Study of Resin Adsorption onto Asphaltene and Silica-Asphaltene Particles

Abstract

We present a methodology to study the adsorption behavior of resins on asphaltenes, which we call silica-asphaltene complex methodology (SACOM), and compare it to a methodology regularly used by many researchers (Acevedo et al., 1995 Acevedo, S., Ranaudo, M., Escobar, G., Gutiérrez, L. and Ortega, P. 1995. Adsorption of asphaltenes and resins on organic and inorganic substrates and their correlation with precipitation problems in production well tubing. Fuel., 74: 595–598. [Crossref], [Web of Science ®] , [Google Scholar]; González et al., 2003 González, G., Neves, G., Saraiva, S., Lucas, E. and Anjos de Sousa, M. 2003. Electrokinetic Characterization of Asphaltenes and the Asphaltenes-Resins Interaction. Energ. Fuel., 17: 879–886. [Crossref], [Web of Science ®] , [Google Scholar]; León et al., 2002 León, O., Contreras, E., Rogel, E., Dambakli, G., Acevedo, S., Carbornani, L. and Espidel, J. 2002. Adsorption of Native Resins on Asphaltene Particles: A Correlation between Adsorption and Activity. Langmuir, 18: 5106–5112. [Crossref], [Web of Science ®] , [Google Scholar]; Marczewski et al., 2002 Marczewski, A. and Szymula, M. 2002. Adsorption of asphaltenes from toluene on mineral surface. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 208: 259–266. [Crossref], [Web of Science ®] , [Google Scholar]; Pereira et al., 2007 Pereira, J. C., López, I., Salas, R., Silva, F., Fernández, C., Urbina, C. and López, J. C. 2007. Resins: The Molecules Responsible for the Stability/Instability Phenomena of Asphaltenes. Energ. Fuel., 21: 1317–1321.  [Google Scholar]) that we call traditional methodology. Three isotherms of resins adsorbed on the complex substrates (asphaltene and its colloidal fractions A₁ and A₂ adsorbed on silica) were built, analyzed, and then compared with two isotherms built by applying a traditional methodology where resins were adsorbed on two organic substrates: asphaltene and its fraction A₁.     

Formation Pore Pressure Prediction Using Velocity Inversion in Southwest Iran

Abstract

Surface seismic data include necessary information for predicting the formation of pore pressure in hydrocarbon reservoirs. In this article, formation pore pressure was predicted based on the velocity inversion method for a gas reservoir located in the southwest of Iran. Firstly, for this purpose, seismic data were inverted to obtain velocity values. Secondly, these values were converted to effective stress by using Bowers' equation (1994). In addition, the overburden stress was estimated from the Amoco equation (Huffman et al., 2011 Huffman, A. R., Meyer, J., Gruenwald, R., Buitrago, J., Suarez, J., Diaz, C., Munoz, J. M. and Dessay, J. 2011. Recent advances in pore pressure prediction in complex geologic environments Manama, , Bahrain March 20–23, SPE Paper No. 142211-PP [Google Scholar]). To obtain formation pore pressure, the effective stress was subtracted from the estimated overburden stress. The results showed a normal distribution of formation pore pressure versus depth.     

Prediction of Surface Tension of Pure Hydrocarbons by An Artificial Neural Network System

Abstract

In this study, a multilayer perceptron neural network with a back-propagation (BP) learning method containing three layers has been developed for prediction of surface tension of pure hydrocarbons. This model was developed using 211 experimental data on surface tension in the literature. Statistical criteria of R² and root mean square error (RMSE) for this network were 0.9997 and 0.0615, respectively. The accuracy and validity of this model were compared with the experimental data and results obtained from the Pazuki-Nikookar (PN) equation of state (EOS; Pazuki et al., 2007; Nikookar et al., 2008 Nikookar, M., Omidkah, M. R. and Pazuki, G. R. 2008. Prediction of density and solubility parameter of heavy oils and SARA fractions using cubic equations of state. Petrol. Sci. Tech., 26: 1904–1912. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) as well as some semi-experimental correlations such as Pitzer (1995) Pitzer, K. S. 1995. Thermodynamics, , 3rd ed. New York: McGraw-Hill..  [Google Scholar], Sastri and Rao (1999) Sastri, S. R. S. and Rao, K. K. 1999. A new temperature–thermal conductivity relationship for predicting saturated liquid thermal conductivity. Chem. Eng. J., 74: 161–169. [Crossref], [Web of Science ®] , [Google Scholar], and Brock and Bird (1955) Brock, J. R. and Bird, R. B. 1955. Surface tension and the principle of corresponding states. AIChE J., 1: 174–177. [Crossref], [Web of Science ®] , [Google Scholar]. Also, considering the results obtained by the artificial neural network system, a correlation is presented for estimation of the parachor constant and the results are compared with those obtained from equations of state.     

Technical and Economical Analysis of Hydrogen Sulfide Removal from the Recycled Hydrogen in a Diesel Hydrodesulfurization Plant

Abstract

Hydrodesulfurization (HDS) is a catalytic process used to remove sulfur compounds, which leads to very low sulfur concentrations. HDS turns more complicated and severe according to the feedstock boiling range, since sulfur compounds present in light cuts, normally sulfides and mercaptanes, are easy to remove, and sulfoaromatic compounds, specially polycyclics, are the more refractive ones (Speight, J. G. (1981 Speight, J. G. 1981. The Desulfurization of Heavy Oils and Residua Chemical Industries 4. , 2nd ed. Marcel Dekker Inc.  [Google Scholar]). The Desulfurization of Heavy Oils and Residua. 2nd ed. Marcel Dekker, Inc.: Chemical Industries 4.) The hydrogen sulfide (H₂S) produced in the HDS has an inhibiting effect on the same reaction, as it has been widely observed (McCulloch, D. C. (1983 McCulloch, D. C. 1983. Applied Ind. Catal., I: 69 [Google Scholar]). Applied Ind Catal. I:69; National Petroleum Refining Association (NPRA). (1993 National Petroleum Refining Association, NPRA. 1993. Questions & Answers 99 [Google Scholar]). Questions & Answers, 99; Leglise, J., Van Gestel, J., Duchet, J. C. (1994 Leglise, J., Van Gestel, J. and Duchet, J. C. Symposium on advances in hydrotreating catalysts presented before the division of petroleum chemistry Inc. 208th National Meeting. pp.pp. 533Washington, D.C.: American Chemical Society.  [Google Scholar]). Symposium on Advances in Hydrotreating Catalysts Presented before the Division of Petroleum Chemistry Inc. In: 208th National Meeting American Chemical Society. Washington D.C. p. 533). This effect is well known even at relatively low H₂S concentrations (2 mol%) for commercial operation conditions (Leglise, J., Van Gestel, J., Duchet, J. C. (1994 Leglise, J., Van Gestel, J. and Duchet, J. C. Symposium on advances in hydrotreating catalysts presented before the division of petroleum chemistry Inc. 208th National Meeting. pp.pp. 533Washington, D.C.: American Chemical Society.  [Google Scholar]). Symposium on Advances in Hydrotreating Catalysts Presented before the Division of Petroleum Chemistry Inc. In: 208th National Meeting American Chemical Society. Washington D.C. p. 533). Due to this, the H₂S removal from the recycled hydrogen to the reactor is mandatory in order to increase the desulfurization levels or to increase the processing capacity of an HDS plant. There are many options to low the H₂S concentration in the H₂ loop (Cooper, A., Stanislaus, A., Hannerup, P. N. (June 1993 Cooper, A., Stanislaus, A. and Hannerup, P. N. 1993. Hyd. Process., June: 84 June [Google Scholar]). Hyd Process 84; Johnson, A. D. (1983 Johnson, A. D. 1983. Oil and Gas J., 10: 78 [Google Scholar]). Oil and Gas J 10:78; Nash, R. M. (1989 Nash, R. M. 1989. Oil and Gas J., 13: 47 [Google Scholar]). Oil and Gas J 13:47; Suchanek, A. J., Dave, D., Gupta, A., Van Stralen, H., Karlsson, K. (1993 Suchanek, A. J., Dave, D., Gupta, A., Van Stralen, H. and Karlsson, K. NPRA Annual Meeting. AM-93-24 [Google Scholar]). In: NPRA Annual Meeting AM-93-24; Tippett, T., Knudsen, K. G. (1999 Tippett, T. and Knudsen, K. G. NPRA Annual Meeting. San Antonio, TX. AM-99-06 [Google Scholar]). In: NPRA Annual Meeting. San Antonio, TX. 1999 NPRA Annual Meeting, San Antonio, TX, AM-99-06.), which are from a simple purge adjustment for light naphtha HDS to a full treatment of the H₂ stream for middle distillate HDS, where the H₂S concentration can reach levels of 10 mol% (National Petroleum Refining Association (NPRA). (1993 National Petroleum Refining Association, NPRA. 1993. Questions & Answers 99 [Google Scholar]). Questions & Answers, 99). This work presents the economical analysis of the introduction of an Amine Treating Unit in an HDS plant in operation to remove H₂S from the H₂ stream recycled to the reactor.     

Kinetic Modeling of Hydrodesulphurization of Residual Oils. II. Hyperbolic Models

Abstract

Fourteen models of the Hougen–Watson type were developed and tested for hydrodesulphurization (HDS) of benzothiophene and thiophene, which form the major part of sulphur usually present in residual oils. Model discrimination based on the positiveness of the rate and equilibrium constants, revealed that four of the models satisfied the set criteria. One of these models corresponds to that proposed by Kilanowski and Gates ([1980] Kilanowski and Gates, B. C. 1980. Kinetics of Hydrodesulphurization of Benzothiophene catalysed by sulphide Co-Mo/AI203. Journal Catalysis, 62: 70–78.  [Google Scholar]) for benzothiophene and the one derived by Satterfield and Roberts ([1968] Satterfield, C. N. and Roberts, G. W. 1968. Kinetics of hiphene Hydrogenolysis on Cobalt Molybdate Catalyst. A. I. Ch. E. Journal, 14: 159[Crossref], [Web of Science ®] , [Google Scholar]) for thiophene. A new model, which was determined by variance function analysis, suggests that the HDS of both benzothiophene and thiophene assumes a dual site mechanism and is first order in sulphur compound and second order in hydrogen.     

Obtaining of Ashless Additives for Diesel Fuel Impoving the Lubricating,Anticorrosion and Protection Properties

Abstract

The production of “ultra pure” diesel fuels is connected with the deterioration of their certain performance characteristics. The lubricating properties of ultra pure diesel fuels are poor; their relative stability worsens; they tend to be corrosion-aggressive toward metal surfaces; and their electrophysical properties sharply deteriorate to increase the possibilities for accumulation of static-electric charge by transportation and feeding into vehicles (Tasheva, Petkov, and Ivanov, 2003 Tasheva, J., Petkov, P. and Ivanov, Sl. 2003. Contemporary trends in connection with the reduction of sulfur oxides at burning of fuels. Annual of University Prof. Dr. Assen Zlatarov, Bourgas, Bulgaria, XXXII(1): 150–155.  [Google Scholar]; 2004 Tasheva, J., Petkov, P. and Ivanov, Sl. 2004. Reduction of the contents of sulphur-containing organic compounds, arene hydrocarbons and resinous products in diesel fuels by applying extraction with selective solvents. Oxidation Communications, 27(1): 48–57.  [Google Scholar]).

These negative properties of the ultra pure diesel fuel are usually overcome by adding special substances to improve their lubricating properties, electric conductivity, and oxidation stability and to eliminate their corrosion aggressiveness.     

A New Modified Compositional Viscosity Model for Medium-heavy Oils

Viscosity of heavy oils is a key parameter in designing potential enhanced oil recovery methods. The recently proposed semiempirical viscosity model by Lindeloff et al. (2004) Lindeloff, N., Pedersen, K. S., Rønningsen, H. P. and Milter, J. 2004. The corresponding states viscosity model applied to heavy oil systems.. J. Can. Pet. Technol., 43: 47–53. [Web of Science ®] , [Google Scholar] was studied in depth. This model is the simplest yet powerful tool for medium-heavy oil viscosities. Based on the analysis, appropriate adjustments have been suggested, with the major one being the division of the pressure-viscosity profile into three different regions. New modifications have improved the overall fit, including the saturated viscosities at low pressures. The %AAD for the data sets studied was found to be 1.37. However, with the limited geographically diverse data, it is not possible to make a comprehensive predictive model. A few limitations of the new model are also stated.     

Prediction of Explosive Performance Properties of z-DBBD and Its Isomers by Quantum Chemical Computations

Theoretical studies have been performed on TACOT, its benzofuroxan derivative z-DBBD, and three different isomers of z-DBBD. The corrected absolute and relative total energies of the geometry-optimized structures were calculated at the theoretical level of B3LYP/6-31G(d,p). The bond dissociation energies were correlated with sensitivity. Mulliken electronegativities (χ_M) and chemical hardness (η) were obtained by employing frontier molecular orbitals at the HF/6-31G(d,p)//B3LYP/6-31G(d,p) theoretical level. Detonation performance analyses for z-DBBD (4,11-dinitro[1 Molchanova , M. S. , T. S. Pivina , E. A. Arnautova , and N. S. Zefirov . 1999 . Computer-aided search for high-density energetic compounds among hydrogen-free heterocycles . Journal of Molecular Structure (Theochem) , 465 : 11 – 24 .[Crossref], [Web of Science ®] , [Google Scholar],2 Kamlet , M. J. and S. F. Jacobs . 1968 . Chemistry of detonations. I. A simple method for calculating detonation properties of C H N O explosives . Journal of Chemical Physics , 48 : 23 – 25 .[Crossref], [Web of Science ®] , [Google Scholar],5 Kamlet , M. J. and H. J. Hurwitz . 1968 . Chemistry of detonations. IV. Evaluation of a simple predictional method for detonation velocities of C-H-N-O explosives . Journal of Chemical Physics , 48 : 3685 – 3692 .[Crossref], [Web of Science ®] , [Google Scholar]]-oxadiazolo[3,4-e][1 Molchanova , M. S. , T. S. Pivina , E. A. Arnautova , and N. S. Zefirov . 1999 . Computer-aided search for high-density energetic compounds among hydrogen-free heterocycles . Journal of Molecular Structure (Theochem) , 465 : 11 – 24 .[Crossref], [Web of Science ®] , [Google Scholar],2 Kamlet , M. J. and S. F. Jacobs . 1968 . Chemistry of detonations. I. A simple method for calculating detonation properties of C H N O explosives . Journal of Chemical Physics , 48 : 23 – 25 .[Crossref], [Web of Science ®] , [Google Scholar],5 Kamlet , M. J. and H. J. Hurwitz . 1968 . Chemistry of detonations. IV. Evaluation of a simple predictional method for detonation velocities of C-H-N-O explosives . Journal of Chemical Physics , 48 : 3685 – 3692 .[Crossref], [Web of Science ®] , [Google Scholar]]oxadiazolo[3′,4′:4,5]benzotriazolo-[2,1-a]benzotriazol-6-ium inner salt 1,8-dioxide), its presently considered isomers, and TACOT were performed. The results showed that the performance of all compounds (compounds 1–4) was as good as that of RDX. The power index results showed that z-DBBD and its isomers were better than TACOT, RDX, and HMX. Compounds 1–4 are all reasonable candidates for high-energy-density materials (HEDMs).     

Asphaltene Precipitation Prediction Using a Micellization Model Based on Experimental Data

Abstract

Thermodynamic modeling is a promising tool for prediction of asphaltene precipitation. However, most thermodynamic models do not consider the micellar nature of petroleum fluids and the interaction between asphaltene-resin molecules. In addition, the accuracy of the predictions from the Peng-Robinson equation of state (PR-EOS) depends on the mixing rule. In this work, a thermodynamic framework based on the micellization model is used to describe the structure of asphaltene micelles as well as asphaltene precipitation in crude oil and the Wong and Sandler (1992) Wong, D. S. H. and Sandler, S. I. 1992. A theoretically correct mixing rule for cubic equations of state. AIChE J., 38: 671–680. [Crossref], [Web of Science ®] , [Google Scholar] mixing rule also is applied. The results show that the model predictions are matched well with the generated data for two Iranian crude oils.     

New Approaches for Permanent Downhole Gauge (PDG) Data Processing

Abstract

One of the major issues in processing permanent downhole gauge (PDG) data is that too many transients exist over a reasonable time period, say 6 months. A formula was proposed to predict the transients that may be detected or missed. Reasonable prediction was achieved via the formula.

Noise usually exists in data recorded by PDGs. Denoising is thus one of the most important steps in PDG data processing. In order to denoise the data, the data noise level must be estimated beforehand. Unfortunately, the data noise level is typically case-dependent, and therefore, it is impossible to identify a universal value for the level that may be used for all the application scenarios.

One appropriate approach to estimate the noise level is to first best fit the data, subtract the predicted pressure response from recorded values, and then calculate the noise level based on the difference. We propose to apply nonlinear regression via the Polytope method (Gill, Murray, and Wright, 1981 Gill, P. E., Murray, W. and Wright, W. H. 1981. Practical Optimization, London: Academic Press.  [Google Scholar]) for best-fitting PDG data to determine the noise level. It is found that the new approach is superior to the least square error (LSE) linear regression as used by Khong (2001) Khong, C. -K. 2001. Permanent downhole gauge data interpretation, Master's thesis Stanford University, Petroleum Engineering Dept.. June [Google Scholar], because the bottom-hole wellbore pressure response in a well should be treated as a nonlinear function of time over the majority of the well production/injection/shut-in period. Unless a very small range of the data (say 2 h) is considered, a linear pressure response with time is not anticipated. Furthermore, with nonlinear regression through the Polytope approach, there is no strong restriction in data quantity and data density, hence, automatic detection of the data noise level can be implemented.     

Major Challenges for Reservoir Upscaling

Abstract

In the past two decades, many upscaling procedures have been proposed. The major methods are power-law average, renormalization technique, pressure-solver method, tenser method, and pseudo-function technique. The common problem of conventional upscaling methods is that they tend to smear out the spatially continuous extremes, such as shale barriers and open fractures. However, experience and previous simulation work in heterogeneous reservoirs have shown that oil recovery (especially water breakthrough oil recovery) mainly depends on the spatial connectivity of the extreme permeability values.

Lasseter et al. (1986) Lasseter, T. J., Waggoner, J. R. and Lake, L. W. 1986. “Reservoir heterogeneities and their influence on ultimate recovery.”. In Reservoir characterization Edited by: Schatzinger, R. A. and Jordan, J. F. 545Orlando: Academic Press, Inc..  [Google Scholar] proposed that scale-up of properties should be done from the scale of a representative elementary volume (REV), a volume for which the measured property does not change with an increase in scale over a given limit of scale. The notion of REV is physical-model oriented and proposed a criterion for upscaling technique. However, the decisive factor in upscaling is the grid system rather than individual physical point.

This article concludes that how to obtain REV for real system, how to evaluate the upscaling results quantitatively, how to treat extremes of permeability, as well as how to perform upscaling for naturally fractured reservoirs and carbonate reservoirs are the remained major challenging problems in this area. It is concluded that a great effort should be made on how to obtain the REV grid, which could best describe the heterogeneity of given reservoir at a given scale. Secondly how to perform the upscaling of all properties based on the REV grid is also a critical aspect and should be considered according to the different extent and pattern of heterogeneity of the original geological model respectively.     

Effects of Memory on the Complex Rock-Fluid Properties of a Reservoir Stress-Strain Model

Abstract

The memory based stress-strain model developed earlier by Hossain et al. (2007) Hossain, M. E., Mousavizadegan, S. H., Ketata, C. and Islam, M. R. 2007. A novel memory based stress-strain model for reservoir characterization. Journal of Nature Science and Sustainable Technology, 1: 653–678.  [Google Scholar] has been solved numerically in this study. The derived mathematical model introduces the effects of temperature, surface tension, and pressure variations and the influence of fluid memory on the stress-strain relationship. The variation of shear stress as a function of strain rate is obtained for fluid in a sample oil reservoir to identify the effects of fluid memory. The stress-strain formulation related with the memory is taken into account, and we obtain the variation of it with time and distance for different values of α. The dependency of the stress-strain relation on fluid memory is considered to identify its influence on time. As pressure is also a function of space, the memory effects on stress and strain are shown in space with the pressure gradient change. The computation indicates that the effect of memory causes nonlinearity, leading to chaotic behavior of the stress-strain relationship. This model can be used in reservoir simulation and rheological study, well test analysis, and surfactant and foam selection for enhanced oil recovery.     

Viscosity Model for CO-Noble Gas Mixtures at Atmospheric Conditions

Abstract

We have presented an empirical model for predicting the viscosity of binary mixtures of gases, based on our previous correlation for natural gas mixtures (Miadonye and Clyburn, 2003 Miadonye, A. and Clyburn, W. 2003. Modelling the Viscosity of Natural Gas Mixtures, Computational Methods and Experimental Measurements, Edited by: Esteve. Southhampton, , UK: WIT Press.  [Google Scholar]). New parameters were derived for binary mixtures of carbon monoxide-noble gases and for carbon monoxide-nitrogen gases, for temperatures from 0–1000°C. The model was validated with the Chapman-Enskog equation for gas mixtures, with and without length scaling factor. For five equimolar and eight non-equimolar mixtures of gases at temperatures from 0–1000°C, the model gave an excellent viscosity prediction with an overall average absolute deviation of 0.45%. The model is simple to incorporate in design and simulation packages, and more accurate than any correlation currently used for estimating the viscosities of gas mixtures.     

A Four Lump Kinetic Model for the Simulation of the Hydrocracking Process

Abstract:

Hydrocracking is a very important secondary refining process used to convert low value vacuum gas oils into high value fuels. The chemistry of the hydrocracking process is very complex due to the involvement of high molecular weight complex hydrocarbons in the reactions. Process modeling and simulation of the hydrocracking unit is very challenging due to the complexities of chemistry and the process. In the present work, a mathematical model is described to analyze the performance of the hydrocracking process in terms of product yields. A four lump discrete lumping approach is employed with a hydrocracking reaction scheme involving six reactions. The kinetic constants for the reactions were estimated by minimizing the error between the experimental and predicted yields of kinetic lumps. Experimental data reported by Ali et al. (2002) Ali, M. A., Tatsumi, T. and Masuda, T. 2002. Development of heavy oil hydrocracking catalysts using amorphous silica-alumina and zeolites as catalyst supports. Applied Catalysis A: General, 233: 77–90. [CSA][Crossref], [Web of Science ®] , [Google Scholar] were used to validate the proposed model. The model predictions were found to agree well with the experimental data. The proposed model can be used to simulate the performance of commercial hydrocrackers using kinetic parameters estimated from pilot plant experiments.     

REV Grid Technique for Reservoir Upscaling

Abstract

Lasseter et al. (Lasseter, T. J., Waggoner, J. R., Lake, L. W. (1986 Lasseter, T. J., Waggoner, J. R. and Lake, L. W. 1986. Reservoir Heterogeneities and Their Influence on Ultimate Recovery. Reservoir Characterization 545Orlando, FL: Academic Press Inc..  [Google Scholar]). Reservoir Heterogeneities and Their Influence on Ultimate Recovery. Reservior Characterization, Orlando, Florida: Academic Press Inc., 545.) proposed that scale-up of properties should be done from the scale of a representative elementary volume (REV), a volume for which the measured property does not change with an increase in scale over a given limit of scale. The notion of REV has been a quite argued concept owing to its definition is not unequivocal, and it did not address how to obtain it in real system, some people even argue if REV really exists. Qi et al. (Qi, D., Wong, P. M., Liu, K. (2001 Qi, D., Wong, P. M. and Liu, K. 2001. An improved global upscaling approach for reservoir simulation. Petroleum Science and Technology, 19(7–8): 779–795. [CROSSREF][Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). An improved global upscaling approach for reservoir simulation. Petroleum Science and Technology 19(7–8):779–795.) based on REV concept, proposed the new idea of REVG (representative elemental volume grid). This article further developed this idea, and based on it, proposed the REV grid upscaling technique. This new technique uses an algorithm, which is a combination of two-procedure-upgridding with reverse stepwise approach, it is a field-oriented 3D model. The new method concentrates on constructing a unique coarse grid, referred to as pseudo-REVG, which could best describe the heterogeneity of the original model at given scale. Mathematically, the variance of properties in REVG is the smallest within each block, and largest between the blocks. The proposed method is applied to two case studies, one of them is a 3D multiphase real reservoir, and the flow simulation results show that the consistency of the reservoir behavior before and after upscaling with REV grid technique is excellent. It is much better than that of the conventional upscaling methods.     

Status of Dual-Continuum Models for Naturally Fractured Reservoir Simulation

Abstract

Naturally fractured reservoirs (NFR) contain significant portions of the world's proven reserves of conventional oil. However, their simulation is one of the most challenging and computationally intensive problems in reservoir engineering. Most commercial reservoir simulators use dual-continuum models to predict performance of an NFR where two overlapping continua for the fracture and matrix medium are considered. Then transfer of multiphase fluid between the two media is taken into consideration by a source-sink transfer function (Zhang and Sun, 2000 Zhang, D. and Sun, A. Y. 2000. Stochastic analysis of transient saturated flow through heterogeneous fractured porous media: A double-permeability approach. Water Resour. Res., 36: 865–874. [Crossref], [Web of Science ®] , [Google Scholar]). After review of different conceptual models to simulate an NFR, major pitfalls related to dual-porosity and dual-permeability models for simulation of such reservoirs will be discussed briefly within this article.     

SOLUTION NONUNIQUENESS FOR SEPARATED GAS–LIQUID FLOW IN PIPES AND WELLS. II. ANALYSIS

ABSTRACT

As shown in [10] Ouyang, L.-B. and Aziz, K. 2001. Solution Nonuniqueness for Separated Gas–Liquid Flow in Pipes and Wells – Part 1: Occurrence. Petroleum Science and Technology, in press [Google Scholar], multiple solutions may occur for upward flow for separated flow in a pipe without wall mass transfer. For the wellbore flow with wall inflow (production well) case, multiple solutions only exist for upward flow for the gas inflow-dominant case, whereas they may exist for upward, horizontal and downward flow for liquid inflow-dominant situations. The opposite is expected for the wall outflow (injection well) case. The transient models have been proposed for separated (stratified and annular-mist) gas–liquid flow in pipes or wells and successfully applied to validate, both physically and numerically, the correct solution of liquid holdup and pressure drop whenever multiple solutions exist for separated flow. Physical considerations and numerical simulation have shown that only the solution with the lowest liquid height (holdup) is physically realistic. The solutions corresponding to the intermediate and the highest liquid holdup may not be able to lead to a stable flow.     

Experimental and modeling asphaltene precipitation in presence of DBSA using PC-SAFT EOS

Asphaltene precipitation and subsequent deposition in production tubing and topside facilities present significant cost penalties to crude oil production. Therefore, it is highly desirable to predict their phase behavior and the efficiency of dispersants in preventing or delaying deposition. Very few studies have been carried out on the molecular interactions between asphaltenes and different dispersants. As a result, the mechanisms by which dispersants stabilize asphaltenes are still open to discussion. The authors introduced a new method to characterize asphaltenes in perturbed chain statistical association fluid theory equation of state (EOS; perturbed-chain statistical association fluid theory EOS [PC-SAFT-EOS]) and correctly model the effect of dodecyl benzene sulfonic acid (DBSA) dispersant on the thermodynamic behavior of asphaltenes. Using the filtration method the effect of the ionic dispersant (DBSA) on asphaltene precipitation for different concentrations of n-heptane was measured experimentally, then modeled through PC-SAFT EOS. In the approach only the hard-chain and the dispersion terms are taken into consideration, and PC-SAFT parameters were calculated based on Gonzales et al. (2007 Gonzalez, D. L., Hirasaki, G. J., Creek, J., and Chapman, W. G. (2007). Modeling of asphaltene precipitation due to changes in composition using the perturbed chain statistical associating fluid theory equation of state. Energy Fuels 21:1231–1242.[Crossref], [Web of Science ®] , [Google Scholar]) based on molecular weight (Mw) and aromaticity factor (γ). Additionally, the model could correctly predict the amount of asphaltene precipitation upon addition of DBSA dispersant.     

Investigation of Low Frequency Elastic Wave Application for Fluid Flow Percolation Enhancement in Fractured Porous Media

In recent years, some numerical models have been proposed to investigate the effects of the elastic wave such as ultrasonic on fluid flow behavior in porous media. Nevertheless, none of these models are applicable to the fractured reservoirs, especially when the fluid is a Bingham plastic. In this work, the model proposed by P. P. Iassonov and I. A. Beresnev (2003) Iassonov, P. P. and Beresnev, I. A. 2003. A model for enhanced fluid percolation in porous media by application of low-frequency elastic waves. J. Geophys. Res., 108: 2138–2146. [Crossref], [Web of Science ®] , [Google Scholar] for flow under exposure of elastic wave in nonfractured porous media is considered and used for development of a new model of steady state flow of a Bingham plastic fluid in fractured reservoirs. The Kazemi's “block and fracture” model assuming negligible vertical permeability in blocks is considered for modeling. In addition, two-phase flow behavior under elastic wave in fractured system is investigated. The results showed that, at higher pressure gradients, vibration amplitude cannot highly influence the fluid percolation, in contrast at lower pressure gradients, the fluid flow through the fractured porous media can considerably be improved by increasing vibration amplitude. Also, it has been found that in two-phase flow systems, wave can increase the produced oil-water ratio in the fractured media. The results of this study can be applied to the fractured reservoir simulations and can be a path breaking to the future studies on the prediction of flow enhancement under elastic wave in the fractured reservoirs.     

Correlations Between the Pour Point/Gel Point and the Amount of Precipitated Wax for Waxy Crudes

Abstract:

The amount of precipitated wax is one of the key factors that governs the flow properties of waxy crudes. Experimental results of 24 crudes have shown that approximately 2 wt% precipitated wax is sufficient to cause a virgin waxy crude gelling. Accordingly, a correlation between the pour point and the temperature at which 2 wt% of wax has precipitated out from a crude oil; i.e., T _c (2 wt%), and a correlation between the gel point and T _c (2 wt%) have been developed. The proposed correlation of the pour point is in accordance with the correlation developed by Letoffe et al. (1995) Letoffe, J. M., Claudy, P., Kok, M. V., Garcin, M. and Vollet, J. L. 1995. Fuel, 74(6): 810–817. [CSA][CROSSREF][Crossref] , [Google Scholar] on the basis of 14 crudes from eight countries. The development of the gel point correlation and further verification of the pour point correlation indicate that there is a relationship between the gelling of virgin waxy crudes and the amount of precipitated wax. According to these correlations and the amount of precipitated wax, which can be determined only with a little sample by thermodynamic models or Differential Scanning Calorimetry (DSC) experiment, the gel point and pour point of virgin waxy crude can be predicted even if the oil sample is very limited. Heat treatment and chemical treatment can greatly improve flow behavior of waxy crudes, and more precipitated wax is present when the beneficiated (thermally beneficiated or PPD-beneficiated) crude oils gel. Experimental results showed that approximately two or three times the amount of precipitated wax presents at the gelling temperature when the oils were in their beneficiated (thermally beneficiated or PPD-beneficiated) conditions.