SAGD technology has been applied by scale in Liaohe Oilfield China, where high pressure steam is injected in a horizontal well to drain tight oil into the lower production well. However, much waste heat has not been exploited, including heat of the hot production fluid, flue gas and HPHT brine separated by the steam-water separator in the boiler.
On-field researches were carried out on many dual-horizontal wells in Liaohe Oilfield to learn the present operation situation and technical capabilities, while thermodynamic models of various types were established and experimental apparatuses were utilized to analyze the present thermal distribution and each of the above waste heat sources. Effects of various media, flow rates and temperatures on heat utilization and the heat deficit rate were studied on the assumption that 1t crude oil was produced each hour.
The high temperature production fluid may be used to heat water in the boiler first and then used as the heat source of the absorption heat pump, so that heat is transferred from the low temperature heat source to the high temperature heat source and the low grade heat energy is recycled. Waste heat of flue gas may be utilized to help combust air and the thermo-coil may be used as the air preheater, which improves boiler's heat efficiency. As a high grade waste heat, the HPHT brine separated from moist steam in the boiler takes up 20% of the total water and shall not be only used to heat injected water. Instead, it may be used to achieve flash evaporation. Thus, waste water is heated and distilled water is recycled.
The optimized waste heat recyling proposal applies the thermo-coil air preheater to recycle flue gas, flash evaporated hot brine to evaporate waste water and high temperature production fluid to heat boiler water. On a basis of the same fuel consumption volume the recovery rate of crude oil is enhanced by 31% and marketability of it is improved by 8.6%. More energy is saved and recycled, which contributes to the green oilfield construction.