The effect of CO2-enriched brine injection on the mechanical properties of calcite bearing sandstone

The mechanical and fluid-flow response of subsurface geological reservoirs due to injection of CO2 is of critical importance for the safe management and storage of anthropogenic carbon emissions. Although the time-lapse seismic method has proven to be an effective tool to remotely monitor changes in underground fluid saturations, variations in reservoir properties caused by geochemical interactions can also influence the seismic response. This can lead to ambiguity and uncertainty in monitoring the movement of injected CO2 and hence determination of reservoir seal integrity. Geochemical interactions can also modify the mechanical strength of the reservoir and therefore threaten its integrity. We conducted experiments to assess how the velocity and rock strength of a calcite-bearing sandstone are affected by flooding with CO2 saturated brine. The results indicate that both seismic velocity and rock strength are significantly reduced due to minor calcite dissolution. The implications at the reservoir scale for CO2 storage are twofold. Firstly, modifications in velocity can complicate seismic monitoring operations and lead to interpretation errors. This can be accounted for if shear wave velocity variations are used to detect fluid-rock interactions. Secondly, reduction in rock strength, caused by calcite dissolution, can threaten reservoir and wellbore integrity under stress conditions typically found in potential carbon repositories

Ectoparasite activity during incubation increases microbial growth on avian eggs

We thank Estefanía López for lab work, and Tomás Pérez-Contreras and Emilio Pagani-Núñez for facilitating collection of some of the flies used in manipulations. We also thank Ángela Martínez-García for help with management of ARISA data and Natalia Juárez and Deseada Parejo for the pictures of owls and roller clutches, respectively. We appreciate the comments provided by Dr. Adèle Mennerat and five anonymous referees on earlier versions of the manuscript.All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.While direct detrimental effects of parasites on hosts are relatively well documented, other more subtle but potentially important effects of parasitism are yet unexplored. Biological activity of ectoparasites, apart from skin injuries and blood-feeding, often results in blood remains, or parasite faeces that accumulate and modify the host environment. In this way, ectoparasite activities and remains may increase nutrient availability that may favour colonization and growth of microorganisms including potential pathogens. Here, by the experimental addition of hematophagous flies (Carnus hemapterus, a common ectoparasite of birds) to nests of spotless starlings Sturnus unicolor during incubation, we explore this possible side effect of parasitism which has rarely, if ever, been investigated. Results show that faeces and blood remains from parasitic flies on spotless starling eggshells at the end of incubation were more abundant in experimental than in control nests. Moreover, eggshell bacterial loads of different groups of cultivable bacteria including potential pathogens, as well as species richness of bacteria in terms of Operational Taxonomic Units (OTUs), were also higher in experimental nests. Finally, we also found evidence of a link between eggshell bacterial loads and increased embryo mortality, which provides indirect support for a bacterial-mediated negative effect of ectoparasitism on host offspring. Trans-shell bacterial infection might be one of the main causes of embryo death and, consequently, this hitherto unnoticed indirect effect of ectoparasitism might be widespread in nature and could affect our understanding of ecology and evolution of host-parasite interactionsFinancial support was provided by Spanish Ministerio de Economía y Competitividad and FEDER (CGL2013-48193-C3-1-P, CGL2013-48193-C3-2-P), by JAE programme to DMG and MRR, and by Juan de la Cierva and Ramón y Cajal programmes to GT. All procedures were conducted under licence from the Environmental Department of the Regional Government of Andalucía, Spain (reference SGYB/FOA/AFR)

Exploring trends in microcrack properties of sedimentary rocks: An audit of dry-core velocity-stress measurements

Rock physics models are being used increasingly to link fluid and mechanical defor- mation parameters for dynamic elastic modelling. In this paper, we explore the input parameters of an analytic stress dependent rock physics model. To do this, we invert for the stress dependent microcrack parameters of over 150 sedimentary rock velocity– stress core measurements taken from a literature survey. The inversion scheme is based on a microstructural effective medium formulation defined by either a second–rank crack density tensor (scalar crack model) or both a second– and fourth–rank crack density tensor (joint inversion model). The inversion results are then used to explore and predict the stress dependent elastic behavior of various sedimentary rock litholo- gies using an analytic microstructural rock physics model via the initial model input parameters: initial crack aspect ratio and initial crack density. Estimates of initial crack aspect ratio are consistent between most lithologies with a mean of 0.0004, but for shales differ by up to several times in magnitude with a mean of 0.001. Estimates of initial aspect ratio are relatively insensitive to the inversion method, though the scalar crack inversion become less reliable at low values of normal to tangential crack compliance ratio (BN/BT ). Initial crack density is sensitive to the degree of damage as well as the inversion procedure. An important implication of this paper is that the fourth–rank crack density term is not necessarily negligible for most sedimentary rocks and evaluation of this term or BN/BT is necessary for accurate prediction of initial crack density. This is especially important since recent studies have suggested that the ratio BN/BT can be used as an indicator of crack fluid content

Passive seismic monitoring of carbon dioxide storage at Weyburn

arbon capture and storage (CCS) is currently one of several candidate technologies for reducing the emission of industrial CO2 to the atmosphere. As plans for large-scale geological storage of CO2 are being considered, it is clear that monitoring programs will be required to demonstrate security of the CO2 within the storage complex. Numerous geophysical monitoring techniques are currently being tested for this purpose, including controlled-source time-lapse reflection seismology, satellite synthetic aperture radar interferometry, electromagnetic sounding, gravity, and others. Passive seismic monitoring is an additional technique under consideration that complements these other techniques, and has potential as a cost-effective method of demonstrating storage security. This is particularly true over longer periods of time, as passive seismic arrays cost relatively little to maintain. Of the large-scale CCS pilot projects currently operational, thus far only the IEA GHG Weyburn-Midale CO2 Monitoring and Storage Project has included passive seismic monitoring. Here we present the results from five years of passive seismic monitoring at Weyburn, and discuss the lessons learnt that can be applied when deploying passive seismics to monitor future CCS operations

Reservoir stress path characterization and its implications for fluid-flow production simulation

The reduction of fluid pressure during reservoir production promotes changes in the effective and total stress distribution within the reservoir and the surrounding strata. This stress evolution is responsible for many problems encountered during production (e.g. fault reactivation, casing deformation). This work presents the results of an extensive series of 3D numerical hydro-mechanical coupled analyses that study the influence of reservoir geometry and material properties on the reservoir stress path. The stress path is defined in terms of parameters that quantify the amount of stress arching and stress anisotropy that occur during reservoir production. The coupled simulations are performed by explicitly coupling independent commercial geomechanical and flow simulators. It is shown that stress arching is important in reservoirs with low aspect ratios that are less stiff than the bounding material. In such cases, the stresses will not significantly evolve in the reservoir, and stress evolution occurs in the over- and sideburden. Stiff reservoirs, relative to the bounding rock, exhibit negligible stress arching regardless of the geometry. Stress anisotropy reduces with reduction of the Young's modulus of the bounding material, especially for low aspect ratio reservoirs, but as the reservoir extends in either or both of the horizontal directions, the reservoir deforms uniaxially and the horizontal stress evolution is governed by the Poisson's ratio of the reservoir. Furthermore, the effect of the stress path parameters is introduced in the calculation of pore volume multiplier tables to improve non-coupled simulations, which otherwise overestimate the average reservoir pore pressure drawdown when stress arching is taking place

Salmonella persisters undermine host immune defenses during antibiotic treatment

Many bacterial infections are hard to treat and tend to relapse, possibly due to the presence of antibiotic-tolerant persisters. In vitro, persister cells appear to be dormant. After uptake of Salmonella species by macrophages, nongrowing persisters also occur, but their physiological state is poorly understood. In this work, we show that Salmonella persisters arising during macrophage infection maintain a metabolically active state. Persisters reprogram macrophages by means of effectors secreted by the Salmonella pathogenicity island 2 type 3 secretion system. These effectors dampened proinflammatory innate immune responses and induced anti-inflammatory macrophage polarization. Such reprogramming allowed nongrowing Salmonella cells to survive for extended periods in their host. Persisters undermining host immune defenses might confer an advantage to the pathogen during relapse once antibiotic pressure is relieved