Utilizing Steam Injection to Improve Performance of Mature Waterflooding Reservoir

Abstract F reservoir, a mature waterflooding reservoir with high wax content and oil viscosity higher than 50cp, is developed by 30-year's waterflooding with 14% oil recovery but 90% water-cut. How to rejuvenate such mature reservoir with ‘secondary water body’ and water channel formed by long-time water flooding? The answer is steam injection. The paper will discuss some of mechanisms, strategies as well as barriers and difficulties to high recovery of steam injection following water flooding. Firstly, the paper will introduce lab experiments, which include single core tube, multi-tube displacement and three-dimension physical experiments and discuss mechanisms of steam injection. Single tube displacement experiment shows steam injection can enhance displacement efficiency to 80% from 40% of waterflooding. Multi-tube and 3-D experiments show steam overriding can help steam to displace oil in the upper un-drived by waterflooding and increase vertical swept efficiency, increase productivity and lower watercut, enhance recovery to 50% from 14%. Secondly, the paper will discuss key factors such as depth, net-to-gross sand rate, oil viscosity, oil saturation and so on, which shows oil saturation left by waterflooding is the most important factor to influence performance of steam injection. Thirdly, the paper will detail numerical simulation study, such as well pattern, development manner and pilot test plan. It shows steam injection following waterflooding should obey to several strategies. One of the important is the well pattern designed for steamflooding should make the steam spread evenly and avoid steam rapidly breakthrough to producers through water channel formed by waterflooding. The paper finally will introduce pilot test performance. More than 100 wells experienced steam injection show high productivity, low water cut and potential to enhance the oil recovery.