Xiang-Zhao Kong

Experimental observation of permeability changes in dolomite at CO2 sequestration conditions.

Injection of cool CO2 into geothermally warm carbonate reservoirs for storage or geothermal energy production may lower near-well temperature and lead to mass transfer along flow paths leading away from the well. To investigate this process, a dolomite core was subjected to a 650 h, high pressure, CO2 saturated, flow-through experiment. Permeability increased from 10(-15.9) to 10(-15.2) m(2) over the initial 216 h at 21 °C, decreased to 10(-16.2) m(2) over 289 h at 50 °C, largely due to thermally driven CO2 exsolution, and reached a final value of 10(-16.4) m(2) after 145 h at 100 °C due to continued exsolution and the onset of dolomite precipitation. Theoretical calculations show that CO2 exsolution results in a maximum pore space CO2 saturation of 0.5, and steady state relative permeabilities of CO2 and water on the order of 0.0065 and 0.1, respectively. Post-experiment imagery reveals matrix dissolution at low temperatures, and subsequent filling-in of flow passages at elevated temperature. Geochemical calculations indicate that reservoir fluids subjected to a thermal gradient may exsolve and precipitate up to 200 cm(3) CO2 and 1.5 cm(3) dolomite per kg of water, respectively, resulting in substantial porosity and permeability redistribution.

Short note: DBCreate: A SUPCRT92-based program for producing EQ3/6, TOUGHREACT, and GWB thermodynamic databases at user-defined T and P

SUPCRT92 is a widely used software package for calculating the standard thermodynamic properties of minerals, gases, aqueous species, and reactions. However, it is labor-intensive and error-prone to use it directly to produce databases for geochemical modeling programs such as EQ3/6, the Geochemists Workbench, and TOUGHREACT. DBCreate is a SUPCRT92-based software program written in FORTRAN90/95 and was developed in order to produce the required databases for these programs in a rapid and convenient way. This paper describes the overall structure of the program and provides detailed usage instructions.

Permeability reduction produced by grain reorganization and accumulation of exsolved CO2 during geologic carbon sequestration: a new CO2 trapping mechanism.

Carbon sequestration experiments were conducted on uncemented sediment and lithified rock from the Eau Claire Formation, which consisted primarily of K-feldspar and quartz. Cores were heated to accentuate reactivity between fluid and mineral grains and to force CO(2) exsolution. Measured permeability of one sediment core ultimately reduced by 4 orders of magnitude as it was incrementally heated from 21 to 150 °C. Water-rock interaction produced some alteration, yielding sub-μm clay precipitation on K-feldspar grains in the cores upstream end. Experimental results also revealed abundant newly formed pore space in regions of the core, and in some cases pores that were several times larger than the average grain size of the sediment. These large pores likely formed from elevated localized pressure caused by rapid CO(2) exsolution within the core and/or an accumulating CO(2) phase capable of pushing out surrounding sediment. CO(2) filled the pores and blocked flow pathways. Comparison with a similar experiment using a solid arkose core indicates that CO(2) accumulation and grain reorganization mainly contributed to permeability reduction during the heated sediment core experiment. This suggests that CO(2) injection into sediments may store more CO(2) and cause additional permeability reduction than is possible in lithified rock due to grain reorganization.

GRANULAR SEGREGATION IN A MULTI-BOTTLENECK CONTAINER: MOBILITY EFFECT

We investigate experimentally and via computer simulations the segregation pattern of binary granular mixtures in a vibrated container with bottlenecks. During the vibration the granular motion is more violent at the bottlenecks than at the bellies. Particles with more mobility congregate to the necks, while those with less mobility congregate to the bellies. We use discrete element simulations to reproduce the main characteristics of the experimental observations.

Microbubble transport in water‐saturated porous media

Laboratory experiments were conducted to investigate flow of discrete microbubbles through a water-saturated porous medium. During the experiments, bubbles, released from a diffuser, moved upward through a quasi-2-D flume filled with transparent water-based gelbeads and formed a distinct plume that could be well registered by a calibrated camera. Outflowing bubbles were collected on the top of the flume using volumetric burettes for flux measurements. We quantified the scaling behaviors between the gas (bubble) release rates and various characteristic parameters of the bubble plume, including plume tip velocity, plume width, and breakthrough time of the plume front. The experiments also revealed circulations of ambient pore water induced by the bubble flow. Based on a simple momentum exchange model, we showed that the relationship between the mean pore water velocity and gas release rate is consistent with the scaling solution for the bubble plume. These findings have important implications for studies of natural gas emission and air sparging, as well as fundamental research on bubble transport in porous media.

Scaling solutions for connectivity and conductivity of continuous random networks.

Connectivity and conductivity of two-dimensional fracture networks (FNs), as an important type of continuous random networks, are examined systematically through Monte Carlo simulations under a variety of conditions, including different power law distributions of the fracture lengths and domain sizes. The simulation results are analyzed using analogies of the percolation theory for discrete random networks. With a characteristic length scale and conductivity scale introduced, we show that the connectivity and conductivity of FNs can be well described by universal scaling solutions. These solutions shed light on previous observations of scale-dependent FN behavior and provide a powerful method for quantifying effective bulk properties of continuous random networks.

High-Resolution Temporo-Ensemble PIV to Resolve Pore-Scale Flow in 3D-Printed Fractured Porous Media

Fractures are conduits that can enable fast advective transfer of (fluid, solute, reactant, particle, etc.) mass and energy. Such fast transfer can significantly affect pore-scale physico-chemical processes, which can in turn affect macroscopic mass and energy transport characteristics. Here, flooding experiments are conducted in a well-characterized fractured porous medium, manufactured by 3D printing. Given steady-state flow conditions, the micro-structure of the two-dimensional pore fluid flow field is delineated to resolve fluid velocities on the order of a sub-millimeter per second. We demonstrate the capabilities of a new temporo-ensemble particle image velocimetry method by maximizing its spatial resolution, employing in-line illumination. This method is advantageous as it is capable of minimizing the number of pixels, required for velocity determinations, down to one pixel, thereby enabling resolving high spatial resolutions of velocity vectors in a large field of view. While the main goal of this study is to introduce a novel experimental and velocimetry framework, this new method is then applied to specifically improve the understanding of fluid flow through fractured porous media. Histograms of measured velocities indicate log-normal and Gaussian-type distributions of longitudinal and lateral velocities in fractures, respectively. The magnitudes of fluid velocities in fractures and the flow interactions between fractures and matrices are shown to be influenced by the permeability of the background matrix and the orientation of the fractures.

Fluid Flow in Unconventional Gas Reservoirs

State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77004, USA School of Mechanical and Mining Engineering, The University of Queensland, St. Lucia, QLD 4072, Australia Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China Department of Earth Sciences Institute of Geophysics, ETH Zürich, 8092 Zurich, Switzerland

Particle Discharge Process from a Capillary Pipe

The particle discharge process from a vertical open-top pipe with a capillary outlet reveals some exceptions to the common belief that the outflux oscillation results solely from dynamic arching of beads at the orifice and that the outflux is not sensitive to the filling height. With beads of a particular size range, the outflux fluctuates greatly with time and the bulk dense granular flow in the pipe shows stop-and-go motion when the filling height is above a threshold. When the filling height falls to the threshold, led by a transitional stage, the outflux and the bulk movement become stable. The dropping velocity variation of the upper surface is measured to study the bulk motion in the pipe. With a heuristic theory, we find that the granular compaction and interstitial air pressure effect are responsible for the stop-and-go oscillation and the transitional behavior.

Discharge oscillation of particles from a vertical pipe with capillary outlet

A new style of discharge process from a vertical open-top pipe with capillary outlet is reported. The outflux fluctuates greatly with time and the bulk condensed granular flow in the pipe shows stopandgo motion when the filling height is above a threshold. When the filling height falls towards the threshold, led by a transitional stage, the outflux and the bulk movement become much stable. The upper surface dropping velocity variation is measured. A heuristic theory is proposed to understand the stop- and-go motion and the transitional behavior