MECHANISTIC STUDIES OF IMPROVED FOAM EOR PROCESSES

The objective of this research is to widen the application of foam to enhanced oil recovery (EOR) by investigating fundamental mechanisms of foams in porous media. This research will lay the groundwork for more applied research on foams for improved sweep efficiency in miscible gas, steam and surfactant-based EOR. Task 1 investigates the pore-scale interactions between foam bubbles and polymer molecules. Task 2 examines the mechanisms of gas trapping, and interaction between gas trapping and foam effectiveness. Task 3 investigates mechanisms of foam generation in porous media. The most significant progress during this period was made on Tasks 2 and 3. Research on Task 2 focused on simulating the effect of gas trapping on foam mobility during foam injection and during subsequent injection of liquid. Gas trapping during liquid injection is crucial both to injectivity during liquid injection in surfactant-alternating-gas foam (SAG) projects and also provides a window into trapping mechanisms that apply during foam flow. We updated our simulator for foam (Rossen et al., 1999; Cheng et al., 2000) to account explicitly for the first time for the effects of gas trapping on gas mobility in foam and in liquid injected after foam, and for the effects of pressure gradient on gas trapping. The foam model fits steady-state foam behavior in both high- and low-quality flow regimes (Alvarez et al., 2001) and steady-state liquid mobility after foam. The simulator also fits the transition period between foam and liquid injection in laboratory corefloods qualitatively with no additional adjustable parameters. Research on Task 3 focused on foam generation in homogeneous porous media. In steady gas-liquid flow in homogeneous porous media with surfactant present, there is often observed a critical injection velocity or pressure gradient {del}{sub p}{sup min} at which foam generation occurs. Earlier research on foam generation was extended with extensive data for a variety of porous media, permeabilities, gases (N{sub 2} and CO{sub 2}), surfactants, and temperatures. For bead- and sandpacks, {del}{sub p}{sup min} scales like (1/k), where k is permeability, over 2 1/2 orders of magnitude in k; for consolidated media, the relation is more complex. For dense-CO{sub 2} foam, {del}{sub p}{sup min} exists but can be less than 1 psi/ft. If pressure drop, rather than flow rates, is fixed, one observes an unstable regime between stable ''strong'' and ''coarse'' foam regimes; in the unstable regime {del}{sub p} is nonuniform in space or variable in time. Results are interpreted in terms of the theory of foam mobilization at a critical pressure gradient (Rossen and Gauglitz, 1990)

Методологія визначення оптимальних технологічних параметрів транспортної інфраструктури при обслуговуванні зернових вантажопотоків

Комплексно проаналізовано на прикладі функціонування багатоканальної динамічної системи з кінцевим числом степенів свободи можливість покращення економічних показників транспортної системи при узгодженні інфраструктурних параметрів для обслуговування підприємств елеваторно-складського господарства. Охарактеризована залежність числового значення логістичних витрат в системі з двома вузлами обслуговування.Комплексно проанализирована на примере функционирования многоканальной динамической системы с конечным числом степеней свободы возможность улучшения экономических показателей транспортной системы при согласовании инфраструктурных параметров для обслуживания предприятий элеваторно-складского хазяйства. Охарактеризована зависимость числового значения логистических расходов в системе с двумя узлами обслуживания.In possibility of improving the economic indicators of a transport system is fully analyzed in the concordance of infrastructural parameters for maintenance of elevator-store enterprises with using, as an example, functioning of a multichannel dynamic system with the finite number of degrees of freedom. The numerical value of logistic charges for the system with two knots is described

Mechanics of Bubbles in Sludges and Slurries: Modeling Studies of Particulate Materials

(1) Model effective compressibility of bubbles dispersed in a rigid porous medium. Account for capillary forces on bubbles that restrain bubble response to ambient pressure changes, and therefore affect compressibility of bubbles. Account for diffusive growth process in context of strong capillary forces, that may bias distribution of bubble sizes in population and thereby affect effective compressibility. (2) Model yield stress and effective compressibility of a dispersion of gas, solids and liquid (assumed here to be deformable), focusing on capillary interactions between solid and bubbles, and effects of these interactions on mechanical properties

Mechanistic Studies of Improved Foam EOR Processes

The objective of this research is to widen the application of foam to enhanced oil recovery (EOR) by investigating fundamental mechanisms of foams in porous media. This research will lay the groundwork for more applied research on foams for improved sweep efficiency in miscible gas, steam and surfactant-based EOR. Task 1 investigates the pore-scale interactions between foam bubbles and polymer molecules. Task 2 examines the mechanisms of gas trapping, and interaction between gas trapping and foam effectiveness. Task 3 investigates mechanisms of foam generation in porous media. The most significant progress during this period was made on Tasks 2 and 3. Research on Task 2 focused on experiments on gas trapping during liquid injection. A novel apparatus, similar to that in Kibodeaux and Rossen (1997), monitors average water saturation in a core moment-by-moment by weighing the core. Our experiments find that water saturation increases more during liquid injection than previously conjectured--in other words, less gas is trapped by liquid injection than previously thought. A number of unexpected trends in behavior were observed. It appears that these can be reconciled to previous theory of gas trapping by foam (Cheng et al., 2001) given that the experimental conditions were different from previous experiments. Results will be described in detail in the PhD dissertation of Qiang Xu, expected to be completed in early 2003. Regarding Task 3, recent laboratory research in a wide range of porous media shows that creating foam in steady flow in homogeneous media requires exceeding a minimum pressure gradient (Gauglitz et al., 2002). Data fit trends predicted by a theory in which foam generation depends on attaining sufficient {del}p to mobilize liquid lenses present before foam generation. Data show three regimes: a coarse-foam regime at low {del}p, strong foam at high {del}p, and, in between, a transient regime alternating between weaker and stronger foam. We for the first time incorporated into a population-balance foam model a bubble-creation function that depends on pressure gradient (Rossen and Gauglitz, 1990). The new model reproduces the three foam regimes seen in the laboratory, the abrupt occurrence of foam generation at a threshold velocity or pressure gradient, hysteresis in experimental results, the interplay between foam stability and foam generation, the effect of injected liquid fractional flow on foam generation, and foam behavior in the high-quality and low-quality steady-state strong-foam regimes. The details of the lamella-creation function have little effect on rheology of strong foam, which is controlled by other mechanisms. The predicted fractional-flow curves are complex. This model is a necessary step toward quantitative prediction of foam performance in the field

Mechanistic Studies of Improved Foam EOR Processes

The objective of this research is to widen the application of foam to enhanced oil recovery (EOR) by investigating fundamental mechanisms of foams in porous media. This research will lay the groundwork for more applied research on foams for improved sweep efficiency in miscible gas, steam and surfactant-based EOR. Task 1 investigates the pore-scale interactions between foam bubbles and polymer molecules. Task 2 examines the mechanisms of gas trapping, and interaction between gas trapping and foam effectiveness. Task 3 investigates mechanisms of foam generation in porous media

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Mechanics of Bubbles in Sludges and Slurries

The Hanford Site has 177 underground waste storage tanks that are known to retain and release bubbles composed of flammable gases. Characterizing and understanding the behavior of these bubbles is important for the safety issues associated with the flammable gases for both ongoing waste storage and future waste-retrieval operations. The retained bubbles are known to respond to small barometric pressure changes, though in a complex manner with unusual hysteresis occurring in some tanks in the relationship between bubble volume and pressure, or V-P hysteresis. With careful analysis, information on the volume of retained gas and the interactions of the waste and the bubbles can be determined. The overall objective of this study is to create a better understanding of the mechanics of bubbles retained in high-level waste sludges and slurries. Significant advancements have been made in all the major areas of basic theoretical and experimental method development

Mechanics of Bubbles in Sludges and Slurries

This project is focusing on key issues associated with the flammable gas safety hazard and its role in safe storage and in future waste operations such as salt-well pumping, waste transfers, and sluicing and retrieval of tank waste. The purpose of this project is to develop a basic understanding of how single bubbles (of flammable gases) behave in representative waste simulants and then develop a framework for predicting macroscopic full-tank behavior from the underlying single-bubble behavior. The specific objectives of this research are as follows: 1. quantitatively describe the interaction of bubbles with waste materials (both sludges and slurries) to understand the physical mechanisms by which barometric pressure changes give rise to a hysteresis between level and pressure 2. develop improved methods for estimating retained gas by properly accounting for the interactions of bubbles with the waste 3. determine how to estimate waste physical properties from the observed hysteresis and the limitations of these estimates 4. determine how barometric pressure fluctuations induce slow upward migration and release of gas bubbles

Development of More-Efficient Gas Flooding Applicable to Shallow Reservoirs Progress Report

The objective of this research is to widen the applicability of gas flooding to shallow oil reservoirs by reducing the pressure required for miscibility using gas enrichment and increasing sweep efficiency with foam. Task 1 examines the potential for improved oil recovery with enriched gases. Subtask 1.1 examines the effect of dispersion processes on oil recovery and the extent of enrichment needed in the presence of dispersion. Subtask 1.2 develops a fast, efficient method to predict the extent of enrichment needed for crude oils at a given pressure. Task 2 develops improved foam processes to increase sweep efficiency in gas flooding. Subtask 2.1 comprises mechanistic experimental studies of foams with N{sup 2} gas. Subtask 2.2 conducts experiments with CO{sup 2} foam. Subtask 2.3 develops and applies a simulator for foam processes in field application. Regarding Task 1, several key results are described in this report relating to subtask 1.1. In particular, we show how for slimtube experiments, oil recoveries do not increase significantly with enrichments greater than the MME. For field projects, however, the optimum enrichment required to maximize recovery on a pattern scale may be different from the MME. The optimum enrichment is likely the result of greater mixing in reservoirs than in slimtubes. In addition, 2-D effects such as channeling, gravity tonguing, and crossflow can impact the enrichment selected. We also show the interplay between various mixing mechanisms, enrichment level, and numerical dispersion. The mixing mechanisms examined are mechanical dispersion, gravity crossflow, and viscous crossflow. UTCOMP is used to evaluate the effect of these mechanisms on recovery for different grid refinements, reservoir heterogeneities, injection boundary conditions, relative permeabilities, and numerical weighting methods including higher-order methods. For all simulations, the reservoir fluid used is a twelve-component oil displaced by gases enriched above the MME. The results for subtask 1.1 show that for 1-D enriched-gas floods, the recovery difference between displacements above the MME and those at or near the MME increases significantly with dispersion. The trend, however, is not monotonic and shows a maximum at a dispersivity (mixing level) of about 4 ft. The trend is independent of relative permeabilities and gas trapping for dispersivities less than about 4 ft. For 2-D enriched gas floods with slug injection, the difference in recovery generally increases as dispersion and crossflow increase. The magnitude of the recovery differences is less than observed for the 1-D displacements. Recovery differences for 2-D models are highly dependent on relative permeabilities and gas trapping. For water alternating gas (WAG) injection, the differences in recovery increase slightly as dispersion decreases. That is, the recovery difference is significantly greater with WAG at low levels of dispersion than with slug injection. For the cases examined, the magnitude of recovery difference varies from about 1 to 8 percent of the original oil-in-place (OOIP). Regarding Task 2, three results are described in this report: (1) New experiments with N{sup 2} foam examined the mobility of liquid injected following foam in alternating-slug (SAG) foam processes. These experiments were conducted in parallel with a simulation study of foam for acid diversion in well stimulation. The new experiments qualitatively confirm several of the trends predicted by simulation. (2) A literature study finds that the two steady-state foam-flow regimes seen with a wide variety of N{sup 2} foams also appears in many studies of CO{sup 2} foams, if the data are replotted in a format that makes these regimes clear. A new experimental study of dense CO{sup 2} foam here failed to reproduce these trends, however; the reason remains under investigation. (3) A number of published foam models were examined in terms of the two foam-flow regimes and using fractional-flow theory. At least two of the foam models predict the two foam-flow regimes. Fractional-flow theory predicts that large-scale simulation using one of the models would lead to numerical artifacts, however