A Review on The Largest Polymer Flood Project in The World

Abstract

This paper presents a systematical review on the largest polymer flood project in the world, applied to a giant field with muti-layered, heterogeneous sandstone reservoirs. In this paper, we begin by talking about reservoir and fluid characteristics to provida basic understanding of reservoir heterogeneity. Next, the authors summarize the project history from laboratory studies, through pilot tests, commercial tests to field wide application. Then, we illustrate typical polymer flood performance and reservoir management for improving EOR process performance. Finally, key understandings and lessons learned based on over 50 years’ polymer flood practice are presented. Three types of reservoir sandsare developed in this field: higher permeability sand (Type I), medium permeability sand (Type II) and relatively low permeability sand(Type III). Prior to the start of field wide polymer flood in Type I reservoir in 1996, more than ten pilot and commercial tests had been implemented. With Type II reservoir polymer flood coming on stream in 2003, the project achieved a peak production of 253,000 BOPD in 1993. Polymer flood reduced water-cut by 24.8%. Effective reservoir management activities include zonal polymer solution injection, profile modification, fracturing of low permeability sand, and injection slug size optimization. During fieldwide polymer flood, the water-cut performance is characterized by four stages:(1) initial declining, (2) sustained low value, (3) rebound and (4) high water-cut chase-water injection. Operators implemented fit-for-purpose measures in each stage to improve the EOR process performance. Key understandings and lessons learned include: (1) polymer flood improves both sweeping and displacing efficiencies; (2) high inter-layer permeability contrast leads to lower incremental recovery; (3) variable well spacing should be adopted on each type of the reservoir sands; (4) optimized high polymer MW and large polymer slug greatly improve recovery; and (5) salt-resistant polymer in particular is beneficial for produced water re-injection in Type II reservoir sand. Compared with 6% to 8% incremental recovery by polymer flood in most pilots and partial application cases in the industry worldwide, this successful large-scale project improved recovery by 12% over water flood. The finding of improved displacing efficiency by polymer flood further expands the understanding of its oil-displacing mechanism. Effective fit-for-purpose reservoir management measures during life-cycle polymer flood process provide experiences and lessons learned.