H. Scott Fogler

Water sensitivity of sandstones

Experimental and theoretical studies have been carried out to elucidate the mechanism of water sensitivity of Berea Sandstone and quantify a number of important parameters. Based on the results of a number of novel experiments, a physical model has been developed. In this model, clay particles are released only when the salt concentration falls below a critical salt concentration. These colloidal clay particles remain dispersed in fresh water and are carried with the flowing fluid until they are captured at a local pore constriction, thereby decreasing permeability. A mathematical model based on this mechanism has been developed. This model contains two parameters stemming from the rate equations of the release and capture of clay particles. Correlations of these parameters with flowrate and temperature are presented. 9 refs.

Prediction of the wax content of the incipient wax-oil gel in a pipeline: An application of the controlled-stress rheometer

High molecular weight paraffins are known to form gels of complex morphology at low temperatures due to the low solubility of these compounds in aromatic or naphthene-base oil solvents. The characteristics of these gels are strong functions of the shear and thermal histories of these samples. A model system of wax and oil was used to understand the gelation process of these mixtures. A significant depression in the gel point of a wax-oil sample was observed by either decreasing the cooling rate or increasing the steady shear stress. The wax-oil sample separates into two layers of different characteristics, a gel-like layer and a liquid-like layer, when sheared with a controlled-stress rheometer at high steady shear stresses and low cooling rates. The phase diagram of the model wax-oil system, obtained using a controlled-stress rheometer, was verified by analyzing the wax content of the incipient gel deposits formed on the wall of a flow loop. Based on the rheological measurements, a law has been suggested for the prediction of the wax content of the gel deposit on the laboratory flow loop walls. The wax content of the incipient gel formed on the wall of a field subsea pipeline was predicted to be much higher than that for the flow loop at similar operating conditions. This variation in the gel deposit characteristics is due to the significant differences in the cooling histories in the two cases.

The kinetics of calcite dissolution in acetic acid solutions

The kinetics of calcite dissolution in acetic acid solutions was investigated over a wide range of pH using a rotating disk apparatus. The results show that the dissolution is influenced by the rate of transport of reactants to the surface, the kinetics of the reversible surface reaction, and the rate of transport of products away from the surface. Below about pH 2.9, the dissolution is influenced by the transport of both reactants and products, while above about pH 3.7, the dissolution is influenced predominantly by the kinetics of the surface reaction. A general model was developed to account for the combined effects of transport and reaction on the rate of dissolution. The effect of acetate ions on the rate of dissolution was investigated in alkaline solutions (pH 8.2 to 14) to eliminate the effects of hydrogen ion attack. The presence of acetate ions was found to have no significant affect on the rate of dissolution when compared to results in potassium chloride and sodium chloride solutions. The rate of dissolution was observed to decrease over this pH range and could not be described by previous reaction mechanisms. Therefore, a surface dissociation mechanism involving water was introduced and was shown to describe the rate of dissolution over the pH range of 8 to 14.

Biomass evolution in porous media and its effects on permeability under starvation conditions

The purpose of this study was to understand bacteria profile modification and its applications in subsurface biological operations such as biobarrier formation, in situ bioremediation, and microbial-enhanced oil recovery. Biomass accumulation and evolution in porous media were investigated both experimentally and theoretically. To study both nutrient-rich and carbon-source-depleted conditions, Leuconostoc mesenteroides was chosen because of its rapid growth rate and exopolymer production rate. Porous micromodels were used to study the effects of biomass evolution on the permeability of a porous medium. Bacterial starvation was initiated by switching the feed from a nutrient solution to a buffer solution in order to examine biofilm stability under nutrient-poor conditions. Four different evolution patterns were identified during the nutrient-rich and nutrient-depleted conditions used in the micromodel experiments. In phase I, the permeability of the porous micromodel decreased as a result of biomass accumulation in pore bodies and pore throats. In phase II, starvation conditions were initiated. The depletion of nutrient in the phase II resulted in slower growth of the biofilm causing the permeability to reach a minimum as all the remaining nutrients were consumed. In phase III, permeability began to increase due to biofilm sloughing caused by shear stress. In phase IV, shear stress remained below the critical shear stress for sloughing and the biofilm remained stable for long periods of time during starvation. The critical shear stress for biofilm sloughing provided an indication of biofilm strength. Shear removal of biofilms occurred when shear stress exceeded critical shear stress. A network model was used to describe the biofilm formation phenomenon and the existence of a critical shear stress. Simulations were in qualitative agreement with the experimental results, and demonstrate the existence of a critical shear stress.

Use of inorgano-organo-clays in the removal of priority pollutants from industrial wastewaters; adsorption of benzo(a)pyrene and chlorophenols from aqueous solutions

Benzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.

Plugging by hydrodynamic bridging during flow of stable colloidal particles within cylindrical pores

This paper describes the flow-induced retention of charge stabilized colloidal particles during flow through cylindrical pores. Current models describing the low-Reynolds-number flow behaviour of particulate suspensions through porous media do not predict retention of stable colloidal particles if the particles are smaller in size than the pores, and the particles and the pores have like surface charges. Retention is not expected under these conditions because the small particle size relative to the pore constriction size precludes straining (physical capture of particles larger than the pore constriction) while particle–pore surface electrostatic repulsion prevents deposition. However, the experiments show that substantial particle retention can occur under these conditions. The mechanism causing particle retention under these conditions, hydrodynamic bridging, is flow-induced. In this mechanism, hydrodynamic forces acting on particles arriving at a pore entrance do not allow their simultaneous passage through the pore, resulting in the formation of a particle bridge across the pore constriction. This paper reports experiments elucidating the effects of velocity, particle concentration, and the ratio of pore size to particle size on retention by hydrodynamic bridging. For flow through cylindrical pores, the effect of velocity on retention by bridging is opposite to that of retention by deposition. Furthermore, observations indicate the existence of a critical flow velocity necessary for particle bridging to occur. This critical velocity is a measure of the net colloidal interparticle and particle–porous medium repulsion that must be overcome by the hydrodynamic forces for bridging to occur. Approximate theoretical calculations of the trajectories of two particles approaching an isolated cylindrical pore are also presented. These calculations show that bridging is indeed possible in the Stokes flow regime for the experimental conditions considered.

Biomass plug development and propagation in porous media.

Exopolymer-producing bacteria can be used to modify soil profiles for enhanced oil recovery or bioremediation. Understanding the mechanisms associated with biomass plug development and propagation is needed for successful application of this technology. These mechanisms were determined from packed-bed and micromodel experiments that simulate plugging in porous media. Leuconostoc mesenteroides was used, because production of dextran, a water-insoluble exopolymer, can be controlled by using different carbon sources. As dextran was produced, the pressure drop across the porous media increased and began to oscillate. Three pressure phases were identified under exopolymer-producing conditions: the exopolymer-induction phase, the plugging phase, and the plug-propagation phase. The exopolymer-induction phase extended from the time that exopolymer-producing conditions were induced until there was a measurable increase in pressure drop across the porous media. The plugging phase extended from the first increase in pressure drop until a maximum pressure drop was reached. Changes in pressure drop in these two phases were directly related to biomass distribution. Specifically, flow channels within the porous media filled with biomass creating a plugged region where convective flow occurred only in water channels within the biofilm. These water channels were more restrictive to flow causing the pressure drop to increase. At a maximum pressure drop across the porous media, the biomass yielded much like a Bingham plastic, and a flow channel was formed. This behavior marked the onset of the plug-propagation phase which was characterized by sequential development and breakthrough of biomass plugs. This development and breakthrough propagated the biomass plug in the direction of nutrient flow. The dominant mechanism associated with all three phases of plugging in porous media was exopolymer production; yield stress is an additional mechanism in the plug-propagation phase.

USE OF INORGANO-ORGANO-CLAYS IN THE REMOVAL OF PRIORITY POLLUTANTS FROM INDUSTRIAL WASTEWATERS: STRUCTURAL ASPECTS

Novel modified clay adsorbents were prepared by blocking cation-exchange sites of an expandable clay, such as montmorillonite, with polymeric or polyvalent inorganic ions and by using cationic surfactants as sources of surface organic carbon. Electrokinetic measurements demonstrated that the adsorbed polycations were essentially nonexchangeable. Adsorption and desorption experiments revealed that about 90% of the cationic surfactant was apparently irreversibly bound to the surface. Flocculation and peptization studies were performed to establish that the adsorbed surfactant moiety was oriented with its hydrocarbon tail towards the surface. Such a configuration of simultaneously adsorbed polycations and cationic surfactants was designated as an inorgano-organo-clay (IOC). As shown in an accompanying paper, these IOCs bind priority pollutants as strongly as granulated activated carbon.

Water sensitivity of sandstones containing swelling and non-swelling clays

Abstract The study presented here focuses on the phenomenon of water sensitivity of sandstones containing swelling and nons-welling clays. This paper describes results of an ongoing investigation on the mechanisms of permeability reduction in sandstones containing swelling and non-swelling clays. These studies show that the critical salt concentrations of sodium chloride and potassium chloride needed to prevent loss of permeability in sandstones containing swelling clay (Stevens sandstone) are considerably higher than the corresponding values for Berea sandstone. A critical salt concentration of calcium chloride is shown to exist for these sandstones. As opposed to Berea sandstone, pH control may not be sufficient to eliminate loss of permeability in swelling clay sandstones. The results show that crystalline swelling of smectites/mixed layer clays induces significant permeability reduction in the swelling clay sandstones considered in this paper.

The fractal aggregation of asphaltenes.

This paper discusses time-resolved small-angle neutron scattering results that were used to investigate asphaltene structure and stability with and without a precipitant added in both crude oil and model oil. A novel approach was used to isolate the scattering from asphaltenes that are insoluble and in the process of aggregating from those that are soluble. It was found that both soluble and insoluble asphaltenes form fractal clusters in crude oil and the fractal dimension of the insoluble asphaltene clusters is higher than that of the soluble clusters. Adding heptane also increases the size of soluble asphaltene clusters without modifying the fractal dimension. Understanding the process of insoluble asphaltenes forming fractals with higher fractal dimensions will potentially reveal the microscopic asphaltene destabilization mechanism (i.e., how a precipitant modifies asphaltene-asphaltene interactions). It was concluded that because of the polydisperse nature of asphaltenes, no well-defined asphaltene phase stability envelope exists and small amounts of asphaltenes precipitated even at dilute precipitant concentrations. Asphaltenes that are stable in a crude oil-precipitant mixture are dispersed on the nanometer length scale. An asphaltene precipitation mechanism is proposed that is consistent with the experimental findings. Additionally, it was found that the heptane-insoluble asphaltene fraction is the dominant source of small-angle scattering in crude oil and the previously unobtainable asphaltene solubility at low heptane concentrations was measured.