The objective of this research was to determine whether the use of polymer compounds with elastic properties can reduce residual oil saturation in porous media below that of brine or inelastic polymerized solutions. One hypothesis is that long-chain polymer molecules experience stress and a resulting strain when they flow through pore throat constrictions. If the fluid residence time in larger pore spaces is insufficient to allow full relaxation, then strain can accumulate. Sufficient strain results in normal forces which can impinge on oil interfaces and potentially mobilize them. A second hypothesis suggests that polymerized solutions can temporarily protect flowing oil filaments from snap off, allowing them to flow longer and de-saturate further than they would otherwise. The approach taken in this thesis was to conduct a series of core floods in several different sandstones using displacement fluids with elasticity ranging from none to those with extremely high relaxation times. Accelerated flow rate was also employed to reduce residence time and maximize the accumulation of elastic strain and normal force potential. Experiments were designed to provide direct comparisons between both non-elastic and elastic floods but also multiple floods with increasing elasticity. The results were inconclusive with some experiments showing additional oil recovery that could be attributed to elastic mechanisms. Most experiments, however, showed no significant difference between elastic and non-elastic floods when experimental parameters were controlled within narrow limits. This research did refine the experimental context in which elastic effects are most likely to be observed. As such, it can serve as a precursor to additional core flooding in oil-wet systems, experiments conducted at reservoir temperature, and those where the pressure gradient of the flood is held constant and the flow rate allowed to vary. Computer aided tomography could also be employed to visualize the mobilization of oil with different displacement fluids, identify where bypassed oil occurs with unstable floods, and determine how oil is subsequently mobilized with better conformance and or elasticity. / text

The objective of this work was to evaluate chemical interactions in phase behavior experiments that make surfactant-polymer formulations with alkali complex to design. This experimental study of sodium carbonate shows improvement of microemulsion phase behavior with many crude oils in addition to its classical use to produce soap in-situ and raise pH to reduce potential for surfactant adsorption. Soap is generally not sufficient by itself for chemical flooding because it has low tolerance to calcium ions and low optimal salinity. The blending of synthetic surfactant with sodium carbonate is needed to increase the optimum salinity, increase the tolerance to calcium, and reduce the sensitivity to changes in salinity by broadening the active salinity window. Sodium carbonate can also be added to the surfactant formulation to adjust electrolyte concentration for optimal salinity. Evidence suggests that additional consideration should be given to sodium carbonate in enhanced oil recovery applications because of benefits that extend beyond the traditional application. The research presented in this work discusses experiments that were conducted for the purpose of studying the benefits of sodium carbonate on surfactant phase behavior. After phase behavior screening, the formulations were tested to demonstrate their performance in porous media. Core floods were conducted to test the potential use of chemical flooding for a field application with several low acid crude oils. Two of the core flood experiments with Berea sandstone reduced the residual oil below 1% with chemical injection. An acceptable pressure gradient was maintained and good sweep was obtained using an AMPS polymer at high temperature. Polymer was needed to make the slug and drive sufficiently viscous to recover the mobilized oil and reduce surfactant retention through good sweep efficiency. The experiments reported in this research have contributed to an ongoing effort to design a suitable alkali-surfactant-polymer chemical formulation for the application in a high permeability, high temperature (85 ºC) sandstone reservoir located in Indonesia. / text

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Enhanced oil recovery by dry forward in-situ combustion has been studied in a combustion tube. Twelve experiments are reported exploring the effects of three factors: oxygen flow, partial pressure and mole fraction, each factor at two levels. The pressures used went up to 790 kPa, and the oxygen mole fraction to 35%. It was discovered that the oxygen partial pressure had no statistically significant effect. The oil recovery was independent of the factors used. The combustion time was dominated by the oxygen flow, as were the reaction rates, while fuel and oxygen consumption depended mainly on the oxygen mole fraction. Increasing the oxygen mole fraction reduced the consumption figures. The reaction stoichiometry was substantially independent of the three factors. It was also found that the total pressure had no statistically significant effect on oil recovery, combustion time, reaction rates, fuel consumption or stoichiometry. The oil produced by the in-situ combustion process tended to be of lower viscosity and density than the original oil. Oil-water emulsions were produced which could not be broken. The experiments were controlled by a computer, and the PID control algorithms and associated equipment proved succesful. Linked in with the control routines was a model of the process to calculate fluid saturations and flows during the course of the experiment. Measured information was used directly in the mass and energy balances. The resultant fluid saturations supplied a reasonable match with experimental oil saturations from two experiments that were stopped early. The computed liquid production histories also matched up well with the experimental results. The oil saturations from the numerical model were used in developing a robust method for calculating reaction constants from the experimental data. A simplified surface-reaction scheme was used involv~ng low-temperature oxidation and fuel burnoff to explain the effects of flow, pressure and oxygen mole fraction on the process.

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