A Novel Cationic Polymer System That Improves Acid Diversion in Heterogeneous Carbonate Reservoirs
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Abstract In-situ gelled acids have been used for acid diversion in heterogeneous carbonate reservoirs for more than two decades. Most of the gelled systems are based on an anionic polymer that has a cleaning problem after the acid treatments that leads to formation damage. This work evaluates a new cationic-polymer acid system with the self-breaking ability for the application as an acid divergent in carbonate reservoirs. Experimental studies have been conducted to examine the rheological properties of the polymer-based acid systems. The apparent viscosities of the live and the partially neutralized acids at pH from 0 to 5 were measured against the shear rate (0 to 1,000 s-1). The impact of salinity and temperature (80 to 250°F) on the rheological properties of the acid system was also studied. The viscoelastic properties of the gelled acid system were evaluated using an oscillatory rheometer. Dynamic sweep tests were used to determine the elastic (G’) and viscous modulus (G") of the system. Single coreflood experiments were conducted on Indiana limestone cores to study the nature of diversion caused by the polymer-acid system. The impact of permeability contrast on the process of diversion was investigated by conducting dual coreflood experiments on Indiana limestone cores which had a permeability contrast of 1.5-20. CT scans were conducted to study the propagation of wormhole post acid injection for both single and dual corefloods. The live acid system displayed a non-Newtonian shear-thinning behavior with the viscosity declining with temperature. For 5 wt% HCl and 20 gpt polymer content at 10 s-1, the viscosity decreased from 230 to 40 cp with temperature increasing from 88 to 250°F. Acid spending tests demonstrated that the acid generated a gel with a significant improvement in viscosity to 260 cp (at 250°F and 10 s-1) after it reached a pH of 2. The highly viscous gel plugged the wormhole and forced the acid that followed to the next higher permeability zone. The viscosity of gel continued to increase until it broke down to 69 cp (at 250°F and 10 s-1) at a pH of 4.8, which provides a self-breaking system and better cleaning. Coreflood studies indicated that the wormhole and the diversion process is dependent on the temperature and the flow rate. There was no indication of any damage caused by the system. The injected acid volume to breakthrough (PVBT) decreased from 2.2 to 1.4 when the temperature increased from 150 to 250°F. The strong elastic nature of the gel (G’= 3.976 Pa at 1 Hz) formed by the partially neutralized acid system proves its suitability as a candidate for use as a diverting agent. This novel acid-polymer system has significant promise for usage in acid diversion to improve stimulation of carbonate reservoirs.Keywords:
Cationic polymerization
Rheology and the study of viscoelastic materials are an integral part of engineering and the study of biophysical systems. Tissue rheology is even used in the study of cancer and other diseases. However, the cost of a rheometer is feasible only for colleges, universities, and research laboratories. Even if a rheometer can be purchased, it is bulky and delicately calibrated, limiting its usefulness to the laboratory itself. The design presented here is less than a tenth of the cost of a professional rheometer. The design is also portable, making it the ideal solution to introduce viscoelasticity to high school students as well as for use in the field for obtaining rheological data.
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ABSTRACT Rheology and the study of viscoelastic materials is an integral part of engineering and the study of biophysical systems however the cost of a rheometer is only feasible for colleges, universities and research laboratories. Even if a rheometer can be purchased it is bulky and delicately calibrated limiting its usefulness to the laboratory itself. The design presented here is less than a tenth of the cost of a professional rheometer and portable making it the ideal solution for high school students as a way to introduce viscoelasticity at a younger age as well as for use in the field for obtaining preliminary rheological data.
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An interfacial rheometer to measure the dynamic response of a liquid–liquid interface subjected to a small amplitude oscillatory shear stress is described. Experiments are conducted in a deep channel rheometer fitted with an oscillatory floor. This instrument is used to examine the rheological behavior of interfaces in the presence of surfactants. Rheological parameters are calculated from a hydrodynamic analysis incorporating interfacial rheological models. It is demonstrated here that an adsorbed layer of macromolecular surfactants at an oil–water interface is viscoelastic even though the adjacent phases are Newtonian.
Dynamic shear rheometer
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In order to serve for studies of viscoelastic and steady-flow properties of various non-Newtonian liquids, a self-recording rheometer has been manufactured, which can be employed not only as a cone-and-plate but also as a Couette type rheometer by exchanging minor parts. It is possible to drive or stop the rheometer suddenly by the use of electro-magnetic clutch. This enables us to measure transient phenomena such as stress-overshoot and thixotropy of polymeric and disperse systems. The thermostat has been equipped to keep temperature constant from room temperature to 300°C. The frequency and number of revolution range rospectively from 10-4 to 1Hz and from 0.05 to 500rpm.Steady-flow properties of several disperse systems and polymer solutions as well as dynamic properties of polystyrene melt have been measured by means of this rheometer.
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To characterize the rheological behaviour of viscoelastic fluids, polymer melts and other soft materials, motor‐drive controlled rheometers are mainly used, either at constant stress or strain rate, or in the oscillatory mode. The latter has proved advantageous to discover the viscoelastic functions G*, η*, J* as fingerprints of the material under investigation, its composition, molecular modelling and applicability. A conclusive analysis of such a viscoelastic spectrum can only be achieved if the amplitudes chosen guarantee linearity and if the frequency range covers more than 6 decades to reach the low kHz‐domain. Investigations of many materials with motor‐drive controlled rheometers are limited at higher frequencies and reach the above mentioned goal by applying the time‐temperature superposition principle, i.e. the mastercurve technique. Since this method is restricted to rheologically simple materials (e.g. some polymer melts), but exclude those of small activation energies and others with temperature‐sensitive chemical/physical structures including phase transitions, oscillating rheometry should be extended into higher real‐frequency ranges, to establish useful linear viscoelastic spectroscopy. This goal has been reached by adapting a new high‐frequency option into a commercially available rheometer. The available continuous frequency range with integrated high frequency option covers now approximately 8–9 decades. In this talk, advantages and limits of classical oscillatory rheometry will be covered, handling and principle of operation of the high frequency option are introduced and typical examples for real frequency spectra on soft matter, such as weak gels, polymer solutions and suspensions will be shown.
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Abstract Highly concentrated biopolymers are used in food extrusion processing. It is well known that rheo-logical properties of biopolymers influence considerably both process conditions and product properties. Therefore, characterization of rheological properties under extrusion-relevant conditions is crucial to process and product design. Since conventional rheological methods are still lacking for this purpose, a novel approach is presented. A closed cavity rheometer known in the rubber industry was used to systematically characterize a highly concentrated soy protein, a very relevant protein in extruded meat analogues. Rheological properties were first determined and discussed in the linear viscoelastic range (SAOS). Rheo-logical analysis was then carried out in the non-linear viscoelastic range (LAOS), as high deformations in extrusion demand for measurements at process-relevant high strains. The protein showed gel behavior in the linear range, while liquid behavior was observed in the nonlinear range. An expected increase in elasticity through addition of methylcellulose was detected. The measurements in the non-linear range reveal significant changes of material behavior with increasing strain. As another tool for rheological characterization, a stress relaxation test was carried out which confirmed the increase of elastic behavior after methylcellulose addition.
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The aim of this work was to investigate the rheological behaviour of human blood, in a controlled stress rheometer, using different cone-plate and parallel plate geometries. Steady-shear (flow curves and kinetics) and oscillatory (strain, frequency and time sweeps) tests were performed at 37°C. The results demonstrated that rheological data are significantly influenced by the measuring geometry and the rheological parameters obtained from rheological models must be analysed with great caution. The Cross model provided a better fit of the flow curves and the Power Law model gave a better concordance between the rheological parameters obtained with the different measuring systems. The oscillatory measurements demonstrated a linear viscoelastic behaviour below a critical frequency and the Friedrich-Braun model described well the frequency sweeps experimental data in that region. The correlation between steady-shear and oscillatory properties (Cox-Merz rule) suggests that the two methods can be complementary and may give important information on red blood cells aggregation and deformability. Results from oscillatory time sweeps confirm a blood aggregation process in two steps.
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