Log Correlation Research Articles

Stratigraphic and Structural Compartmentalization Observed Within a Model Turbidite Reservoir,"Pennsylvanian Upper Jackfork Formation, Hollywood Quarry, Arkansas: ABSTRACT"

Hollywood Quarry is a 600 x 375 x 150 ft. (200 x 125 x 50m) excavation which provides a window into lower Pennsylvanian Jackfork Formation turbidite stratal architecture along the crest of a faulted anticlinal fold. A variety of turbidite facies are present, including: (a) lenticular, channelized sandstones, pebbly sandstones, and conglomerates within shale, (b) laterally continuous, interbedded thin sandstones and shales, and (c) thicker, laterally continuous shales. The sandstone and shale layers we broken by several strike-slip and reverse faults, with vertical displacements of up to several feet. This combination of facies and structural elements has resulted in a highly compartmentalized stratigraphic interval, both horizontally and vertically, along the anticlinal flexure. The quarry can be considered analogous to a scaled-down turbidite reservoir. Outcrop gamma-ray logs, measured sections, a fault map, and cross sections provide a database which is analogous to what would be available for a subsurface reservoir. Thus, the quarry provides an ideal outdoor geologic and engineering {open_quote}workshop{close_quote} venue for visualizing the potential complexities of a combination structural-stratigraphic (turbidite) reservoir. Since all forms of compartmentalization are readily visible in the quarry, problems related to management of compartmentalized reservoirs can be discussed and analyzed first-hand while standing in themore » quarry, within this {open_quote}model reservoir{close_quotes}. These problems include: (a) the high degree of stratigraphic and structural complexity that may be encountered, even at close well spacings, (b) uncertainty in well log correlations and log-shape interpretations, (c) variations in volumetric calculations as a function of amount of data available, and (d) potential production problems associated with specific {open_quote}field{close_quote} development plans.« less

Simpson-Arbuckle Contact Revisited in Northwest Oklahoma County, Oklahoma: ABSTRACT

Abstract The Joins Formation, the lowermost formation of the Simpson Group, is traditionally the least studied or understood of the Simpson formations. The Joins, not known to produce hydrocarbons in central Oklahoma, is frequently overlooked by those more interested in the productive Simpson formations above and the Arbuckle carbonates below. In a study of the lower Simpson to upper Arbuckle interval in northwestern Oklahoma County, Oklahoma, the Joins Formation was found to be present. The formation in this area varies from 65-195 feet in thickness, which is considerably thicker than most published literature for the area; some of which state that the formation is absent. Lithologically, the Joins Formation in central Oklahoma closely resembles the Arbuckle Mountain type section. The central Oklahoma section consists of interbedded gray, olive gray and green splintery moderately waxy shale, cream to light gray homogeneous microcrystalline dolomite, and microcrystalline to fine crystalline fossiliferous slightly glauconitic limestone. In the lower half of the formation fine to medium grain slightly conglomeratic and glauconitic well cemented sandstones are also noted. The entire Joins Formation is moderately to very fossiliferous; primarily consisting of crinoids, ostracods, brachiopods, and trilobites. The ostracod fauna closely resembles and correlates with the Arbuckle Mountain section, which has been extensively studied over the years by such authors as Taff, Ulrich and Harris. Beneath the Joins in this area is a normal section of Arbuckle dolomites. Due to the absence of a basal sand in the Joins the separation of the Joins and Arbuckle, utilizing electric logs only, is frequently tenuous. In comparison with the Arbuckle, the Joins tends to have higher gamma ray and S.P. values. Other tools, such as resistivity, bulk density and photoelectric (PE), are frequently inconclusive. The newest of the above tools, the photoelectric that was primarily designed as a lithology identification tool, is particularly ineffective due to the very thin bedded nature of the Joins and the two feet minimum resolution limits of the PE tool during normal logging. For geologists studying the Simpson-Arbuckle contact in central Oklahoma, the presence or absence of the Joins Formation is best determined through conventional lithologic and paleontologic sample identification techniques. Once this has been done, correlation of electric logs with this type log is possible for the local area. Care must be taken not to extend these correlations to far from the type well, primarily due to the frequent inconclusive nature of electric logs over the Joins interval.

Reservoir Description and Future Development Plans for the Unam/Mfem Fields OML 67, Nigeria: ABSTRACT

The Unam/Mfem fields, which are currently produced from three platforms, are, located 25 km offshore (southeastern Nigeria) in water depths of 60 feet to 100 feet. Over 100 MMBO have been produced to date from both unconformity bounded and fault trap reservoirs in the Upper and Middle Biafra Sands. These structural and stratigraphic geometries define at least eleven different reservoirs that are not interconnected. STOIIP for all eleven reservoirs is estimated to exceed 900 MMBO based on a recently completed reservoir characterization study. A two year reservoir description study followed the acquisition of a 1991 3-D seismic survey and resulted in the drilling of six successful wells and two sidetracks. A 3-D model of reservoir geometries and fluid flow properties was generated by integrating geologic, geophysical, and reservoir engineering data. These diverse data sets were interpreted using a combination of workstations, software packages, and displays that included Landmark, IREX, wireline log and seismic correlation charts. A detailed stratigraphic zonation scheme with 28 zones was defined and correlated field wide and subregionally to build the reservoir framework. Twenty seismic horizons were created. More than 300 critical compute, generated grids were then used to calculate STOIIP volumes. This study led to themore » identification of new pay zones along with a much better understanding of the spatial distribution of all pays within the fields. A revised exploitation strategy has subsequently been proposed which calls for 5 new platforms and the drilling of 21 additional wells over the next few years.« less

A Multidisciplinary Approach to Reservoir Subdivision of the Maastrichtian Chalk in the Dan Field, Danish North Sea

Correlation of wireline log data from the North Sea chalk reservoirs is frequently hampered by rather subtle log patterns in the chalk section due to the apparent monotonous nature of the chalk sediments, which may lead to ambiguous correlations. This study deals with a correlation technique based on an integration of biostratigraphic data, seismic interpretation, and wireline log correlation; this technique aims at producing a consistent reservoir subdivision that honors both the well data and the seismic data. This multidisciplinary approach has been used to subdivide and correlate the Maastrichtian chalk in the Dan field. The biostratigraphic subdivision is based on a new detailed dinoflagellate study of core samples from eight wells. Integrating the biostratigraphic r sults with three-dimensional seismic data allows recognition of four stratigraphic units within the Maastrichtian, bounded by assumed chronostratigraphic horizons. This subdivision is further refined by adding a seismic horizon and four horizons from wireline log correlations, establishing a total of nine reservoir units. The approximate chronostratigraphic nature of these units provides an improved interpretation of the depositional and structural patterns in this area. The three upper reservoir units pinch out and disappear in a northeasterly direction across the field. We interpret this stratal pattern as reflecting a relative sea level fall or regional basinal subsidence during the latest Maastrichtian, possibly combined with local synsedimentary uplift due to salt tectonics. Isochor maps indicate that the underlying six non-wedging units are unaffected by salt tectonics.

A Multi-Disciplinary Approach for Reservoir Characterization in the Glenn Pool Field, Oklahoma: ABSTRACT

Abstract Glenn Pool, a mature marginal oil field, is located on the Northeastern Oklahoma Platform. It has been under production since the first discovery in 1905. Several reservoir treatments have been implemented in the last 50 years following the primary production. However, high reservoir complexity resulted in a large volume of oil to be left in place. Our research is focused on a 160-acre block (Self Unit) where a detailed multi-disciplinary (Geology, Geophysics, Petroleum Engineering) reservoir study was conducted. The purpose of the study is to improve the secondary recovery performance of the field through the use of proper reservoir description and better reservoir management. Prior to drilling a cooperative project well (Uplands Self #82) Self Unit was studied with conventional methods. Stratigraphic framework of the Glenn Sand reservoir has been established through a series of stratigraphic cross sections. Based on well log correlations the reservoir was divided into six discrete genetic intervals (DGI). Channel-fill, splay, channel-mouth bar, levee and interdistributary mudstone facies were recognized from well log profiles and core analysis. Attempts were made in simulating geology using simple kriging methods; results were not entirely satisfactory. Uplands Self #82 was drilled in late December, 1993. The project objectives for drilling the well were: 1) evaluate reservoir predictions; 2) collect data using conventional and advanced technologies. Facies architectural characterization before drilling was reasonably successful. Advanced technologies including microresistivity imaging log and crosswell tomography data were acquired as well as the conventional well log suites and core. Simulation of the DGI distribution was undertaken using truncated Gaussian simulation method. Simulation results strongly agree when comparing probability input distributions with the output distributions. Porosity distribution was simulated using the simulated annealing method, and permeability distribution was transformed from porosity using a conditional distribution approach. For a selected well location (Self #82) the comparison between simulated and core porosity/permeability is very good. Crosswell transmission and migrated reflection tomography images between Self #82 and three offset wells constrained lateral reservoir continuity. A reservoir management plan was developed from reservoir performance simulation, well test data, facies architecture and crosswell tomography.

THE EASTERN OTWAY BASIN WANGERRIP GROUP REVISITED USING AN INTEGRATED SEQUENCE STRATIGRAPHIC METHODOLOGY

Recent exploration by BHP Petroleum in VIC/ P30 and VIC/P31, within the eastern Otway Basin, has contributed significantly to our understanding of the depositional history of the Paleocene to Eocene siliciclastic Wangerrip Group. The original lithostratigraphic definition of this group was based on outcrop description and subsequently applied to onshore and, more recently, offshore wells significantly basinward of the type sections. This resulted in confusing individual well lithostratigraphies which hampered traditional methods of subsurface correlation.A re-evaluation of the Wangerrip Group stratigraphy is presented based on the integration of outcrop, wireline well log, palynological and reflection seismic data. The Wangerrip Group can be divided into two distinct units based on seismic and well log character. A lower Paleocene succession rests conformably on the underlying Maastrichtian and older Sherbrook Group, and is separated from an overlying Late Paleocene to Eocene succession by a significant regional unconformity. This upper unit displays a highly progradational seismic character and is named here as the Wangerrip Megasequence.Regional seismic and well log correlation diagrams are used to illustrate a subdivision of the Wangerrip Megasequence into eight third-order sequences. This sequence stratigraphic subdivision of the Wangerrip Group is then used to construct a chronostratigraphic chart for the succession within this part of the Otway Basin.

Bismuth(III)-catalyzed oxidative cleavage of aryl epoxides: Substituent effects on the kinetics of the oxidation reaction

Bismuth(III)mandelate catalyses the oxidative CC bond cleavage of a series of styrene epoxides in DMSO, to the corresponding aryl carboxylic acids. The reaction is accelerated in the presence of electron-donating groups substituting the phenyl ring. A good Hammet correlation of log k obs, versus σ has been obtained, with a ϱ of −1.08.

Electron transfer reactivity of cuboidal heterometallic Mo 3MS 4 clusters in aqueous acidic solutions

Rate constants (25 °C) are reported for the first time for the oxidation of the cuboidal heterometallic Mo 3CoS 4 cluster, which in 2 M ClO 4 −/HClO 4 solutions exists predominantly as the edge-linked double cube [{Mo 3CoS 4(H 2O) 9} 2] 8+. Reactions with one-equivalent oxidants, the outer-sphere reagent [Co(dipic) 2]- (E°′ = 0.75 V) (dipic=pyridine-2,6-dicarboxalate) and hexaaqua Fe(III) (E°′ = 0.77 V), have been studied, I = 2.00 M (LiClO 4). Comparisons are made with rate constants already reported for the same two oxidants with [Mo 4S 4(H 2O) 12] 4+, and heterometallic cuboidal clusters [Mo 3CrS 4(H 2O) 12] 4+, [Mo 3FeS 4(H 2O) 10] 4+, [Mo 3NiS 4(H 2O) 10] 4+, edge-linked [{Mo 3PdS 4(H 2O) 9} 2] 8+, [Mo 3CuS 4(H 2O) 10] 4+ and [Mo 3CuS 4(H 2O) 10] 5+, all of which are derivatives of the trinuclear incomplete cuboidal Mo(IV) 3 cluster [Mo 3S 4(H 2O) 9] 4+. Rate constants for the reactions of [Co(dipic) 2] − ( k co) are independent of [H +] in the range 0.50-2.00 M. In the case of the Fe(III) oxidations ( k Fe), the dependence k Fe = k a + k b[H +] −1 is observed for all the clusters except [Mo 4S 4(H 2O) 12] 4+. The term k a is assigned as an outer-sphere reaction of [Fe(H 2O) 6] 3+, and k b as an inner-sphere reaction of [Fe(H 2O) 5OH] 2+. Linear correlations of log k Co versus log k a, and of log k co versus log k b, have slopes close to 1.0. Exceptions are the edge-]inked [{Mo 3PdS 4(H 2O) 9} 2] 8+, and to a lesser extent the k b term for [{Mo 3CoS 4(H 2O) 9} 2] 8+. The correlation of log k co versus log k b values is unexpected since k b is for an inner-sphere process. It can be concluded that electron transfer following OH- bridging of the Fe(III) to the heterometal atom is rate determining. Rate constants k co and k Fe for [W 3CuSn(H 2O) 10] 5+, the first heterometallic cluster obtained from [W 3Sn(H 2O) 9] 4+, also conform to the same two correlations.

Retention behaviour of metal chelates in ion-pair reversed-phase liquid chromatography as a function of mobile phase composition with methanol-water and acetonitrile-water mobile phases

The retention behaviour of Cu(II), Co(III), Ni(II) and Fe(II) chelates with 2-(5-bromo-2-pyridylazo)-5-[ N-propyl- N-(3-sulphopropyl) amino]phenol (5-Br-PAPS) and 2-(5-nitro-2-pyridylazo)-5-[ N-propyl- N-(3-sulphopropyl)amino]-phenol (nitro-PAPS) in ion-pair reversed-phase liquid chromatography was examined with mobile phases of methanolwater and acetonitrilewater binary systems containing 0.05 M sodium ion and 0.02 M Tris buffer (pH 7). The correlation of log k′ with the solubility parameter was different between the methanolwater acetonitrilewater systems. The resolution among chelates and reagents was complete with the acetonitrilewater system and far better than with the methanolwater system.

Backus averaging, scattering and drift1

Differences between traveltimes from sonic to seismic frequencies, commonly known as drift, can be attributed to a combination of multiple scattering and absorption. The portion due to scattering can be estimated directly by calculating synthetic seismograms from sonic logs. A simple alternative approach is suggested by the long-wave equivalent averaging formulae for the effective elastic properties of a stack of thin layers, which gives the same traveltime delays as the low-frequency limit of the scattering dispersion. We consider the application of these averaging formulae over a frequency-dependent window with the hope of extending their use to frequencies higher than those allowed by the original validity conditions. However, comparison of the time delay due to window-averaging with the scattering dispersion predicted by the O'Doherty-Anstey formula reveals that it is not possible to specify a form of window that will fit the dispersion across the spectrum for arbitrary log statistics. A window with a width proportional to the wavelength squared matches the behaviour at the low-frequency end of the dispersive range for most logs, and allows an almost exact match of the drift across the entire spectrum for exponential correlation functions. We examine a real log, taken from a hole in nearly plane-layered geology, which displays strong quasi-cyclical variations on one scale as well as more random, smaller-scale fluctuations. The details of its drift behaviour are studied using simple models of the gross features. The form of window which gave a good theoretical fit to the dispersion for an exponential log correlation function can only fit the computed drift at high or low frequencies, confirming that there are at least two significant scale-lengths of fluctuation. A better overall fit is obtained for a window whose width is proportional to the wavelength. The calculated scattering drift is significantly less than that observed from a vertical seismic profile, but the difference cannot be wholly ascribed to absorption. This is because the source frequency of the sonic tool is not appropriate for its resolution (receiver spacing) so that the scattering drift from sonic to seismic frequencies cannot be fully estimated from the layer model derived from the log.

Molecular recognition in acetylcholinesterase catalysis: free-energy correlations for substrate turnover and inhibition by trifluoro ketone transition-state analogs.

Ten meta-substituted aryl trifluoromethyl ketones (m-XC6H4COCF3; X = H, CH3, CF3, C2H5, isopropyl, t-butyl, NH2, NMe2, N+Me3, NO2) have been evaluated as inhibitors of acetylcholinesterases from Electrophorus electricus and Torpedo californica. Trifluoro ketones that have small meta substituents (X = H, CH3, CF3, C2H5, NH2, NO2) are rapid reversible inhibitors, whereas the remaining compounds in this study show time-dependent inhibition. Dissociation constants (Ki values) for these compounds span a range of approximately 10(7)-fold, with trifluoroacetophenone (X = H) being the least potent and m-(N,N,N-trimethylammonio)trifluoroacetophenone (X = Me3N+) being the most potent inhibitor. For the latter compound Ki values are 1.5 and 15 fM for inhibitions of the respective acetylcholinesterases (Nair, H. K., Lee, K., & Quinn, D. M. (1993) J. Am. Chem. Soc. 115, 9939-9941). Linear correlations of log(kcat/Km) for substrate turnover versus pKi of inhibitors have slopes of approximately 0.6, which suggest that aryl trifluoro ketones bind to AChE in a manner that structurally resembles transition states in the acylation stage of catalysis. Substituent variation in the inhibitors allows one to gauge the importance for AChE function of molecular recognition in the quaternary ammonium binding locus of the active site. This locus is frequently termed the "anionic site" and consists of E199, W84, and perhaps Y130 and F330. Correlations of pKi versus hydrophobicity constant are linear for alkyl and trifluoromethyl substituents but fail for nitrogen-containing substituents. However, three-dimensional correlations of pKi versus sigma m and molar refractivity of substituents indicate that dispersion interactions in the anionic locus contribute approximately 10(5)-fold (delta delta G = 7 kcal mol-1) to the above-mentioned 10(7)-fold range of inhibitor potencies. The remaining approximately 100-fold arises from the inductive electronic effects of substituents on the stability of the tetrahedral adduct that forms between the ketone carbonyl of inhibitors and S200 in the esteratic locus of the active site. Values of k(on), the second-order rate constant for binding of time-dependent inhibitors, monitor a diffusion-controlled process. Moreover, k(on) for the quaternary ammonio inhibitor is 20-70-fold higher than for inhibitors that have uncharged meta substituents, which likely reflects the effect of the electrical field of AChE on ligand and substrate binding.

Interactive intelligent well logs correlation (in Chinese) : Li Nan, Li Yan-Da & Chang Tong, Acta Geophysical Sinica, 36(4), 1993, pp 537–543

Interactive intelligent well logs correlation (in Chinese) : Li Nan, Li Yan-Da & Chang Tong, Acta Geophysical Sinica, 36(4), 1993, pp 537–543

Theoretical study of homogeneous electron self-exchange in polar aromatic molecules: the role of the reactant structure

The solvent reorganization energies λ 0 of the electron self-exchange reaction between neutral molecules (nitrobenzene, its five para-substituted derivatives and benzonitrile) and the corresponding radical anions are discussed in terms of the Kirkwood approach combined with a semi-empirical calculation of the reactant structure (AM1 and intermediate neglect of differential overlap (INDO) methods). The theoretical values of λ 0 are compared with the experimental reorganization energies λ calculated from the Marcus equation and the homogeneous rate constants k ex. It is found that the values of λ 0 obtained using the INDO method are approximately equal to the experimental λ, whereas the AM1 method gives poor results for para-substituted nitrobenzenes. The linear correlation of log k ex with a N 2 where a N is a nitrogen coupling constant, established for para-substituted nitrobenzenes is interpreted. A simple criterion for slow electron transfer of an arbitrary flat polar arene is formulated in terms of the reactant structure and the model of the “specifying group” suggested earlier by some of the authors.

Knowledge-based processing approach for well-to-well correlation

A traditionally manual task, the well-to-well logs correlation in geophysical exploration, is attacked by a knowledge-based automatic approach. Problem nature and knowledge concerned are analyzed, and properties of various signal matching algorithms are studied. The proposed processing formality combines knowledge integration through constraints and optimal adaptation, step-wise solution search by signal scale hierarchy, data fusion and interactive instant evaluation. Its realization and experiments on a computer workstation proved its effectiveness.

Two-Dimensional Synthetic Seismic and Log Cross Sections from Stratigraphic Forward Models

In an effort to fully use deterministic stratigraphic forward-modeling techniques in subsurface stratigraphic analysis, we developed a computer interface to routinely create synthetic logs and one-dimensional and two-dimensional (2-D) seismic responses from 2-D stratigraphic simulations. Each 2-D stratigraphic model can contain up to 200 timelines defining age-equivalent stratigraphic layers with laterally variable lithofacies and depths. Synthetic gamma ray, density and velocity responses are calculated for the simulated lithofacies using user-specified rock and fluid properties. Vertically incident synthetic seismograms are created using calculated reflection coefficients and user-defined input wavelets. Because stratigraphic simulations provide chronostratigraphy as a nown, log correlations and the interpolated seismic geometries follow timelines exactly. The power of this technique as an aid in sequence stratigraphic interpretations is shown from three examples: (1) a simulation of an idealized clastic system assuming constant clastic input and sinusoidal fourth-order and third-order sea level variations, (2) a detailed simulation of one third-order carbonate depositional sequence (lower-middle San Andres Formation) from the Northwest shelf, Permian basin, and (3) simulations of the Permian mixed clastic-carbonate infill of the Midland basin. Some general conclusions from these examples include the following: (1) seismic and well log-defined topsets, foresets, bottomsets, and related event terminations can be directly related to relative sea level fluctuations, (2) Exxon-type sequence boundaries (i.e., unconformities) are not necessarily seismically imageable, and their identification on well logs is not straightforward, and (3) lateral variations in amplitude related to lithofacies variations can be modeled. Synthetic logs and seismic sections from stratigraphic forward models such as these may be useful in constraining interpretations of subsurface data and thus aiding the prediction of reservoir and seal.

Missing Stratigraphic Sections in Tertiary Sandstone Reservoirs of the Gulf Coast: Faults or Unconformities and Implications for Development Strategies: ABSTRACT

ABSTRACT Missing section identified by log correlation in Gulf Coast boreholes is typically interpreted as displacement by downward movement along the upper surface of a growth fault. A common interpretation strategy is to link wells containing missing section with a growth fault having a curvilinear geometry in map view. We present here an alternative possibility: section missing because of erosion. This interpretation has a very different geometry and results in alternative implications for compartmentalization in stacked sandstone/shale reservoirs. Missing stratigraphic section in the F39 Frio reservoir of Lavaca Bay field, an Oligocene barrier/strandplain reservoir in Calhoun County, Texas, has been attributed to growth faulting. The geometry of missing sections in wells in this reservoir is complex, however, and the standard fault interpretation results in an unusual and geologically unlikely structural configuration. A dipmeter log from a key well in this reservoir indicates a sharp boundary at the depth of missing section and a distinct change in northwest dip from 8° above to 14° below. The map-view geometry of missing section defines two subcircular areas of erosion. These features are interpreted to have formed by local uplift due to shale diapirism and concomitant erosion of an overlying sandstone, which was deposited as a widespread tabular strandplain. The current structural crest of the field occurs between the two eroded paleohighs. Two wells in the present structural crest penetrated thick reservoir sandstone and have yielded approximately 20 percent of the cumulative production from this reservoir. Distinguishing missing section caused by erosional unconformities from that caused by growth faulting has three implications for reservoir development and resource assessment: (1) compartments bounded by faults can contain sandstones of nearly uniform reservoir properties throughout, whereas compartments caused by erosion will contain thin sandstones along the margins, (2) interpreting compartment boundaries as faults will result in very different compartment shapes than would result from the unconformity interpretation, and (3) misinterpreting missing section can lead to miscorrelation of productive zones in stacked reservoirs and, thus, to incorrect estimations of remaining resources. End_of_Record - Last_Page 767-------

Expert systems for automated correlation and interpretation of wireline logs

CORRELATOR is an interactive computer program for lithostratigraphic correlation of wireline logs able to store correlations in a data base with a consistency, accuracy, speed, and resolution that are difficult to obtain manually. The automatic determination of correlations is based on the maximization of a weighted correlation coefficient using two wireline logs per well. CORRELATOR has an expert system to scan and flag incongruous correlations in the data base. The user has the option to accept or disregard the advice offered by the system. The expert system represents knowledge through production rules. The inference system is goal-driven and uses backward chaining to scan through the rules. Work in progress is used to illustrate the potential that a second expert system with a similar architecture for interpreting dip diagrams could have to identify episodes—as those of interest in sequence stratigraphy and fault detection- and annotate them in the stratigraphic column. Several examples illustrate the presentation.

Reactivity of 2-substituted cyclohex-1-enylacetic acids with diazodiphenylmethane in various alcohols

The reactivities of 2-substituted cyclohex-1-enylacetic acids with diazodiphenylmethane in eleven alcohols has been investigated. The solvent effect is interpreted in terms of the influence of the relative permittivity on the rate constants. The multiple linear correlation of log k with the Kirkwood function of relative permittivity, Taft σ* value for the alkyl group of the alcohol and the number of γ-hydrogen atoms in the alcohol nγH was highly successful (R= 0.9927). The log k values for the various acids were correlated by using the appropriate form of the extended Hammett equation involving inductive, resonance and steric parameters.

Hydrolysis of glycosylpyridinium ions by anomeric-configuration-inverting glycosidases

The hydrolyses of five β- d-xylopyranosylpyridinium ions by the β- d-xylosidase of Bacillus pumilus proceed with k cat values 10 8–10 9-fold larger than the rates of spontaneous hydrolysis of the same compounds. Log( k cat) values correlate well with aglycon p K a [β 1g( V) = −0.52, r = 0.99], whereas the correlation of log( k cat/ K m) is poor [r = 0.77; β 1g( V/K) = ∼ −0.6]. The (1 → 3)-β- d-glucanase of Sporotrichum dimorphosporum hydrolyses 4-bromo-2-(β- d-glucopyranosyl)isoquinolinium ion with a rate enhancement of 10 8. The amyloglucosidase II of Aspergillus niger hydrolyses three α- d-gluco-pyranosylpyridinium ions with rate enhancements of 10 5–10 8. The efficient hydrolysis of glycosylpyridinium ions by these three inverting glycosidases, the catalytic mechanism of which is unlikely to involve a nucleophile from the enzyme, makes it imporable that the hydrolysis of glycosylpyridinium ions by retaining glycosidases discovered some years ago, is initiated by addition of a catalytic nucleophilic carboxylate group of the enzyme to the pyridinium ring.

The use of velocity and conductivity data for the quantification of heterogeneity: A comparison

Hydraulic conductivities of a portion of the Twin Lake aquifer are derived from grain size analyses performed at 3‐cm vertical sampling intervals in four boreholes, spaced l m apart. Correlation of conductivity logs between four boreholes leads to a geometrical model which corresponds closely to the spatial structure derived from the velocity field of previous tracer tests. Histogram and correlogram analyses of conductivities agree closely with those of velocities, and the two data sets appear equally useful for characterizing the aquifer and its spatial variability. Using Darcy's law, flow velocities and conductivities are combined to calculate a theoretical, hydraulic gradient. Comparison to gradients observed at the site reveals agreement on a large scale. However, differences exist in detail because observed piezometric heads fail to reflect small‐scale heterogeneity. Since these differences are significant for contaminant transport prediction, it is recommended for future studies to directly measure flow velocities from a tracer experiment, rather than to reply on head measurements and on Darcy's law for the calculation of transport parameters.