Stripping Mechanism of Surfactant System Based on Residual Oil on the Surface of Sand-Conglomerate Rocks with Different Grain Size Mineral Compositions.

During the development of a sand-conglomerate reservoir, there is a huge variation in rock grain size and different åmineral compositions of different-sized sand grains. The mineral composition and microstructure of the rock both have an impact on the characteristics of the remaining oil in the reservoir. The stripping mechanism of a surfactant system on sand-conglomerate surface crude oil with varied grain size minerals was explored in this paper. Sand-conglomerate was classified and analyzed to determine their wettability and stripping oil effects. The optimization of the surfactant solution system and molecular dynamics simulation revealed the surfactant stripping mechanism on crude oil on distinct sandstone minerals. The results of the study showed that montmorillonite minerals are more readily adsorbed by surfactants. The crude oil within them is more likely to compete for adsorption and to be stripped off, and then extracted with the recovery fluid. The surfactant solution system can increase the hydrophilicity of the rock surface, make the crude oil on the rock surface shrink and gather, and enhance the transportation ability of the displacement fluid. And the emulsification seals part of the pore in the reservoir, increases the displacement pressure, and improves the overall wave volume. The results of this paper are of great significance for the efficient development of sand-conglomerate reservoirs.

Study on Oil Recovery Mechanism of Polymer-Surfactant Flooding Using X-ray Microtomography and Integral Geometry.

Understanding pore-scale morphology and distribution of remaining oil in pore space are of great importance to carry out in-depth tapping of oil potential. Taking two water-wet cores from a typical clastic reservoir in China as an example, X-ray CT imaging is conducted at different experimental stages of water flooding and polymer-surfactant (P-S) flooding by using a high-resolution X-ray microtomography. Based on X-ray micro-CT image processing, 3D visualization of rock microstructure and fluid distribution at the pore scale is achieved. The integral geometry newly developed is further introduced to characterize pore-scale morphology and distribution of remaining oil in pore space. The underlying mechanism of oil recovery by P-S flooding is further explored. The results show that the average diameter of oil droplets gradually decreases, and the topological connectivity becomes worse after water flooding and P-S flooding. Due to the synergistic effect of "1 + 1 > 2" between the strong sweep efficiency of surfactant and the enlarged swept volume of the polymer, oil droplets with a diameter larger than 124.58 µm can be gradually stripped out by the polymer-surfactant system, causing a more scattered distribution of oil droplets in pore spaces of the cores. The network-like oil clusters are still dominant when water flooding is continued to 98% of water cut, but the dominant pore-scale oil morphology has evolved from network-like to porous-type and isolated-type after P-S flooding, which can provide strong support for further oil recovery in the later stage of chemical flooding.

Oil recovery for fractured-vuggy carbonate reservoirs by cyclic water huff and puff: performance analysis and prediction.

Cyclic water huff and puff (CWHP) has proven to be an attractive alternative to improve oil production performance after depletion-drive recovery in fractured-vuggy carbonate reservoirs. However, due to the impact of strong heterogeneity, multiple types of fractured-vuggy medium, poor connectivity, complex flow behaviors and oil-water relationship, CWHP is merely suitable for specific types of natural fractured-vuggy medium, usually causing a great difference in actual oil-yielding effect. It remains a great challenge for accurate evaluation of CWHP adaptability and quantitative prediction of production performance in fractured-vuggy carbonate reservoir, which severely restricts the application of CWHP. For this study, we firstly enable the newly developed fuzzy grey relational analysis to quantify the adaptability of CWHP. With production history of several targeted producers, the accuracy of the proposed method is validated. Based on the traditional percolation theory and waterflood mechanisms in various types of fractured-vuggy medium, a quantitative prediction model for cyclic water cut fwp and increased recovery factor ΔR is presented. The CWHP production performance is discussed by using the Levenberg-Marquardt algorithm for history matching. With a better understanding of the fwp ~ ΔR curve characteristics in different types of fractured-vuggy medium, proper strategies or measures for potential-tapping remaining oil are provided. This methodology can also offer a good basis for engineers and geologists to develop other similar reservoirs with high efficiency.

An efficient and environmental-friendly dispersant based on the synergy of amphiphilic surfactants for oil spill remediation.

Eliminating the adverse environmental impact of chemical dispersants for oil spill has been a significant challenge since decades ago. Here, we prepared an effective and environmentally-friend dispersant with stable emulsifying capacity by the soybean lecithin and Tween 80. The mean droplet diameters of emulsions prepared by decane decreased from 11.3 to 4.1 µm, the emulsification index of emulsion climbed from 0 to 22.0% by 0.5 wt% dispersant. This dispersant exhibits favorable emulsifying capacity when the temperature ranges from 10 to 40 °C, pH within 5-7, and the concentration of inorganic cation is 30000 mg/L. Fluorescence microscopy analysis, FTIR, and the interfacial tension meter were employed to investigate the interaction between the soybean lecithin and Tween 80, a clear redshift of the hydroxyl group on the lecithin/Tween 80 dispersant and the detected surfactants over the oil-water interface confirm that there exists a synergy between the lecithin and Tween 80 due to the electrostatic attractions, which tremendously contribute to the reduction in the interfacial tension between water and oil. To further understand the influence of the dispersant on the oil hydrocarbon concentration in the water column, visualization simulation with the varying depths were performed. The results showed that the oil hydrocarbon concentration in the water column bottom was proportional to the addition of the dispersant, which facilitates spilled oil dispersing into smaller droplets, accelerates the biodegradation process. Hence, the lecithin/Tween 80 dispersant can be perceived as a promising alternative for oil spill remediation.

Numerical simulation of reservoir parameters' synergetic time-variability on development rules.

Time variability of reservoir parameters in water flooding has an effect on oilfield development rules. Meanwhile, time variability of different reservoir macro-parameters has certain synergetic relationship with each other. Based on microscopic network simulation and reservoir numerical simulation, a new simulation method is presented, which can describe the influence of reservoir parameters' synergetic time-variability on oilfield development rules both in macroscopic and microscopic scales. Microscopic network simulation can effectively simulate the impact of micro-parameters' variation on macro-parameters, thus a comprehensive model is built to reflect the variability of reservoir parameters. On the basis of considering time variability of porosity, permeability, and relative permeability in water flooding, an improved reservoir numerical simulator is established, which can effectively simulate the effect of reservoir parameters' synergetic variation on oilfield development rules.