Determination of Adsorption-Retention Constants and Inaccessible Pore Volume for High-Molecular Polymers

The application of chemical enhanced oil recovery methods is based mainly on data from experiments. Determining the adsorption constants without destroying the sample remains a relevant problem. It is necessary for accurate data. The determination of filtration parameters of high-molecular polymers in a porous medium using special model is considered in this paper. The aim of the investigation is the solution of inverse problem of polymer transport with adsorption. The key data for this are the characteristic times of the polymer front propagation, water and rock densities, porosity, and initial polymer concentration. The solutions of the direct problem and the inverse problem from the characteristic form of equations are obtained. The algorithm of interpretation of adsorption-retention parameters and inaccessible pore volume form non-destructive experimental studies is developed. Comparison of the calculated values of the inaccessible pore volume with the results of laboratory studies leads to an error within 10%. The practical application of the algorithm was carried out using the data obtained in previously conducted experiments.

Comparative Study of Green and Synthetic Polymers for Enhanced Oil Recovery

Several publications by authors in the field of petrochemical engineering have examined the use of chemically enhanced oil recovery (CEOR) technology, with a specific interest in polymer flooding. Most observations thus far in this field have been based on the application of certain chemicals and/or physical properties within this technique regarding the production of 50–60% trapped (residual) oil in a reservoir. However, there is limited information within the literature about the combined effects of this process on whole properties (physical and chemical). Accordingly, in this work, we present a clear distinction between the use of xanthan gum (XG) and hydrolyzed polyacrylamide (HPAM) as a polymer flood, serving as a background for future studies. XG and HPAM have been chosen for this study because of their wide acceptance in relation to EOR processes. To this degree, the combined effect of a polymer’s rheological properties, retention, inaccessible pore volume (PV), permeability reduction, polymer mobility, the effects of salinity and temperature, and costs are all investigated in this study. Further, the generic screening and design criteria for a polymer flood with emphasis on XG and HPAM are explained. Finally, a comparative study on the conditions for laboratory (experimental), pilot-scale, and field-scale application is presented.

Experimental evaluation of low concentration scleroglucan biopolymer solution for enhanced oil recovery in carbonate

Injection of polymers is beneficial for Enhanced Oil Recovery (EOR) because it improves the mobility ratio between the displaced oil and the displacing injected water. Because of that benefit, polymer flooding improves sweep and displacing efficiencies when compared to waterflooding. Due to these advantages, polymer flooding has many successful applications in sandstone reservoirs. However, polymer flooding through carbonatic rock formations is challenging because of heterogeneity, high anionic polymer retention, low matrix permeability, and hardness of the formation water. The scleroglucan is a nonionic biopolymer with the potential to overcome some of those challenges, albeit its elevated price. Thus, the objective of this work is to characterize low concentration scleroglucan solutions focusing on EOR for offshore carbonate reservoirs. The laboratory evaluation consisted of rheology, filtration, and core flooding studies, using high salinity multi-ionic brines and light mineral oil. The tests were run at 60 °C, and Indiana limestone was used as a surrogate reservoir rock. A rheological evaluation was done in a rotational rheometer aiming to select a target polymer concentration for the injection fluid. Different filtration procedures were performed using membrane filters to prepare the polymer solution for the displacement process. Core flooding studies were done to characterize the polymer solution and evaluate its oil recovery relative to waterflooding. The polymer was characterized for its retention, inaccessible pore volume, resistance factor, in-situ viscosity, and permeability reduction. Rheology studies for various polymer concentrations indicated a target scleroglucan concentration of 500 ppm for the injection solution. Among the tested filtration methods, the best results were achieved when a multi-stage filtration was performed after an aging period of 24 h at 90 °C temperature. The single-phase core flooding experiment resulted in low polymer retention (20.8 μg/g), inaccessible pore volume (4.4%), and permeability reduction (between 1.7 and 2.4). The polymer solution in-situ viscosity was slightly lower and less shear-thinning than the bulk one. The tested polymer solution was able to enhance the oil recovery relative to waterflooding, even with a small reduction of the mobility ratio (38% relative reduction). The observed advantages consisted of water phase breakthrough delay (172% relative delay), oil recovery anticipation (159% and 10% relative increase at displacing fluid breakthrough and 95% water cut, respectively), ultimate oil recovery increase (6.3%), and water-oil ratio reduction (38% relative decrease at 95% water cut). Our results indicate that the usage of low concentration scleroglucan solutions is promising for EOR in offshore carbonate reservoirs. That was supported mainly by the low polymer retention, injected solution viscosity maintenance under harsh conditions, and oil recovery anticipation.

NANOFLUID INJECTIVITY STUDY FOR ITS APPLICATION IN A PROCESS OF ENHANCED OIL RECOVERY (CEOR)

The application of tertiary recovery techniques through chemical injection (CEOR) is in full development in the mature oil fields of Argentina. An experimental study of nanofluids intended for enhanced oil recovery is presented in this work. A polyacrylamide solution prepared in brine with addition of silica nanoparticles was used as the focus of the study. Dynamic sweep tests of the displacement fluids in a laboratory-scale triaxial cell using a standard Berea sandstone cores that simulates the formation of the reservoir allow the calculation of parameters related to its injectivity, which take into account damage to the formation and blockade of poral throats , such as the resistance factor (FR), the residual resistance factor (FRR), the inaccessible pore volume (VPI) and the dynamic retention of the nanofluid (RD). The injection of the nanofluid has not produced an increase in the damage of the porous medium, so it is potential for its application in the displacement of crude oil.

Rheology-based method for calculating polymer inaccessible pore volume in core flooding experiments

Polymer flooding is an enhanced oil recovery (EOR) method that reduces the mobility ratio between the displaced oil and the displacing injected water. The flow of polymer solutions through porous media is subject to some process-specific phenomena, such as the inaccessible pore volume (IAPV). Due to IAPV, polymer molecules move faster through the porous medium than smaller ones. Thus the IAPV value needs to be accounted for in experiments and field projects. Recent reports found that polymer in-situ rheology correlates with the IAPV. The objective of this paper is to develop a method for estimating IAPV based on the in-situ rheology of polymers. The methodology proposed here can be used in both single- and two-phase experiments. The technique requires measurement of polymer resistance factor (RF) and residual resistance factor (RRF) at steady state conditions. Core permeability, porosity, and residual oil saturation, as well as water and polymer bulk viscosities, also need to be taken into account. Correlations for polymer in-situ viscosity and shear rate are solved simultaneously, to wield an estimative for the IAPV. Aiming at to prove the method, we report 16 core-flooding experiments, eight single- and eight two-phase experiments. We used a flexible polymer and sandstone cores. All the tests were run using similar rock samples. In the single-phase experiments, we compare the alternative method with the classic tracer method to estimate IAPV. The results show an average relative difference of 11.5% between the methods. The two-phase results display, on average, an 18% relative difference to the IAPV measured in the single-phase experiments. The difference between single- and two-phase results can be an effect of the higher shear rates experienced in the two-phase floodings since, in these cases, the aqueous phase shear rate is also dependent on the phase saturation. Additionally, temperature, core length, pore pressure, and iron presence on the core did not show any influence on the IAPV for our two-phase experiments. The method proposed in this paper is limited by the accuracy of the pressure drop measurements across the core. For flexible polymers, the method is valid only for low and mid shear rates, but, accoording to literature, for rigid polymers the method should be accurate for a broad range of shear rates. The method proposed here allows the measurement of polymer IAPV on two- and single- phase core-flooding experiments when a tracer is not used.