Mingzhe Dong

Further enhanced oil recovery by branched-preformed particle gel/HPAM/surfactant mixed solutions after polymer flooding in parallel-sandpack models

How to further sweep residual oil from unswept areas is crucial to enhance oil recovery after polymer flooding, which is widely used. Branched-preformed particle gel (B-PPG) is a newly developed chemical agent for enhanced oil recovery in heterogeneous reservoirs. In this paper, B-PPG/HPAM/surfactant mixed solutions were investigated to further enhance oil recovery after polymer flooding in parallel-sandpack models by core flood test. First of all, laboratory experiments about fractional flow and enhanced oil recovery were performed to determine the optimal composition and concentration of B-PPG and HPAM mixed solutions. The results show that B-PPG/HPAM mixed solutions have higher abilities to adjust fractional flow in parallel-sandpack models than HPAM alone when the mass percentage of B-PPG is larger than 50%. Moreover, B-PPG/HPAM mixed solutions can displace more oil in low permeability sandpacks and the total oil recovery is the highest when the mass percentage of B-PPG is 50%. The concentration also has a great effect on fractional flow and oil recovery of B-PPG/HPAM mixed solutions. The ability of adjusting fractional flow and enhancing oil recovery increases with increase in concentration. Furthermore, the presence of surfactant in the flooding solutions can further enhance total oil recovery, especially that in high permeability sandpacks, and has no obvious effect on the ability to adjust fractional flow. When the permeability ratio of the parallel sandpacks becomes 1 : 9, the B-PPG/HPAM/surfactant mixed solutions still have strong abilities to adjust fractional flow and enhance the oil recovery. This is because the presence of a surfactant can improve displacement efficiency, while B-PPG and HPAM can enhance sweep efficiency.

Enhanced heavy oil recovery by organic alkali combinational flooding solutions

ABSTRACT Although alkaline/surfactant/polymer (ASP) flooding is successfully applied in oil fields, some disadvantages such as scales, corrosion effects, and viscosity reductions of polymer solutions appear. Usage of organic alkalis can avoid or decrease these disadvantages. In this paper, the physicochemical properties, including interfacial tension (IFT), and viscosity, of organic alkali combinational flooding solutions and their effectiveness as enhanced oil recovery agents are investigated. Monoethanolamine (MEA) is the optimal one for decreasing the IFT among the three organic alkalis studied in this paper. Although MEA cannot decrease the IFT as low as NaOH does, it has good compatibility with both surfactant and the polymer hydrolyzed polyacrylamide (HPAM). MEA not only helps a surfactant solution or HPAM/surfactant mixture attain ultralow IFT values, but can also promote better viscosity stability for HPAM or HPAM/surfactant solutions compared to NaOH. Moreover, core flood experiments show that adding MEA can obtain additional tertiary oil recovery of 6%–10% original oil in place (OOIP) on the top of HPAM or HPAM/surfactant flooding, although MEA has a lower enhanced oil recovery than NaOH. The experimental results show that MEA is a good choice to replace NaOH in enhancing heavy oil recovery. GRAPHICAL ABSTRACT

Effect of diutan microbial polysaccharide on the stability and rheological properties of O/W nanoemulsions formed with a blend of Span20-Tween20

ABSTRACT The stability and rheological behavior of oil-in-water (O/W) nano-emulsions formed with a blend of Span20-Tween20 have been studied with and without diutan microbial polysaccharide. It is found that there exist thresholds for the water content and emulsifier to obtain stable nano-emulsions using the emulsion inversion phase (EIP) method. The viscosity of the nano-emulsion is proportional to the emulsifier content and inversely proportional to the water content. High emulsifier content is not conducive to the thermal stability of the nano-emulsion. The addition of diutan gum with negative charge into the nano-emulsions increases the electrostatic repulsion between droplets and makes the droplet size smaller and more unifom, slowing down the coalescence and Ostwald ripening of the nano-emulsions. Due to the association of the diutan gum double helix, a three-dimensional network structure is formed in the continuous phase of nano-emulsions, which improves the stability of nano-emulsions and is also the main factor giving the nano-emulsion high viscoelasticity at high temperature. This study offers new insight into the nano-emulsion containing microbial polysaccharide and may serve as a guideline for practical applications of new nano-emulsion systems. GRAPHICAL ABSTRACT