چكيده به لاتين
With respect to the limited oil reservoirs and the declining trend of oil exploration in the world, how to exploit oil reservoirs to obtain the highest production rate is one of the most important issues that has been considered in the oil industry today. The amount of easy oil reserves is decreasing and on the other hand the demand for oil is high and therefore, more sophisticated methods are needed to improve the techniques and processes that lead to enhanced oil recovery (EOR). In a general classification, EOR includes chemical, thermal processes, injection of various miscible and immiscible gases based on water and gas as fluids, and heat distribution in the reservoir. Each methods faces its own challenges and advantages. In recent years, the approach of using various nanoparticles as helping agents in EOR methods, especially chemical methods, has attracted much attention in order to overcome the challenges and problems of the aforementioned method. Therefore, the focus of this thesis is on the nanoclay assisted surfactant injection method. One of the types of nanoparticles with unique properties that has been less frequently used in EOR studies is nanoclay (montmorillonite). To investigate the effect of nanoclay with surfactant on EOR, six cores (for flooding and Amut cell test) and a number of thin sections (for contact angle measurement, XRD and SEM analysis) from a carbonate and oil-wet reservoir in southwestern part of Iran were used. To simulate reservoir conditions as much as possible, formation water and oil (in the amount required in the experiments) from the same reservoir were used. On the other hand, the consumables used as recovery enhancement fluids include nanoclay (0.1, 0.25, 0.5, and 1 weight percentages) and 0.5 weight percentages of CTAB and SDS surfactants. Therefore, Comprehensive experiments were designed to evaluate the nanoclay co-injection process in surfactant injection. These tests include measuring the stability of nanoclay using zeta potential and DLS analysis, the clay swelling index, the interfacial tension (IFT), the contact angle, static displacement with Ammott cell and core flooding. The most important challenge in evaluating this process was the stability of the nanoclay suspension, which was analyzed with using two different surfactants (cationic CTAB and anionic SDS surfactants). The results of stability tests showed that CTAB has a higher ability to stabilize nanoclay. Among the tests performed on different samples, 0.1 wt% nanoclay in the presence of 0.5 wt% CTAB had an acceptable stability for more than 24 hours, which was also confirmed by DLS analysis and zeta potential measurement experiments. According to DLS analysis and PDI index, the best value (3.92) is related to the case where CTAB is used as a nanoclay stabilizer. The zeta potential (50+ mV) also confirms the superiority of CTAB over other stabilizers. The presence of a positive charge in CTAB and the distribution of negative charges on the surface of nanoclay lead to ion exchange between the two, and as a result, the nanoclay does not clump in the suspension. After selecting the most stable sample (0.1 wt% nanoclay and 0.5 wt% CTAB), other tests were designed. IFT measurement by pendant drop method showed that nanoclay reduced IFT by approximately 5 dyne/cm (IFT decreased from 24.99 dyne/cm in the initial water-oil mixture to 20 dyne/cm in the nanoclay-oil mixture) because the accumulation of dispersed nanoclay particles on the water-oil interface leads to a decrease in IFT. In the case where CTAB was used, the highest IFT reduction was observed at the initial interaction times between the nanoclay-based nanofluid (0.1 wt% nanoclay and 0.5 wt% CTAB) and oil, where the IFT decreased to 0.157 dyne/cm, which is related to the greater stability of this composition at the initial interaction times. In the next step, in order to evaluate the possible role of nanoclay in changing wettability, a series of contact angle measurement experiments were designed using the Young model and the results showed that CTAB had the greatest effect on changing wettability (changing the contact angle from the initial value of 135 degrees to 69 degrees) and made the tested core surface hydrophilic, while in samples containing nanoclay, the contact angle remained almost unchanged (changing the contact angle from 135 degrees to 125), and as a result, the core surface remained oleophilic. The hydrophilic properties of CTAB and the tendency of this surfactant to form ion pairs with fatty acids present in the oil composition cause the detachment of these compounds from the surface of the positively charged calcite core and provide hydrophilicity of the core. However, adding nanoclay along with CTAB (i.e., nanoclay-based nanofluid sample) prevented CTAB from playing the role of changing wettability because in this sample, CTAB, due to its interaction with nanoclay particles dispersed in the suspension, stabilized the nanoclay and penetrated less into the interface area of the core and oil, so we did not see any change in wettability in this sample. According to the results of the aforementioned tests, in this thesis, CTAB has a stabilizing role for nanoclay and the main agent in increasing recovery. To evaluate the recovery factor in the process of nanoclay assistance in surfactant injection, Amut cell and flooding tests were designed. The results of the Amut cell (static displacement test) to determine the role of wettability change and IFT reduction mechanisms showed that the highest oil recovery factor from the core was in the case of CTAB (23.93%), the mixed nanofluid (19.53%), and the nanoclay (15.09%), respectively. The reason for the higher recovery factor in the case of CTAB is the effectiveness of the wettability alteartion in addition to the IFT reduction mechanism (the other two cases only use the IFT reduction mechanism to produce oil). In the dynamic mode, by testing the flooding experiment in three cases of mixed nanofluid (approximately 3.5 hours), nanoclay and distilled water (approximately 2.5 hours) and recording the recovery factor curve over time, it was observed that the final recovery facor for the mixed nanofluid is approximately 79%, distilled water is 61% and nanoclay is 54.5% of oil in place of the cores. Among the active mechanisms in the flooding, the IFT reduction and wettability alteration occurs only in the case of the mixed nanofluid, the mechanisms of pore blocking and disjoinig pressure occur in the two cases of mixed nanofluid and nanoclay. On the other hand, pore blocking mechanism is stronger in the case of the mixed nanofluid than the nanoclay, but the disjoinig pressure mechanism is stronger in the case of the mixed nanofluid. Finally, considering the selected concentrations of materials and the experiments performed, as well as economic evaluation that indicate the creation of added value of 135,105 Rials per unit of time and pore volume of the core, the optimal fluid proposed in this study for increasing oil recovery is a suspension containing 0.1% wt of nanoclay along with 0.5% wt of the cationic surfactant CTAB.
