arginine residues in target protein acceptors. Many pathogenic bacteria utilize ADP-ribosylating toxins to modify and alter essential functions of eukaryotic cells. NarE was proposed to bind iron through a Fe–S center which is supposed to be implied in catalysis. We have produced and purified uniformly labeled 15N- and 15N/13C-NarE and assigned backbone and side-chain resonances using multidimensional heteronuclear NMR spectroscopy. These assignments provide the starting point for the three-dimensional structure determination of NarE and the characterization of the role of the Fe–S center in the catalytic mechanism

Biofortified yellow cassava and vitamin A status of Kenyan children: a randomized controlled trial.

BACKGROUND: Whereas conventional white cassava roots are devoid of provitamin A, biofortified yellow varieties are naturally rich in β-carotene, the primary provitamin A carotenoid. OBJECTIVE: We assessed the effect of consuming yellow cassava on serum retinol concentration in Kenyan schoolchildren with marginal vitamin A status. DESIGN: We randomly allocated 342 children aged 5-13 y to receive daily, 6 d/wk, for 18.5 wk 1) white cassava and placebo supplement (control group), 2) provitamin A-rich cassava (mean content: 1460 μg β-carotene/d) and placebo supplement (yellow cassava group), and 3) white cassava and β-carotene supplement (1053 μg/d; β-carotene supplement group). The primary outcome was serum retinol concentration; prespecified secondary outcomes were hemoglobin concentration and serum concentrations of β-carotene, retinol-binding protein, and prealbumin. Groups were compared by using ANCOVA, adjusting for inflammation, baseline serum concentrations of retinol and β-carotene, and stratified design. RESULTS: The baseline prevalence of serum retinol concentration <0.7 μmol/L and inflammation was 27% and 24%, respectively. For children in the control, yellow cassava, and β-carotene supplement groups, the mean daily intake of cassava was 378, 371, and 378 g, respectively, and the total daily supply of provitamin A and vitamin A from diet and supplements was equivalent to 22, 220, and 175 μg retinol, respectively. Both yellow cassava and β-carotene supplementation increased serum retinol concentration by 0.04 μmol/L (95% CI: 0.00, 0.07 μmol/L); correspondingly, serum β-carotene concentration increased by 524% (448%, 608%) and 166% (134%, 202%). We found no effect on hemoglobin concentration or serum concentrations of retinol-binding protein and prealbumin. CONCLUSIONS: In our study population, consumption of yellow cassava led to modest gains in serum retinol concentration and a large increase in β-carotene concentration. It can be an efficacious, new approach to improve vitamin A status. This study was registered with clinicaltrials.gov as NCT01614483

Randomized comparison of primary stenting and provisional balloon angioplasty guided by flow velocity measurement.

BACKGROUND: Coronary stenting improves outcomes compared with balloon angioplasty, but it is costly and may have other disadvantages. Limiting stent use to patients with a suboptimal result after angioplasty (provisional angioplasty) may be as effective and less expensive. METHODS AND RESULTS: To analyze the cost-effectiveness of provisional angioplasty, patients scheduled for single-vessel angioplasty were first randomized to receive primary stenting (97 patients) or balloon angioplasty guided by Doppler flow velocity and angiography (523 patients). Patients in the latter group were further randomized after optimization to either additional stenting or termination of the procedure to further investigate what is "optimal." An optimal result was defined as a flow reserve >2.5 and a diameter stenosis <36%. Bailout stenting was needed in 129 patients (25%) who were randomized to balloon angioplasty, and an optimal result was obtained in 184 of the 523 patients (35%). There was no significant difference in event-free survival at 1 year between primary stenting (86.6%) and provisional angioplasty (85.6%). Costs after 1 year were significantly higher for provisional angioplasty (EUR 6573 versus EUR 5885; P:=0.014). Results after the second randomization showed that stenting was also more effective after optimal balloon angioplasty (1-year event free survival, 93.5% versus 84.1%; P:=0. 066). CONCLUSIONS: After 1 year of follow-up, provisional angioplasty was more expensive and without clinical benefit. The beneficial value of stenting is not limited to patients with a suboptimal result after balloon angioplasty