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The Gibbs-ensemble Monte Carlo simulation methodology for phase equilibrium calculations proposed by Panagiotopoulos [1] is generalized and applied to mixture and membrane equilibria. An alternative derivation of the Gibbs simulation criteria based on the limiting distributions for the appropriate statistical mechanical ensembles is presented. The method is then generalized for the calculation of phase equilibria of mixtures by simulation in a constantpressure Gibbs ensemble and the calculation of equilibria across semipermeable membranes with an imposed osmotic pressure difference. The method is used to calculate phase equilibria for binary mixtures of Lennard-Jones molecules. Good agreement is found with published results obtained using other simulation techniques. The computer time required for the Gibbs method is only a small fraction of the corresponding requirement for previously available simulation techniques. Calculations for simple osmotic systems are performed for the first time by simulation, with results in agreement with exact theoretical predictions.

The synthesis, characterization, and ethylene polymerization behavior of a series of iron and cobalt halide complexes, LMX n (M = Fe, X = Cl, n = 2, 3, X = Br, n = 2; M = Co, X = Cl, n = 2), bearing chelating 2,6-bis(imino)pyridyl ligands L [L = 2,6-(ArNCR 1 ) 2 C 5 H 3 N] is reported. X-ray diffraction studies show the geometry at the metal centers to be either distorted square pyramidal or distorted trigonal bipyramidal. Treatment of the complexes LMX n with methylaluminoxane (MAO) leads to highly active ethylene polymerization catalysts converting ethylene to highly linear polyethylene (PE). LFeX 2 precatalysts with ketimine ligands (R 1 = Me) are approximately an order of magnitude more active than precatalysts with aldimine ligands (R 1 = H). Catalyst productivities in the range 3750−20600 g/mmol·h·bar are observed for Fe-based ketimine catalysts, while Co ketimine systems display activities of 450−1740 g/mmol·h·bar. Molecular weights ( M w ) of the polymers produced are in the range 14000−611000. Changing reaction conditions also affects productivity and molecular weight; in some systems, a bimodal molecular weight distribution is observed. On the basis of evidence gathered to date, the lower molecular weight fraction is a result of chain transfer to aluminum while the higher molecular weight fraction is produced by a combination of mainly β -H transfer and some chain transfer to aluminum.

The idea of injecting low salinity water into a petroleum reservoir is not novel and was often used in the 70s prior to the injection of surfactant. Recently it was shown that simply injecting sufficiently low salinity water improves oil recovery. Many possible mechanisms concerning low-salinity waterflood have been proposed in the literature. This paper describes an experimental investigation into some of the factors controlling the increased oil recovery observed when low salinity brine is injected into oil saturated reservoir core samples. Extensive chemical analyses were performed on the effluent showing the extent of interaction between the injected brine, the oil and the rock matrix.

This paper discusses the migration of petroleum from its formation in a source rock to its subsequent possible entrapment in a reservoir. The chemical and physical properties of petroleum gases and liquids are stressed, particularly their phase behaviour under subsurface conditions which is shown to be a very important factor in determining migration behaviour. Engineering correlations are presented for estimating the properties of petroleum fluids under geologically realistic conditions. The directions and magnitudes of the forces acting on migrating petroleum are deduced from the combined effects of buoyancy and water flow in compacting sediments. These forces are combined, using a fluid potential description. This procedure allows the direction of migration to be denned. The rate of migration is then estimated from the properties of the sediments involved, allowing a distinction to be made between ‘lateral’ and ‘vertical’ carrier beds. This simplified approach is suitable for rapid predictive calculations in petroleum exploration. It is compared with the more complex 3-D computer modelling approaches which are currently becoming available. Migration losses are related to the cumulative pore volume employed by the petroleum in establishing a migration pathway. The petroleum migration mechanism is shown to be predominantly by bulk flow, with a small diffusive contribution for light hydrocarbons over distances less than c. 100 m. The loss factors involved in secondary migration are estimated from field evidence. The mechanism of reservoir filling is presented as a logical extension to those described for migration. This, together with the inefficiency of in-reservoir mixing by diffusion or convection, is shown to tend to cause significant lateral compostional gradients in reservoirs over and above the gravitationally induced vertical gradients described by other workers.

Enhanced oil recovery (EOR) techniques can significantly extend global oil reserves once oil prices are high enough to make these techniques economic. Given a broad consensus that we have entered a period of supply constraints, operators can at last plan on the assumption that the oil price is likely to remain relatively high. This, coupled with the realization that new giant fields are becoming increasingly difficult to find, is creating the conditions for extensive deployment of EOR. This paper provides a comprehensive overview of the nature, status and prospects for EOR technologies. It explains why the average oil recovery factor worldwide is only between 20% and 40%, describes the factors that contribute to these low recoveries and indicates which of those factors EOR techniques can affect. The paper then summarizes the breadth of EOR processes, the history of their application and their current status. It introduces two new EOR technologies that are beginning to be deployed and which look set to enter mainstream application. Examples of existing EOR projects in the mature oil province of the North Sea are discussed. It concludes by summarizing the future opportunities for the development and deployment of EOR.

Overpressure can be produced by the following processes: (1) increase of compressive stress, (2) changes in the volume of the pore fluid or rock matrix, and (3) fluid movement or buoyancy. Loading during burial can generate considerable overpressure due to disequilibrium compaction, particularly during the rapid subsidence of low- permeability sediments. Horizontal stress changes can rapidly generate and dissipate large amounts of overpressure in tectonically active areas. Overpressure mechanisms involving change in volume must be well sealed to be effective. Fluid volume increases associated with aquathermal expansion and clay dehydration are too small to generate significant overpressure unless perfect sealing occurs. Hydrocarbon generation and cracking to gas could possibly produce overpressure, depending upon the kerogen type, abundance of organic matter, temperature history, and rock permeability; however, these processes may be self-limiting in a sealed system because buildup of pressure could inhibit further organic metamorphism. The potential for generating overpressure by hydrocarbon generation and cracking must be regarded as unproven at present. Fluid movement due to a hydraulic head can generate significant overpressure in shallowly buried, well-plumbed basins. Calculations indicate that hydrocarbon buoyancy and osmosis can generate only small amounts of localized overpressure. The upward movement of gas in an incompressible fluid also could generate ©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.1Manuscript received October 17, 1995; revised manuscript received September 4, 1996; final acceptance January 20, 1997. 2Department of Geological Sciences, Durham University, South Road, Durham DH1 3LE, United Kingdom. Osborne e-mail: M.J.Osborne@ durham.ac.uk; GeoPOP web site http://www.dur.ac.uk/~dgl0zz7/ We wish to thank the companies that support the Geosciences Project on Overpressure (GeoPOP) at the universities of Durham, Newcastle, and Heriot-Watt: Agip, Amerada Hess, Amoco, ARCO, Chevron, Conoco, Elf Exploration, Mobil, Norsk Hydro, Phillips Petroleum UK Company Limited, Statoil, and Total. We also thank Neil Goulty (Durham) for commenting on an earlier draft of this paper. Osborne thanks Gordon Macleod (Newcastle) for help with geochemical modeling.

We present a predictive calculation of two-phase relative permeabilities in granular porous media formed from a dense random packing of equal spheres. The spatial coordinates of every sphere in the pack have been measured, enabling the microstructure of the medium to be completely determined. From these data we extract a network model that replicates the pore space. By compacting the packing or swelling individual spheres, we may generate model porous media of different porosities whose microstructure is also completely determined. We simulate both viscous- and capillary-dominated invasion of a nonwetting fluid into a wetting fluid contained in these media. During invasion we calculate the average hydraulic conductance of each phase to obtain the relative permeabilities as a function of fluid saturation. Because the microstructure is known, the calculations do not involve any adjustable parameters or supplementary measurements of pore structure. The computed relative permeabilities are successfully compared with experimental values previously measured on sand packs, bead packs, and a simple sandstone.

Research Article| May 01, 1988 Interpreting benthic oxygen levels in mudrocks: A new approach Paul B. Wignall; Paul B. Wignall 1Department of Geological Sciences, University of Birmingham, Birmingham B15 2TT, England Search for other works by this author on: GSW Google Scholar Keith J. Myers Keith J. Myers 2BP Research Centre, Sunbury-on-Thames, Middlesex TW16 7LN, England Search for other works by this author on: GSW Google Scholar Author and Article Information Paul B. Wignall 1Department of Geological Sciences, University of Birmingham, Birmingham B15 2TT, England Keith J. Myers 2BP Research Centre, Sunbury-on-Thames, Middlesex TW16 7LN, England Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (5): 452–455. https://doi.org/10.1130/0091-7613(1988)016<0452:IBOLIM>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul B. Wignall, Keith J. Myers; Interpreting benthic oxygen levels in mudrocks: A new approach. Geology 1988;; 16 (5): 452–455. doi: https://doi.org/10.1130/0091-7613(1988)016<0452:IBOLIM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Quantified paleoecology and gamma-ray spectrometry have been applied in the analysis of the Kimmeridge Clay, a highly organic-rich British Jurassic mudrock. Decreasing benthic oxygen trends are reflected in decreasing species richness and dominance-diversity values. Similarly, the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen. The calculation of authigenic uranium values from data gathered by gamma-ray spectrometry shows enrichment in more oxygen-deficient environments. The good correlation between the independently derived paleoecological and authigenic U data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Low-salinity enhanced oil recovery (EOR) effects have for a long time been associated with sandstone reservoirs containing clay minerals. Recently, a laboratory study showing low-salinity EOR effects from composite carbonate core material was reported. In the present paper, the results of oil recovery by low-salinity water flooding from core material sampled from the aqueous zone of a limestone reservoir are reported. Tertiary low-salinity effects, 2–5% of original oil in place (OOIP), were observed by first flooding the cores with high-saline formation water (208 940 ppm) and then with 100× diluted formation water or 10× diluted Gulf seawater at 110 °C. It was verified by flooding the core material with distilled water that the core samples contained small amounts of anhydrite, CaSO 4 (s). The oil recovery was tested under forced displacement using different injection brines and oils with different acid numbers, 0.08, 0.34, and 0.70 mg of KOH/g. The low-salinity effect depended upon mixed wet conditions, and the effect increased as the acid number of the oil increased. No low-salinity effect was observed using a chalk core free from anhydrite. The chemical mechanism for the low-salinity effect is discussed, and in principle, it is similar to the wettability modification taking place by seawater described previously. In field developments, the oil reservoir is normally flooded with the most available water source. For offshore reservoirs, this means seawater or modified seawater. Thus, a relevant question addressed in this paper is can diluted seawater act as a low-saline EOR fluid after a secondary flood with seawater? Previous experiments have shown that both spontaneous imbibition and forced displacement tests using chalk cores, which were free from sulfate, did not show a low-salinity EOR effect when exposed to diluted seawater. This paper shows that, if anhydrite is present in the rock formation, diluted seawater or diluted produced water can act as an EOR injectant to improve recovery over that achieved with high-salinity brines.

There is an increasing awareness that the separation of overlapping bands by the mathematical technique of curve fitting offers many pitfalls and should not be undertaken lightly. This review discusses critically the various factors involved, with particular reference to vibrational band systems; other types of overlapping band systems encountered in analytical work are considered in less detail. Five parameters are involved: the number of component bands, their positions, shapes and widths, and the form of the baseline. Curve fitting, by a least squares optimization method to a suitable goodness of fit criterion, is considerably facilitated if approximate values for some of the parameters are known at the outset. The methods available for peak finding are discussed and, although not free from problems, are reasonably effective. Similarly, band shapes can usually be defined semiquantitatively. However, it is seldom possible to obtain prior information on band widths; these should be determined during the curve fitting calculations. Although statistical goodness of fit criteria are available they should be used in conjunction with a visual plot, to locate any regions of poor fit. Furthermore, the overriding consideration must always be that the computer fit is plausible in terms of acceptable chemical species for the system being examined.

Abstract Carbon dioxide is the main compound identified as affecting the stability of the Earth’s climate. A significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating against climate change. Geological storage of CO 2 , or the injection and stabilization of large volumes of CO 2 in the subsurface in saline aquifers, existing hydrocarbon reservoirs or unmineable coal-seams, is one of the more technologically advanced options available. A number of studies have been carried out aimed at understanding the behaviour and long term fate of CO 2 when stored in geological formations.

Abstract We make the case for Early Cretaceous transfer zones that segment the obliquely rifted Atlantic margin of southeastern Brazil. Our interpretation is based on published literature, Bouguer-corrected gravity, regional reflection seismic profiles, and well data. In the Santos and Campos basins, Neocomian rift architecture was strongly influenced by preexisting fabric and structures of the Late Proterozoic (Brasiliano orogeny). The Atlantic margin inherited an east-northeast-west-southwest orientation so that rifting was oblique to the margin. On a regional map of Bouguer-corrected gravity, a nearshore belt of positive anomalies correlates with an interpreted broad Moho uplift in the footwall of Neocomian extensional faults. Farther offshore, a second belt of positive anomalies correlates with a presalt ridge of eroded volcanic or basement anticlines covered by thin Aptian evaporites, interpreted as a failed spreading center. Intervening negative anomalies coincide with the main rift basin. All three belts show apparent offsets along linear zones trending west-northwest-east-southeast, which we interpret as transfer zones. The vergence of half rifts tends to change across transfer zones, compartmentalizing the rifted margin into subbasins. Our results have implications for the risks associated with distribution, maturation, and migration of hydrocarbons within the prolific Early Cretaceous lacustrine petroleum system of the Campos and Santos basins.

Transfer zones form important structural elements in extensional basins, accommodating displacement changes between individual fault and basin segments. Transfer zone geometry is related to the extension direction and the displacement, dip polarity, overlap and overstep of fault/basin segments adjacent to the zone. Topographic changes associated with transfer zones have a direct influence on drainage basin evolution, sediment transport and stratigraphy. Two main categories of transfer zone can be identified: (i) interbasin transfer zones, linking individual half graben, and (ii) intrabasin transfer zones, linking individual fault segments within a half graben. Interbasin transfer zones range from interbasin ridges to broad faulted highs and major relay ramps. They have a marked influence on basin stratigraphy and drainage evolution, often separating half graben with distinct stratigraphies and acting as conduits through which major axial depositional systems enter the rift zone. Intrabasin transfer zones range from relay ramps separating adjacent en echelon normal faults to discrete fault jogs. Intrabasin transfer zones commonly act as a conduit for local sediment transport, but have minimal effect on basin-scale stratigraphy. Transfer zones also affect early post-rift sedimentation and are important elements in controlling fluid migration in the subsurface.

Streamline Simulation: Theory and Practice presents a systematic exposition of current streamline simulation technology—its foundations, historical precedents, applications, field studies, and limitations. This textbook emphasizes the unique features of streamline technology that in many ways complement conventional finite-difference simulation. The book should appeal to a broad audience in petroleum engineering and hydrogeology; it has been designed for use by undergraduate and graduate students, current practitioners, educators, and researchers. Included in the book is a CD-ROM with a working streamline simulator and exercises to provide the reader with hands-on experience with the technology.

An understanding of the origin of depletion in the high field strength elements (HFSE), Nb, Zr and Ti, relative to rare earth elements (REE) in arc lavas is critical to models both for magmagenesis in ares and for the relationship between are magmatism and growth of the continental crust. The presence of HFSE depletion in both are lavas and in the bulk continental crust constitutes some of the strongest evidence that continental crust is/was generated in subduction zones, especially if the HFSE are retained relative to REE in the subducting slab (Saunders et al., 1980; McDonough, 1991). Recently, however, it has been proposed that HFSE depletion develops during the main are magma melting event in the mantle wedge (McKenzie & O'Nions, 1991), during melt ascent to the surface (Kelemen et al., 1990), or even that a world-wide shallow mantle reservoir with HFSE depletion exists (Salters & Shimizu, 1988). If so, it is possible that HFSE depletion may have developed in magmas unrelated to subduction zones during crust-generation processes in the Precambrian. The common presence of high-MgO lavas in the Southern Lesser Antilles provides a rare opportunity to test these models, because their chemistry is essentially unmodified since derivation from the mantle. We show that depletion (relative to REE) in the HFSE Ti, Zr, and Nb exists in the mantle wedge before melting, and is probably produced by an REE-rich slab flux. In contrast to many other arcs (Woodhead et al., 1993), there is no evidence that the Lesser Antilles mantle source is more depleted in HFSE than the source of mid-ocean ridge basalts. Relative to REE, Ti depletion in melts is enhanced during melting, requiring a Ti-rich phase in the residue at low melt fractions. Ti depletion is also enhanced during fractionation of magnetite and amphibole, whereas relative Zr depletion is reduced during fractionation. In most arc magmas (usually <6% MgO), fractionation is probably a major control on the extent of Ti and Zr depletion. In the Lesser Antilles, the extent of Nb depletion relative to La is largely unaffected by melting or crystal fractionation processes.

ABSTRACT Detailed sampling and analysis of Jurassic pelagic limestones and marls from Italy, Hungary and Switzerland have enabled construction of an isotope stratigraphy across the Pliensbachian‐Toarcian boundary with resolution to the zonal level. The oxygen‐isotope record is unremarkable. The carbon isotopes, however, show two positive excursions: one, relatively minor, during the Pliensbachian, margaritatus Zone, subnodosus Subzone, the other, more major, during the Toarcian. early falciferum Zone, where a maximum δ 13 C value of 4·52% PDB is attained. These intervals are known to be favoured periods of organic‐rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record. A comparable phenomenon has been documented from the Cenomanian‐Turonian boundary in the Cretaceous where it has been referred to the influence of an ‘Oceanic Anoxic Event’. Some Italian sections spanning this Lower Jurassic interval contain organic‐rich shales in the falciferum Zone; the isotopic signatures from their included, locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve. Carbon isotopes from the organic carbon itself are extremely negative, falling to –33δ PDB and, in one section examined in detail, correlate with the calcium‐carbonate content of the shales; they may reflect a partial change to a non‐calcified planktonic biota during deposition of this lime‐poor interval, possibly responding to upwelling and increased fertility of near‐surface waters. The onset of upwelling may have been as early as spinatum‐tenuicostatum Zone time, that is, at the Pliensbachian‐Toarcian boundary.

Abstract Constant angle projections of seismic sections can be designed to provide maximum discrimination between fluids or lithologies. The optimum projection for a noise-free, isotropic environment can be obtained using an extension to the elastic impedance concept, which itself is an extension of acoustic impedance (AI) to nonzero angles of incidence. To achieve this, we modify the definition of elastic impedance (EI) beyond the range of physically meaningful angles by substituting tanχ for sin2θ in the two-term reflectivity equation. The primary variable now becomes χ rather than θ. We allow it to vary between −90° and +90°, which gives an extension of EI for any combination of intercept and gradient. We refer to this form of elastic impedance as extended elastic impedance (EEI). In this paper we demonstrate that EEI can be tuned using different χ values to be approximately proportional to a number of elastic parameters, and we give EEI expressions for shear impedance (SI), bulk modulus, shear modulus, Lamé's parameter, and Vp/Vs. This leads to the identification of different areas of EEI space that tend to be optimum for fluid and lithology imaging. Having identified an appropriate χ value, the equivalent seismic section can be obtained from combinations of intercept and gradient stacks from routine AVO processing.

This paper presents a comparison study in which several partners have applied methods to quantify uncertainty on production forecasts for reservoir models conditioned to both static and dynamic well data. A synthetic case study was set up, based on a real field case. All partners received well porosity/permeability data and ‘historic’ production data. Noise was added to both data types. A geological description was given to guide the parameterization of the reservoir model. Partners were asked to condition their reservoir models to these data and estimate the probability distribution of total field production at the end of the forecast period. The various approaches taken by the partners were categorized. Results showed that for a significant number of approaches the truth case was outside the predicted range. The choice of parameterization and initial reservoir models gave the largest influence on the prediction range, whereas the choice of reservoir simulator introduced a bias in the predicted range.

Abstract A study was made of adsorption of n-dotriacontane and n-butanol dissolved in n-heptane onto graphitized carbon black and various ground graphites having surface areas ranging from 5 to 700 m2 g-1. It was established that the adsorption of n-dotriacontane by the graphites is confined entirely to the basal planes of graphite crystals. This is attributed to a remarkable fit between the hydrogen atoms attached to one side of the zig-zag carbon chain in the normal paraffins and the centres of hexagons formed by the carbon atoms in the basal planes of the substrate. The longer the chain the more contacts it can form with the graphite surface and the more strongly it is adsorbed. More detailed studies of the adsorption of n-paraffins on ground graphites have shown that they form close-packed monolayers of horizontally disposed molecules on the basal planes. There is little further adsorption after the monolayers are complete. The heat of adsorption per molecule increases uniformly with the chain length reaching very high values for the normal paraffins having more than 30 carbon atoms. The formation of the close-packed layers has been used for the measurement of the proportion of basal plane surface in different types of graphites. n-Butyl alcohol also forms closely packed monolayers, but on the polar sites of graphites, which can be used for the estimation of their area. The basal plane and polar sites act independently in adsorption and their relative proportions characterize the adsorptive properties of graphites. Examination of graphite ground in n-heptane, which consists of plates of average area of several square micrometres and average thickness of 5 nm, shows that its surface consists predominantly of basal planes having a high adsorptive capacity for n-paraffins.

Chromium complexes of ligands of the type Ar2PN(Me)PAr2 (Ar = ortho-methoxy-substituted aryl group), on activation with MAO, are extremely active and selective catalysts for the trimerisation of ethylene.