Abstract: It is a conventional heavy oil reservoir with edge water in X Oilfield, the South China Sea, and its reservoirs cover the large area but they are thin. After it is put into production, the formation energy decays fast and liquid production rate declines quickly. The oil reservoirs were not cognized sufficiently in the early stage, and offshore oilfields are characterized by great oil well investment, limited platform area and fewer well slots, so the ground water injection technology is not suitable. In order to solve the difficulty of formation energy supplement, the technologies and experience of injection and production in the same well at home and abroad were investigated in this paper. Then, a completion string suitable for hot water injection and oil production in the same well in heavy oil reservoirs was designed and optimized. By virtue of this string, the high-temperature formation water in the deep layers is pressurized and then injected into oil layers to supplement its driving energy, increase reservoir temperature, reduce oil/water mobility ratio and improve sweep efficiency and oil displacement efficiency. Field test results show that the completion string for water injection and oil production in the same well is reliable and stable, and it realizes formation energy supplement of heavy oil reservoirs at lower cost. Besides, oil enhancement of its neighboring oil wells is remarkable. The research results provide the valuable experience for the efficient development of similar oilfields.