A Novel Methodology to Reduce Carbon Footprints: Trials of Residual Heat Recycling in China and Middle Asia

Abstract

As a mature methodology to enhance recovery of heavy oil, ultra-heavy oil and tar oil, steam assisted gravity drainage has been adopted in several oil production regions in China since 1990's. Liaohe Oilfield which is located in the northeastern part of China has become the most important production base of heavy oil in China. Heavy oil reservoirs in Kenkyak Oilfield Kazakhstan are found on a semi-dessert plain where saline soils are widely distributed. The cold production techniques used to be deployed in Kenkyak Oilfield, but the relatively low recovery rates have made the operator to carry out a feasibility research on steam injection. The steam assisted gravity drainage technology enhances recovery rates of heavy oil, producing a large amount of heat at the same time. The thermal resources are residual heat of hot separated water from the boiler's moisture separator, residual heat of produced fluid associated by crude oil, residual heat flue gas injected into the boiler. The separated water is as hot as steam, with a flow rate of 25% of the gas injection volume. The produced fluid associated by crude oil is at 160°C, with a flow rate of 1.1 times of the gas injection volume. The flue gas is at 240-250°C, much hotter than flue gas generated by conventional boilers. The residual heat does not only affect on-site operation and management, but also results in waste of thermal energy. Now the residual heat of produced fluid and separated water is deployed to heat supply water and fuel. Based on geological conditions and on-site operation requirements, there is neither a river to cool the residual heat, nor a common heating system to generate a large amount of thermal energy. Besides, both Chinese government and Kazakhstani government are adopting strict environment protection laws, banning direct discharge of waste water and extraction of underground water in the oilfields. A once-through boiler steam injection boiler generates humid steam with a dryness fraction of 75%, and is compatible with purified water dehydrated from crude oil. Now a research on deployment of drum-type boilers to enhance recovery rates is carrying on. A drum-type boiler has strict requirements about supply water quality. In some developed countries where the assisted gravity drainage technology is widely deployed, the mechanical vapor compression technology is much more welcome, which requires re-processing of produced waste water to obtain distilled condensate water that is compatible with a drum-type boiler. The mechanical vapor compression technology, regarded as one of the most advanced integrated technologies to reduce carbon footprints arising from SAGD, is expected to be deployed in Liaohe Oilfield and Kenkyak Oilfield in the near future. This paper focuses on comprehensive deployment of thermal resources, based on local conditions and requirements in China and Kazakhstan, proposing several feasible solutions to reduce carbon footprints arising from heavy oil extraction, in order to select the most appropriate one in the future.