Johannes Bruining

Characterization of geochemical constituents and bacterial populations associated with As mobilization in deep and shallow tube wells in Bangladesh.

While millions of people drink arsenic-contaminated tube well water across Bangladesh, there is no recent scientific explanation which is able to either comprehensively explain arsenic mobilization or to predict the spatial distribution of affected wells. Rather, mitigation strategies have focused on the sinking of deep tube wells into the currently arsenic-free Pleistocene aquifer. In this study, Bangladesh shallow tube wells identified as contaminated and uncontaminated, as well as deep tube wells, were analyzed for geochemical and in situ microbiological composition. Whereas arsenic was detected in all Holocene aquifer wells, no arsenic was found in wells accessing the Pleistocene aquifer. Bacterial genera, including Comamonadaceae, Acidovorax, Acinetobacter, and Hydrogenophaga, associated with tolerance of high arsenic concentrations, rather than dissimilatory Fe(III) or As(V) reduction, were identified in shallow tube wells, indicating that mobilization may not occur at depth, but is rather due to drawdown of surface contaminated water. Deep tube wells contained microbes indicative of aerobic conditions, including the genera Aquabacterium, Limnobacter, and Roseomonas. It is concluded that through drawdown of arsenic or organic matter, further utilization of the Pleistocene aquifer could result in contamination similar to that observed in the Holocene aquifer.

Enhanced Mass Transfer of CO2 into Water: Experiment and Modeling

Concern over global warming has increased interest in quantification of the dissolution of CO 2 in (sub-)-surface water. The mechanisms of the mass transfer of CO 2 in aquifers and of transfer to surface water have many common features. The advantage of experiments using bulk water is that the underlying assumptions to the quantify mass-transfer rate can be validated. Dissolution of CO 2 into water (or oil) increases the density of the liquid phase. This density change destabilizes the interface and enhances the transfer rate across the interface by natural convection. This paper describes a series of experiments performed in a cylindrical PVT-cell at a pressure range of p i = 10―50 bar, where a fixed volume of CO 2 gas was brought into contact with a column of distilled water. The transfer rate is inferred by following the gas pressure history. The results show that the mass-transfer rate across the interface is much faster than that predicted by Fickian diffusion and increases with increasing initial gas pressure. The theoretical interpretation of the observed effects is based on diffusion and natural convection phenomena. The CO 2 concentration at the interface is estimated from the gas pressure using Henrys solubility law, in which the coefficient varies with both pressure and temperature. Good agreement between the experiments and the theoretical results has been obtained.

Mass Transfer of CO2 Into Water and Surfactant Solutions

Abstract The mass transfer of CO2 into water and aqueous solutions of sodium dodecyl sulphate (SDS) is experimentally studied using a pressure, volume, temperature (PVT) cell at different initial pressures and a constant temperature (T = 25°C). It is observed that the transfer rate is initially much larger than expected from a diffusion process alone. The model equations describing the experiments are based on Ficks Law and Henrys Law. The experiments are interpreted in terms of two effective diffusion coefficients—one for the early-stages of the experiments and the other one for the later stages. The results show that at the early stages, the effective diffusion coefficients are one order of magnitude larger than the molecular diffusivity of CO2 in water. Nevertheless, in the later stages the extracted diffusion coefficients are close to literature values. It is asserted that at the early stages, density-driven natural convection enhances the mass transfer. A similar mass transfer enhancement was observed for the mass transfer between a gaseous CO2 rich phase with an oil (n-decane) phase. It is also found that at the experimental conditions studied addition of pure SDS does not have a significant effect on the mass transfer rate of CO2 in water.

Microbial diversity of an oil-water processing site and its associated oil field: the possible role of microorganisms as information carriers from oil-associated environments.

The phylogenetic diversity of Bacteria and Archaea in water retrieved from a Dutch oil field and units of the associated oil-water separation site were determined using two culture-independent methods. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments was used to scan the microbial diversity in (1) the oil-water emulsion produced, (2) two different oil-water separator tanks, (3) a wash tank and (4) a water injector. Longer 16S rRNA gene fragments were amplified, cloned and sequenced to determine the diversity in more detail. One of the questions addressed was whether the detected microorganisms could serve as indicators for the environments from which they were retrieved. It was observed that the community found in the production water resembled those reported previously in oil reservoirs, indicating that these ecosystems harbor specific microbial communities. It was shown that changes, like a decrease in temperature, cause a distinctive shift in these communities. The addition of SO(3)(2-) to the wash tank as ammonium bisulphite, used in the oil industry to scavenge oxygen, resulted in a complete community change, giving rise to an unwanted sulphate-reducing community. The fact that these changes in the community can be linked to changes in their environment might indicate that these tools can be used for the monitoring of changing conditions in oil reservoirs upon, for example, water flooding.

Capillary Pressure and Wettability Behavior of CO 2 Sequestration in Coal at Elevated Pressures

Summary Enhanced coalbed-methane (ECBM) recovery combines recovery of methane (CH4) from coal seams with storage of carbon dioxide (CO2). The efficiency of ECBM recovery depends on the CO2 transfer rate between the macrocleats, via the microcleats to the coal matrix. Diffusive transport of CO2 in the small cleats is enhanced when the coal is CO2-wet. Indeed, for water-wet conditions, the small fracture system is filled with water and the rate of CO2 sorption and CH4 desorption is affected by slow diffusion of CO2. This work investigates the wetting behavior of coal using capillary pressures between CO2 and water, measured continuously as a function of water saturation at in-situ conditions. To facilitate the interpretation of the coal measurements, we also obtain capillary pressure curves for unconsolidated-sand samples. For medium- and high-rank coal, the primary drainage capillary pressure curves show a water-wet behavior. Secondary forcedimbibition experiments show that the medium-rank coal becomes CO2-wet as the CO2 pressure increases. High-rank coal is CO2-wet during primary imbibition. The imbibition behavior is in agreement with contact-angle measurements. Hence, we conclude that imbibition tests provide the practically relevant data to evaluate the wetting properties of coal.

The Modeling of Velocity Enhancement in Polymer Flooding

In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur.

An empirical theory for gravitationally unstable flow in porous media

In this paper, we follow a similar procedure as proposed by Koval (SPE J 3(2):145–154, 1963) to analytically model CO2 transfer between the overriding carbon dioxide layer and the brine layer below it. We show that a very thin diffusive layer on top separates the interface from a gravitationally unstable convective flow layer below it. Flow in the gravitationally unstable layer is described by the theory of Koval, a theory that is widely used and which describes miscible displacement as a pseudo two-phase flow problem. The pseudo two-phase flow problem provides the average concentration of CO2 in the brine as a function of distance. We find that downstream of the diffusive layer, the solution of the convective part of the model, is a rarefaction solution that starts at the saturation corresponding to the highest value of the fractional-flow function. The model uses two free parameters, viz., a dilution factor and a gravity fingering index. A comparison of the Koval model with the horizontally averaged concentrations obtained from 2-D numerical simulations provides a correlation for the two parameters with the Rayleigh number. The obtained scaling relations can be used in numerical simulators to account for the density-driven natural convection, which cannot be currently captured because the grid cells are typically orders of magnitude larger than the wavelength of the initial fingers. The method can be applied both for storage of greenhouse gases in aquifers and for EOR processes using carbon dioxide or other solvents.

Filtration Combustion in Wet Porous Medium

We consider the filtration combustion for configuration where air is injected behind the wave into a porous medium containing a solid fuel. The simplest flow contains planar combustion and thermal waves, each propagating with its own speed. In this work, we study such a flow, in the case where the porous medium contains initially also some amount of liquid; therefore, vaporization and condensation occur too, giving rise to a wave structure richer than in dry combustion. We find two possible sequences of waves, and we characterize the internal structure of all waves. In an example for typical parameters of in-situ combustion, we compare the analytical results with direct numerical simulations.

Flexible Spectral Methods for the Generation of Random Fields with Power-Law Semivariograms ~

Random field generators serve as a tool to model heterogeneous media for applications in hydrocarbon recovery and groundwater flow. Random fields with a power-law variogram structure, also termed fractional Brownian motion (fBm) fields, are of interest to study scale dependent heterogeneity effects on one-phase and two-phase flow. We show that such fields generated by the spectral method and the Inverse Fast Fourier Transform (IFFT) have an incorrect variogram structure and variance. To illustrate this we derive the prefactor of the fBm spectral density function, which is required to generate the fBm fields. We propose a new method to generate fBm fields that introduces weighting functions into the spectral method. It leads to a flexible and efficient algorithm. The flexibility permits an optimal choice of summation points (that is points in frequency space at which the weighting function is calculated) specific for the autocovariance structure of the field. As an illustration of the method, comparisons between estimated and expected statistics of fields with an exponential variogram and of fBm fields are presented. For power-law semivariograms, the proposed spectral method with a cylindrical distribution of the summation points gives optimal results.

An Integrated 3D Model for Underground Coal Gasification

Underground coal gasification has received renewed interest in both Western and Eastern Europe because of the vast amounts of otherwise unminable coal deposits that occur on the European continent. A field test is currently being held in Spain, and other countries have also shown interest in this method of utilizing coal resources. In this study we have developed a model to combine reactive heat and mass transport together with thermomechanical failure behavior. In the model, we use multigrid methods to solve the flow equations in the entire domain. This is combined with thermo-mechanical failure properties of both coal and rock overlying the coal formation. With this approach, a 3D picture of the development of an underground coal gasifier is obtained, and the influence of well-layout and the sensitivity of the process to other model parameters can be investigated in detail, with high computational efficiency. The model consists of two modules : The first module solves the flow equations in the entire flow domain. The second module selects a block of coal for gasification and a block of coal and/or rock for thermo-mechanically induced spalling. Other features such as ash content, the possibility of including heterogeneities, and natural convection-driven cavity gasification are also incorporated in the model.