Secondary Pore System Research Articles

Heterogenization of 12-tungstophosphoric acid on stabilized zeolite Y

12-tungstophosphoric acid (PW12) has been supported on dealuminated zeolite Y, containing a secondary pore system with the predominant pore radii of 15 A. The interaction between the heteropolyacid and the zeolite matrix has been studied using 29Si, 27Al and 31P MAS NMR. Distribution of two types of the Keggin anions, strongly and weakly interacting with the support, has been estimated quantitatively. Increased acidic properties of the PW12/zeolite Y system were demonstrated by a change in the selectivity pattern of m-xylene transformations in the gas phase (significantly increased dealkylation and transalkylation paths at the expense of isomerization). Redox properties were evaluated in oxidation reactions with H2O2 in the liquid phase. It has been shown that the PW12/zeolite Y catalysts can selectively oxidize a number of organic compounds at relatively low temperatures.

Influence of chemical dealumination on the properties of USY zeolite

AbstractThree series of dealuminated Y zeolites have been prepared by chemical extraction of hydrothermally dealuminated Y zeolite (USY) with H2Na2EDTA, HCl and H4EDTA. The unit cell constant, mesopore distribution, acidity and extraframework aluminum (EFAL) of the zeolites were studied with XRD, chemical analyses, adsorption, IR and NH3‐TPD techniques. It was shown that H2Na2EDTA only removed EFAL species deposited in the pores of USY, by contrast, HCl and H4EDTA extract both extraframework and framework aluminum, and make the zeolite framework further dealuminated. Adsorption tests gave evidence that a secondary pore system exists in these dealuminated zeolites. H2Na2EDTA extraction increased both micropore and mesopore volumes, but after HCl and H4EDTA treatments, new mesopores formed and the micropore volume was decreased. The pyridine‐IR and NH3‐TPD measurements demonstrated that EFAL had no evident contribution to the zeolite acidity.

Changes in Physico-Chemical and Catalytic Properties of Synthetic Erionite after Various Treatment

Influence of decationization by ammonium ions and dealumination by HCl as well as calcination under self-steaming conditions at 1053 K with following treatment by ammonium ions or by HCl solution on the extent of alkali metals extraction was studied together with surface, sorption, acidic and catalytic properties of synthetic erionite. Samples were also characterized by X-ray diffraction spectra and IR skeletal vibration spectra. Results showed increasing catalytic activity and acidity after thermal treatment, followed by ion exchange with HCl or ammonium ions, which can be connected with deeper substitution of potassium cations of erionite. At the same time by the treatment under self-steaming conditions, as a result of framework dealumination, the zeolite obtained a secondary pore system, which resulted in increasing sorption capacity for aromatics, suppression of coking during o-xylene conversion and also increased diffusion of Hammet indicators into the zeolite.

Geology and Reservoir Description of a Dolomitized Upper Devonian Reef, Westerose Field, Alberta: ABSTRACT

The Westerose field produces hydrocarbons from a dolomitized Upper Devonian Leduc reef. The reef is 1.6 km wide, 5.5 km long, and up to 175 m thick. Core description, statistical analysis of whole core data, well logs, and pressure buildup data, were integrated in the development of a reservoir model. In contrast to well-known limestone reservoirs in western Canada, the organic reef margin facies and reef interior facies are not strongly differentiated. The reef interior does not contain laterally extensive barriers to vertical fluid flow. The secondary pore system dominates porosity. The large solution vugs and fossil molds are well connected through the dense matrix by a vertical fracture system. Porosity and permeability increase from the reef flank to the interior and are optimum within the lower reef interior. The reservoir model, interpreted from pore system distribution and supported by reservoir pressure response, is a disordered arrangement of permeability blocks. Cumulative probability plots indicate that the horizontal permeability data set is top truncated, with up to 35% of the highest permeability values not represented in the data set. Examination of a Leduc equivalent outcrop yielded data on pore-size frequency and porosity at scales larger as well as smaller than coremore » diameter. The sample size necessary to make representative measurements of reservoir properties can be estimated from the outcrop analysis.« less

Partial destruction of USY and its effect on the hydrothermal stability

The hydrothermal stabilities of ultrastabilized Y under 100% steam were examined in relation with the results of XRD, chemical analyses, and MAS n.m.r. The hydrothermal stability of USY was affected mainly by the retention of crystallinity, but not by the amounts of residual alkali metal oxides. The populations of Si(3Al) in sodium Y affect the partial destruction of structure during the dealumination. Some of Si(3Al) units were converted to nonframework Si(4Al) units and left the vacants larger than four OH nests in the zeolite framework, which causes the formation of secondary pore systems and amorphous fraction.

Magic-angle-spinning nuclear magnetic resonance and adsorption studies of dealumination and realumination of zeolite ZSM-5

Adsorption of nitrogen, 27Al and 1H magic angle spinning nuclear magnetic resonance show that non-framework aluminium species created by deep dealumination of zeolite H-ZSM-5 can be partially reintroduced into the framework upon treatment (2 h, 350 K) with 0.1 M aqueous solution of NaOH. However, the treatment also causes a loss of micropore volume and creates a secondary pore system. No realumination or loss of porosity are observed after dealumination performed under mild hydrothermal conditions, i.e. when the Si/Al ratio of the dealuminated material is less than ca. 25.

NMR investigations on molecular transport in ZSM-5 type zeolites containing structural defects

NMR spectroscopy is used to study the transport properties in ZSM-5 type zeolites containing structural irregularities. Using methane as a probe molecule, the structural distortions in polycrystalline aggregates are found to lead to an enhanced molecular mobility. After coking, molecular mobility is more reduced than in the monocrystalline specimen. This finding is explained by a preferential coke deposition in the secondary pore system. A variation of the concentration of non-acidic OH groups (silanol groups) indicating non-intact SiOSi bonds as structural defects of the pentasil structure, leads to characteristic changes in the sorption and diffusion properties of water. Bronsted acid sites are probed by methane self-diffusion measurements after chemisorption of ammonia and pyridine.

Characterization of the textural properties of dealuminated HY forms

The secondary pore system of dealuminated HY zeolites has been studied quantitatively at each step of the preparation procedure by electron microscopy and N 2 adsorption. The respective roles of self steaming and acid leaching in the creation of the secondary pore system have been determined. The structure of the secondary pore system can be viewed approximately as being formed by cavities of spherical shape connected by small restrictions. Although large channels have been observed to break the surface of the crystals, by far the greater part of the external surface is embedded in an amorphous layer.

Productive Lower Wilcox Distributary Channel Sands of Hallettsville Embayment, Lavaca County, Texas: ABSTRACT

Productive Lower Wilcox Distributary Channel Sands of Hallettsville Embayment, Lavaca County, Texas: ABSTRACT

Nature of Secondary Porosity Created by Dissolution of Aluminum Silicates: ABSTRACT

Porosity enhancement in sandstone reservoirs cannot be due to dissolution of aluminum silicates without implying aluminum mobility. However, aluminum has yet to be reported in reservoir fluids at greater than trace concentrations. Predicted aqueous aluminum concentrations in subsurface fluids approach level that Curtis has termed a good approximation of zero. Several studies of secondary pore systems formed by aluminum silicate dissolution demonstrate that aluminum is conserved on scale of few inches, in the form of diagenetic clay minerals--notably kaolinite. Our examinations indicate that the products of dissolution of aluminum silicate grains (which include feldspar and many rock fragments) can be accounted for in thin section primarily by the presence of adjacent pore-filling kaolinite and possibly authigenic quartz and albite. At high temperatures, the diagenetic mineral is often illite. Secondary porosity formed by dissolution of aluminum silicate grains should not necessarily be construed as adding to total porosity, but should rather be thought of as rearrangement of porosity already present. Indeed, the process may actually be harmful, inasmuch as the newly formed clay minerals can greatly reduce permeability. Calcite resorption remains the principal means of adding to total porosity through dissolution process. End_of_Article - Last_Page 311------------

Comparison of Eogenetic and Mesogenetic Porosity-Diagenetic Trends in Deeply-Buried Limestone Reservoir in West Texas: ABSTRACT

Stratigraphically trapped gaseous hydrocarbons occur in porous limestones of Atokan (Middle Pennsylvanian) age in the Chapman Deep field, along the northern shelf edge of the Delaware basin in Reeves County, Texas. These rocks were deposited as a shallow-water mosaic of cyclic algal bioherms, grainstone shoals, and low-energy interbank facies. A relatively uninterrupted sequence of porosity evolution related to early and burial diagenesis is recognized in these rocks. Syndepositional subaerial exposure resulted in the formation of a secondary pore system, including biomolds, non-fabric-selective vugs and channels, and solution-enlarged fractures. However, most of this porosity was occluded rapidly in the vadose and phreatic environments by calcite cementation, dolomitizat on, and internal sedimentation. Progressive burial to minimum depths of 13,000 ft (3,962 m) was accompanied by bulk-volume reduction via physical and chemical compaction. However, simultaneous fabric-selective dissolution rejuvenated a pore system of relatively low permeability which, enhanced by natural fractures and the presence of open stylolites, comprises the principal reservoirs in the field. Pore types include ooid and cement-solution molds; although not recognized in these rocks, burial-solution channels and vugs are reported to be relatively abundant in Smackover carbonates of the Gulf Coast region. Such tertiary porosity is easily misinterpreted as of meteoric origin, and its occurrence attests to a possible parallel evolution of eogenetic and burial-diagenetic processes and pr ducts. End_of_Article - Last_Page 955------------

Tests for absence of intraparticle diffusion effects in branched-pore systems

Tests which have been recommended for detecting the presence or absence of mass transport in continuous-pore systems are considered for their applicability in branched-pore systems. When diffusion effects are absent in the primary pore system, three of the tests—the Weisz—Prater—Bischoff criterion, Hudgins' approach, and the Stewart—Villadsen criteria—can be used to show the presence or absence of these effects in the secondary system. In addition, two upper bounds are derived for the quotient of the secondary system Thiele modulus devided by the primary system modulus. These bounds can also be used for showing the absence of mass transport effects in the secondary pore system whenever the primary pore system is unaffected. Application of this latter development to porous materials suggests that if the primary pore system is unaffected by mass transport, then the secondary system is also unaffected, except under abnormal circumstances.

The Role of Bubble Formation in Oil Recovery by Solution Gas Drives in Limestones

Abstract Laboratory data show that the gas-oil ratio perforce of non-uniform porosity limestones produced by solution gas drive is sensitive to producing rate and to fluid properties. Non-uniform porosity lime st ones are those for which laboratory solution and external gas drive tests yield considerably different relative permeability ratio characteristics. The oil recovery performance by solution gas drive depends directly on the number of gas bubbles formed. Laboratory rates of pressure decline, which are 100 to 10,000 times greater than normal field rates, cause the formation of an unusually large number of gas bubbles. This results in abnormally high oil recovery efficiencies, Since it is impractical to reproduce the number of bubbles formed under field conditions, laboratory solution gas drive data on non-uniform porosity limestones are therefore not directly applicable to field operations. However, certain laboratory data can be used to make a conservative estimate of field performance. The concepts presented in this paper indicate the possibility that increased field oil recoveries may be obtained from non-uniform porosity limestones by rapidly reducing reservoir pressure for a short interval of time. It has yet to be established that significant improvements in oil recovery from such reservoirs can be realized by varying the pressure decline rate within limits possible in the field. However, the possibility that recovery may be increased in this manner warrants further study. Introduction Limestone reservoir rocks can be divided into two general classes according to the nature of their pore space. One class has a comparatively uniform pore system composed mainly of voids between grains of the rock (intergranular type porosity). The other class, in addition to having intergranular porosity, has a secondary pore system composed of combinations of solution cavities, fractures, etc., and is considered to have non-uniform porosity.