Showing papers in "Oil & Gas Science and Technology-revue De L Institut Francais Du Petrole in 1998"

Rock-Eval 6 Applications in Hydrocarbon Exploration, Production, and Soil Contamination Studies

Abstract: Successful petroleum exploration relies on detailed analysis of the petroleum system in a given area. Identification of potential source rocks, their maturity and kinetic parameters, and their regional distribution are best accomplished by rapid screening of rock samples (cores and/or cuttings) using the Rock-Eval apparatus. The technique has been routinely used for about fifteen years and has become a standard tool for hydrocarbon exploration. This paper describes how the new functions of the latest version of Rock-Eval (Rock-Eval 6) have expanded applications of the method in petroleum geoscience. Examples of new applications are illustrated for source rock characterization, reservoir geochemistry, and environmental studies, including quantification.

Stress-Induced Seismic Anisotropy Revisited

Abstract: This summary contains formulas (***) which can not be displayed on the screenA general principle outlined by P. Curie (1894) regarding the influence of symmetry in physical phenomena states, in modern language, that the symmetry group of the causes is a sub-group of the symmetry group of the effects. For instance, regarding stress-induced seismic anisotropy, the most complex symmetry exhibited by an initially isotropic medium when tri-axially stressed is orthorhombic, or orthotropic, symmetry characterized by three symmetry planes mutually perpendicular (Nur, 1971). In other respects, Schwartz et al. (1994) demonstrated that two very different rock models, namely a cracked model and a weakly consolidated granular model, always lead to elliptical anisotropy when uniaxially stressed. The addressed questions are : Is this result true for any rock model? and more generally : Do initially isotropic rock form a well-defined sub-set of orthorhombic media when triaxially stressed?Under the hypothesis of 3rd order nonlinear isotropic hyperelasticity (i. e. , no hysteresis and existence of an elastic energy function developed to the 3rd order in the strain components) it is demonstrated that the qP-wave stress-induced anisotropy is always ellipsoidal, for any strength of anisotropy. For instance point sources generate ellipsoidal qP-wave fronts. This result is general and absolutely independent of the rock model, that is to say independent of the causes of nonlinearity, as far as the initial assumptions are verified. This constitutes the main result of this paper. Thurston (1965) pointed out that an initially isotropic elastic medium, when non-isotropically pre-stressed, is never strictly equivalent to an unstressed anisotropic crystal. For instance the components of the stressed elastic tensor lack the familiar symmetry with respect to indices permutation. This would prohibit Voigt's notation of contracted indices. However if the magnitude of the components of the stress deviator is small compared to the wave moduli, which is always verified in practical situations of seismic exploration, the perfect equivalence is re-established. Under this condition, the 9 elastic stiffnesses C'ij (in contracted notation) of an initially isotropic solid, when triaxially stressed, are always linked by 3 ellipticity conditions in the coordinate planes associated with the eigen directions of the static pre-stress, namely :(***)Thus only 6 of the 9 elastic stiffnesses of the orthorhombic stressed solid are independent (Nikitin and Chesnokov, 1981), and are simple functions of the eigen stresses, and of the 2 linear (2nd order) and the 3 nonlinear (3rd order) elastic constants of the unstressed isotropic solid. Furthermore, given the state of pre-stress, the strength of the stress-induced P- or S-wave anisotropy and S-wave birefringence (but not the magnitude of the wave moduli themselves) are determined by only 2 intrinsic parameters of the medium, one for the P-wave and one for the S-waves. Isotropic elastic media, when triaxially stressed, constitute a special sub-set of orthorhombic media, here called ellipsoidal media , verifying the above conditions. Ellipsoidal anisotropy is the natural generalization of elliptical anisotropy. Ellipsoidal anisotropy is to orthorhombic symmetry what elliptical anisotropy is to transversely isotropic (TI) symmetry. Elliptical anisotropy is a special case of ellipsoidal anisotropy restricted to TI media. In other words, ellipsoidal anisotropy degenerates in elliptical anisotropy in TI media. In ellipsoidal media the qP-wave slowness surface is always an ellipsoid. The S-wave slowness surfaces are not ellipsoidal, except in the degenerate elliptical case, and have to be considered as a single double-valued self-intersecting sheet (Helbig, 1994). The intersections of these latter surfaces with the coordinate planes are either ellipses, for the S-vave polarized out of the coordinate planes, or circles, for the qS-wave polarized in the coordinate planes. The nearly exhaustive collection of experimental data on seismic anisotropy in rocks (considered as transverse isotropic) by Thomsen (1986) show that elliptical anisotropy is more an exception than a rule. Since stress-induced anisotropy is essentially elliptical when restricted to transversely isotropic media, as a consequence this work clearly shows that stress can be practically excluded as a unique direct cause of elastic anisotropy in rocks.

Wetting Alteration of Solid Surfaces by Crude Oils and Their Asphaltenes

Abstract: Crude oils contain a variety of components - including asphaltenes - that can adsorb onto mineral surfaces and alter wetting. What distinguishes the asphaltenes from other constituents of an oil is their tendency to aggregate and even separate from the oil in response to changes in oil solvency. Because they change in size, asphaltenes can be viewed as both macromolecules and colloids. Their influence on wettability can change with this shift from molecular to colloidal regimes. As macromolecules, asphaltenes and other crude oil components with polar functionality can adsorb on mineral surfaces. Many different crude oils have been shown to have similar effects on wetting of dry silicate surfaces. When water is present, however, the results of exposing surfaces to different oils can be quite complex, depending on the distribution of water, the compositions of oil and brine, and mineralogy of rock surfaces. Acid and base numbers and the relationship between them provide a measure of the potential for a particular oil to alter wetting through ionic interactions. As colloids, asphaltenes can alter wetting by an additional mechanism. Near the onset of precipitation, wetting alteration occurs by surface precipitation because of the interfacial aggregation of the colloidal asphaltenes, which can precede flocculation in bulk. The influence of asphaltenes on wetting is thus strongly dependent on the environment in which they are found. Mixture refractive index is a useful measure for quantifying the stability of asphaltenes in a crude oil and thus in differentiating between macromolecular and colloidal contributions of asphaltenes to wetting alteration.

A Rapid and Efficient Methodology to Convert Fractured Reservoir Images Into a Dual-Porosity Model

Abstract: Both characterization and dynamic simulation of naturally-fractured reservoirs have benefited from major advances in recent years. However, the reservoir engineer is still faced with the difficulty of parameterizing the dual-porosity model used to represent such reservoirs. In particular, the equivalent fracture permeabilities and the equivalent matrix block dimensions of such a model cannot be easily derived from observation of the complex images of natural fracture networks. This paper describes a novel and systematic methodology to compute these equivalent parameters. The results of its implementation with specially-designed software demonstrate its validity and efficiency in dealing with field situations. A tensor of equivalent fracture permeability is derived from single-phase steady-state flow computations on the actual fracture network using a 3D resistor network method and specific boundary conditions. The equivalent block dimensions in each layer are derived from the rapid identification of a geometrical function based on capillary imbibition. The methodology was validated against fine-grid reference simulations with a conventional reservoir simulator. Then, a complex outcrop image of a sandstone formation was processed for demonstration purposes. This innovative tool enables the reservoir engineer to build a dual-porosity model which best fits the hydraulic behavior of the actual fractured medium.

Permeability Damage Due to Asphaltene Deposition : Experimental and Modeling Aspects

Abstract: The flow properties of several asphaltenic crudes were studied at reservoir temperature in rocks of different morphology and mineralogy. The experiments performed showed a progressive reduction in permeability to oil during injection, varying in rate according to the system considered. The existence of organic deposits was verified by Rock-Evalpyrolysis measurements made on sections of samples taken at the end of flow at different distances from the entry face. This technique enables the profile of the deposits to be quantified. The interpretation of the permeability damage experiments and their simulation are treated by comparing the asphaltenes in oil to colloidal particles in suspension, capable of being deposited at the surface of the pores and thus reducing the permeability of the porous medium. The first simulations were carried out using the PARISIFP particle damage model, which has recently been extended to the case of multi-layer deposition. A satisfactory qualitative agreement is observed with the experimental results.

Thermodynamic Aspects of Supercritical Fluids Processing: Applications of Polymers and Wastes Treatment

Abstract: Supercritical fluid processes are of increasing interest for many fields : in supercritical fluid separation (petroleum-chemistry separation and purification, food industry) and supercritical fluid chromatography (analytical and preparative separation, determination of physicochemical properties); as reaction media with continuously adjustable properties from gas to liquid (low-density polyethylene, waste destruction, polymer recycling); in geology and mineralogy (volcanoes, geothermal energy, hydrothermal synthesis); in particle, fibber and substrate formations (pharmaceuticals, explosives, coatings); in drying materials (gels). This paper presents the unusual physicochemical properties of supercritical fluids in relation to their engineering applications. After a short report of fundamental concepts of critical behavior in pure fluids, we develop in more details the tunable physicochemical properties of fluid in the supercritical domain. The second part of this paper describes the engineering applications of supercritical fluids relevant of chemical reactions and polymer processing. Each application presentation is divided in two parts : the first one recalls the basic concepts including general background, physicochemical properties and the second one develops the engineering applications relevant of the advocated domain.

Kelvin Notation for Stabilizing Elastic-Constant Inversion

Abstract: Inverting a set of core-sample traveltime measurements for a complete set of 21 elastic constants is a difficult problem. If the 21 elastic constants are directly used as the inversion parameters, a few bad measurements or an unfortunate starting guess may result in the inversion converging to a physically impossible solution . Even given perfect data, multiple solutions may exist that predict the observed traveltimes equally well. We desire the inversion algorithm to converge not just to a physically possible solution, but to the best(i. e. most physically likely) solution of all those allowed. We present a new parameterization that attempts to solve these difficulties. The search space is limited to physically realizable media by making use of the Kelvin eigenstiffness-eigentensor representation of the 6 x 6 elastic stiffness matrix. Instead of 21 stiffnesses, there are 6 eigenstiffness parametersand 15 rotational parameters . The rotational parameters are defined using a Lie-algebra representation that avoids the artificial degeneracies and coordinate-system bias that can occur with standard polar representations. For any choice of these 21 real parameters, the corresponding stiffness matrix is guaranteed to be physically realizable. Furthermore, all physically realizable matrices can be represented in this way. This new parameterization still leaves considerable latitude as to which linear combinations of the Kelvin parameters to use, and how they should be ordered. We demonstrate that by careful choice and ordering of the parameters, the inversion can be relaxedfrom higher to lower symmetry simply by adding a few more parameters at a time. By starting from isotropy and relaxing to the general result in stages (isotropy, transverse isotropy, orthorhombic, general), we expect that the method should find the solution that is closest to isotropy of all those that fit the data.

Three Dimensional Coupled Simulation of Furnaces and Reactor Tubes for the Thermal Cracking of Hydrocarbons

Abstract: Thermal cracking of hydrocarbons has gone through a significant evolution over the past 20 years. Improved metallurgical properties together with a better understanding of the chemical aspects have led to new configurations for furnace and reactor, all aiming for high severity cracking. A full 3D CFD model containing transport equations for mass, momentum and energy has been implemented in the software code FLOWSIM, together with the k-epsilon turbulence model. It has been coupled with the appropriate kinetic models (the radical reaction scheme CRACKSIM for the reactor and combustion kinetics for the furnace) and an overall iteration scheme has been developed for a coupled furnace-reactor simulation allowing to simulate industrial units. This approach has been applied for a propane cracking furnace, providing detailed understanding of the transport mechanisms taking place.

Reaction Mechanism of Calcium Hydroxide with Gaseous Hydrogen Chloride

Abstract: The reduction of acid gas content in combustion or incineration flue gases can be carried out by reaction with dry, fine alkaline sorbents such as calcium oxide or calcium hydroxide In the present work, in addition to the thermodynamic study of the different reactions involved in the dechlorination process, an experimental study to identify the reaction products by means of X-ray diffraction, electron microscopy and thermogravimetry has been carried out It has been shown that the reaction of hydrochloric acid with hydrated lime leads to the formation of not only calcium chloride but calcium hydroxichloride

Transient Simulation of Two-Phase Flows in Pipes

Abstract: Transient simulation of two-phase gas-liquid flow in pipes requires considerable computational efforts. Until recently, most available commercial codes are based on two-fluid models which include one momentum conservation equation for each phase. However, in normal pipe flow, especially in oil and gas transport, the transient response of the system proves to be relatively slow. Thus, it is reasonable to think that simpler forms of the transport equations might suffice to represent transient phenomena. Furthermore, these types of models may be solved using less time-consuming numerical algorithms.

Study of Asphaltene Solutions by Electrical Conductivity Measurements

Abstract: The asphaltene interactions in model solutions were studied using a technique based on the electrical conductivity measurement. Interactions with n-heptane, resins, surfactants, water, phenol and NaCI were investigated. The conclusions drawn from this study confirmed previous opinions on aggregation mechanism of asphaltenes in solutions. They confirmed also the interpretation of asphaltene behaviour in terms of colloidal solution theories.

Characterization of rock wettability through dielectric measurements

Abstract: The wettability of glass filters and Berea sandstone was investigated using the electric response in the interval 10² - 10 (to the power of 8) Hz. The natural wettability of the materials was modified to get two different sets of samples, one with strong water and the other with strong oil wettability. The samples were saturated to various degrees up to 40% with deionized water or brine. Measurements showed that the electric responses of water-wet and oil-wet samples were markedly different and more complex than those predicted by two standard models. The dispersivity and the loss tangent were found to be the most suitable parameters to check the wettability of the samples.

Performance of Cubic Eos At High Pressures

Abstract: This paper presents an evaluation of the performance of cubic equations of state in the prediction of the phase behavior of hyperbaric mixtures. It points out a number of problems that should be resolved in a cooperative way. Items related to EoS parameter definitions such as interaction coefficients, critical properties of hydrocarbon compounds and volume translation are investigated. VLE experimental data, isothermal flash compositional and volumetric data up to 4000 bar as well as PVT data up to 2000 bar for binary mixtures and synthetic multicomponent systems have been considered in this study. Correlation and prediction results are presented with the translated and modified Peng-Robinson (t-mPR) EoS. It is shown that serious problems are encountered at high pressure, when extrapolated interaction coefficients are used. Prediction of saturation pressures of gas condensates is more satisfactory when binary interaction parameters are obtained from high pressure dew point correlations. Compositional and volumetric predictions are remarkable under the assumption that definition of the EoS parameters is based on high pressure VLE binary data. Contradictory results are obtained with different methods for estimating the critical properties of high molecular weight hydrocarbons. Generalized expressions for the volume translation appear to be very efficient even at very high temperatures and pressures (up to 2000 bar).

Shear-wave splitting in a critical crust: the next step

Abstract: Arguably, shear-wave splitting displaying azimuthal anisotropy has not lived up to its initial promise of opening a new window for understanding cracks and stress in the crust. This paper reviews two recent related developments which appear to renew these initial hopes and provide new opportunities for monitoring, modelling, and even predicting, the (pre-fracturing) deformation of fluid-saturated microcracked rock. A recently developed model of anisotropic poro-elasticity (APE) for the stress-induced evolution of fluid-saturated microcracked rock matches a wide range of otherwise inexplicable or dissociated phenomena and appears to be a good first-order approximation to the evolution of fluid-saturated microcracked rock. Since the parameters that control small-scale (pre-fracturing) deformation also control shear-wave splitting, it appears that the evolution of fluid-saturated microcracked rock can be directly monitored by shear-wave splitting, and the response to future changes predicted by APE. The success of APE-modelling and observations of shear-wave splitting imply that almost all rock is close to a state of fracture criticality associated with the percolation threshold, when shear-strength is lost and through-going fractures can propagate. This confirms other evidence for the self-organized criticality of in situ rock. The significance of this identification is that the small-scale physics that controls the whole phenomena can now be identified as the stress-induced manipulation of fluids around intergranular microcracks. This has the possibly unique advantage amongst critical systems that details of the pre-fracturing deformation and the approach to the criticality threshold (in this case the proximity to fracturing) can be monitored at each locality by appropriate observations of shear-wave splitting. This paper reviews the these developments and discusses their implications and applications, particularly the implications of self-organized criticality. The next step is to employ these techniques to model, monitor, and predict the effects of changing conditions on the deformation of the rockmass.

A Formalism for the Consistent Description of Non-Linear Elasticity of Anisotropic Media

Abstract: The propagation of elastic waves is generally treated under four assumptions: - that the medium is isotropic,- that the medium is homogeneous, - that there is a one-to-one relationship between stress and strain, - that stresses are linearly related to strains (equivalently, that strains are linearly related to stresses). Real media generally violate at least some-and often all-of these assumptions. A valid theoretical description of wave propagation in real media thus depends on the qualitative and quantitative description of the relevant inhomogeneity, anisotropy, and non-linearity: one either has to assume (or show) that the deviation from the assumption can - for the problem at hand - be neglected, or develop a theoretical description that is valid even under the deviation. While the effect of a single deviation from the ideal state is rather well understood, difficulties arise in the combination of several such deviations. Non-linear elasticity of anisotropic (triclinic) rock samples has been reported, e. g. by P. Rasolofosaon and H. Yin at the 6th IWSA in Trondheim (Rasolofosaon and Yin, 1996). Non-linear anisotropic elasticity matters only for non-infinitesimalamplitudes, i. e. , at least in the vicinity of the source. How large this vicinity is depends on the accuracy of observation and interpretation one tries to maintain, on the source intensity, and on the level of non-linearity. This paper is concerned with the last aspect, i. e. , with the meaning of the numbers beyond the fact that they are the results of measurements. As a measure of the non-linearity of the material, one can use the strain level at which the effective stiffness tensor deviates significantly from the zero-strain stiffness tensor. Particularly useful for this evaluation is the eigensystem (six eigenstiffnesses and six eigenstrains) of the stiffness tensor : the eigenstrains provide suitable strain typesfor the calculation of the effective stiffness tensor, and the deviation can be expressed by the relative change of the eigenstiffnesses and by the variation in the direction of the eigenstrains (expressed as vectors in six-dimensional strain space). The suggested procedure is applied to the two materials discussed by Rasolofosaon and Yin (1996). The results allow a heuristic evaluation of the meaning of the reference strain , the square root of the ratio of the norms of the fourth-rank and sixth-rank stiffness tensors. It is stressed that this is not a new theory of non-linearity, but only a different way of viewing the existing theory and results.

Aqueous Solubility of Hydrocarbon Mixtures

Abstract: The solubility of hydrocarbon components in water is of great importance for the environmental sciences. Its prediction is usually based on using the pure component solubilities and the mole fraction of the components in the mixture. While the pure component solubilities are generally well known, few data exist on the solubility of mixtures. Using a simple relationship leads to an underestimation of the true solubility. This paper presents some new data on the aqueous solubility of binary hydrocarbon mixtures. Using a rigorous thermodynamic analysis, we explain the observed behavior, as well as other data from the literature, including the solubility of jet fuel mixtures in water. The activity coefficient models used for this purpose are NRTL, UNIQUAC and UNIFAC. Considering the small concentration in oil of some very soluble substances, the activity coefficient can become significant and thus explain the fact that solubilities of some component may be as much as twice as large as expected.

A Mechanical Modelling of the Primary Migration

Abstract: In order to address the question of oil-induced microfracturing, we propose under specific assumptions (plane circular kerogen flake surrounded by an homogeneous microfractured porous medium) an analytical method for the determination of the oil pressure increase. It is based on a mechanical modelling of the kerogen-oil-rock interaction at the microscopicscale of a kerogen particle. It is shown that the oil pressure tends towards an asymptotic value when the chemical transformation of kerogen is completed. The effect of the macroscopic stress variation during oil formation process proves to be negligible. However, this effect must be taken into account for describing the evolution of oil pressure at earlier stages of oil formation process. The increase in burial depth induces an increase of oil pressure as well as a variation of the macroscopic stress which both determine the microscopic stress field. The possibility of microfracturing depends on the position of the microscopic stress state with respect to the fracture criterion. If the duration of the oil formation process is short enough, so that the macroscopic stress change associated with the corresponding (small) burial depth increase can be neglected, it is found that microfracturing is likely for the usual values of rock tensile strength. However, in the general case, neglecting the macroscopic stress change can significantly overestimate the possibility of fracture initiation due to oil-pressure increase. Considering now the macroscopicscale of the source bed, the evolution equation of the oil pressure are derived within the framework of Biot's poroelasticity theory. The oil pressure rate proves to be the sum of a diffusion term which accounts for oil migration within the source bed, and of two source terms respectively associated with the volume expansion tendency of the kerogen - oil transformation and the overburden pressure increase.

The importance of water-hydrocarbon phase equilibria during reservoir production and drilling operations

Abstract: The inevitable presence of water in high pressure-high temperature reservoirs leads to a number of new challenges for petroleum engineers. A brief state of the art on water-hydrocarbon phase equilibria is presented. It appears that large amounts of water may be present in the hydrocarbon phase (up to 10% molar), and non negligible amounts of gas can dissolve in water. Based on experimental data, a large number of models have been developed. However, concerning the limitations of the data, caution is expressed about the correctness of some models. Recent studies have proven the usefulness of Henry's constants to predict hydrocarbon solubilities in water. The new challenges that are raised by this problem are discussed based on a number of recent publications. The water present in the hydrocarbon may lead to salt deposits downwell, and it must be taken into account in order to estimate the amount of gas in place. It can also result in modifications of the saturation pressure. Due to the presence of water, additional treatment is needed for pipe transport. On the other hand, the large amount of hydrocarbons dissolved in the water phase may result in a modification of the hydrocarbon composition, especially when reservoir pressure becomes very low. The increased toxicity of the water, containing either H2S or aromatics, can become a real burden for gas reservoirs in contact with aquifers or when disposing of production water. During drilling, large amounts of dissolved gas can become very hazardous, increasing the risk of eruption. A particular attention must be paid to acid gas injection in reservoirs, as the true effect of the injected gas may not be straightforward to predict. In conclusion, in light of the industrial importance of this information, some general guidelines are provided concerning additional data to be gathered and ideas for improving current models.

Processing Pp and Ps Wave in Multicomponent Sea-Floor Data for Azimuthal Anisotropy : Theory and Overview

Abstract: Assuming fracture-induced azimuthal anisotropy, we review the theory and develop processing methods for recovering the fracture orientation and density from multicomponent sea-floor data. The azimuthal variations in PP amplitude, normal move-out velocity, and interval move-out show elliptical variations in an azimuthally anisotropic medium. This can be used to determine the fracture strike of the medium and has been verified from real data. However, the P-wave effects only occur with multi-azimuths, and are often complicated by other factors. This limits the application of P-wave analysis to some extent. Analysis of PS waves may thus prove to be beneficial. For near vertical propagating PS waves, the polarization and time delay of the shear-waves provide a direct measurement of the fracture orientation and intensity. For a 2D acquisition where the survey line is along the receiver cable, an optimum method is proposed for determining the fracture strike from the polarization azimuth of the fast shear-wave. The method uses rotation analysis and assumes that the fast and slow shear-waves have similar waveforms. For a 3D cross geometry where the survey line is perpendicular to the receiver cable, two deterministic methods are proposed. The first one is based on the polarity change and amplitude dimming in the azimuthal gathers of the transverse-geophone component. The second one involves a rotation of orthogonal pairs of source-receiver azimuthal gathers. The determined polarization azimuth can then be used to separate the fast and slow shear waves in the inline-shooting gathers for time-delay estimation.

Multiphase, multicomponent fluid flow in homogeneous and heterogeneous porous media*

Abstract: The flow of several components and several phases through a porous medium is generally described by introducing macroscopic mass-balance equations under the form of generalized dispersion equations. This model raises several questions that are discussed in this paper on the basis of results obtained from the volume averaging method, coupled with pore-scale simulations of the multiphase flow. The study is limited to a binary, two-phase system, and we assume that the momentum equations can be solved independently from the diffusion/advection equations. The assumption of local-equilibrium is discussed and several length-scale and time-scale constraints are provided. A key issue concerns the impact on the dispersion tensors of the pore-scale equilibrium condition at the interface between the different phases. Our results show that this phenomenon may lead to significant variations of the dispersion coefficients with respect to passive dispersion, i. e. , dispersion without interfacial mass fluxes. Macroscopic equations are then obtained in the general case, and several local closure problems are provided that allow one to calculate the dispersion tensors and others properties, from the pore-scale geometry, velocities, and fluid characteristics. Examples of solutions of these closure problems are given in the case of two-dimensional representative unit cells. The two-phase flow equations are solved in two different ways : a boundary element technique, or a modified lattice Boltzmann approach. Solutions of the closure problems associated with the dispersion equations are then given using a finite volume element formulation of the partial differential equations. The results show the influence of velocity and saturation on the effective parameters. They emphasize the importance of geometry on the behavior of the dispersion tensor. Extension of these results to a larger-scale including the effect of heterogeneities is proposed in a limited case corresponding to the flow of one phase, the other phase being at residual saturation. A new large-scale dispersion equation is provided, which features a large-scale dispersion tensor that can be determined from the heterogeneity characteristics through a set of closure problems. Results are extended to a more general two-phase flow problem, when the large-scale two-phase flow can be assumed to be quasi-static. Indications are given on the difficulties associated with flow under large-scale dynamic conditions, with abnormal dispersion.

Measurement and Prediction of Volumetric and Transport Properties of Reservoir Fluids At High Pressure

Abstract: Discoveries of oil and gas fields under severe conditions of temperature (above 150°C) or pressure (in excess of 50 MPa) have been made in various regions of the world. In the North Sea, production is scheduled from deep reservoirs at 190°C and 110 MPa. This brings with it important challenges for predicting the properties of reservoir fluids, both from an experimental and a theoretical standpoint. In order to perform fluid studies for these reservoir conditions, IFP has developed a specific mercury-free high pressure apparatus with sapphire windows, a phase sampling device and viscosity determination by the capillary tube method. Its application is illustrated here using examples of real fluids and model mixtures. This equipment was first used to measure volumetric properties for gases. It has been shown that very high compressibility factors can be found with HP-HT gas condensates. This has a strong influence on recovery factors during primary depletion. In order to predict more accurately the volumetric properties of mixtures under these conditions, we propose to use a conventional equation of state, such as Peng-Robinson, with two improvements :- a modified temperature-dependent volume translation method, calibrated for high pressure density data; the method is simple, more accurate than other volume translation methods and fully consistent with lumping procedures;- a quadratic mixing rule on the covolume. Specific phase behavior can also be found. At low temperatures, wax crystallization can occur from a fluid which is a gas condensate at reservoir temperature. This feature is due to the simultaneous presence of abundant methane and heavy paraffins. A study of model fluids in a sapphire cell has allowed us to identify the possible types of phase diagrams. Although generally not considered to be an important parameter, gas viscosity may have some importance in the production of HP-HT accumulations, because of high flow rates. Viscosity models exhibit significant uncertainties because of large viscosity contrasts between the individual components of the reservoir fluid. In order to test and improve prediction methods, we started the acquisition of viscosity data under representative conditions. Special care was taken in the implementation of the capillary tube method, so that low viscosities (down to 0. 02 mPa. s) could be measured with high accuracy at pressures up to 120 MPa on simple systems, such as methane, n-pentane, nitrogen, and nitrogen-pentane mixtures. As a result, it was possible to evaluate mixing rules for viscosity predictions.

Application de la spectroscopie de fluorescence a l'étude du pétrole : le défi de la complexité

Abstract: Grâce a sa sensibilite et a sa selectivite, la spectroscopie de fluorescence est de plus en plus employee dans l'etude du petrole. Dans un premier temps, les principes fondamentaux de cette technique sont rappeles, en mettant l'accent sur les difficultes inherentes a la complexite du milieu et sur les developpements recents comme la spectroscopie de fluorescence par excitation synchrone et la detection a distance. Par la suite, les principaux domaines d'application de la fluorescence a la technologie du petrole sont successivement passes en revue, en particulier la detection de la pollution, la caracterisation rapide des bruts, l'information pour l'exploration et le forage, et enfin l'analyse fine des constituants. Les reactifs fluorogeniques ne sont utilises qu'apres mineralisation de l'echantillon et essentiellement pour detecter les traces de metaux.

Experimental Determination and Representation of Binary and Ternary Diagrams of N-Hexacosane, N-Octacosane and N-Heptane

Abstract: Accumulation of waxy deposits is a commonly occurring problem during exploitation and transportation of paraffinic crude oils. Limitation of these undesirable solids or removal by methods such as addition of chemical inhibitor, scrapping or heat tracing of flowlines, increase production costs. A better knowledge of this phenomenon will make it possible to adjust process operating parameters and limit the operating costs. Thermodynamic models can be used in order to calculate the wax appearance temperature and the amount of solid deposit versus temperature. In these models, the crude oil is represented as a mixture of pure or pseudo-components(which content several pure components). To describe the thermodynamic properties of those mixtures, data on pure components and on their mixtures are necessary but they are very scarce for heavy components in the literature. This work is devoted to the study of a mixture of heavy components including two heavy n-alkanes (n-hexacosane, denoted C26 and n-octacosane, denoted C28) and a solvent (n-heptane denoted C7). Measurements of solubility of C26 and C28 and of equimolar mixture of C26 and C28 in C7, and an isothermal ternary diagram of the mixture of the three components at 303K are presented. Their calculations using simple expressions of Gibbs molar energy (NRTL and Redlich-Kister) are in good agreement with experimental data. The work allows to consider calculating complex systems with the only use of binary interaction coefficients.

A 3d regional scale photochemical air quality model application to a 3 day summertime episode over paris

Abstract: This paper presents AZUR, a 3D Eulerian photochemical air quality model for the simulation of air pollution in urban and semi-urban areas. The model tracks gas pollutant species emitted into the atmosphere by transportation and industrial sources, it computes the chemical reactions of these species under varying meteorological conditions (photolysis, pressure, temperature, humidity), their transport by wind and their turbulent diffusion as a function of air stability. It has a modular software structure which includes several components dedicated to specific processes :-MERCURE, a meso-scale meteorological model to compute the wind field, turbulent diffusion coefficients, and other meteorological parameters. It is a 3D regional scale model accounting for different ground types and urban densities. It includes a complete set of physical parameterizations in clear sky. -MIEL, an emission inventory model describing the pollutant fluxes from automotive transportation, domestic and industrial activities. This model includes a mobile source inventory based on road vehicle countings together with global information on transportation fluxes extracted from statistical population data. It uses specific emission factors representative of the vehicle fleet and real driving patterns. -MoCA a photochemical gas phase model describing the chemistry of ozone, NOx, and hydrocarbon compounds. This model, with 83 species and 191 reactions, is a reduced mechanism well adapted to various air quality conditions (ranging from urban to rural conditions). For interpretative reasons, the identity of primary hydrocarbons is preserved. -AIRQUAL, a 3D Eulerian model describing the transport by mean wind flux and air turbulent diffusion of species in the atmosphere, associated with a Gear type chemical equation solver. The model has been applied to a 3-day summertime episode over Paris area. Simulation results are compared to ground level concentration measurements performed by the local monitoring network (Airparif).

Utilisation de la DSC pour la caractérisation de la stabilité des émulsions eau dans pétrole

Abstract: La technique DSC (Differential Scanning Calorimetry) a ete appliquee a l'etude des emulsions eau dans petrole, qui se forment naturellement apres un deversement de petrole en mer. Ces emulsions, egalement appelees mousses au chocolat , peuvent contenir de 50 a 80% d'eau et se presentent souvent sous la forme d'un produit visqueux, difficile a recuperer mecaniquement, a traiter ou a bruler. Il est par consequent important de pouvoir estimer leur stabilite pour optimiser le choix du traitement. Un grand nombre de techniques, generalement fondees sur l'analyse de la distribution de tailles de gouttes, peuvent etre utilisees pour estimer la stabilite d'une emulsion. Malheureusement, la plupart ne sont pas adaptees a l'etude des emulsions eau dans huile opaques. La methode la plus utilisee pour caracteriser la stabilite de ce type d'emulsions est le bottle test. Elle consiste a mesurer la separation de phases en fonction du temps. Ce test est la source d'une quantite d'informations appreciables quant a la stabilite de l'emulsion et a la qualite de la phase aqueuse separee, mais il reste tres empirique. La technique DSC est generalement utilisee pour determiner la composition des emulsions eau dans huile, car elle permet de distinguer l'eau libre de l'eau emulsifiee. Cette etude a montre qu'il s'agit d'une technique tres utile qui permet a la fois l'etude de l'evolution de la taille des gouttes dans l'emulsion, et une determination precise de la quantite d'eau.

TERNARY MIXTURES OF n-DOCOSANE, n-TRICOSANE AND n-TETRACOSANE

Abstract: Binary phase diagrams of the systems: n-docosane: n-tricosane (C22H46 : C23H48), n-tricosane: n-tetracosane (C23H48: C24H50) and n-docosane: n-tetracosane (C22H46: C24H50) have been established by means of structural and differential scanning calorimetry analyses. On the basis of these results and of X-ray examination of forty one ternary mixtures, it is proposed the ternary phase diagram (C22H46: C23H48: C24H50) at room temperature. This work has indicated the existence of limited terminal solid solutions near the three pure n-alkanes and three domains of orthorhombic intermediate phases (noted s' 1, s'' 1, s' 2) identical to those observed in the binary systems. X-ray experiments have showed that the phases s' 1, s'' 2 situated on the both sides of the middle intermediate phase s' 1, are isostructural as in the binary systems.

Frequency Dependence of Physical Parameters of Microinhomogeneous Media. Space Statistics

Abstract: The diagram technique for calculation of the dynamic properties of an anisotropic media with randomly distributed inclusions (pores, cracks) is developed. Statistical description of inclusions is determined by distribution function dependent on five groups of parameters :- over coordinates; - over angles of orientation of shapes;- over angles of orientation of crystallographic axes;- over aspect ratio (in a case of ellipsoidal inclusions);- over types of phase of inclusions. Such statistical approach allows to take into consideration any type and order of correlation interactions between inclusions. The diagram series for an average Green function is (GF) constructed. The accurate summation of this series leads to a nonlinear dynamic equation for an average GF (Dyson equation). The kernel of this equation is a mass operator which depends on frequency and can be presented in a form of diagram series on accurate GF. The mass operator coincides with effective complex tensor of elasticity (or conductivity) in a local approximation. An expansion of effective dynamic elastic (transport) tensor on distribution functions of any order is obtained. It is shown that correlation between homogeneities can produce an effective elastic and transport parameters anisotropy. In correlation approximation the dispersion dependencies of the effective elastic constants are studied. Frequency dependencies of a coefficient anisotropy of the elastic properties as function of statistical distributed inclusions over coordinates (isotropic matrix and isotropic (spherical) inclusions) are obtained.

Prediction of Volumetric Properties and (Multi-) Phase Behaviour of Asphaltenic Crudes

Abstract: Asphaltenes flocculation is described as a thermodynamic transition inducing the formation of a new liquid phase with a high asphaltenic content; this phase being the asphaltenic deposit. The thermodynamic model selected is the Peng-Robinson Equation of State associated with the Abdoul and Peneloux group contribution mixing rules. The oil is modeled by 33 pseudocomponents. Mainly, the heavy F(11+) residue is represented as one pseudocomponent for the F11 - F20 cut and as 4 pseudocomponents for the F(20+) cut : Sat F(20+) , Aro F(20+) , Resinsand Asphaltenes . The physical properties of the Sat F(20+) , Aro F(20+)and Resinspseudocomponents are calculated using the group contribution methods of Avaullee, and of Rogalski and Neau, based on the knowledge of their molecular structure. The physical properties of the F11 - F20and Asphaltenespseudocomponents are fitted in order to reproduce correctly the bubble pressure, the relative volumes and the flocculated quantities at 303 K. The model gives the proportion and the composition of asphaltene deposits in the oil at different temperatures (303 - 403 K) within a relatively large pressure range (0. 1 - 50 MPa) including the bubble pressure of the considered crude.

Fluid Sampling under Adverse Conditions

Abstract: Valid samples are essential to the proper description of reservoir fluids; if the samples are not representative, all measurements on them will be invalid. This paper discusses the principal challenges facing fluid sampling including gas condensate reservoirs, compositional gradients, water content of hydrocarbon fluids, asphaltene deposition, wax formation, oil base mud contamination, and reactive components. It also reports the major technological advances recently made in this field. It reviews developments in sampling techniques such as MDT-type tools, new DST sampling tools, coiled tubing sampling, and isokinetic techniques, and it highlights common limitations. The value of making proper use of existing technology is emphasized, both with traditional techniques and new developments, with reference to correct well conditioning, interpretation of field data, and especially to optimum handling of samples. The paper emphasizes the need for better exchange of sampling knowledge between organizations, and highlights the lack of up-to-date industry standards with respect to fluid sampling. A solution is proposed in the form of a joint industry project to identify and document best practices.

Calcul des propriétés élastiques des tissus utilisés dans les matériaux composites

Abstract: Les renforts textiles s'imposent des qu'il faut realiser des structures massives ou complexes en materiaux composites, comme certains raccords et jonctions de tubes, des panneaux d'habitation legere, des carters de protection de tetes de puits en fond de mer, etc. Cet article expose les caracteristiques generales d'un renfort textile, puis differentes approches micromecaniques analytiques representant les tissus a tissage bidimensionnel sont presentees. En partant du plus simple et en allant vers le plus complexe, ces modeles sont l'analogie a un stratifie [0°/90°], la mosaique en serie et en parallele, les ondulations 1D et les ondulations 2D serie-parallele et parallele-serie. Toutes ces approches sont fondees sur la theorie mecanique des stratifies. En analysant les resultats d'applications numeriques de ces modeles et les resultats experimentaux, on constate que les modeles des ondulations en 2D procurent les meilleures valeurs estimees des modules elastiques. Les autres modeles n'indiquent que des ordres de grandeurs.