Case study: Multi-component thermal fluid technology to enhance production on thin-bedded heavy oil reservoir in Bohai Bay of China

This paper discusses procedure of the multi-component thermal fluid technology on thin-bedded heavy oil to enhance oil recovery in Bohai bay of China. Offshore heavy oil reserves are abundant, among which thin-bedded heavy oil reservoirs are the main ones. For conventional cyclic steam stimulation (CSS) in onshore thin-bedded heavy oil reservoir, the heat loss is significant as the injected steam can easily spread to the top and the bottom of the reservoir which leads to problems poor recovery efficiency, short valid production period and great production decline rates. For a more efficient and economic development of offshore heavy oil, it is necessary to enhance the recovery of thin-bedded heavy oil. Laboratory experiments, numerical simulation and field trials are used to study the influence of Multi-component Thermal Fluid (MCTF) on heavy oil, porous medium and the recovery enhancement on horizontal well production. Result from the laboratory simulation show that it was studied that the viscosity of the injected gas (N 2 : CO 2 = 11:3) is significantly lower than that of the degassed heavy oil, with a drop of 36 % - 50 %; compared with the injected MCTF and steam under the same heat, the scope of spread is significantly expanded, the average temperature of heating is reduced to a certain extent, the heating cavity formed by MCTF is more than 4 times of that formed by steam, and the oil displacement efficiency is 10 % - 25 % higher than that of steam thermal recovery. The thermal conductivity of nitrogen and carbon dioxide in the MCTF is smaller than that of rock and heavy oil. The MCTF techonology improves the thermal utilization efficiency by forming a protective layer in the upper part of the gas cavity, which reduces the heat loss to the overlying strata. Field practice shows that for thin-bedded oil reservoirs with thickness less than 5 m, horizontal well production using MCTF is 2–3 times more effective than that of ordinary cold production. The use of MCTF increases the short-term production, while the heavy oil recovery can be further improved through the comprehensive adjustment of well pattern and well spacing or later stage steam flooding. • the viscosity of the injected gas (N 2 : CO 2 = 11:3) is significantly lower than that of degassed oil, with a drop of 36 % - 50 %; the heating cavity formed by MCTF is more than 4 times than by steam, and the oil displacement efficiency is 10 % - 25 % higher. • MCTF in horizontal well has the advantages of sweep volume increase, less heat loss to the top and thermal displacement efficiency improvement. A protective layer is formed in the upper part of the gas cavity. Field practice shows that horizontal well + MCTF has better production effect even with thickness less than 5m. • The oil production of Oilfield A is about 218 t/d for cold and after MCTF applied, the maximum daily oil production reaches 641t/d.