Low-salinity water (LSW) flooding has become a quite simple, effective, and economically feasible enhanced oil recovery (EOR) technology under the background of low oil price. The B425 block with a low permeability in Shengli oilfield, China, has achieved an excellent LSW flooding performance, but the main EOR mechanisms in the block are still not clear. Therefore, in order to investigate the LSW flooding mechanisms in the B425 block, a set of core-flooding experiments were conducted. The water contact angle on core slice and the zeta potential of rock particle were also measured. Then the main EOR mechanisms of LSW flooding in the block were discussed. The experimental results show that the LSW injection can indeed enhance the oil recovery in the low-permeability oil reservoir. Compared with the direct high salinity water (HSW) injection, direct LSW injection and HSW–MSW (medium salinity water)–LSW successive injection can increase the oil recovery factor by 10% and 29.52%, respectively (when the core permeability is about 0.5 md). The water wettability of rock can be strengthened when the LSW is injected. This can be demonstrated by the right shift of oil–water relative permeability curves, the increase of Ca2+ and Mg2+ concentrations in the produced water, and the reduction of both water contact angle and zeta potential of rock particles during core flooding or in the LSW environment. Clay particle migration was also observed during core flooding. It can be verified by the direct evidence of the produced water containing many clay particles and the indirect evidence of the identified abnormal increase in the displacement pressure. Overall, the EOR performance of LSW flooding in the B425 block is remarkable, which has brought great confidence for the low-permeability oil reservoirs to conduct the LSW flooding in China.

No abstract

Most of the natural gas hydrates on Earth are buried in shallow formations under deep water. Comprehensively understanding the reaction kinetic characteristics of gas hydrate in porous media is very beneficial to the deep exploration of the hydrate accumulation in nature. In this paper, the formation process of CH4 hydrate in porous media was simulated physically, using a reactor that is operating at high pressure and low temperature. The hydrate phase equilibrium and reaction kinetic characteristics at different temperatures, pressures, sand grain sizes, and clay contents were assessed. Based on the determination of relevant hydrate kinetic parameters, a novel mixing-flux hydrate reaction model was proposed, which can be used for numerical simulation of gas hydrate accumulation. The experimental results show that the porous media can make the phase equilibrium of CH4 hydrate shift to the right under the capillary effects on the gas and hydrate phases. Low temperature and high pressure can provide a large driving force for hydrate formation, but large clay content and small sand grain size usually give a negative effect on the CH4 transfer in the porous media. It often leads to a slow hydrate formation rate and hard distinction of pressure drop between hydrate nucleation and growth stages. Based on the experimental results, the hydrate nucleation kinetic parameters were regressed, and the activation energy (E a), as well as the reaction frequency factor (k fo), of hydrate growth were fitted to be 75.45–90.85 kJ/mol and 8.72 × 108–6.02 × 1011 mol/(m2 kPa day), respectively. In the numerical simulation of hydrate accumulation, the hydrate formation process can be described by coupling the low-flux reaction and the high-flux reaction, which consume the CH4 dissolved in water and the free CH4 gas in pores, respectively. This novel mixing-flux hydrate formation model is suitable for the flexible and practical hydrate accumulation simulation, which can consider various gas sources and transfer states in the hydrate reservoir.

Cellulose is the most abundant natural biopolymer material, which has been widely used in film making and food packaging in recent years. However, lignin, a natural bioaromatic material, is always applied as a waste resource due to its low utilization efficiency. In this study, a ZnCl 2 /CaCl 2 /cellulose mixed system was used to prepare film materials via a regeneration method. The chemical structure and corresponding properties were characterized. The thermal decomposition process of film materials showed that with an increase of the heating rate, the maximum weight loss temperature gradually shifted to the higher-temperature region. Additionally, the combination of lignin with cellulose as composite films can effectively improve thermal stability. Furthermore, kinetics methods such as Kissing–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Friedman were used to calculate the average activation energy ( E ). This study proposed a facile method for preparing biobased multifunctional composite films using two kinds of naturally renewable materials.

No abstract