Reduction In Gas Permeability Research Articles

High‐Density Polyethylene Micro‐ and Nanocomposites: Effect of Particle Shape, Size and Surface Treatment on Polymer Crystallinity and Gas Permeability

AbstractSummary: High‐density polyethylene (HDPE) micro‐ and nanocomposites with spherical and platelike inclusions were prepared and the effect of filler particles on polymer crystallinity and gas permeability was investigated. Platelike inclusions strongly reduce the polymer permeability coefficient, while spherical ones have no influence on it, irrespective of their size. The reduction in gas permeability depends on the average aspect ratio of the inclusions, which in turn depends on the exfoliation of the organo‐montmorillonites (OM) and consequently on its surface treatment.A TEM micrograph of 3 vol.‐% 2C18 · M‐HDPE nanocomposite, showing partial exfoliation of the organo‐montmorillonite.imageA TEM micrograph of 3 vol.‐% 2C18 · M‐HDPE nanocomposite, showing partial exfoliation of the organo‐montmorillonite.

Gas Permeability of Partially Hydrated Geosynthetic Clay Liners

A series of gas permeability tests were performed on four partially hydrated geosynthetic clay liners (GCLs) (GCL1, GCL2, GCL3, and GCL4). All GCLs consisted of essentially dry bentonite (powder or granular) sandwiched between geotextile layers. The geotextiles were held together as a composite material by needle-punching, except GCL-4, which was stitch bonded. GCL-2 had a special characteristic, which consisted of a cover nonwoven geotextile layer impregnated with powdered bentonite. The gas permeability was found to be very sensitive to the change of moisture content and volumetric water content. The results also highlighted the effects of the GCL structures (bentonite impregnation, needle punching, and stitch bonding) and bentonite forms (granular and powdered) on the gas permeability. The needle punched GCLs tended to have lower gas permeability than the stitch bonded GCLs, and the GCLs containing granular bentonite tended to have higher gas permeability than the GCLs containing powdered bentonite. The bentonite impregnation of the nonwoven geotextile also contributed to lower gas permeability. For comparable conditions, these effects resulted in a reduction of up to three orders of magnitude of gas permittivity from one GCL to another. However, the effect of the differences between the GCLs on gas permeability, at high volumetric water content (>70%), was overridden by the presence of the overburden pressure during hydration. Furthermore, the overburden pressure also had an important role in the reduction of gas permeability, which implies that the GCL should be subjected to confinement at the time of installation or hydration in order to obtain a low gas permeability.

Structure and properties of nitrile rubber (NBR)–clay nanocomposites by co‐coagulating NBR latex and clay aqueous suspension

AbstractNitrile rubber (NBR)–clay nanocomposites were prepared by co‐coagulating the NBR latex and clay aqueous suspension. Transmission electron microscopy showed that the silicate layers of clay were dispersed in the NBR matrix at the nano level and had a planar orientation. X‐ray diffraction indicated that there were some nonexfoliated silicate layers in the NBR–clay nanocomposites. Stress–strain curves showed that the silicate layers generated evident reinforcement, modulus, and tensile strength of the NBR–clay nanocomposites, which were significantly improved with an increase in the amount of clay, and strain‐at‐break was higher than that of the gum NBR vulcanizate when the amount of clay was more than 5 phr. The NBR–clay nanocomposites exhibited an excellent gas barrier property; the reduction in gas permeability in the NBR–clay nanocomposites can be described by Nielsen's model. Compared with gum NBR vulcanizate, the oxygen index of the NBR–clay nanocomposites increased slightly. The feasibility of controlling rubber flammability via the nanocomposite approach needs to be evaluated further. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3855–3858, 2003

ポリ（１‐トリメチルシリル‐１‐プロピン）の紫外線照射下および未照射状態での臭素化反応とそれらの膜の気体透過特性

Bromination of poly (1-trimethylsilyl-1-propyne) [PMSP] films were performed with and without ultraviolet (UV) irradiation. Bromine atoms were added to carbon-carbon double bonds on the chain backbone of PMSP without UV irradiation. In the case of bromination with UV irradiation, removal of trimethylsilyl groups and oxidation occurred on the UV-irradiated side of the polymer film, while the non-irradiated side had the same structure as that of films brominated without UV irradiation. As bromine content in the polymer increases, the gas permeability decreases. The reduction in gas permeability is dependent on a decrease in gas diffusivity. Unlike conventional glassy polymers, PMSP and brominated PMSP films do not exhibit decreasing gas permeabilities with increasing penetrant size. For example, permeability coefficients of hydrocarbons in these films increase as hydrocarbon penetrant size increases. No difference between the gas permeabilities of irradiated and non-irradiated films is observed. As bromine content increases, the activation energies of permeation (E p) increase because of higher activation energies of diffusion (E D). However, the activation energies of permeation decrease with increasing critical temperature (T c) of the penetrants as a result of a decrease in the heat of solution (ΔH s). No difference between the activation energies of permeation for irradiated and non-irradiated films is observed.

Transport properties of polyimide/silica composite membranes.

Polyimide/silica composite membranes were prepared by the sol-gel reaction of tetraethoxysilane, methyltriethoxysilane or phenyltriethoxysilane in the solution of polyamic acid prepared by condensation of equimolar amount of pyromellitic dianhydride, 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride or 2, 2-bis(3, 4-dicarboxyphenyl)hexafluoropropane dianhydride with 4, 4′-oxydianiline in N-methyl pyrollidone. Silica-coated polyimide membranes were also prepared by the sol-gel method. Gas permeation for H2, CO2, CO, O2, N2 and CH4 and water vapor permeation were reported. A slight reduction in gas permeability was observed for the composite membrane. The permeability of water vapor increased in polyimide/silica composite membranes, while silica coating resulted in a reduction of the permeability. Transient sorption and desorption experiments were also investigated at water vapor activity of 0.5. An increase in permeability of water vapor can be attributable to an increase in solubility of water vapor due to the presence of hydroxy species of silica.

Effects of Physical Aging on Viscoelastic and Ultrasonic Properties of Poly[1-(trimethylsilyl)-1-propyne] Films

Effects of physical aging and heat-treatment on the viscoelastic and ultrasonic properties of poly[1-(trimethylsilyl)-1-propyne] (designated as PTMSP) films were examined. The loss modulus and loss tangent decreased with physical aging and heat-treatment, and the attenuation coefficient increased. However the storage modulus and ultrasonic velocity little changed with heat-treatment. This indicates that no conformational change occurs in backbone carbon with physical aging and heat-treatment, but aggregation of substituents may change. Accordingly, reduction in gas-permeability with physical aging is ascribable to the change in the aggregation of substituents. Furthermore, we found that casting solvents and catalysts affect viscoelastic and ultrasonic properties of PTMSP films as well as gas-permeability.

Foam Flow Through an Oil-Wet Porous Medium: A Laboratory Study

Summary A laboratory study of the steady generation and flow of gas and surfactant solution through an oil-wet porous medium indicates that foam is formed and is effective in reducing gas permeability. A comparison of the flow characteristics of foam in oil-wet and water-wet media showed that at similar surfactant concentrations gas permeability reduction in both systems is approximately equal. The ability to form stable foam in situ in an oil-wet porous medium appears to result from the alteration of the initially hydrophobic surface to hydrophilic by two mechanisms: surface tension reduction and surfactant adsorption. Wettability alteration of the hydrophobic surface is evidenced by a dramatic shift in liquid relative permeability when surfactant is present in the aqueous phase. The liquid relative permeability curve of the oil-wet porous medium, in the presence of surfactant, essentially matched that of the water-wet porous medium. Such shifts in liquid relative permeability have not been observed for foam flow in strongly water-wet porous media. No alteration in either liquid or gas relative permeability occurred with added surfactant when a residual mineral oil was present in the oil-wet system. Transient measurements, however, indicated the formation of foam in the water-wet system when residual oil was present.

The Effect of Microscopic Heterogeneity on CO2-Foam Mobility: Part 1--Mechanistic Study

Summary The mixing and flow behavior of a CO2/surfactant-solution/oil system in porous media depends on the pore structure. Two-dimensional (2D) flow-visualization experiments in several glass micromodels, each with a different length scale of heterogeneity, were performed at reservoir conditions. The mechanisms associated with gas permeability reduction were investigated in terms of microscopic heterogeneity, presence of oil phase, surfactant concentration, and flow rate in secondary and tertiary miscible CO2 floods. Results showed that foam can be generated by upstream and downstream snapoff. Fluid diversion was obtained not only by lamellae and foam, but also by multiple interfaces of CO2, surfactant solution, and oil. depending on the pore structure of the micromodel. The most important factors in the in-situ generation of foam, however, were the mixing of fluids and the aspect ratio of the pore structure. Introduction CO2 field projects have frequently experienced early gas breakthrough, and production will stop when an uneconomically high CO2/oil ratio is attained. Both high-pressure gas-foams and chemical gels are currently being considered for use as high-permeability-zone blocking agents--i.e., in profile modification--in many on-going CO2 flooding operations. This paper presents our preliminary investigation into the mechanisms responsible for CO2 fluid diversion, increased CO2 sweep efficiency, and the mobilization of bypassed oil when using high-pressure CO2-foam as a blocking agent. The capillary-tube model was used in one of the first attempts to study the generation and propagation Of a single lamella or bubble. Fried reported that in his glass-tube model, larger foam bubbles subdivided into smaller bubbles as they passed through pore constrictions. At the same time, some of the oil in the region invaded by the foam became emulsified, and the newly formed oil particles soon became immobile. He reported that this foam subdivision and emulsification could have been responsible for the resulting flow blockage. JPT P. 872^

Mechanics Of Foam Flow In Porous Media And Applications

Abstract Foams are receiving increasing attention in the petroleum industry in a number of roles, notably as mobility control agents and blocking materials in enhanced recovery operations. This paper discusses the rheology of foams in general, and then examines the mechanics of foam flow through porous media. It is shown that appropriate foams can indeed improve the recovery efficiency of a given process, and foams can serve as temporary blocking agents. The paper discusses the mechanics of foam generation, and the effects of the nature of surfactant, concentration, shear rate-related to pore velocity, pressure and temperature on foam quality and stability, both in a porous medium and in capillaries. These two characteristics are intimately related. The apparent viscosity and mobility of a foam in a porous medium is of direct concern in any process where foam is used as a mobility control agent. It is seen that the apparent viscosity decreased with increased shear rate and decreasing quality. The flow mechanics of foam are still open to question. This paper examines both views, viz. foam flowing as an integral material. and gas flowing separately. The importance of the type of porous medium in foam viscosity is pointed out. The blocking action in a porous medium is also discussed. Experimental evidence suggests that foam tends to flow in the larger pores, while temporary blockage seems to occur in the smaller pores. Capillary forces have considerable influence in this regard. Twenty one experimental runs have been conducted in the presence of oil and water in this run. A few other runs were conducted to investigate the foam flow mechanism in the presence of water alone. In the presence of oil, the flow of foam has been experimentally investigated both in homogeneous and in heterogeneous (in the presence of a bottom-water zone) porous media. Surfactant concentration, injection pressure, oil-to- water viscosity ratio, and oil-to-water zone thickness and permeability ratios appear to have a prominent role in oil recovery with foam. In the presence of bottom water, foam is very effective in blocking the bottom-water zone for subsequent nitrogen injection. Consequently, the oil recovery with foam is improved manifold over conventional waterflooding. Introduction Fried(1) was the earliest researcher who studied the usefulness of foam in enhancing the displacement efficiency in oil recovery. He reported that foam causes a rapid reduction in gas phase relative permeability, leading to delayed gas breakthrough. Hecontended that the presence of surfactant alone did not improve the oil recovery and that the improvement with foam was mainly due to reduction in gas permeability. He observed that the presence of surfactant increased the residual gas saturation. His observation would suggest that the relative permeability to gas is not a single-valued function of saturation and the curve shifts to the left as the interfacial forces resisting flow increase. He showed that the flow resistance of the foam increases with increasing surfactant concentration. Therefore, the effective permeability to gas is also a multivalued function of surfactant concentration.

Effects of Pressure and Partial Water Saturation on Gas Permeability in Tight Sands: Experimental Results

Summary Effective permeability to gas with various degrees of brine saturation has been measured in the laboratory for several very tight sandstones from the Spirit River formation of Alberta, Canada. Gas permeability as low as 20 × 10 -9 darcy was measured successfully with a pulse-decay permeameter with nitrogen as the mobile fluid. Results show that gas permeability depends very strongly on the degree of saturation, with 40% saturation causing permeability to decrease an order of magnitude relative to the dry rock. Therefore, accurate knowledge of in-situ saturations is crucial before natural-gas production rates can be estimated in these formations. The experiments also show that confining pressure causes significant permeability reduction in these sandstones. A Spirit River sample recovered from 2133.6 m and subjected to in-situ levels of pore pressure and confining pressure shows a seven fold reduction of gas permeability. It also was found that as brine saturation increased, the sensitivity of the rock's permeability to small changes in confining pressure increased. Introduction In recent years the importance of natural gas contained in low-permeability rock has increased tremendously. Reservoirs that once were dismissed as too tight now are being reevaluated in the light of new technology, such as massive hydraulic fracturing. In some cases, very tight gas-saturated rock is found directly above or below higher-permeability gas reservoirs, which creates the possibility that gas from the tight sand can migrate vertically into the producing formation. In any case, the permeability of the tight rock is of utmost importance in estimating the future recoverable reserves and the recovery rate. The most common method of determining permeability in cores recovered from depth has been to measure air permeability in systems that apply only enough pressure to the core to prevent gas flow around the jacket. The results of this study indicate that gas permeability of tight sandstones determined by this method can be an order of magnitude higher than when in-situ levels of confining pressure are applied. Using steady-state flow methods to measure permeability of these samples with confining pressure becomes quite difficult because long times are required to establish equilibrium conditions. The addition of partial water or brine saturation further reduces gas permeability, compounding the problem. For these reasons, we have constructed an apparatus that uses a fast and accurate pulse-decay technique and allows independent control of confining pressure (pc), pore pressure (pp), and fluid saturation (Sw). Permeability as low as 20 × 10 -9 darcy can be measured quite easily with this equipment. The samples studied here are from the Spirit River member of the Fahler formation in western Alberta, Canada. This formation is believed to contain large volumes of natural gas in low-porosity, tight sandstones. Spirit River samples are denoted by SR followed by a number that corresponds to the depth (in feet) from which they were recovered. Detailed mineralogy data from thin-sectioned, X-ray diffraction, and scanning electron microscope (SEM) methods are given in Table 1. Experimental Technique A pulse-decay technique was used to make the large number of permeability measurements required for this experiment in a reasonable period of time. The concept of this method has been described by a number of experimenters, including Brace et al., Sanyal et al., and Zoback and Byerlee. JPT P. 930^