Abstract

This paper introduces laboratory and numerical simulation studies on selection of polymer injection parameters and project design optimization in a Third Class (Class ???) reservoir of Daqing oilfield--the effective permeability is less than 100 md and the effective thickness is smaller than 1 m. Because of these physical properties, multiple producing layers, low permeability and highly dispersed residual oil, the recovery factor of water flooding is low. The amount of incremental producible oil is not large enough to further drill infill wells economically, so polymer flooding was proposed and a pilot test of polymer flooding was conducted.

On the basis of the reservoir response to waterflooding, polymer flooding could substantially increase the amount of recoverable reserves. Results of numerical simulation show that the recovery factor using the technique of separate-layer injection with different molecular weight polymers is 8.60% higher than that of water flooding. Compared with common polymer flooding (polymer concentration 1,000 mg/L, viscosity 30 ~50 mPa·s), the incremental recovery efficiency of the technology is 3%. The polymer flooding technique of separate-layer injection with different molecular weight polymers will not only improve oil recovery, but is also more economic.

Based on the results of these studies, a pilot test was conducted in March 2007. By the end of September 2007, the pilot test achieved desirable results: the allocated injection rate can be achieved, the injection pressure increased, and the watercut is decreasing, which indicate that polymer flooding can get good results in a Third Class reservoir with low permeability formations and thin pay zones.

Introduction

Early in 1964, Sandiford (1964) published the fact that the mobility of water used in water flooding was greatly reduced by the addition of very small amounts of partially hydrolyzed polyacrylamide (HPAM). Many additional papers sustaining and extending this idea have been published (Du, 2004). In past forty years, researchers around the world has carried out extensive investigation on the mechanism of polymer flooding and laid a solid foundation to the field scale application of polymer flood. Also many field scale polymer flooding projects have been put into production. However, few large-scale successes with these processes have been reported, except in China (Chang et al., 2006). Daqing oilfield, the largest field of China, is a typical example of polymer flood, even chemical flooding, in the world petroleum industry. Daqing oilfield started industrial scale polymer flooding in 1996. The oil production rate of Daqing field by polymer flooding has rapidly increased since then (Wang et al., 2002). Annual oil production of the polymer flood has exceeded 10 million tons (Wang and Liu, 2006). It has become an important supporting technology for the high and stable production of Daqing.

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