Low salinity or adjusted brine composition waterflooding (LSW or ABCW) is considered a promising improved/enhanced oil recovery (IOR/EOR) method. Despite the large number of studies documented in the literature, there are contradictory results and a lack of consensus regarding the mechanisms that operate in this recovery process. The proposed fluid:rock and fluid:fluid mechanisms are still under discussion and investigation. However, the impact of oil geochemistry and its importance on the fluid:fluid interactions that can occur with brines during LSW or ABCW have been overlooked and studied in a lesser extent.The scope of the present study is to preliminary evaluate crude oil:brine interactions to validate the influence of its compositions. These interactions were evaluated at static conditions for a week and reservoir temperature (60°C) using two oil samples from different Colombian basins and brine solutions of different composition at a constant ionic strength (I = 0.086). Specifically, this investigation evaluated the effect of the type of cation (Na+ and Ca2+) and anion (Cl- and SO4=) on crude oil:brine interactions. The results of these experiments were compared with tests using distilled water (DW). Although a basic characterization of brines (i.e. pH, alkalinity and ionic composition) and oil (oil viscosity) was performed, the main objective of this study is the analysis of water-soluble organic compounds (WSOC) using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). The results demonstrate that water:oil interactions are dependent on brine and crude oil compositions. The main changes observed in the aqueous phase were the increase in inorganic components (desalting effects) and organic compounds soluble in water. Only the system crude oil A and NaCl (5,000 ppm) showed the formation of a micro dispersion. Negative electrospray ionization (ESI (-)) FT-ICR MS data shows that WSOC’s identified in DW and Na2SO4 after the interaction with crude oil A belongs to similar classes but there is marked selectivity of species solubilized with different brines. The relative abundance of classes Ox, OxS and NOx (x > 2) decreases while Ox, OxS and NOx (x ≤ 2) increase their solubility in the presence of Na2SO4 compared to DW. The analysis of O2 and O3S classes using double bond equivalence (DBE) vs. carbon number (CN) contour plots shows that the isoabundance of water-soluble species are within the range of DBE £ 10 and CN £ 20 regardless the brine used in the experiments. Finally, the method of solvent extraction in silica columns used in this investigation for the analysis of WSOC using FT-ICR MS represents a powerful and new approach to study LSW and ABCW.
With the design of experiments (DoE), this study analyses the influence of physical (capillary diameter and pressure drop) and chemical variables (salinity, polymer concentration, and molecular weight) on the mechanical degradation of partially hydrolyzed polyacrylamide-type polymer solutions (HPAM) used in enhanced oil recovery processes. Initially, with the help of a fractional factorial design (2k-p), the variables with the most significant influence on the polymer's mechanical degradation were found. The experimental results of the screening demonstrate that the factors that statistically influence the mechanical degradation are the molecular weight, the diameter of the capillary, and the pressure differential. Subsequently, a regression model was developed to estimate the degradation percentages of HPAM polymer solutions as a function of the significant factors influencing the mechanical degradation of polymer solutions. This model had a 97.85% fit for the predicted values under the experimental conditions. Likewise, through the optimization developed by the Box Behnken response surface methodology, it was determined that the pressure differential was the most influential factor. This variable was followed by the capillary diameter, where less than 50% degradation rates are obtained with low polymer molecular weight (6.5 MDa), pressure differentials less than 500 psi, and diameters of the capillary greater than 0.125 inches.
Un diseño de experimentos de mezcla (SCMD) fue usado para determinar el efecto de la dureza y salinidad del agua de preparación en la viscosidad final de una solución polimérica con modificaciones con unidades ATBS (Acrilamidas-Terbutil Sulfonadas). Con los resultados experimentales del SCMD se construyó un modelo cuadrático especial, y se implementó un modelo numérico que permite determinar la concentración de polímero necesaria para alcanzar la viscosidad deseada, dependiendo de la salinidad y dureza del agua de preparación. Adicionalmente, el modelo numérico desarrollado fue validado con datos experimentales de la literatura. Este puede predecir la concentración requerida de un polímero modificado con ATBS para alcanzar la viscosidad deseada con un 95% de confiabilidad en los rangos evaluados. El modelo numérico de Newton-Raphson desarrollado usando un SCMD es el primero reportado en la literatura que permite determinar la concentración de polímeros ATBS necesaria para conocer un rango de viscosidad.
HPAM type polymers and modifications with ATBS (Acrylamide Tertiary Butyl Sulfonated) units are used for EOR processes. Polymer adsorption is key to the success of these processes and is affected by variables such as molecular weight, hydrolysis, salinity, and permeability of the porous medium. Nevertheless, few studies corelate the dependence of these variables with adsorption. This work presents experimental results of the influence of variables on the dynamic adsorption of different polymers using sandstone type porous media. Modified polymers show adsorption less than 10 μg/g in low permeability and Sor condition. The adsorption of modified HPAM and HPAM polymers has an inverse relationship with molecular weight and permeability. At higher molecular weight, fewer pores are accessed due to their hydrodynamic radius and lower permeability, greater mechanical and hydrodynamic retention. Water salinity and hardness are directly related to adsorption, with less influence for modified HPAM.
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