Dow Chemical (Canada)

Nanomaterials are used in practically every aspect of modern life, including agriculture. The aim of this study was to evaluate the effectiveness of iron oxide nanoparticles (Fe2O3 NPs) as a fertilizer to replace traditional Fe fertilizers, which have various shortcomings. The effects of the Fe2O3 NPs and a chelated-Fe fertilizer (ethylenediaminetetraacetic acid-Fe; EDTA-Fe) fertilizer on the growth and development of peanut (Arachis hypogaea), a crop that is very sensitive to Fe deficiency, were studied in a pot experiment. The results showed that Fe2O3 NPs increased root length, plant height, biomass, and SPAD values of peanut plants. The Fe2O3 NPs promoted the growth of peanut by regulating phytohormone contents and antioxidant enzyme activity. The Fe contents in peanut plants with Fe2O3 NPs and EDTA-Fe treatments were higher than the control group. We used energy dispersive X-ray spectroscopy (EDS) to quantitatively analyze Fe in the soil. Peanut is usually cultivated in sandy soil, which is readily leached of fertilizers. However, the Fe2O3 NPs adsorbed onto sandy soil and improved the availability of Fe to the plants. Together, these results show that Fe2O3 NPs can replace traditional Fe fertilizers in the cultivation of peanut plants. To the best of our knowledge, this is the first research on the Fe2O3 NPs as the iron fertilizer.

Numerous redox transformations that are essential to life are catalyzed by metalloenzymes that feature Earth-abundant metals. In contrast, platinum-group metals have been the cornerstone of many industrial catalytic reactions for decades, providing high activity, thermal stability, and tolerance to chemical poisons. We assert that nature's blueprint provides the fundamental principles for vastly expanding the use of abundant metals in catalysis. We highlight the key physical properties of abundant metals that distinguish them from precious metals, and we look to nature to understand how the inherent attributes of abundant metals can be embraced to produce highly efficient catalysts for reactions crucial to the sustainable production and transformation of fuels and chemicals.

Simulation optimization (SO) refers to the optimization of an objective function subject to constraints, both of which can be evaluated through a stochastic simulation. To address specific features of a particular simulation-discrete or continuous decisions, expensive or cheap simulations, single or multiple outputs, homogeneous or heterogeneous noise-various algorithms have been proposed in the literature. As one can imagine, there exist several competing algorithms for each of these classes of problems. This document emphasizes the difficulties in SO as compared to algebraic model-based mathematical programming, makes reference to state-of-the-art algorithms in the field, examines and contrasts the different approaches used, reviews some of the diverse applications that have been tackled by these methods, and speculates on future directions in the field.

A new weighted least-squares method is described which is generally applicable for the nonsubjective evaluation of the best set of thermodynamic functions from a given data set of equilibrium (ΔG) and calorimetric (ΔH, Cp) measurements. The method, applied to model a wide range of 2428 measurements for the water-sodium chloride system between −21 and 154 °C, accurately represents all measurements within experimental error. The resulting model is used to predict the thermodynamic functions and their standard errors for aqueous sodium chloride up to 110 °C. Tables are given for freezing point, solubility, boiling point, osmotic and activity coefficients, vapor pressure, apparent molal relative enthalpy, partial molal relative enthalpies, integral heat of solution, specific heat, apparent molal heat capacity, partial molal heat capacities, apparent molal relative heat capacity, partial molal relative heat capacities, standard thermodynamic functions, and their changes for dissolution.

Flavor is an important quality attribute which relates to the organoleptic characteristics of meat. Although perception of flavor is a complex phenomenon, odor is the most important single factor contributing to the overall characteristics of flavor. A large number of compounds have been identified in the volatile fraction of red meats and poultry. An overview of the chemical constituents present in the volatiles of beef, pork, mutton, and chicken is presented according to species and arranged by chemical class--hydrocarbons, alcohols, acids, aldehydes, ketones, sulfides, heterocyclic compounds, etc. The volatile components of cured and uncured pork are compared. The field of meat flavor is assessed in terms of what has been accomplished and the direction in which it may proceed. Techniques for analysis of these volatiles are briefly described.

A comprehensive multimedia assessment of the environmental fate of bisphenol A (BPA) is presented. Components of the assessment include an evaluation of relevant partitioning and reactive properties, estimation of discharge quantities in the U.S. and the European Union (E.U.) resulting in conservative and realistic emission scenarios, and a review of monitoring data. Evaluative assessments of chemical fate using the Equilibrium Criterion (EQC) model are described from which it is concluded that the low volatility of BPA will result in negligible presence in the atmosphere. It is relatively rapidly degraded in the environment with half-lives in water and soil of about 4.5 days and less than 1 day in air, and with an overall half-life of 4.5 to 4.7 days, depending on the medium of release. The degradation rate in water is such that it may be transported some hundreds of kilometres in rivers, but long-range transport potential in air is negligible. Its low bioconcentration factor is consistent with rapid metabolism in fish (half-life less than 1 day). The estimated concentrations were generally consistent with the monitoring data, with the exception of sediment-water concentration ratios. Several hypotheses for the apparent nonequilibrium sediment-water partitioning are presented.

The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been recorded using transmission, fluorescence, and electron yield detection. The corresponding electron energy loss spectra (EELS) have been recorded in a scanning transmission electron microscope. These results are compared to the C 1s and O 1s spectra of gas phase 1,4-dimethyl terephthalate (the monomer of PET) recorded using EELS. The comparison of monomer and polymer materials in different phases and with different techniques has aided the understanding of the relative strengths and limitations of each technique as well as assisting the spectral interpretation. Good agreement is found in the overall shape and the energies of the spectral features. Relatively minor differences in intensities can be understood in terms of the properties of the individual spectroscopic techniques. The critical dose for radiation damage by 100 keV electrons incident on PET at 100 K is found to be (1.45 ± 0.15) × 103 eV nm-3. In contrast, the critical dose for radiation damage by 302 eV X-rays incident on PET at 300 K is (1.2 ± 0.6) × 104 eV nm-3. A figure of merit involving the product of critical energy dose and spectral efficiency (as expressed by the appropriate G value) is developed. This indicates that, for near-edge studies involving a 20 eV spectral width, there is ∼500-fold advantage of X-ray absorption studies on room temperature PET relative to electron energy loss studies of cooled PET.

Advances, developments and applications in 2-D comprehensive GC (GC x GC) from 2007 through October 2008 are reviewed, with emphasis on modulation, and data handling, and applications of current relevance. Industrial perspectives as well as suggestions where further developments would be beneficial are summarized in the concluding remarks.

The vibrational and K-type rotational levels of the [Xtilde] 2 B 1 and à 2 A 1 states of NH2 and H2O+ have been fitted by least squares to give sets of Born-Oppenheimer potential curves for the combining electronic states. The model used allows a simultaneous fit to all the observed vibronic levels for each of the two molecules, using a large amplitude formalism and making no approximations other than to neglect Fermi (anharmonic) resonance effects. An accurate description of the effects of orbital angular momentum on the level positions in the two molecules has been obtained, and relative transition moments have been calculated for the vibronic bands of the à 2 A 1-[Xtilde] 2 B 1 transitions. For NH2 the relative transition moments permit the calculation of the emission lifetimes (with the absolute value of the electronic transition moment taken from the ab initio calculations of Peyerimhoff and Buenker); the calculated lifetimes are found to agree very well with the experimental values of Halpern et al., and Donnelly et al. Relative transition moments for the photoelectron spectrum of H2O(H2O+, à 2 A 1 and [Xtilde] 2 B 1 ← H2O, [Xtilde] 1 A 1) have also been calculated. The à 2 A 1 state of H2O+ is confirmed as being linear at equilibrium, with the potential function having an unusual wide flat minimum.

This study was conducted to develop a statistical understanding of exposures to bisphenol A (BPA) in aquatic environments in North America and Europe. Concentrations of BPA have been reported by 89 investigations published between 1997 and 2007. On the basis of an analysis of weighted observations (n = 1068 and 848 for North America and Europe, respectively), BPA was reported at concentrations above the detection limit in 20-51% of freshwater samples. Median BPA concentrations for fresh surface waters for North America and Europe were 0.081 and 0.01 microg/L, respectively, while 95th percentiles were 0.47 and 0.35 microg/L, respectively. In contrast to fresh surface waters, only limited data are available for sediments and less for marine ecosystems. For freshwater sediments in North America (n = 71), the median and 90th percentile concentration (the 95th percentile was not calculable) were 0.6 and 3.4 ng/ g-dw, respectively, while the median and 95th percentile concentration in Europe (n = 249) were 16 and 256 ng/g-dw, respectively. To assess the potential ecological significance, we compared exposure concentrations with available regulatory criteria. The results suggest the frequency of locations in which concentrations are likely to cause adverse effects on aquatic ecosystems is low, with the exception of sediments collected from some highly urbanized and industrial locations.

Abstract Hydrofluoric-hydrochloric acid mixtures have been successfully used to stimulate sandstone reservoirs for a number of years. Hydrofluoric acid (HF) has a specific reactivity with silica which makes it more effective than HC1 for use in sandstone. Kinetics of the reactions of HF have been studied to determine the related effects of reservoir composition, temperature, acid concentration and pressure on the spending rate of HF. Secondary effects from by-product formation are noted and described. Predictions are made concerning the improvement in productivity resulting from HF treatment of skin damage. The kinetic order of HF reaction in sandstone was experimentally determined to be first order, i.e., the reaction rate is proportional to concentration. HF reacts faster on calcite than on clay, which, in turn, is faster than the reaction rate of HF on sand. Static conditions retard the HF reaction rate. As HF is forced into cores, there is a temporary reduction as a function of flow rate and acid concentration. Extensive deposition of calcium fluoride in acidized cores was not observed. Although some CaF, was detected, it was not considered a major source of damage in cores containing moderate amounts of carbonate. Other fluosilicates could be potentially more dangerous than CaF, in reducing permeability. Introduction Hydrofluoric acid has been widely used in stimulation treatments since 1935, when mud acid was introduced to the petroleum industry. Originally, this hydrochloric-hydrofluoric acid mixture was intended to remove mud filter cake, but it has since been successfully applied to many other oilfield problems. Mud acid treatments have been unusually successful in sandstone reservoirs where hydrochloric acid is unreactive due to a lack of enough calcite in the formation. The relatively small amount of hydrofluoric acid present (2.1 per cent) reacts with sand grains, clays and traces of calcite which are generally present in sandstone reservoirs. Since hydrofluoric acid (HF) is the key to mud acid success, this research effort has been dedicated to gaining a more thorough understanding of the basic chemical and physical principles involved as HF reacts. Hydrofluoric acid's reactivity with silica makes it unique in application. Other mineral acids such as hydrochloric, sulfuric or nitric are unreactive with most silicious materials which comprise sandstone formations. A typical sandstone reservoir may contain 50 to 85 per cent silicon dioxide, more commonly called sand or quartz. Hydrofluoric acid reacts as follows: 4HF + SiO2 ->SiF4 + 2H2O The silicon tetrafluoride (SiF4) is a soluble gas, in some ways similar to CO2, and is capable of undergoing further reaction when held in solution by pressure. These reactions will be considered in detail later. Kinetics of the reactions of HF have been studied to determine the effect of reservoir composition, temperature and pressure on the spending of the acid. Secondary effects from by-product formation have been noted and described. The individual reactions of HF on quartz, glass and clay are reported. Mathematical correlations have been drawn, then applied to studies of HF spending in cores obtained from actual producing sandstone formations. The research reported herein is only the beginning of a continuing approach to better understanding and use of HF in petroleum reservoirs. THEORY AND DEFINITIONS Through the years, a concentrated effort has been made to understand the effects of many variables on hydrochloric acid (HC1) spending in limestone. Hendrickson et al., have given mathematical relationships for HC1 reactions which made possible the engineered approach to acidizing. The same variables-temperature, acid concentration, formation composition, pressure and permeability-porosity relationships-which affect HC1 behavior in limestone also govern HF behavior in sandstone. Insoluble byproducts of HF reaction have been isolated and identified. Their effect on fluid flow has been measured under varying conditions in an attempt to evaluate the extent of possible damage and means of eliminating it. In general, HF follows the same reaction paths as HC1. It will react with limestone and dolomite with speed and ease. Thin sections of acidized cores show the reaction of HF with limestone or calcite faster than its reaction with either clay or sand. When HF reacts with calcite (CaCO3), theoretically, calcium fluoride (CaF2) is precipitated, and has been blamed as a major cause of reduced permeability. On the other hand, pH and pressure such as that encountered in an underground formation under acid treatment definitely retard CaF2 formation, so the whole question of CaF2 deposition in wells is a subject for study. JPT P. 215ˆ

Viscosity of bitumen solutions in heptol (80:20) and heptane above the onset of asphaltene precipitation decreases continually with aging for up to 30 days, while in toluene, there was no detectable change in the viscosity. The decrease of the viscosity at these conditions was related to the formation of asphaltene aggregates and aggregate clusters, which precipitated out and, as a result, decreased the bitumen (asphaltene) content of the solution. The observed time dependence of the viscosity reduction suggests that the asphaltene aggregation/precipitation is a continuous process with the time scale of weeks. The asphaltene aggregation/precipitation rate depends upon the aromaticity of the diluent, with higher rates observed for heptane compared to heptol (80:20). These results add to the current understanding of the relation between aggregation of asphaltenes and viscosity of diluted bitumen, which is important for improving heavy oil extraction and processing technologies.

A qualitative review of the epidemiological literature on the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and health after 2001 is presented. In order to compare the exposure of the general population, bystanders and occupational groups, their urinary levels were also reviewed. In the general population, 2,4-D exposure is at or near the level of detection (LOD). Among individuals with indirect exposure, i.e. bystanders, the urinary 2,4-D levels were also very low except in individuals with opportunity for direct contact with the herbicide. Occupational exposure, where exposure was highest, was positively correlated with behaviors related to the mixing, loading and applying process and use of personal protection. Information from biomonitoring studies increases our understanding of the validity of the exposure estimates used in epidemiology studies. The 2,4-D epidemiology literature after 2001 is broad and includes studies of cancer, reproductive toxicity, genotoxicity, and neurotoxicity. In general, a few publications have reported statistically significant associations. However, most lack precision and the results are not replicated in other independent studies. In the context of biomonitoring, the epidemiology data give no convincing or consistent evidence for any chronic adverse effect of 2,4-D in humans.

Polymer-clay nanocomposites are a newer class of flame retardant materials of interest due to their balance of mechanical, thermal and flammability properties. Much more work has been done with natural clays than with synthetic clays for nanocomposite flammability applications. There are advantages and disadvantages to both natural and synthetic clay use in a nanocomposite, and some of these, both fundamental and practical, will be discussed in this paper. To compare natural and synthetic clays in regards to polymer flammability, two clays were used. The natural clay was a US mined and refined montmorillonite, while the synthetic clay was a fluorinated synthetic mica. These two clays were used as inorganic clays for control experiments in polystyrene, and then converted into an organoclay by ion exchange with an alkyl ammonium salt. The organoclays were used to synthesize polystyrene nanocomposites by melt compounding. Each of the formulations was analysed by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Flammability performance was measured by cone calorimeter. The data from the experiments show that the synthetic clay does slightly better at reducing the heat release rate (HRR) than the natural clay. However, all the samples, including the inorganic clay polystyrene microcomposites, showed a decreased time to ignition, with the actual nanocomposites showing the most marked decrease. The reason for this is postulated to be related to the thermal instability of the organoclay (via the quaternary alkyl ammonium). An additional experiment using a more thermally stable organoclay showed a time to ignition identical to that of the base polymer. Finally, it was shown that while polymer-clay nanocomposites (either synthetic or natural clay based) greatly reduce the HRR of a material, making it more fire safe, they do not provide ignition resistance by themselves, at least, at practical loadings. Specifically, the cone calorimeter HRR curve data appear to support that these nanocomposites continue to burn once ignited, rather than self-extinguish. Copyright © 2004 John Wiley & Sons, Ltd.

Although in nearly 200 field treatments of producing oil wells polymers have effectively reduced the WOR, not all such wells polymers have effectively reduced the WOR, not all such wells with a high water cut are candidates for polymer treatment. This paper discusses the probable working mechanisms of polymers and presents guidelines for selecting wells to be treated. Introduction The use of polymers to reduce water production in high-watercut oil-producing wells has proved highly successful in many areas of the Mid-Continent region. This process is an outgrowth of the use of polymers to adjust permeability profiles for water polymers to adjust permeability profiles for water injection wells. It has been used in nearly 200 wells to date and has resulted in a water-oil-ratio (WOR) decrease of 60 to 90 percent in most wells. In many cases, oil production has been substantially increased. The flow of polymer solutions through porous media has been a subject of intense research over the past decade. A thorough review of this subject has been given by Savins and therefore will not be repeated here. Polymers are of interest to the petroleum industry because they are useful in secondary petroleum industry because they are useful in secondary recovery and in the improvement of injection profiles in waterflooding. The behavior of polymer solutions in porous media has been controversial and several mechanisms have been proposed as an explanation of polymer behavior. Perhaps more than one mechanism is operative, depending on conditions. We believe that the basic behavior of the polymers is independent of the process, but the techniques of using polymers and the way they are applied in different processes do vary. The treatment of producing wells with polymer solutions is a unique process to reduce the WOR by selectively reducing water production without greatly hindering oil flow. As the polymer solution is injected into the formation, it tends to seek out and flow into the higher-permeability water zone. For this reason, deeper penetration is obtained with the polymer than is possible with conventional nonselective plugging agents. For producing wells, when the treatment is successful, the response is usually rapid and dramatic and occurs in a matter of days. In contrast, with water injection wells and polymer flooding, the results of a polymer treatment may not be evident for 6 to 12 months or even longer. How Polymers Work Before discussing the details of how polymers work, we shall outline the salient features of this process. This paper is aimed at those persons unfamiliar with the process and is not intended to be technically precise. The terms "resistance factor" and "residual precise. The terms "resistance factor" and "residual resistance factor" have been defined elsewhere. Although these terms are applicable as defined, we also use them in a general sense, as shown in the following discussion and in Fig, 1. Because of its viscosity, a polymer solution would be expected to offer a given resistance to flow in a rock. The actual or total resistance to flow offered by some polymers, however, is some 5 to 20 times this expected resistance. The total resistance is important in polymer floods and injection wells, but is effective in producing wells only until the solution is returned producing wells only until the solution is returned to the wellbore. Core tests show, however, that after a polymer treatment, even after hundreds of pore volumes of brine have been produced, enough polymer is retained in the rock to provide a residual resistance that will reduce the brine flow by as much as 60 to 95 percent. JPT P. 143

Five activated carbons (ACs) and two biochars were tested as amendments to reduce the availability of aged polychlorinated dibenzo-p-dioxin/dibenzofurans (PCDD/Fs) in two soils. All sorbents (ACs and biochars) tested substantially reduced the availability of PCDD/Fs measured by polyoxymethylene (POM) passive uptake and earthworm (E. fetida) biouptake. Seven sorbents amended at a level of 0.2 × soil total organic carbon (0.2X) reduced the passive uptake (physicochemical availability) of total PCDD/Fs in POM by 40% to 92% (or toxic equivalent by 48% to 99%). Sorbents with finer particle sizes or more macropores showed higher reduction efficiencies. The powdered regenerated AC and powdered coconut AC demonstrated to be the most effective and the two biochars also performed reasonably well especially in the powdered form. The passive uptake of PCDD/F in POM increased approximately 4 to 5 fold as the contact time between POM and soil slurry increased from 24 to 120 d while the efficacy of ACs in reducing the physicochemical availability remained unchanged. The reduction efficiencies measured by POM passive uptake for the regenerated AC were comparable to those measured by earthworm biouptake (bioavailability) at both dose levels of 0.2X and 0.5X. The biota-soil accumulation factor (BSAF) values for unamended soil ranged from 0.1 for tetra-CDD/F to 0.02 for octa-CDD/F. At both dose levels, the regenerated AC reduced the BSAFs to below 0.03 with the exception of two hexa-CDD/Fs. The reduction efficiencies measured by earthworm for coconut AC and corn stover biochar were generally less than those measured by POM probably due to larger particle sizes of these sorbents that could not be ingested by the worms.

A five-year retrospective study of workers exposed to hydrogen sulfide in Alberta, Canada, was conducted, using the records of 250 workers who submitted claims to the provincial compensation board from 1979 through 1983. Fifty-four percent of the exposed workers became unconscious after exposure. Signs and symptoms with a neurological component accounted for the largest group of clinical findings. Respiratory and ophthalmologic effects were the other major groups of signs and symptoms. The overall fatality rate was 2.8%, significantly lower than that reported (6.0%) in a similar study a decade earlier. This is attributed to improved first-aid training and increased awareness of the dangers of hydrogen sulfide. Traumatic injury as a result of a fall after exposure was noted in 31 cases.

Sand production, from a well completed in an incompetent formation without a metal screen, can be attributed to failure of the sand to form a stable arch around the wellbore or over a perforation. This study shows the usefulness of having a sand of high grain strength outside the perforations, and indicates that even a low-strength plastic can provide the restraint necessary to stabilize an arch. Introduction The petroleum industry has used both mechanical and chemical methods for controlling the production of sand from wells completed in unconsolidated formations. In developing sand control methods, mechanical studies have dealt mostly with the design of screens and slotted liners and the placement of gravel packs; chemical studies have dealt with the composition and performance of sand consolidation plastic systems, and techniques of applying them. Little attention has been paid in the literature to the mechanical process of failure of the sand structure around a wellbore and the factors that affect the stability of the formation. Our laboratory has conducted, in the past several years, both theoretical and experimental studies on the mechanics of sand failure. W.M. Ayers,1 in 1965, presented results of his theoretical studies combined with field experience. He discussed the stress field around a wellbore and its relation to the formation stability in terms of the shear strength properties of the sand. The work being reported here was a laboratory extension of Ayers' studies. It was conducted as a basic study of sand control and was carried out. in two phases:elucidation of the failure mechanisms of unconsolidated sands and of the mechanism of stabilization of sands by consolidating plastics, using triaxial strength tests; anda direct study of the arching behavior of sand, or the manner in which sand can form a stable structure spanning an opening. Background Shear Strength of Sand The study of the strength of bodies of granular materials generally falls within the realm of soil mechanics. A widely used criterion for shear failure of soils is the Mohr-Coulomb theory.2 This states that failure will occur when the major and minor principal stresses s1 and s3 combine to produce a critical and characteristic value of the obliquity, which is the ratio of shear stress t to normal stress s in the plane of shearing. The validity of this criterion, which ignores the intermediate principal stress s2, is supported by experimental evidence cited by Bishop.3 The shear strength of a sand may therefore be described in terms of a Mohr envelope and its slope a, the angle of shearing resistance. Shear Strength of Sand The study of the strength of bodies of granular materials generally falls within the realm of soil mechanics. A widely used criterion for shear failure of soils is the Mohr-Coulomb theory.2 This states that failure will occur when the major and minor principal stresses s1 and s3 combine to produce a critical and characteristic value of the obliquity, which is the ratio of shear stress t to normal stress s in the plane of shearing. The validity of this criterion, which ignores the intermediate principal stress s2, is supported by experimental evidence cited by Bishop.3 The shear strength of a sand may therefore be described in terms of a Mohr envelope and its slope a, the angle of shearing resistance.

Abstract Hypothetical model structures for magadiite and sodium octosilicate, based on the structure of the zeolite dachiardite, are proposed that consist of layers of 6-member rings of tetrahedra and blocks containing 5-member rings attached to both sides of the layers. The infrared (IR) and nuclear magnetic resonance spectra of magadiite and sodium octosilicate have features in common with spectra of zeolites in the ZSM-5 and mordenite groups. A peak at 1225 cm -1 in the IR spectra of magadiite and sodium octosilicate is characteristic of zeolites containing 5-member rings, such as ZSM-5- and mordenite-type zeolites. The defect structures of pentasil zeolites may therefore be akin to layered alkali metal silicates containing zeolite-like domains, in which part of the silanol groups from adjacent silicate layers are condensed (cross-linked) forming siloxane linkages.

Abstract Formation of asphaltic sludge during acid stimulation has been a serious problem in many areas for several years. Recent studies have shown that sludge may also affect results in many areas where it has not yet been recognized as such. These studies indicate that: sludge is a precipitate of colloidal materials present in crude oil; the precipitates occur due to changes in environmental conditions of the crude by addition of materials such as, acid, once formed, sludge is insoluble in most treating chemicals; and sludge can be prevented or controlled by use of stabilizing agents in treating fluid or by use of certain solvents as the outer phase of acid-in- oil emulsions. The purpose of this paper will be to show how and why sludge is formed and how it can be prevented or controlled. Simple laboratory tests to determine the probability of sludge formation prior to treatment are discussed. Introduction Formation of sludges by crude oil on contact with acid has been recognized as a serious problem in isolated areas for some time. The problem apparently was first observed in certain California wells. Following acidizing treatments, the wells were very slow to clean up, and often a great deal of asphalt-like material was returned with the treating fluids. In some cases, complete or partial plugging of the well resulted from the treatment. A study of this problem revealed that the crude oils produced from these wells actually formed solid precipitates upon contact with acid. These precipitates were mainly asphaltenes, resins, paraffin waxes, and other high-molecular-weight hydrocarbons. These materials were apparently precipitated from the crude by the reduction in pH as a result of acid contact. Recently, it was found that the formation of crude oil sludge during acidizing is also a serious problem in many other formations throughout the United States. A comprehensive study recently undertaken indicates that these sludges may also be a problem in many areas where it has not been recognized as such. A survey of crude oils from many fields and formations in all the oil- producing areas of the United States and Canada showed that a substantial percentage (28 to 35 per cent) of all naturally occurring oils tested produced precipitates upon contact with acid. Nature of Asphaltic Material in Crude Oil The colloidally dispersed asphaltic and related substances in crude oils which are precipitated upon contact with acid are of such a complex nature that they are classified chiefly on the basis of their physical properties. The most common classification is as follows. Neutral Resins These substances are high-molecular-weight aromatic hydrocarbons, which are insoluble in alkalies and acids and completely miscible with petroleum oils, including light fractions (C fraction). Asphaltenes These materials are similar to the neutral resins, but insoluble in light gasolines and petroleum ether. In contrast to the neutral resins, the asphaltenes are precipitated in the presence of an excess of petroleum ether. Both asphaltenes and neutral resins are completely soluble in benzene, chloroform and carbon disulfide. Asphaltogenic Acids These substances are soluble in alkaline solutions and in such solvents as benzene. Since these are present in petroleum in insignificant quantities, the neutral resins and asphaltenes are the most important asphaltic compounds of petroleum. The asphaltic material present in crude oil is in the form of colloidal particles. Detailed analytical ultracentrifuge studies of several crudes have shown that the asphaltic particles range from 35 to 45 angstroms (A) in diameter. The colloidal range is generally considered to be from 10 to 5,000 A. Other studies have indicated that colloidal particles in crude oil are composed of asphaltic material surrounded by absorbed peptizing materials. These studies have proposed the concept that asphaltenes form the center of the micelles, wth neutral resins absorbed on the surface of the asphaltene particles. JPT P. 1023ˆ