Research On Development Effect Of Using Superheated Steam In SAGD

As an important heavy oil recovery method,SAGD has been a research hotspot due to abundant heavy oil reserves.In view of the complex formation conditions in different blocks,the conventional SAGD has the problems of decreasing production efficiency and high water content,so improved forms appears such as nitrogen-assisted SAGD,solvent-assisted SAGD and flue gas-assisted SAGD.As one of the improved forms,SAGD assisted by superheated steam can improve the recovery efficiency and expand the sweep area of the steam chamber and the influence law is different from that of conventional SAGD.Therefore,the study on the improvement of the effect of superheated steam on SAGD and the optimization of injection-production plan is of guiding significance to reveal the development rules.Firstly,the influence of reaction time on physical properties changes of heavy oil was studied through the thermochemical reaction experiment of high-temperature heavy oil and superheated steam.The reaction time is determined to be 3d to reach the equilibrium state and high asphaltene content will increase the reaction time.In this paper,we studied the influence of reaction temperature ranging from 240? to 330? and found that viscosity reduction rate reached 45% in 330? after 72 h.The increase of reaction temperature will increase the content of C and S and reduce the content of H.Asphalt is sensitive to environment temperature and the content reduces by 16.3% in 240? after 72 h.Secondly,numerical simulation was carried out with CMG software STARS module,and the viscosity-temperature changes were inserted into the homogeneous model to study the effect of viscosity changes on the development of SAGD.The reduced viscosity can obviously shorten the development time and improve the drainage rate during the transverse expansion of the steam chamber.The influence law of injection-production parameters was studied through the homogeneity model and the weight analysis was compared.For superheated steam injection to improve SAGD technology,compared with production-injection ratio and well spacing,steam quality,subcool and steam injection speed have more influence on cumulative steam oil ratio.Superheated steam can accelerate the moving speed of the steam chamber,especially in the rising stage and horizontal expansion stage,greatly shorten the development time and reduce the cumulative steam oil ratio.When steam quality ranging from dryness 0.9 up to the superheating temperature 30?,production time was shortened by 22% and the cumulative steam oil ratio was reduced by 21.1%.Low subcool can improve the temperature and oil drainage efficiency of production wells,which was acting on the middle and late stage of production and has little influence on production time.Finally,a geological model was established to optimize the scheme of superheated steam SAGD.In this paper,the influences of initial formation temperature,production time and initial oil saturation on steam mass range and steam injection velocity range were compared.It is found that the influence of initial oil saturation is the greatest.Low oil saturation reservoir requires higher steam quality and steam injection speed.The development time increases and the influence of steam injection speed decreases.The expansion of the SAGD steam chamber in the case of superheated steam injection was studied through a three-dimensional physical simulation experiment at high temperature and pressure.