Abstract

It is very challenging to run polymer/alkaline flooding in a high water-cut (Sw>96%) and viscous oil (μ:114mPa.s at 60°C) reservoir using produced water to mix chemicals. This work is aimed at applying Alkili-polymer flooding under a circumstance there is a shortage of fresh water supply. The selected chemicals are compatible to hard components such as Ca and Mg in the produced water. A less polymer solution degradation in the treated produced water is obtained. A pilot test program was carried out in Yangsanmu oilfield from 1998 to 2008.

During the pilot test, based on lessons obtained, a series of new technologies were developed (1) to reduce active composition and in produced water, the produced water was air-bubbled extensively and improved water quality. (2) Removed chemicals the produced water was filtered using sandy filter. (3) using anti-salt polymer to replace previous used pyacrylamide to increase polymer solution viscosity. (4) using active alkaline to replace dicarbonate on high acid value oil (1.84mgKOH/g oil). As a result, the IFT decreased from 0.1 to 0.001 mN/m and no more crust. The core test showed that the oil recovery by selected alkali-polymer solution increased 22.8% even we started it at a water cut of 90%. The optimized chemical system is 1% alkaline plus 0.15% polymer.

The pilot was run with a test area of 0.71km2, including 4 injectors and 18 producers. The solution was prepared in a central station and delivered to injectors by pipelines. Total injected polymer solution was 1.1 million cubic meter with concentration 0.15%, and alkaline solution was 0.72 million cubic meter with concentration 0.8%. About 6 moths later, dynamic monitored residual oil saturation with fiber glass casing in 2 producers showed the residual oil decreased from52.8% to39.6%. Injecting pressure increased by 2MPa and water cut decreased from 96.4 to 71.6%. The total oil incremental reached 0.94 million bbl.

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