Surfactant-Polymer (SP) flooding has been successfully used in some heavy oilfields in China. However, it still remains a challenge to extend the application of this method to more complex reservoirs especially considering the current low oil price, the high chemical cost and the complex reservoir conditions. So the paper studies the effect of liquid flow rate, SP injection mode, reservoir properties, well patterns and well spacing on the development performance of SP flooding, which can provide valuable guidance for economic design of SP flooding for various reservoir conditions under low oil price.

In order to evaluate the technical and economic suitability of the SP flooding, the ratio of enhanced oil production to equivalent chemical injection (EOPPC) is defined. In this paper, a basic reservoir model is established and history matched based on the pilot test in Shengli Oilfield. Then, a series of typical reservoir conditions are simulated by changing geological properties such as permeability heterogeneity and oil viscosity. Based on these reservoir models, the effect of liquid flow rate, SP injection mode, reservoir properties, well patterns and well spacing on SP flooding is studied. Besides, the relationships between optimum SP design and reservoir properties are discussed. Finally, a mathematical model characterizing the relationship between SP flooding performance, operational parameters and reservoir properties is established.

Results show that a lower SP flooding rate of 0.1PV/a and a higher post-SP water flooding rate of 0.2PV/a obtains the highest EOPPC of 44.73m3/t. As the permeability heterogeneity and oil viscosity increase, a lower concentration and larger slug size are preferred for better SP flooding performance when the total amount of chemicals is kept unchanged. Streamline analysis indicates injection and production well pairs should be located perpendicular with high permeable channels in order to increase sweep efficiency. In this paper, the line drive and five-spot well patterns obtain a higher sweep efficiency of over 82%. Considering the cost of well drilling and surface facilities, the economic well spacing is 140m between each pair of injector and producer. The developed quantitative prediction model has a fitting precision of over 98% and it is capable of assisting economic design of SP flooding for various reservoir conditions under low oil price.

The paper carries out studies on economic design of SP flooding according to particular reservoir properties. It also provides effective guidance for future pilot tests and commercial applications in more complex heavy oilfields under low oil price.

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