蒸汽辅助重力泄油新模型研究

Study on new mathematical model of steam assisted gravity drainage

蒸汽辅助重力泄油技术(SAGD)是稠油油藏开发的一种有效手段。SAGD生产过程中,高压蒸汽通过上部的水平井注入油藏,通过热交换作用加热附近的油砂。之前的研究中多忽略对流作用对SAGD的影响,或者考虑了对流作用,但认为对流相只有水相,而忽略了油相的流动。基于蒸汽腔前缘温差引起的导热作用以及压差引起的对流作用,笔者建立了SAGD生产中热交换的新模型。通过对比可以发现,新模型可以更好地拟合UTF矿场数据。敏感性分析表明:提高注入压力会降低单位井长的产油量,增大含水率,不利于油藏开发;较大的Corey系数a同样不利于SAGD生产,因此采取措施增大油相相对渗透率,减小a值,将明显改善SAGD生产;蒸汽腔界面运移速度过快会导致产油量降低,同样不利于油藏开发。该研究将理论与实际生产相结合,对稠油油藏开发有指导意义。

Steam assisted gravity drainage( SAGD) is an effective method for bitumen and heavy oil reservoirs.In SAGD process,steam is injected into the reservoir with a high pressure from the upper horizontal well,and the injected steam will heat the surrounding oil sands through a conduction and convection heat transfer process.In this paper,a novel unified model was developed to investigate the heat transfer mechanism in SAGD process.Typically,the multiphase flow assumption at the edge of steam chamber was introduced in the model.And the effect of both the conduction and convection heat transfer in steam chamber were considered.Especially,in this model,the convective heat transfer process caused by pressure difference was studied.Then the simulation results are compared against the UTF field data to confirm the accuracy of our model.Results indicate that our model can match the UTF field data very well,and it can be used to investigate the heat transfer process in SAGD process.It is found that though increasing pressure will be better for increasing the injection temperature and the temperature distribution at the edge of the steam chamber,it will result in a lower oil production and a higher water cut.So,it is disadvantage to heavy oil reservoir development.A higher Corey coefficient a means a lower oil relative permeability.So decreasing the coefficient a will be better for production.Though a higher velocity of steam chamber interface can result in a lower water cut,but the oil production rate will decrease more.So,it is also disadvantage to reservoir development.The study in this paper is a combination of theory and practice and has guided significance for the oil production behavior on the field.