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Geologic carbon capture and storage (CCS) is an option for reducing CO2 emissions, but leakage to the surface is a risk factor. Natural CO2 reservoirs that erupt from abandoned oil and gas holes leak to the surface as spectacular cold geysers in the Colorado Plateau, United States. A better understanding of the mechanisms of CO2‐driven cold‐water geysers will provide valuable insight about the potential modes of leakage from engineered CCS sites. A notable example of a CO2‐driven cold‐water geyser is Crystal Geyser in central Utah. We investigated the fluid mechanics of this regularly erupting geyser by instrumenting its conduit with sensors and measuring pressure and temperature every 20 sec over a period of 17 days. Analyses of these measurements suggest that the timescale of a single‐eruption cycle is composed of four successive eruption types with two recharge periods ranging from 30 to 40 h. Current eruption patterns exhibit a bimodal distribution, but these patterns evolved during past 80 years. The field observation suggests that the geyser's eruptions are regular and predictable and reflect pressure and temperature changes resulting from Joule–Thomson cooling and endothermic CO2 exsolution. The eruption interval between multiple small‐scale eruptions is a direct indicator of the subsequent large‐scale eruption.

[1] Injection of CO 2 may perturb subsurface temperatures, leading to a dynamic temperature system in the storage formation and adjacent seal strata. In most cases, the individual effects from wellbore dynamics, solvation reactions, and phase changes are incremental, but collectively these relevant processes may cause significant temperature changes compared to ambient conditions. In this work, we evaluated several potential nonisothermal effects resulting from CO 2 injection activity. These include the Joule-Thomson (heating and cooling) effect, exothermic CO 2 dissolution, and heat changes associated with concomitant water vaporization. Results suggest that three effects: a) the adiabatic (de-) compression of CO 2 , b) the frictional energy losses, and c) conductive heat exchange between the injected CO 2 and surrounding fluid/rock, govern the resulting CO 2 thermal profiles within an injection well. In addition, as supercritical-phase CO 2 comes into contact with formation brine, the CO 2 will dissolve into the aqueous phase, and such dissolution is exothermic at typical conditions for CO 2 sequestration. However, we still seek a better understanding of heat effects associated with water vaporization into the supercritical-phase CO 2 . Finally, sensitivity studies, simulating supercritical-phase CO 2 injection into a 1-D radially symmetric domain, are conducted to evaluate the magnitude of different heat disequilibrium potentials and spatial location in the CO 2 plume affected by thermal processes. In addition, time-scales associated with migration rates of temperature fronts, pressure pulses, and dissolved-and supercritical-phase CO 2 profiles are investigated with a function of heat capacities of rock, different effective thermal conductivities, permeabilities, and porosities. Our results demonstrate that adiabatic CO 2 compression occurring in injection wells could have the most significant impact on the temperature change whilst the exothermic CO 2 dissolution occurred at the largest spatial domain.

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Available online xxxx Editor: P. Shearer Keywords: geyser CO 2 -driven eruptions faults carbon sequestration wellbore leakageThe CO 2 bubble volume fraction, eruption velocity, flash depth and mass emission of CO 2 were determined from multiple wellbore CO 2 -driven cold-water geysers (Crystal and Tenmile geysers, in Utah and Chimayó geyser in New Mexico). At shallow depths the bubble volume fraction ranges from 0 to 0.8, eruption velocities range from 2 to 20 m/s and flash depths are predominately shallow ranging from 5 to 40 m below the surface. Annual emission of CO 2 is estimated to be (4.77 ± 1.92) × 10 3 , (6.17 ± 1.73) × 10 1 , (6.54 ± 0.57) × 10 1 t/yr for Crystal, Tenmile and Chimayó geysers, respectively.These estimates are coherent with Burnside et al. (2013) showing that the rate of CO 2 leakage from wellbores is greater than fault-parallel or diffuse CO 2 leakage. The geyser plumbing geometry consists of a vertical wellbore which allows for the upward migration of CO 2 -rich fluids due to artesian conditions. The positive feedback system of a CO 2 -driven eruption occurs within the well. Active inflow of CO 2 into the regional aquifers through faulted bedrock allows geysering to persist for decades. Crystal geyser erupts for over 24 h at a time, highlighting the potential for a wellbore in a natural environment to reach relatively steady-state high velocity discharge. Mitigating high velocity CO 2 -driven discharge from wellbores will, however, be easier than mitigating diffuse leakage from faults or into groundwater systems.

Geological storage of carbon dioxide will usually be at conditions above the critical temperature and pressure, so the carbon dioxide will exist as a single dense phase. However, conditions in the upper part of a carbon dioxide well with surface temperatures below the critical point of 31 C can lead to boiling and condensation in the well. The consequences of this are most apparent when flow rate changes, for example when a well is shut-in or if there is a well blowout. We have calculated density profiles for wells experiencing different thermal conditions to determine how bottom-hole pressures are related to wellhead pressures. There are two limiting cases, one when the fluid is in thermal equilibrium with the rock at the same horizon, the other when there is no heat exchange with the casing or the rock. We find that in deeper wells static columns can exist in a stable state with liquid to the surface, but for shallower wells or wells in depleted reservoirs that a static column can be initially unstable with two-phase conditions near the surface. In producing wells, as the flow rate increases from static conditions, the pressure and temperature at the wellhead increases until high production rates are reached when the wellhead temperature then decreases, which can be to very low values. For injection wells, bottom-hole conditions are confined between the wellhead and the reservoir temperature. In general, phase change does not prevent carbon dioxide injection. Nevertheless care is needed in shallower or depleted reservoirs for the interpretation of reservoir pressure, the use of pressure for monitoring, and in all reservoirs for the management of blowouts. Introduction Carbon dioxide (CO2) wells are used for both injection and production. Injection wells have been used in enhanced oil recovery (EOR) for many decades (Jarrell et al. 2002). CO2 wells for production from underground natural accumulations have been used to provide a source of CO2 for EOR and other industrial uses. Recently, however, interest in CO2 wells has intensified as a result of investigation into geological storage as a means of reducing atmospheric greenhouse gases. Accurate determination of downhole pressures is particularly important if pressure is being used to monitor the performance of a geological storage reservoir. Reliable knowledge of bottom hole pressure is also helpful in preventing injection above the pressures than can damage the formation (Kelly, 2006). While bottom-hole pressure can be measured using gauges, there is always the prospect that over a long period of time downhole gauges may fail. Hence it is convenient to be able to calculate downhole pressure from wellhead pressure. CO2 has a critical pressure of 7.38 MPa [1071 psi] and critical temperature of 31.0 C, so if the fluid is near usual surface temperatures, conditions in the upper part of a well can cross the saturation line of CO2 with boiling and condensation in the well if fluid pressures are in the vicinity of the critical pressure. Furthermore, near the saturation line of CO2, fluid properties display severely nonlinear behavior that makes numerical simulation challenging. This parallels the situation in gas condensate wellbore modeling where retrograde condensation, liquid holdup and varying fluid composition make pressure drop calculations difficult (Sadegh et al 2006). This issue of phase change is usually not of concern during injection of CO2 for EOR, as EOR normally involves continuous columns of liquid to the surface because of the reservoir pressures required for minimum miscibility. For example, in the Denver Unit CO2 flood, injection pressure is around 12.4 MPa (Fleming et al. 1992), far above the critical pressure at 7.38 MPa. As another example, measurements of pressure and temperature during EOR described by Kelly (2006) have surface pressures always above 8.6 MPa even though some of the wells have fluid temperatures at the surface around 27 C, hence below the critical temperature.

Hematogenous dissemination of Mycobacterium tuberculosis (M. tb) occurs during both primary and reactivated tuberculosis (TB). Although hematogenous dissemination occurs in non-HIV TB patients, in ∼80% of these patients, TB manifests exclusively as pulmonary disease. In contrast, extrapulmonary, disseminated, and/or miliary TB is seen in 60–70% of HIV-infected TB patients, suggesting that hematogenous dissemination is likely more common in HIV+ patients. To understand M. tb adaptation to the blood environment during bacteremia, we have studied the transcriptome of M. tb replicating in human whole blood. To investigate if M. tb discriminates between the hematogenous environments of immunocompetent and immunodeficient individuals, we compared the M. tb transcriptional profiles during replication in blood from HIV- and HIV+ donors. Our results demonstrate that M. tb survives and replicates in blood from both HIV- and HIV+ donors and enhances its virulence/pathogenic potential in the hematogenous environment. The M. tb blood-specific transcriptome reflects suppression of dormancy, induction of cell-wall remodeling, alteration in mode of iron acquisition, potential evasion of immune surveillance, and enhanced expression of important virulence factors that drive active M. tb infection and dissemination. These changes are accentuated during bacterial replication in blood from HIV+ patients. Furthermore, the expression of ESAT-6, which participates in dissemination of M. tb from the lungs, is upregulated in M. tb growing in blood, especially during growth in blood from HIV+ patients. Preliminary experiments also demonstrate that ESAT-6 promotes HIV replication in U1 cells. These studies provide evidence, for the first time, that during bacteremia, M. tb can adapt to the blood environment by modifying its transcriptome in a manner indicative of an enhanced-virulence phenotype that favors active infection. Additionally, transcriptional modifications in HIV+ blood may further accentuate M. tb virulence and drive both M. tb and HIV infection.

In this paper a rigorous dual-porosity model is formulated, which accurately represents the coupling between large-scale fractures and the micropores within dual porosity media. The overall structure of the porous medium is conceptualized as being blocks of diffusion dominated micropores separated by natural fractures (e.g. cleats for coal) through which Darcy's flow occurs. In the developed model, diffusion in the matrix blocks is fully coupled to the pressure distribution within the fracture system. Specific assumptions on the pressure behaviour at the matrix boundary, such as step-time function employed in some earlier studies, are not invoked. The model involves introducing an analytical solution for diffusion within a matrix block, and the resultant combined flow equation is a nonlinear integro-(partial) differential equation. Analyses to the equation in this text, in addition to the theoretical development of the proposed model, include: (1) discussion on the "fading memory" of the model; (2); one-dimensional perturbation solution subject to a specific condition; and (3) asymptotic analyses of the "long-time" and "short-time" responses of the flow. Two previous models, the Warren-Root and the modified Vermeulen models, are compared with the proposed model. The advantages of the new model are demonstrated, particularly for early time prediction where the approximations of these other models can lead to significant error.