Browsing by Subject "Optimum salinity"
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Item A novel ASP flood design for CO₂ contaminated sandstone reservoirs at low salinity and low permeability(2016-12) Nguyen, Vu Quoc; Nguyen, Quoc P.ASP flooding relies the ability of surfactant to reduce the oil-water inter facial tension (IFT) and to alter the wettability towards water-wet conditions in order to promote oil mobilization. During this process surfactants must show long term stability under reservoir conditions as well as low adsorption on to the rock surface. Surfactant screening is particularly challenging for low salinity formation brines with low target salinity injection brine since most commercially available surfactants show optimum salinity ranges above 3 wt% total dissolved solid (TDS). A series of propylene oxide (PO) sulfate surfactants, internal olefin sulfonates (IOS), and alkyl benzene sulfonates (ABS) have been used for surfactant screening. Co-solvents were incorporated to improve aqueous stability of the surfactant mixture, reduce equilibration time, and minimize formation of viscous phases. More than 300 phase behavior scans were performed in order to optimize a chemical formulation for optimum salinity within a range of 1.0 to 2.0 wt% TDS. PO surfactant formulations show viscous oil-water microemulsion, and thus does not meet our criteria due to high surfactant retention. Therefore, PO formulations were not selected for coreflood experiments. ABS and IOS surfactant combination shows the optimum salinity in the desired range and Winsor Type III microemulsion which has low interfacial tension with oil and water within the Type III region. In addition, viscous emulsions were not observed over an incubation period of 60 days. This combination of surfactants has the ability to tune the optimum salinity within the range by changing the ratio of two surfactants. A Na2CO3 preflood was introduced before slug injection to neutralize the acidic nature of the core. ABS and IOS were blended at a 7:3 ratio in the surfactant slug based on our findings from our phase behavior study. Co-solvent (Butoxypolyglycol Basic) was added at 1.0 wt% concentration to achieve suitable low IFT conditions and less viscous microemulsions. We have conducted more than 20 corefloods using the above surfactant combination and with our final optimized coreflood yielding 98% oil recovery with 0.6% S [subscript orc].Item Investigation of the correlation between waterflood maturity and appropriate optimum salinity(2020-06-30) Wagner, Ryan James; Nguyen, Quoc P.This work sets out to establish a correlation between waterflood maturity and the appropriate optimum salinity of a surfactant formulation. This is done by introduction of the novel concept of a critical waterflood “pre-flush,” specifically its presence and effect on Low-Tension-Gas (LTG) injection. The conditions of this work are for an offshore process with high salinity, moderate permeability, and only seawater available for use during enhanced oil recovery (EOR). LTG is a process that involves the co-injection of a surfactant solution and gas in order to achieve ultra-low interfacial tension from Type III microemulsion and mobility control due to generation of foam in the porous media. This technology has been used in various severe reservoir conditions such as high salinity, high temperature, and low permeability. Furthermore, field studies with similar injection strategy and use of foam have been conducted. Phase behavior testing was first conducted to create and identify two surfactant formulations. These formulations would allow for the testing of different scenarios along the research methodology outlined for this offshore project. Five coreflood experiments were then conducted to test these various scenarios. The pertinent data gained from the coreflood experiments were pressure drop during LTG, and oil cut, oil recovery, and effluent salinity of the LTG process. The presence of a critical pre-flush and its effects on LTG were shown from the dataset gathered. It was determined that the salinity maturity of a waterflood and the resulting salinity environment for LTG was heavily impacted by the waterflood pre-flush. The impact of the pre-flush on the presence of foam and effectiveness of each coreflood is also analyzed. The existence of a correlation between the waterflood maturity and appropriate optimum salinity for EOR is shown in this workItem New correlation for predicting the best surfactant and co-solvent structures to evaluate for chemical EOR(2014-12) Chang, Leonard Yujya; Pope, G.A.; Weerasooriya, UpaliThe focus of this study was the development of an improved correlation that more accurately quantifies the relationships between optimum salinity, optimum solubilization ratios, chemical formulation variables such as surfactant and co-solvent structures, and the EACN. Entrained in this study are improved correlations for co-solvent partition coefficients and correlations for the optimum salinity and solubilization ratio with EACN. Several trends in the oil-water partition coefficient were observed with the alcohol type (IBA and phenol), the number of ethylene oxide groups in the co-solvent, the EACN of the oil, temperature, and salinity. New EACN measurements were made using optimized formulations containing various combinations of primary surfactants, co-surfactants, co-solvents and alkali. The new EACN measurements ranged from 11.3 to 21.1. These new data significantly expand the total number of reliable EACN values available to understand and correlate chemical EOR formulation results. An improved correlation that more accurately quantifies the relationship between surfactant structure, co-solvents, oil, temperature, and optimum salinity was developed using a new and much larger high quality formulation dataset now available from studies done in recent years in the Center for Petroleum and Geosystems Engineering at the University of Texas at Austin. The correlation is useful for understanding the now very large number of microemulsion phase behavior experiments as well as the uncertainties associated with these data, and for suggesting new chemical structures to develop and test.