This research investigated the effect of ion concentration on the performance of low salinity water under different conditions. First, the effect of injection water composition on interparticle forces in quartz-kaolinite, kaolinite-kaolinite, and quartz-oil complexes was tested and modeled. The study used two oil samples, one with a high total acid number (TAN) and the other with a low TAN. The results illustrated that reducing the concentration of divalent ions to 10 mM resulted in the electric double layer (EDL) around the clay and quartz particles and the high TAN oil droplets, expanding and intensifying the repulsive forces. Next, the study investigated the effect of injection water composition and formation oil type on wettability and oil/water interfacial tension (IFT). The results were consistent with the modeling of interparticle forces. Reducing the divalent cation concentration to 10 mM led to IFT reduction and wettability alteration in high TAN oil, but low TAN oil reacted less to this change, with the contact angle and IFT remaining almost constant. Sandpack flooding experiments demonstrated that reducing the concentration of divalent cations incremented the recovery factor (RF) in the presence of high TAN oil. However, the RF increment was minimal for the low TAN oil sample. Finally, different low salinity water scenarios were injected into sandpacks containing migrating fines. By comparing the results of high TAN oil and low TAN oil samples, the study observed that fine migration was more effective than wettability alteration and IFT reduction mechanisms for increasing the RF of sandstone reservoirs.

To understand the influence of the Fukushima accident on the Northwest Pacific, the distributions and transportations of 134Cs and 137Cs in the seawater in the Northwest Pacific in May and September 2015 were studied. The data showed that the Fukushima-derived 134Cs and 137Cs at some stations can still be distinguished from background level ~ 4 years later. On the whole, the activities of 137Cs and 134Cs in seawater were decreasing from May to Sep 2015. But the increased inventories and the surface activities of 137Cs imply that there has ever been an extra 137Cs from offshore water transported to this study area (from 31° N to 27° N, 145° E to 152.5° E) in May 2015. The average activities of 137Cs in subtropical gyre area in south of KE were the highest and the least were to the east of Luzon Strait in 2015. In vertical direction, 137Cs in subtropical gyre area were mainly distributed at 100 ~ 500 m layer and 137Cs only at 500 m layer in this area showed an increasing trend from May to Sep 2015 which reflects more 137Cs were still penetrating to deeper layer of 500 m from upper water. But they were almost not found below 1000 m layer. It was associated with the subsurface transport of radiocesiums by Northwest Pacific Mode Water (NPMW) and the diffusion of mesoscale eddy. Different distribution characteristics of 137Cs existed between north of KE and south of KE. The low-temperature-low-salinity water mass likely to be the first Oyashio Intrusion was the main factor that resulted in higher 137Cs appearing at the upper 100 m layers in north of KE.

In the enhanced oil recovery (EOR) process, interfacial tension (IFT) has become a crucial factor because of its impact on the recovery of residual oil. The use of surfactants and biosurfactants can reduce IFT and enhance oil recovery by decreasing it. Asphaltene in crude oil has the structural ability to act as a surface-active material. In microbial-enhanced oil recovery (MEOR), biosurfactant production, even in small amounts, is a significant mechanism that reduces IFT. This study aimed to investigate fluid/fluid interaction by combining low biosurfactant values and low-salinity water using NaCl, MgCl2, and CaCl2 salts at concentrations of 0, 1000, and 5000 ppm, along with Geobacillus stearothermophilus. By evaluating the IFT, this study investigated different percentages of 0, 1, and 5 wt.% of varying asphaltene with aqueous bulk containing low-salinity water and its combination with bacteria. The results indicated G. Stearothermophilus led to the formation of biosurfactants, resulting in a reduction in IFT for both acidic and basic asphaltene. Moreover, the interaction between asphaltene and G. Stearothermophilus with higher asphaltene percentages showed a decrease in IFT under both acidic and basic conditions. Additionally, the study found that the interaction between acidic asphaltene and G. stearothermophilus, in the presence of CaCl2, NaCl, and MgCl2 salts, resulted in a higher formation of biosurfactants and intrinsic surfactants at the interface of the two phases, in contrast to the interaction involving basic asphaltene. These findings emphasize the dependence of the interactions between asphaltene and G. Stearothermophilus, salt, and bacteria on the specific type and concentration of asphaltene.

An understanding of clay mineral surface chemistry is becoming critical as deeper levels of control of reservoir rock wettability via fluid-solid interactions are sought. Reservoir rock is composed of many minerals that contact the crude oil and control the wetting state of the rock. Clay minerals are one of the minerals present in reservoir rock, with a high surface area and cation exchange capacity. This is a first-of-its-kind study that presents zeta potential measurements and insights into the surface charge development process of clay minerals (chlorite, illite, kaolinite, and montmorillonite) in a native reservoir environment. Presented in this study as well is the effect of fluid salinity, composition, and oilfield operations on clay mineral surface charge development. Experimental results show that the surface charge of clay minerals is controlled by electrostatic and electrophilic interactions as well as the electrical double layer. Results from this study showed that clay minerals are negatively charged in formation brines as well as in deionized water, except in the case of chlorite, which is positively charged in formation water. In addition, a negative surface charge results from oilfield operations, except for operations at a high alkaline pH range of 10-13. Furthermore, a reduction in the concentrations of Na, Mg, Ca, and bicarbonate ions does not reverse the surface charge of the clay minerals; however, an increase in sulfate ion concentration does. Established in this study as well, is a good correlation between the zeta potential value of the clay minerals and contact angle, as an increase in fluid salinity results in a reduction of the negative charge magnitude and an increase in contact angle from 63 to 102 degree in the case of chlorite. Lastly, findings from this study provide vital information that would enhance the understanding of the role of clay minerals in the improvement of oil recovery.

Nearly half of the world\'s oil reserves are found in carbonate reservoirs, which have heterogeneous formation characteristics and are naturally fractured. Because of the permeability contrast between the matrix and fracture network in these reservoirs, primary and secondary oil recovery processes are ineffective. Consequently, there has been a growing interest in enhanced oil recovery (EOR) from fractured carbonate reservoirs (FCRs) over the past years and many successful attempts have involved the use of different thermal or non-thermal EOR methods to improve oil recovery. Nonetheless, many researchers have recently directed their studies towards the use of low salinity water (LSW), nanoparticles (NPs), and surfactant (LNS) as EOR agents in carbonates because they are environmentally friendly and incur low costs. Several studies have reported the successful application of the solutions of LSW, NPs, and surfactants either as individual solutions or in combinations, to carbonate formations. The challenges associated with their implementations such as fines migration for LSW flooding, surfactant adsorption onto the pore walls, and instability of NPs under harsh conditions, have also been identified in literature and addressed. However, relatively few investigations have been conducted on FCRs to study the effectiveness of these LNS EOR applications in the presence of fractures. This review, therefore, presents the reports of EOR in FCRs using LNS and identifies the mechanisms that influence these results. It has been shown that fines migration could either promote EOR or reduce recovery based on the occurrence of formation damage. In addition, surfactants with the tendency to form micro-emulsions will be efficient for EOR applications in FCRs. Finally, LNS solutions show promising results with emerging techniques such as alternating injection, which could be applied in FCRs. The findings from this study set the stage for future investigations into EOR in FCRs.

OBJECTIVE: We present a systematic study of the \"smart water\" induced wettability alteration. This process is believed to be greatly affected by the brine salinity and the presence of Mg2+ and SO42- in the brine.
UNASSIGNED: To characterize the wettability alteration, we perform spontaneous imbibition measurement using Indiana limestone cores and a model oil with added naphthenic acid. Both single-electrolyte-based and seawater-based \"smart water\" are tested to investigate the effect of Mg2+, SO42- and salinity on wettability alteration. Rock/brine and oil/brine zeta potentials are measured, and the electrostatic component of disjoining pressure is calculated to understand the role of electrostatics in the wettability alteration. The surface concentration of charged species on the limestone surface is analyzed based on a natural carbonate surface complexation model (SCM).
RESULTS: Both the reduction of Na+ and addition of SO42- are found to contribute to wettability alteration. Mg2+ is found to be unfavorable for wettability alteration. Ca2+ is believed to facilitate SO42- with wettability alteration based on the comparison between the single-electrolyte-based and seawater-based brines. The reduction of the Na+ surface complexation (>CaOH⋯Na+0.25) in low salinity brines is believed to be a critical mechanism responsible for wettability alteration based on the SCM calculations.

In 2010, a massive bloom of the raphidophycean flagellate Chattonella occurred in the Ariake Sea and Tachibana Bay. Bloom dynamics and hydrographical conditions were examined by field survey. The development and decline of the bloom occurred three times in Tachibana Bay. First and third bloom developments synchronized with precipitation, and the second bloom developed in synchronization with a salinity decrease which occurred in relation to an increase of river discharge from the Chikugo River which takes several days to flow from the Ariake Sea. These results imply that the bloom was transported with the low salinity water from the Ariake Sea to Tachibana Bay. During blooms along the northern coast of Shimabara Peninsula, the predominant phytoplankton species changed from Chattonella to Skeletonema. Low salinity water intrusion induced an interregional difference of the Chattonella and Skeletonema bloom spatially-differentiated by the salinity in the Ariake Sea and Tachibana Bay.