After tertiary recovery from the oilfields, improving the production of the remaining hydrocarbon is always challenging. To significantly improve oil recovery, a heterogeneous composite flooding system has been developed with preformed particle gels (PPG) and polymers according to the technical approach of plugging and flooding combination. In addition, an oil saturation monitoring device and a large-scale 3D physical model were designed to better evaluate the performance of the technique. The evaluation results show that the viscosity, stability, and elasticity of the heterogeneous composite flooding system are better than the single polymer system. In addition, both systems exhibit pseudoplastic fluid characteristics and follow the principle of shear thinning. The results of seepage experiments showed that PPG migrates alternately in porous media in the manner of “piling plugging-pressure increasing-deformation migration”. The heterogeneous composite system can migrate to the depths of the oil layer, which improves the injection profile. In the visualization experiment, the heterogeneous composite system preferentially flowed into the high-permeability layer, which increased the seepage resistance and forced the subsequent fluid to flow into the medium and low permeability layers. The average saturation of the high, medium, and low permeability layers decreased by 4.74%, 9.51%, and 17.12%, respectively, and the recovery factor was further improved by 13.56% after the polymer flooding.

Background:Polymer flooding is the most commonly applied chemical enhanced-oil-recovery technique in offshore oilfields. However, there are challenges and risks in applying the technology of polymer flooding to offshore heavy oil development. Objective:This paper compared the spread law and the displacement effect of different injection modes and validated the feasibility of enhancing oil recovery by variable concentrations polymer flooding. Method:Two types of laboratory experiments were designed by using micro etching glass models and heterogeneous artificial cores. Furthermore, in order to determine a better polymer flooding mode, the displacement results, displacement characteristic curves and oil saturation distribution of heterogeneous artificial cores were also compared, respectively. Results:The experimental results showed that the recovery of variable concentrations polymer flooding was higher than that of constant concentration polymer flooding, under conditions of same total amount of polymer and similar water flooding recovery. Its sweep efficiency and displacement efficiency were also significantly higher than those of constant concentration polymer flooding. Moreover, variable concentrations polymer flooding had lower peak pressure and was at lower risk for reaching the formation fracture pressure. Conclusion:As a consequence, variable concentrations polymer flooding has certain feasibility for heterogeneous reservoir in offshore oilfields, and can improve interlayer heterogeneity to further tapping remaining oil in medium and low permeability layer. Conclusions of this paper can provide reference for the field application of polymer flooding in offshore oilfields.

Aim at the reservoir characteristics of Suizhong 36-1 Oil Field, this paper has developed typical twodimensional physical model in parallel between the layers and studied the macroscopic displacement effect of polymer flooding and binary compound flooding, and studied the interlayer spread law and oil displacement efficiency of polymer flooding and binary combination flooding by using saturation monitoring system deeply. The results show that: when the multiples of pore volume injected for polymer was 0.3 after water flooding, the recovery efficiency increased by 10.3%, and when the multiples of pore volume injected for binary combination flooding was 0.3 after polymer flooding and the recovery efficiency could also increase by 19.3%, and the effect of enhanced oil recovery was obvious during the binary combination flooding and polymer flooding; Saturation monitoring data showed that there formed oil wall and increased the flow resistance and expanded the swept volume during the stage of polymer flooding and binary combination flooding, effective use of low-permeability layer was the key to improve oil recovery.

This paper researches on the characteristics of the foam system chosen for CO 2 foam flooding in the low permeable oil fields. In view of the actual situation of the oilfield high temperature, high salinity and water injection difficulty, the selected agents must also meet the requirements of stability and foaming property. Through the specific half-life and foam volume under different temperature conditions, found: FP388, FP246 and FP275 three kinds of foaming agent have good foaming properties; the half-life of bubble down quickly as the temperature from 45 °C to 100 °C; the half-life of FP275 is the largest of the three when they at the same temperature; The difference of FP388 and FP275 stability decreases with temperature increasing; all of the three kinds of foam system can meet the needs of the refinery, and the property of the foam system of FP388 is the best among them through the comprehensive consideration.

Heterogeneity is a significant feature of the reservoirs after polymer flooding, resulting in challenges for further enhanced oil recovery (EOR) in heterogeneous reservoirs. In order to further improve oil recovery in the reservoirs after polymer flooding, a novel EOR system (ASP-PPG composite system) was developed using preformed particle gel (PPG) and alkali-surfactant-polymer system (ASP system). We designed an oil saturation monitoring device and a large-scale 3D heterogeneous physical model to evaluate the performance of the system. The performance of the system and the ASP system were tested. Based on the testing results, the fluid migration patterns and enhanced oil recovery mechanisms of the ASP-PPG system in an actual heterogeneous reservoir were investigated using the oil saturation monitoring device and the 3D physical model. Experimental results indicate that the ASP-PPG system has a higher viscosity and better profile control ability than the ASP system. Additionally, the interfacial tension can be maintained at a low level, around 10-3 mN/m. Flooding experiments using the three-dimensional heterogeneous physical model demonstrated the excellent elastic deformation ability of PPG, which can dynamically block the large pores that formed after the polymer flooding and effectively improve the heterogeneity of reservoirs. After injecting the ASP-PPG system, the recovery factor of the model increased by 15.8%. Specifically, the sweep coefficient of high, medium, and low permeability layers increased by 4.36%, 19.6%, and 37.55%, respectively. Moreover, the oil displacement efficiency increased by 7.4%, 14.4%, and 17.9%, respectively. These results highlight the synergistic effect of combining PPG and ASP systems, significantly enhancing heterogeneous reservoir recovery after polymer flooding.

For the development of oil and gas field, the effective viscosity determination of the viscoelastic fluid is always the problem of chemical flooding and there are technical problems to verify difficultly. The common methods include bulk phase viscosity method, the rheological curve method, and the drag coefficient method. This article tested and compared the methods respectively by adopting the binary system of fixed concentration. The results showed that using the method is more scientific that calculate the effective viscosity according to the curve transformation. The viscosity curve was obtained from the along sample tests in the long cores. For the experimental core with the length of 300mm and permeability of 2500×10-3μm, the average of the injection viscosity and the viscosity of produced liquid is closer to the effective viscosity of binary system in the core. Keywords-Offshore oil field; binary system; viscoelastic fluid; the effective viscosity; average viscosity methodAsia-Pacific Energy Equipment Engineering Research Conference (AP3ER 2015)

By comparing the oil displacement experiment of Huading I and Haibo BI polymer surfactant based on the actual the situation of reservoir in Daqing oil field in this paper, the displacement efficiency for two kinds of polymer surfactant in different concentration and different slug were compared. In the optimized concentration experiments, there was an inflection point of increasing range for the degree of reserve recovery when concentration of Huading I and Haibo BI polymer surfactant is 1000mg/l. The increasing of recovery efficiency slow down gradually with the increasing of concentration; In the optimized slug experiments, the increasing range of the oil recovery was the largest when the injection of Huading I and Haibo BI polymer surfactant was 1 multiple of pore volume injected. Considering concentration and degree of reserve recovery, optimized concentration of Huading I and Haibo BI was 1000mg/l and their optimized slug were 1 multiple of pore volume injected.

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