Abstract
Bohai is rich in heavy oil reservoirs with edge and bottom water. The existence of bottom water will lead to rapid water cut increase and worsen thermal recovery performance, so it is long-term undeveloped. And this poses a great challenge to the thermal recovery, of which it is also a worldwide industry problem. Therefore, it's of great significance to take effective control measures in time and realize the efficient development of bottom water heavy oil reservoirs.
The research shows that thermal chemical technology can better improve thermal recovery. Combined with experimental and numerical simulation research, this paper has carried out some very significant explorations. Firstly, the experiments of different chemical composite thermal media were carried out and the enhanced-effect mechanism was clarified, that is viscosity reducer reducing viscosity, gas dissolved& reducing viscosity, gel and foam's plugging effect, surfactant reducing oil-water interfacial tension. Meanwhile, through numerical simulation the thermal and chemical mechanism was characterized by relative permeability interpolation method with experimental results taking into account.
The above research shows that it is feasible to control water channeling in bottom water heavy oil reservoirs by thermal composite huff and puff technology, which strengthens confidence of thermal recovery and development of offshore bottom water heavy oil reservoirs, and also opens a new way for the development of offshore bottom water heavy oil reservoirs. Firstly, hot water or steam can reduce the viscosity of crude oil, and viscosity reducer can further reduce viscosity. Gel and foam can block bottom water channeling and improve thermal efficiency. At the same time, the surfactant can reduce oil-water interfacial tension and reduce crude oil viscosity through emulsification effect. Secondly, the thermal-gas-agent characterization method finely characterizes the synergistic mechanism of each component, which lays a foundation for the development and implementation of composite huff and puff plan. Thirdly, through the combination of hot water and heat-resistant foam plugging, obvious effect of precipitation and oil increase was achieved in two horizontal wells of LD2 bottom heavy oilfield. After the measures, the daily oil rate increase from 10 m3 to 40 ~ 70 m3, the water cut reduced from 74% ~ 92% to 1% ~ 10%.
LD2 is the first bottom water heavy oil oilfield developed by thermal recovery. The successful pilot test of hot water chemical combined huff and puff in two horizontal wells of LD2 oilfield has opened a new development mode and strengthened the confidence of developing offshore bottom water heavy oil. Therefore, 18 new horizontal thermal wells are designed, expecting to increase recoverable reserves of 327 million tons, which is of great significance for offshore thermal development.