Improving recovery factor and heat efficiency of SAGD process has always been the main pursuit of EOR technology. This paper will provide the experimental study results of urea assisted SAGD process in reducing the steam consumption and improving the sweeping efficiency of SAGD process.
Based on previous 1-D flooding test results, this paper futher discussed the advantage of urea-SAGD process with series of 2-D experiment. After evaluation of heat loss effect for SAGD with numerical simuatoin approach, 2-D high experimental study on urea-SAGD process experiment plan were carefully designed. 3 groups of 2-D SAGD experiment with different additives (including ammonia, CO2, urea) were run to evaluate the influence to SAGD process. The performance of different additives were compared. The effects of different products from urea were analyzed in detail.
Study reveals that SAGD process can be greatly influenced by urea. Urea can gradually decompose into ammonia and CO2 over 150℃. Great solubility of ammonia in water can effectively increase sweeping efficiency and decrease residual oil saturation. CO2 is soluble in crudes and can improve the oil water mobility ratio. The 2D experimeint results shows that CO2 can stay in the higher position of the model and drive the oil down to the producer. And ammonia-SAGD experiment also shows that the ammonia can imrove steam efficiency when pure steam can not sustain production in the experiment. Urea SAGD process shows and comprehensive advantage over conventional SAGD process. The decomposed CO2 and NH3 can jointly improve the sweeping volume and sweeping efficiency in SAGD process. The recovery factor of urea-SAGD process can as high as 75% while other runs (including CO2-SAGD, ammonia-SAGD and pure steam SAGD) of experiment no more than 50%. The improvement of ammonia to SAGD process is comparable with CO2, both of them can improve about 10~12% comparing to conventional SAGD process. With the result of this paper, urea can reduce the consumption of steam by 1/3 and improve the oil production by 30% when it was co-injected with steam in SAGD process.
This study provides a new and effective approach of improving SAGD performance with inexpensive chemical products.