SW Calculations Research Articles

The Comparation of Water Saturation Approaches to Reveal a Low Resistivity Reservoir Potential Case in Gumai Formation, South Sumatra Basin

The LRLC reservoir zone has been identified in SN-3 well, at the DAP-1 interval on Gumai Formation. This interval has a low resistivity value from 3-5 ohm.m and the drill stem test (DST) results show oil with gas without water. This study is objected to identify the causes of LRLC reservoir in gumai formation and finding a suitable sw calculation method. Some data such as well logs, reports, cores, and XRD are used to calculate petrophysical parameters such as Vsh, Phie, and Sw, and would be validated by DST data. Water saturation (Sw) calculations from Archie and the CEC method (Waxman Smits, Dual Water, Juhasz) were performed and the results were compared. The results showed that the main cause of the DAP-1 interval LRLC zone was the presence of clay minerals consisting of mixed layers (Illite/smectite). These clay minerals will be associated with high cation exchange capacity (CEC) values, with the value 70 (meq/100g), which can increase conductivity and reduce resistivity values. Based on lumping the more optimistic results of sw calculation from Waxman Smits Sw method (Sw based on CEC method). The DST data on the SN-3 well does not have water test data, so the calculation of the Sw value that is close to the Swirr value is considered the most suitable Sw for the low resistivity reservoir conditions of the Gumai Formation in the study area. The best practice for low resistivity reservoir for suitable petrophysical calculation is necessary to pay attention to the rock lithology conditions, the presence of mineral clay, and determining suitable Sw appropriate to the reservoir conditions

New Iterative Resistivity Modeling Workflow Reduces Uncertainty in the Assessment of Water Saturation in Deeply Invaded Reservoirs

A new iterative modeling workflow has been designed to reduce the uncertainty of water saturation (Sw) calculations in the tight Barik sandstone in the Sultanate of Oman. Results from this case study indicate that Sw can be overestimated by up to 20 s.u. if the as-acquired deep resistivity is used in volumetric calculations. Overbalanced drilling causes deep invasion of water-based mud (WBM) filtrate into porous and permeable rocks, leading to the radial displacement of in-situ saturating fluids away from the wellbore. In low-porosity reservoirs drilled with WBM, the inability of the filtration process to quickly build impermeable mudcake translates into long radial transition zones. Under certain reservoir and drilling conditions, deep resistivity logs cannot reliably measure true formation resistivity and are, therefore, unable to provide an accurate assessment of hydrocarbon saturation. The effect of mud-filtrate invasion on resistivity logs has been extensively documented. Processing techniques use resistivity inversion and tool-specific forward modeling to provide uninvaded formation resistivity logs, which are much better suited for in-place resource volume assessment. However, sensitivity analysis shows that the accuracy of invasion-corrected logs dramatically decreases as the depth of invasion increases, whereby the inversion process needs to be further constrained. The new workflow is designed to reduce the non-uniqueness of true formation resistivity models so that they honor multiple and independent petrophysical data. The inversion routine utilizes a Bayesian algorithm coupled with Markov-Chain Monte Carlo (MCMC) sampling. Inversion results are iteratively modified based on two rock property models : one derived from rock-core data (helium expansion porosity and Dean-Stark saturations) and the other using an equivalent log interpretation of thick reservoir intervals from oil-based mud (OBM) wells. Simulated borehole resistivity is compared to field logs after each validation loop against rock property models. The new inversion-based workflow is extensively tested in the unconventional tight Barik Formation across water-free hydrocarbon and perched water intervals, and inversion-derived Sw models are independently validated by capillary-pressure-derived saturation-height models and fluid inflow rate from production logs.

Monitoring the membrane scaling propensity of retentate in reverse osmosis desalination plants

Scaling appears first in the tail spiral wound membrane (SWM) elements of desalination plants due to increased salt concentration in the retentate; in particular, membrane scaling starts locally when supersaturation of sparingly soluble salts (commonly CaCO3 and CaSO4) is attained. Reliable determination of the onset of membrane scaling in the tail elements (as a function of the local retentate physico-chemical properties) provides a threshold condition serving a dual purpose; i.e., it imposes essentially an upper limit to the degree of permeate recovery, and guides the selection of an appropriate anti-scaling program involving additives. Judicious use of the latter is important for reduction of desalination cost and environmental impact. The current practices for estimating incipient scaling within the spacer filled reverse osmosis (RO) membrane elements involve a great deal of uncertainty. In this study, slightly supersaturated in CaCO3 brackish waters were desalinated in a test section comprising a narrow gap spacer filled channel simulating local (constant flux) conditions in SWM modules. Detailed data on incipient membrane scaling were obtained leading to the following main conclusions: (a) minute quantities of very small particles, ever present in RO plants, apparently promote heterogeneous nucleation; moreover, under the conditions tested, induction period for membrane scaling is practically nonexistent. (b) the initial scale deposit rates measured by special techniques (but undetectable with common bulk flow measurements) are substantial, and if not mitigated would be detrimental to SWM performance over a relatively short operating time period. (c) accurate determination of supersaturation ratio at the membrane surface Sw can be a reliable criterion for the onset of scaling, instead of currently used indices (e.g. Langelier Saturation Index) or practical type recommendations; a reliable method has been employed to determine Sw under local retentate conditions. Based on these results, a novel system was developed for monitoring the scaling propensity of retentate, which involves combination of a limited number of measurements in key locations of a RO plant, reliable algorithms for local equilibria and supersaturation (Sw) calculations, and a modern wireless electronic system for plant wide monitoring.

APPLICATION OF RESISTIVITY INVERSION MODELLING TO ENHANCE WATER SATURATION CALCULATIONS FROM WIRELINE LOGS

Water saturation (Sw) values calculated from resistivity or induction logs are often higher than those measured from core-derived capillary pressure (Pc) measurements. The core-derived Sw measurements are commonly applied for reservoir simulation in preference to the log-derived Sw calculations. As it is economically and logistically impractical to core every hydrocarbon reservoir, a method of correlating the core-derived Sw to resistivity/induction logs is required. Two-dimensional resistivity modelling is applied to dual laterolog data to ascertain the applicability of this technique.The Griffin and Scindian/Chinook Fields, offshore Western Australia, have been producing hydrocarbons since 1994 from two early-to-middle Cretaceous reservoirs, the clean quartzose sandstones of the Zeepaard Formation and the overlying glauconitic, quartzose sandstones of the Birdrong Formation. Routine and special core analysis of cores recovered from wells intersecting these two reservoirs creates an excellent data set with which to correlate the good quality wireline log data.A strong relationship is noted between the modelled water saturation from resistivity logs, and the irreducible water saturation measured from core capillary pressure data. Correlation between the core-derived permeability and the invasion diameter calculated from the modelled laterolog data is shown to produce a locally applicable means of estimating permeability from the resistivity modelling results.The evaluation of these data from the Griffin and Scindian/Chinook Fields provides a method for reducing appraisal and development well analysis costs, through the closer integration of core and wireline log data at an earlier stage of the field appraisal phase.

Interpretation of complicated NEXAFS spectra by comparison with Xα:-SW calculations

Interpretation of complicated NEXAFS spectra by comparison with Xα:-SW calculations

Supramolecular Aggregation of Pd6Cl12, a Cluster of Comparable Size to a Fullerene, with Aromatic Donors and with C60

Molecular solids comprised of octahedra, hexagonal plates, and truncated icosahedra result from the co-crystallization of Pd6Cl12, benzene and its methylated derivatives, and C60. Solutions of bis(benzonitrile)palladium(II) dichloride in benzene deposit deep red crystals of solvate-free Pd6Cl12, 1, while solutions of bis(benzonitrile)palladium(II) dichloride in the following solvents or solutions produce binary or ternary compounds as follows: from mesitylene, Pd6Cl12·(CH3)3C6H3 (2); from mesitylene/benzene, Pd6Cl12·(CH3)3C6H3·0.5C6H6 (3); from durene/benzene, Pd6Cl12·(CH3)4C6H2 (4); from benzene/hexamethylbenzene, Pd6Cl12·1.5(CH3)6C6 (5); from benzene/biphenyl, Pd6Cl12·(C6H5)2 (6); and from benzene/fullerene C60, Pd6Cl12·0.5C60·1.5C6H6 (7). The geometric structures of each of these seven compounds have been determined by X-ray crystallography, and the electronic structure of Pd6Cl12 has been probed with SCF−Xα−SW calculations. In each crystalline compound the structure of the Pd6Cl12 unit is virtually invariant. It consists of an octahedral array of six palladium atoms that are surrounded by twelve equivalent chlorine atoms in edge-bridging sites. The long face-to-face Pd···Pd separations (4.675 Å in 1) indicate that there is no direct Pd−Pd bonding in the cluster. In 1 these octahedra interact with one another through pairwise Pd···Cl contacts. In 2, 3, 4, and 6, layer-like structures are found in which each Pd6Cl12 cluster makes face-to-face contact with an arene moiety on opposite PdCl4 faces and each arene makes contact with two Pd6Cl12 clusters. In these four compounds, the clusters also make contact with each other through pairwise Pd···Cl contacts that are like those found in 1. The structure of Pd6Cl12·1.5(CH3)6C6 (5) is unique in that three hexamethylbenzene molecules make face-to-face contact with orthogonal faces of the Pd6Cl12 cluster and the cluster−cluster separations are larger than those in 1−4 and 6. The structure of Pd6Cl12·0.5C60·1.5C6H6 (7) consists of a complex array of molecular components with face-to-face contacts between the benzene molecules and both C60 and Pd6Cl12. Pd6Cl12 itself dissolves in aromatic solvents. The electronic spectra of the resulting solutions show variations that are indicative of a degree of charge transfer between the Pd6Cl12 cluster as an electron acceptor and the arene as an electron donor.

Electronic structure of paramagnetic clusters of transition metal ions. 3. Magnetic properties and scattered wave description of the electronic structure of the hexanuclear octahedral cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2

AbstractSpin‐polarized Xα–SW calculations of [Fe6(μ3−S)8(PH3)6]2+ as a model of the cluster [Fe6(μ3−S)8(PEt3)6] (BPh4)2 have been performed. The highest occupied energy levels are well separated from empty levels, and up to a maximum of eight electrons can be unpaired, giving a maximum spin state with S = 4. This electronic state is consistent with the magnetic data of [Fe6(μ3−S)8(PEt3)6](BPh 4)2, which have been interpreted using the Heisenberg–Dirac–Van Vleck exchange spin Hamiltonian. The S = 4 state arises from the magnetic coupling between five low‐spin (Si = 1/2) and one intermediate‐spin (S = 3/2) iron(III) center. © 1994 John Wiley & Sons, Inc.

Structure of x-ray photoelectron 2p and 1s spectra and x-ray K? emission line of copper in YBa2Cu3O7?? and CuO, on the basis of SCF-X?-SW calculations

Through an analysis of the electronic structure of the ground state and 2p and 1s hole states of the CuO4 6− cluster, modeling the immediate environment of a copper atom (one of the two types) in YBa2Cu3O7−δ and the immediate environment of the copper atom in CuO, it has been shown that upon ionization of core levels of copper, there is a radical reconstruction of the valence band of the cluster with a change in character of the chemical bond from covalent to ionic. Along with this, charge is transferred from the copper-oxygen bond to the central atom. Ionization of core levels leads to intense excitation of electrons into the upper semifilled valence level of the cluster 3b1g, and also leads to the appearance in the x-ray photoelectron and x-ray spectra (Kα spectra, for example) of intense satellite lines with strong multiplet splitting (with the exception of the satellite of the x-ray photoelectron 1s spectrum). We have confirmed the interpretation of the x-ray photoelectron 2p3/2 (2p1/2) spectrum and have predicted the form of the x-ray photoelectron 1s spectrum of copper(II). On the basis of the same approach, a complex structure has been predicted for the x-ray Kα emission line and it has been confirmed that the shift of this line in compounds of copper(II) must be made with some caution, as the shift may be due (for example) to a change in relative intensities of the main and satellite lines, which are located relative to each other at a distance of ≃0.4 eV.

Bonding in tris(.eta.5-cyclopentadienyl) actinide complexes. 2. The ground electronic configurations of "base-free" Cp3An complexes (An = thorium, protactinium, uranium, neptunium, plutonium)

Quasi-relativistic X{alpha}-SW calculations have been carried our on the base-free tris({eta}{sup 5}-cyclopentadienyl) actinide complexes Cp{sub 3}Th (1) and Cp{sub 3}U (2). Unlike the actinide complexes Cp{sub 3}AnL (L = neutral two-electron donor), for which all of the An 6d orbitals are used as electron acceptors, 1 and 2 both contain a low-lying 6d{sub z{sup 2}} orbital that competes with the 5f orbitals for the metal-based electrons. It is predicted that 1 will have a 6d{sup 1} electron configuration, which agrees with recent EPR experiments by Edelstein, Lappert, et al. It is also predicted that, unlike Cp{sub 3}UL complexes, which have a 5f{sup 3} electron configuration, 2 might have a 6d{sup 1}5f{sup 2} ground configuration. Results are also presented for Cp{sub 3}Pa, Cp{sub 3}Np, and Cp{sup 3}Pu.

Determination of Hydrogen Site Occupancy in Cubic Mg2NiH4 by SCF-Xα-SW Calculations and Free Energy Considerations*

Determination of Hydrogen Site Occupancy in Cubic Mg₂NiH₄ by SCF-X<i>α</i>-SW Calculations and Free Energy Considerations*

SCF X?-SW calculations of XANES and EXAFS of Pt atom in chloride complexes

SCF X?-SW calculations of XANES and EXAFS of Pt atom in chloride complexes

Mud Filtrate Effects On The Laterolog In Alberta Foothills Carbonates

Abstract This report proposes a new set of invasion correction curves for the laterolog that can be used quantitatively for a variety of mud systems and various diameters of invasion to obtain the true resistivity of the formation. Present resistivity tool designs do not appear to allow measurement deep enough to provide resistivity values of the undisturbed formation; nor do present laterolog invasion correction charts appear to correct sufficiently for invasion. At Shell Canada, the laterolog has been the primary resistivity tool used in the evaluation of deep, 3000 m to 5500 m Alberta Foothills carbonates. Low water saturations, calculated after the high resistivities have been corrected for invasion using existing charts, have led to costly production testing of wet zones. In this report, the Resistivity Index(I) was used to develop new invasion corrections. By assigning an I value to each of the flushed, transition and uninvaded zones and establishing the resistivity contribution of each zone to the laterolog reading from industry-published pseudo-geometrical factors, invasion corrections were determined. The effects of changing the Rmf/Rw value and the diameter of invasion were included in the design of the invasion correction curves. Open-hole logs of actual field cases are used to demonstrate the new invasion corrections for the laterolog. The proposed invasion corrections have resulted in the calculation of more accurate water saturations as substantiated by production test results. Introduction The laterolog is strongly affected by invasion, therefore, the ratio of the mud filtrate resistivity to the formation water resistivity is crucial because invasion often adds a resistive medium to the formation. Most Shell Canada wells are drilled with muds having a different resistivity than the formation water. Invasion occurs to some unknown depth and to obtain a true resistivity, the effect of the invading mud filtrate on the resistivity must be removed. Logging companies have attempted to minimize the effects of invasion on their resistivity tools through tool designs that utilize geometrical factors(1). A resistivity tool's reading can be considered to be the sum of the weighted values of the resistivities of the borehole, the invaded and non-invaded zones (Fig. 1). The deep reading resistivity tools are designed to obtain the major portion of their resistivity reading from as far away from the borehole as possible. For cases where invasion is shallow to moderate, this is usually the undisturbed zone. In deep invasion cases the resistivity reading must be corrected using service company charts to provide a value closer to the true resistivity. In foothills evaluation, very obvious gas zones with high resistivities (e.g. &amp;gt; 1000 ohm-m) and very obvious wet zones with low resistivities (e.g. &amp;lt;50 ohm-m) do not usually pose evaluation problems because they are readily identified from resistivity logs. Zones that appear to exist at some intermediate water saturation (e.g. Sw 30% to 60%) can be extremely difficult to evaluate for a variety of reasons. Today's resistivity tools run in situations with high resistivity mud systems (Rmf/Rw &amp;gt; 1.0) and large diameters of invasion will provide resistivity readings reflecting this and in turn will result in incorrect Sw calculations unless properly corrected for invasion.

SCF-Xα scattered wave cluster study of molecularly adsorbed NO on Ni

SCF-Xα SW calculations have been performed on model clusters representing molecularly adsorbed NO on different sites of Ni surfaces: on-top and fourfold hollow positions on Ni(100) and a threefold site on Ni(111). The chemisorption bond is found to be formed through adsorbate-to-metal donation mainly via 4σ̃gs and 1π̃gp orbitals and back donation into the 2π ∗ orbital of NO. The molecular 2π ∗ orbital interacts with a manifold of substrate levels leading to a “broadening” of this level. A strong mixing of the 2π ∗ orbital both to the 1 \\ ̃ gp cluster orbital and to the band like 2π manifold leads to a weakening of the intramolecular bond of the adsorbate, especially for hollow site adsorption. The chemisorptive bond strength is found to increase with the metal coordination of the adsorption site leading to a definite preference of hollow positions over on-top positions.

Determination of Productivity, Wilcox-Frio Sands, South Texas: ABSTRACT

The sharp lithological contrasts between and within the Wilcox and Frio Formations in south Texas frequently necessitate that different basic assumptions be used in interpreting logs of the formations. Accurate determination of the type, quantity, and rate of production of the interstitial fluids depends upon accurate interpretation of the well logs and the lithology of the rock. Ideally, geologic data should be quantified, digitized, and then integrated with digital well-log data. This allows log interpretation to be based on a detailed knowledge of the rocks. Use of logs allows this detailed knowledge of rocks to be extrapolated vertically for the well or used for older nearby wells where sample data may be unavailable. Detailed geologic data may be derived from small s mples (cuttings, sidewall cores, or pieces of conventional core). Lithological differences, such as those existing between the Wilcox and Frio, can significantly affect the radioactivity and density of the rocks. This, in turn, will influence calculations of shale volume and porosity. Differences in the composition of dispersed clays will affect Sw calculations. The calculation of porosity and water saturation does not identify either the amount or type of fluid production. Special log interpretation techniques, along with the detailed knowledge of the different clay varieties, allow an accurate prediction of the type of expected production. Examples will be presented from the Wilcox and Frio of south Texas. These will include wells in which over-optimistic log interpretation resulted in repeated unsuccessful stimulation attempts, and examples of bypassed production. End_of_Article - Last_Page 469------------

High-resolution HeI and HeII photoelectron spectra of the zinc and cadmium dihalide valence bands

We have recorded high-resolution HeI and HeII photoelectron spectra of the valence bands of six MX 2 compounds (M = Zn, Cd: X = Cl, Br, I) in the gas phase. Transition-state Xα SW calculations on all six compounds confirm the assignments. For the first time, we have clearly resolved the spin-orbit splitting of the II g and II u states in the bromide and iodide spectra: and calculated Π u splittings, using a simple MO LCAO model and the D xh double group, are in very good agreement with the experimental values. The relative intensities of the photoelectron peaks change markedly from HeI to HeII spectra, and Xα SW cross section calculations on ZnCl 2 predict these intensity changes rather well.

Geologic Implications of Dewatering of Coal and Other Carbonaceous Lithologies--A Hypothesis: ABSTRACT

A large amount of water is released from coal and other non-coal carbonaceous lithologies during the coalification process. Calculations of the amount of water released from coal and carbonaceous lithologies in low-permeability Upper Cretaceous rocks in the Green River basin of Wyoming reveal that this source of water is as important as any other sediment-derived water. Based on water resistivity (Rw) calculations and coal compositional changes during coalification, we suggest that this organically derived water is fresh relative to most formation waters. The addition of this water to the pore fluids is of sufficient quantity to create a chemical disequilibrium between the pore fluid and rock constituents, thereby producing a potential for precipitation or diss lution of cements. The addition of fresh water in conjunction with the variable stratigraphic distribution of coal beds and a restricted hydrologic communication between lithologic units implies that variable water resistivities (Rw) could occur that might adversely affect geophysical well-log responses and water-saturation (Sw) calculations. In coal-bearing rocks, the addition of organically derived water into the pore system may, in part, contribute to the development of abnormally high pressures. The effectiveness of this dewatering process depends on the amount and stratigraphic distribution of coal, stage of coalification, and degree of hydrologic isolation or impermeability of the coal-bearing sequence. End_of_Article - Last_Page 500------------

Mössbauer studies of FeSn molecules isolated in rare-gas solids and SCF–Xα–scattered-wave molecular-orbital analyses of Sn2and FeSn diatomic molecules

Iron–tin molecules were isolated in rare-gas solids and studied using both 57Fe and 119Sn Mössbauer isotopes. Experiments at very dilute concentrations were performed to detect FeSn diatomic molecules. Larger clusters were identified by concentration dependence studies and Monte Carlo calculations. The 57Fe and 119Sn isomer shifts (IS) for FeSn diatomic molecules suggest a covalent bonding between Fe and Sn atoms. Similar behaviour was observed for large iron–tin clusters (FexSny; x, y 3). SCF–Xα–SW calculations were performed for Sn2 and FeSn diatomic molecules. Sn2 shows a 3∑g ground state and gives a quadrupole splitting (QS) consistent with the experimentally measured value at an equilibrium distance of 2.75 Å. The most probable ground state for FeSn is a 7Δ{σ2(3dFe, 5sSn)σ1(3dFe)σ2(4sFe 5pSn)σ2(4pFe,5pSn)π2.75(3dFe)δ2.25(3dFe)π1(5pSn)} configuration which gives the QS values for iron and tin atoms in agreement with the experimentally measured values at an equilibrium distance of 2.5 Å.

Bulk properties or not: The electronic structure of small metal clusters

The dependence of the properties of small copper clusters on their size, and their relationships to the properties of the bulk metal have been studied through ab initio SCF calculations (with the emphasis on the clusters Cu8 and Cu13). The basis set used is of double-zeta quality for the valence shells 3d and 4s. The analysis focuses on the following properties of the clusters: geometrical structure, binding energy, and distribution of energy levels. For the 13-atom cluster, the icosahedron is found more stable than the cubo-octahedron corresponding to the fcc structure of the bulk metal. The binding energy per atom increases almost linearly with the number of atoms of the cluster. From the orbital energy values, the sets of 3d and 4s levels are well separated for Cu8 and just begin to overlap for Cu13. This situation looks rather different from the one for the bulk metal where the s band totally overlaps the d band. The relationship between the orbital energies from the ab initio SCF calculations and the ionization potentials is discussed. For the 13-atom cluster, the relaxation effect is probably small enough that the above conclusions, based on Koopmans’ theorem and the use of orbital energies, should not be altered by including it. On the whole, the ab initio results contradict the conclusion of the SCF–Xα–SW calculations that the electronic structure of small metal clusters and of the bulk metal are not fundamentally different and that not many atoms are needed in a cluster to have a resemblance to the bulk. This idea was based on the analysis of the orbital energy values from the Xα calculations, which showed that the ’’d band’’ was completely overlapped by the ’’s band.’’ However, this represents probably a spurious effect, since the Xα eigenvalue differs from the corresponding ionization potential by a ’’self-interaction term,’’ with rather different values for the orbitals of the 3d type and of the 4s type.

Theoretical calculation of shakeup intensities using Xα–SW wave functions

The ground and 1s core hole state molecular wave functions of CH4, NH3, H2O, and HF obtained from Xα–SW calculations using the touching spheres (TS) and overlapping spheres (OS) approximations are used to calculate the intensity of shakeup satellites observed in their ls core level photoelectron spectra. The sudden approximation was assumed in the calculation. In case of TS Xα–SW wave functions, the one electron overlap integral inside the intersphere was calculated via Green’s theorem. For OS Xα–SW wave functions, the integration over the awkwardly shaped intersphere region was circumvented by distributing the intersphere charge into the atomic spheres according to the charge partition scheme suggested by Case and Karplus. Our results show that there are no significant differences between the shakeup energies calculated from the TS and OS approximations. However, shakeup intensities calculated from TS Xα–SW wave functions are more reliable and in better numerical agreement with experiment.

Experimental and theoretical shakeup studies. IV. Main group Me2M (M=Zn,Cd,Hg) compounds

We report the first observation of shakeup in the core level ESCA of main group metal compounds. By recording the C 1s and metal (Zn 2p, Cd 3d, Hg 4f) level of Me2M (M=Zn, Cd, and Hg) to high statistics, satellite structures on the higher binding energy side of the respective primary photolines are observed. The peaks are assigned to shakeup transitions by theoretical Xα–SW calculations. Good agreement for both energies and intensities is obtained for the metal core level spectra. The calculations yield C 1s intensities which are much smaller than those observed experimentally.