Dynamic Storage Capacity Research Articles

Impact-driven pressure management via targeted brine extraction—Conceptual studies of CO2 storage in saline formations

Large-scale pressure buildup in response to carbon dioxide (CO2) injection in the subsurface may limit the dynamic storage capacity of suitable formations, because elevated pressure can impact caprock integrity, induce reactivation of critically stressed faults, drive CO2 and/or brine through conductive features into shallow groundwater resources, or may affect existing subsurface activities such as oil and gas production. It has been suggested that pressure management involving the extraction of native fluids from storage formations can be used to control subsurface pressure increases caused by CO2 injection and storage, thereby limiting the possibility of unwanted effects. In this study, we introduce the concept of “impact-driven pressure management (IDPM),” which involves optimization of fluid extraction to meet local (not global) performance criteria (i.e., the goal is to limit pressure increases primarily where environmental impact is a concern). We evaluate the feasibility of IDPM for a hypothetical CO2 storage operation in an idealized multi-formation system containing a critically stressed fault zone. Using a newly developed analytical solution, we assess alternative fluid extraction schemes and test whether a predefined performance criterion can be achieved, in this case the maximum allowable pressure near the fault zone. Alternative strategies for well placement are evaluated, comparing near-injection arrays of extraction wells with near-impact arrays. Extraction options include active extraction wells and (passive) pressure relief wells, as well as combinations of both, with and without reinjection into the subsurface. Our results suggest that strategic well placement and optimization of extraction may allow for a significant reduction in the brine extraction volumes. Additional work is required in the future to test the general concept of IDPM for more complex and realistic CO2 storage scenarios.

Understanding waterflood performance with modern analytical techniques

Application of reservoir simulation models to understand and forecast reservoir performance is the norm. In contrast, analytical tools provide required simplicity while capturing the events occurring at smaller time scales, which are ordinarily sacrificed in numerical simulations to keep the run time reasonable.This study illustrates the use of some recently developed analytical tools with high-frequency production data to understand field-wide and well-based flood performance. Also, modified definitions of coupled capacitance–resistance-aquifer model and reciprocal productivity index are introduced. Dynamic flow and storage capacity curve concept is developed using production data only. The use of these curves for characterizing the type of interwell and reservoir connectivity is illustrated with two case studies.The methods presented are based on fundamental-reservoir engineering concepts; therefore, they are versatile and easy to use. Synthetic examples illustrate and verify the methods used in the study. Case studies demonstrate the power of integrating analytical models for better understanding of evolving waterfloods.

CO2 storage in a depleted gas field: An overview of the CO2CRC Otway Project and initial results

The Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) Otway Project in Australia is the first heavily monitored pilot site for CO2 storage in a depleted natural gas reservoir. With the site characterisation and risk analysis complete, the new CRC-1 injection well was drilled in April 2007. An updated static and dynamic model forecast an injected gas transit time of between 4 and 8months between CRC-1 injection and Naylor-1 observation wells. Injection began on March 18th 2008 and was halted on August 29th 2009 with 65,445 tonnes of CO2 mixed gas stored. Two pulses of tracer compounds were added to help identify the injected CO2 from other naturally occurring CO2 and to track dispersion and diffusion.Assurance monitoring included surveillance of the atmosphere, soil gas and shallow groundwater. To date, no tracer compounds have been detected above background levels in samples taken as part of the assurance monitoring system. Monitoring of the reservoir has been accomplished with a combined geophysical and geochemical approach. Formation fluids are sampled at pressure with the multilevel U-Tube system. The transient geochemistry at the observation well has: (1) recorded injected gas arrival at the Naylor-1 observation well; (2) recorded tracer compound arrival at Naylor-1; (3) shown a mixing trend between the isotopic signature of the Naylor indigenous CO2 and that of the injection supply gas; and (4) provided an estimate for the dynamic storage capacity for a portion of the Naylor reservoir. The data collected are compared with the pre-injection dynamic model forecasts and provide a means of calibration.The CO2CRC Otway Project has successfully demonstrated the storage of CO2 in a depleted gas field. Geochemical assurance monitoring and reservoir surveillance will continue post injection. Continued analysis of the data will serve to reduce uncertainty in forecasting long term fate of the injected CO2 mixed gas.

On scale and magnitude of pressure build‐up induced by large‐scale geologic storage of CO2

AbstractThe scale and magnitude of pressure perturbation and brine migration induced by geologic carbon sequestration is discussed assuming a full‐scale deployment scenario in which enough CO2 is captured and stored to make relevant contributions to global climate change mitigation. In this scenario, the volumetric rates and cumulative volumes of CO2 injection would be comparable to or higher than those related to existing deep‐subsurface injection and extraction activities, such as oil production. Large‐scale pressure build‐up in response to the injection may limit the dynamic storage capacity of suitable formations, because over‐pressurization may fracture the caprock, may drive CO2/brine leakage through localized pathways, and may cause induced seismicity. On the other hand, laterally extensive sedimentary basins may be less affected by such limitations because (i) local pressure effects are moderated by pressure propagation and brine displacement into regions far away from the CO2 storage domain; and (ii) diffuse and/or localized brine migration into overlying and underlying formations allows for pressure bleed‐off in the vertical direction. A quick analytical estimate of the extent of pressure build‐up induced by industrial‐scale CO2 storage projects is presented. Also discussed are pressure perturbation and attenuation effects simulated for two representative sedimentary basins in the USA: the laterally extensive Illinois Basin and the partially compartmentalized southern San Joaquin Basin in California. These studies show that the limiting effect of pressure build‐up on dynamic storage capacity is not as significant as suggested by Ehlig‐Economides and Economides, who considered closed systems without any attenuation effects. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd

Flow processes and pressure evolution in aquifers during the injection of supercritical CO 2 as a greenhouse gas mitigation measure

ABSTRACT Regional saline aquifers offer the greatest potential for very large-scale underground CO 2 storage as a means of mitigating greenhouse gas emissions. Their dynamic storage capacity, in terms of induced increases in formation pressure, will limit the rate at which CO 2 can be injected and may ultimately limit the amount of CO 2 that can be stored. Generic flow models were generated to examine the effects on pressure evolution of various reservoir parameters (dimensions, permeability, porosity, presence and nature of flow barriers). CO 2 injection involves dominantly hydrogeological (single-phase flow) processes in much of the reservoir and surrounding adjacent strata, with additional two-phase flow effects around the CO 2 plume itself. Large, thick aquifers with no significant flow barriers can accept high injection rates ( c . 10 million tonnes of CO 2 per year) without undue pressure effects. However, flow barriers, such as faults, increase induced pressures considerably; for reservoirs with such features, careful site characterization and operational planning will be required for large storage projects. The principles established from the generic modelling were applied to a real aquifer storage operation at Sleipner in the North Sea. Here, CO 2 is being injected into the Utsira Sand, a large relatively homogeneous reservoir. Modelling indicates that pressure increase should be negligible. In fact, observed wellhead pressures do show a small rise, but this can be attributed to temperature changes in the fluid column in the wellbore. Pressure changes in the reservoir are likely to be very small.

The heat storage capacity of a periodically heated slab under general boundary conditions

The well-known problem of evaluating the dynamic heat storage capacity of a 1D slab is analysed and extended to case of general boundary conditions and general periodic excitation profiles of any form. A general relation to calculate the storage capacity is obtained in closed form for the harmonic case. Equations in time and frequency domain to calculate the storage capacity under periodic (non-harmonic) heating are also obtained. Some particular cases are analysed and examples are given to show the applicability of the analysis.

The heat storage capacity of a solid spherical body under general periodic thermal excitation

The problem of evaluating the dynamic heat storage capacity of a solid sphere is analysed for the case of general periodic thermal excitation profiles of any form. A general relation to calculate the storage capacity is obtained in closed form for the harmonic case, and in term of Fourier series for the intermittent one, and it is shown that the harmonic heating is not the most efficient heat storage procedure. Equations in frequency domain to calculate the heat storage capacity under general periodic (non-harmonic) heating are given. A comparison with the results, in terms of storage efficiency, obtainable by lumped capacitance method and by an approximation based on linear combination of first order systems is reported.

Hydrodynamic behaviour of karstic aquifers in Boroujerd, western Iran

Considering the geological conditions of the southwest of Boroujerd and northwest of Doroud, Iran, karst development is analysed with respect to the hydrodynamic behaviour of the main draining springs of the units and the karstic aquifers are classified as either those developed in Cretaceous limestone or those developed in Oligomiocene limestone. For this purpose, the yields of the main karstic springs of the region—Absardeh and Zoorabad (Cretaceous karstic limestone aquifer), Kalamsooz and Azizabad (Oligomiocene karstic limestone aquifer)—were measured and analysed. Analysis of the recession curve is used for hydrodynamical analysis and to construct the conceptual model for estimation of karst development in the selected aquifers. Based on the results, the dynamic storage capacity of the saturated zone in Cretaceous limestone is evaluated as low to medium and that in Oligomiocene limestone as medium to high. The dynamic storage capacity of the unsaturated zone in Cretaceous limestone is evaluated as high and that in Oligomiocene limestone as low to medium. Moreover, the contribution of quickflow in karstic aquifers developed in the Cretaceous limestone drained by the Absardeh and Zoorabad springs is 23.5 and 82.2%, respectively, and that for the Kalamsooz and Azizabad springs (Oligomiocene limestone) is 5.7 and 22.5%, respectively. Flow in the Cretaceous limestone aquifer drained by the Zoorabad Spring is of concentrated type and the main flow occurs in the well-developed karstic conduits. The main flow in the Oligomiocene limestone aquifer, drained by the Kalamsooz Spring, occurs in a network of joints and fractures and the contribution of concentrated flow is very low. The transmissivity of the saturated zone in the karstic aquifer drained by the Zoorabad and Absardeh springs is medium to high and that for the Kalamsooz and Azizabad springs is found to be low.

Thermal analysis of adsorptive natural gas storages during dynamic charge phase at room temperature

The thermal behavior of an adsorptive natural gas (ANG) vessel pressurized continuously with light hydrocarbon gases and their mixture at 27 °C was analyzed using two different activated carbons. Activated carbon AC-L showed better isothermal storage capacity than AC-D due to its sufficient porous structure. However, higher adsorption capacity claimed more extreme thermal fluctuation represented by a temperature rise of 99.2 °C at the center region of the bed charged continuously with methane at 1 L min −1 up to pressure of 4 MPa, corresponding to 82.5 °C in AC-D bed. Higher charge rate of 5 L min −1 claimed severer thermal fluctuation of 116 °C in AC-L/methane system calling for a serious reduction of 26.9% in the dynamic storage capacity with respect to the isothermal storage capacity. This reduction brought the storage system to a working pressure of about 2.5 MPa rather than the desired working pressure of ∼4 MPa (about 40% reduction in storage pressure). The severest temperature rise was at the center region caused by bed poor thermal conductivity leading to limited heat transfer. High ethane and propane portions in natural gas may contribute to the thermal fluctuation of the storage system as their heats of adsorption are higher than that for methane.

The dynamic storage capacity of a periodically heated slab

The well-known problem of evaluating the dynamic heat storage capacity of a 1D slab is analysed extending the results to the more general case of periodic excitation profiles of any form. Equations in time and frequency domain to calculate the storage capacity are obtained and applied to some cases, showing that harmonic heating is not the most efficient way to store energy in finite and semi-infinite slabs. Quantitative comparisons show that, for slab of finite thickness, intermittent heating may yield up to 40% more heat storage capacity (and up to 52% for semi-infinite slab) than harmonic heating.

The effect of exothermic reactions during regeneration on the NOX trapping efficiency of a NOX storage/reduction catalyst

An unusual behavior was observed during experiments conducted at 371 and 465 °C with a commercial NOX storage/reduction catalyst: the outlet NOX concentration during the trapping phase reached a cycle minimum after regeneration, increased for 20–30 s, as expected, but then surprisingly decreased, indicating the catalyst had become more efficient in trapping the entering NOX. The results reported in this letter indicate that this phenomenon was caused by a superposition of two factors: a substantial exotherm associated with the regeneration event from reductant reacting with surface oxygen species and a negative impact of an evolving temperature profile on the dynamic NOX storage capacity.

Dynamics of storage and reaction in a monolith reactor: lean NO [formula omitted] reduction

The NO x storage and reduction performance of a series of supported Pt/BaO washcoated monolith catalysts is investigated ( y %Pt/ x %BaO/Al 2 O 3 ; y = 2 –2.6%; x = 0 –25%). Storage experiments over a range of exposure (storage) times and feed flow rates (space velocities) show the importance of the NO oxidation to NO 2 reaction. At high space velocities, kinetic limitations reduce the NO conversion and NO x trapping efficiency (fraction of NO x trapped). Higher trapping efficiencies are achieved at lower space velocities when the NO oxidation approaches the equilibrium conversion limit. The NO x trapping efficiency increases with barium loading, but the extent of increase depends on the exposure time. Cycle-averaged NO x conversions and N 2 selectivities exceeding 80% are achieved over a range of operating conditions, including cycle time, space velocity, and reductant (propylene) concentration. The NO x conversion exhibits a maximum at an intermediate cycle time, and the location and magnitude of the maximum depends on the barium loading. The conversion also achieves a maximum at an intermediate barium loading, indicating that increases in dynamic storage capacity of the catalyst do not guarantee improved reduction performance. The dependence of the trapping efficiency on the exposure (storage) time provides a good estimate for the lean storage time needed to achieve a prescribed cycle-averaged NO x conversion during cycling. The dependence of the cycle-averaged NO x conversion on barium loading parallels that of the short-time NO x storage, indicating the importance of the NO x trapping step in the overall monolith catalyst performance.

Nondestructive Evaluation of Complex Moduli in Asphalt Concrete with an Energy Approach

A modified version of the impulse-echo method is presented to nondestructively estimate the average Poisson’s ratio and the average dynamic complex bulk, shear, extensional, and longitudinal moduli of asphalt concrete specimens made of different mixtures. The estimated moduli represent an average over the volume of the specimens and over the frequency band of 10 to 50 kHz. By using principles of statistical energy analyses, the proposed methodology is based on the energydensity decay function of a diffuse wave field. The methodology allows evaluation of the energy dissipation characteristics of different asphalt concrete mixtures and their dependence on material microstructure. As a consequence, energy-density decay functions may be used to search for an optimum asphalt concrete microstructure. In this study, it was observed that the typical Superpave mixture generally exhibits higher average dynamic energy storage capacity and higher energy decay rates (i.e., loss moduli).

The storage capacity of a harmonically heated slab revisited

The physical origin of the well-known maximum occurring in the dynamic heat storage capacity of a harmonically excited stab is analysed in terms of the fundamental solutions of Fourier's equation. It is shown that, in addition to this maximum, an infinite sequence of exponentially decaying lateral minima and maxima occur which are generated by a coherent superposition of two thermal waves propagating in opposite directions within the slab. By passing from the parabolic to the hyperbolic description of heat conduction, this effect becomes much more pronounced.

Investigation of the Crick-Mitchison reverse-learning dream sleep hypothesis in a dynamical setting

Crick and Mitchison have proposed that dream sleep involves a reverse-learning (or unlearning) mechanism by which the brain eliminates internal parasitic modes from memory and avoids the overloading catastrophe. We perform stimulations on the Hopfield neural network to test this hypothesis. In our dynamical model, the neural network is allowed to learn (while awake) and unlearn (while dreaming) in alternate cycles, in much the same was as in a biological system. Our results show that with the appropriate mix of learning and unlearning (dreaming) the neural network can continue to function for ever and ever, avoiding the overloading catastrophe. As found in other palimpsest models, the dynamic storage capacity in our model is lower in comparison to the static model. This would seem to suggest that the function of dream sleep may not be primarily concerned with improving the storage capacity of the brain as is commonly thought. On the basis of this we suggest that dream sleep may be more important as a means to gradually forget weak (that is, old, irrelevant and parasitic) memories.