Experimental Study Of Shallow Supper Heavy Oil Solvent-assisted SAGD Start-up

Nowadays,Steam Assist Gravity Drainage(SAGD)technique is one of the most important thermal methods for heavy oil development.Nearly 80 percent of heavy oil is developed by this kind of technique in the world.However,in the process of development by SAGD method,the first step is Start-up.This period is long which is usually last for about 120 days.Low interest with high expense is one of the most serious problems especially in the current low oil price situation.Something must be done to improve the start-up process so as to decrease the cost at this period.One of the methods to improve SAGD start-up is to inject solvent to the heavy oil reservoir for.Then close the well soaking for some time.During the soaking time,the injected solvent will diffuse into the reservoir so that the viscosity of heavy oil is decreased.When solvent cycling,small number of reservoir oil is produced.A solvent chamber exist in the reservoir,which lead to a fast oil rate when SAGD stable yield stage come.In this paper,firstly,one dimensional mathematical models are built up to study two physical process,one is the temperature distribution for traditional start-up of SAGD,the other is oil concentration distribution in the process of solvent soaking.The result shows that the start-up of traditional SAGD lasts at least 120 days.It is extremely slow that the solvent diffuse into the oil.Different kinds of solvent are mixed with the heavy oil in different concentration.With the help of rheometer,the viscosity of these mixtures is measured in different temperature.The solvent is petroleum ether,Xylene and kerosene.The result shows that Xylene has the best effect for decreasing the heavy oil viscosity if the concentration of solvent is low.But in condition of high concentration of solvent,there is no obvious difference between three kinds of solvent.One dimensional solvent soaking and cycling experiment is done.Firstly,short man-made cores and short natural core are used to do solvent soaking and cycling experiment.Secondly,a long unconsolidated sand pack is used to do solvent soaking and cycling by gaseous solvent.Finally,a long unconsolidated sand pack with confining pressure is used to do solvent soaking and cycling by gas and liquid solvent alternating.The results show that solvent soaking and cycling by gas and liquid solvent alternating can get best oil recovery and can make the best use of liquid solvent.