Alkaline-surfactant-polymer (ASP) combination flooding field tests showed that it could significantly enhance oil recovery for high water cut mature oilfields in China. The main problem in ASP flooding was the difficulties in lifting system and produced liquid treatment process due to scaling, erosion and strong emulsification caused by alkali. To avoid the side effects caused by alkali, the tendency of chemical combination flooding changes from ASP flooding to low damage combination flooding formulations such as alkali-free surfactant-polymer (SP) combination flooding. The main challenge in SP flooding is to develop surfactants with highly effective interfacial tension (IFT) reducing ability, low adsorption and good oil displacement ability especially at high salinity reservoir conditions. Yumen oilfield is a high salinity sandstone reservoir. It is a mature oilfield developed by water flooding over 60 years. A candidate EOR technique with SP chemical flooding has been proposed.

This article related the surfactant screening, IFT properties measuring, surfactant adsorption loss testing and oil displacement experiments of SP chemical flooding formulation for Yumen oilfield based on a new type surfactant alkyl polyoxypropylene ether sulfate (APES).

A series of APES surfactants were synthesized by carbon chains with different lengths and structures. The IFT measurements of both model oil/water and crude oil/formation water indicated that IFT could be significantly affected by the molecular structure of surfactants such as the length of carbon chain and propylene oxide (PO) units. The formulations of SP systems were optimized with crude oil/formation water. Ultralow IFT between crude oil and SP fluid could be obtained at the concentration range of surfactants from 0.1wt% to 0.3wt%. The dynamic adsorption experiments showed that adsorption loss of surfactant APES on the core was about 0.36 mg/g rock. Core flooding experiments of SP combination flooding showed that the incremental oil recovery for Yumen oilfield crude oil could reach to 17%-21% over water flooding.

The synthetic process of APES is simple and the surfactant is environmentally friendly. It has potential to be applied in SP chemical combination flooding to enhance oil recovery under high salinity reservoir conditions.

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