Conglomerate reservoir is characterized by high water cut, poor sweep efficiency and inefficient oil recovery during the end-period of water flooding. Surfactant/polymer (SP) flooding has been proved as one of the most promising CEOR methods to improve remaining oil recovery after water flooding, due to the unique synergy of polymer/surfactant. The mechanism and performance of SP flooding in conglomerate reservoir need be studied thoroughly.

We took Karamay oilfield, the biggest conglomerate pilot for SP flooding in China, as an example. Three critical issues, surfactant formulation, relationship between oil displacement and lithology, and filed adjustment methods based on development data, for successful SP flooding in conglomerate were investigated in this paper. Firstly, Petroleum sulfonate surfactant was extracted from Karamay crude oil and three properties including molecular structure and phase behavior were tested to optimize surfactant formations. Then the pore structure difference between conglomerates and sandstones was compared through thin section photographs and mercury-injection capillary pressure tests. Meanwhile, these typical cores of different lithology were used to conduct core flooding experiments, and pore-scale displacement of different concentrations of polymer and surfactant was also evaluated using nuclear magnetic resonance (NMR). After these laboratory researches, a pilot test (18 injection 26 production) at Karamay oilfield was performed in November 2011. Finally, technical issues related to scale-up and unique phenomena of development in conglomerate reservoir were discussed.

The complex of two anionic surfactants made surfactant solution achieve longer range of carbon number distribution, lower CMC and ultra-low interfacial tension with low concentration. Compared with sandstone, the diagenesis of conglomerates normally takes place in a shallower depth and then possesses more tortuous pore structures. Unlike sandstone cores, increasing polymer concentration cannot increase oil efficiency. The result of NMR test showed polymer flooding was hard to mobilize residual oil in pores whose radius was below 5μm. However, residual oil in these pores obviously decreased in SP flooding. For the pilot test, heterogeneous reservoir pressure and very low liquid production were observed in first 2 years. We had to stop some well group tests whose permeability was below 30mD and decrease molecular weight and concentration of polymer to continue testing in those wells (8 injection 13 production) whose permeability is relatively high. It has some good performances including appropriate emulsification, low water cut and high oil recovery (15.5%) until December 2016.


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