Abstract:Understanding the deformation and break-up of drops is of great significance in various applications such as emulsification and phase separation. Most practical systems contain surface-active agents that are present as impurities affecting the properties of the system, e.g. modifying the rigidity of the film that affects emulsion stability. In this paper, the effect of surfactants on the deformation and break-up of an aqueous drop in an immiscible dielectric oil under the action of an electric field is addressed. The experiments were carried out on a single drop in a microscopic cell under an applied external electric field. A nonionic surfactant, polyethylene glycol sorbitan monolaurate (Tween 20), and an ionic surfactant, sodium dodecyl sulfate (SDS), were used at different concentrations. The drop adopted in most cases a prolate shape. However, the presence of the surfactant affected both the extent of deformation and the modes of break-up. The drop deformation extent increased rapidly with the surfactant concentration, while smaller drops deformed less under the same external electric field strength.When the surfactant concentration was high, the position of break-up could be from both poles along the main axis of the drops in the direction of the electric field.
Foam injection is a proven technique for improved oil recovery in both light and heavy oil reservoirs, especially for those with high heterogeneity, in which foam can improve the displacement and sweeping efficiency effectively. In this study, the feasibility of nitrogen foam injection for IOR from viscous oil reservoirs are investigated via laboratory experiments and field pilot analysis. The targeted oilfield is located offshore Bohai Bay (China), featured with high oil viscosity (up to 924 mPa.s) and severe heterogeneity of pay-zones. Water flooding has been applied in the oilfield, but the recovery factor is less than 20% and high water cut (over 85%) has been observed. Nitrogen foam injection was proposed in order to solve the problems and improve oil recovery. In this study, laboratory evaluation of nitrogen foam was conducted via foam testing and sandpack flooding. The results indicate that polymer enhanced foaming agents can greatly increase foam's performance. High blocking capability and displacement efficiency were observed in enhanced foam flooding experiments, indicating that nitrogen foam injection can mitigate the problems of heterogeneity and increase oil recovery in low permeability zones. A field pilot with 2 injectors and 13 producers involved has been conducted to verify the feasibility of the foam technique. The wellhead injection pressure was effectively increased after foam injection, and nearly all producers exhibited good response with incremental oil recovery and the average water cut dropped by 6.3% over 8 months of the field operation. The field pilot demonstrates the effectiveness of the nitrogen foam injection technique as an effective IOR method for the targeted oilfield and other similar oil reservoirs.
Comprehensively understanding the gas hydrate accumulation mechanism is significant for the investigation of subsea gas hydrate reservoir which can provide further guidance for the hydrae exploration and development as well as the safe deep-water drilling. In this paper, a preliminary conceptual model is established to study the characteristics of gas hydrate accumulation in the typical shallow formation under the sea using a reservoir simulation method. A partial equilibrium reaction model based on the phase equilibrium of gas hydrate is used to describe the trigger mechanism of hydrate formation when methane from deep formation migrates into the upper hydrate stability zone under the seabed. Two cases are simulated for comparison, one considering the barrier effect of cap rock at seabed while the other assuming a cold spring at seabed. The simulation results indicate that in the cap rock case, a thick hydrate layer tends to be formed in the upper subsea formation but with a relatively smaller hydrate saturation, while in the case of cold spring, nearly 90% of methane from deep reservoir would leak into the sea water, nevertheless the long-term slowly gas driving water process is favorable for generating high hydrate saturation. Generally, low flux of methane gas, cap rock barrier, deep water depth, and small geothermal gradient below mud line are beneficial to forming valuable hydrate reservoirs with larger thickness and high abundance. This study has proven that the reservoir simulation method can be an effective tool to simulate the process of gas hydrate formation and accumulation in the shallow formation under the sea, which deserves for further study.
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