Characteristics Of Profile Control And Oil Displacement By Partially Hydrolyzed Polyacrylamide And Aluminum Citrate Gelling System

Polymer-flooding is one of the most important EOR methods in the stage of high water-cut in China.But it can not be conducted in the reservoirs with critical conditions,such as high temperature and high salty.Further more,how to improve the oil recovery factor of the conventional polymer-flooding reservoirs is another problem we are faced with now.In order to improve oil recovery further,new oil displacement agents and methods must be developed. A new oil displacement system,named Partially Hydrolyzed Polyacrylamide and Aluminum Citrate Gelling System (HAGS) was prepared,and the effecting factors were evaluated.The particle size distribution of HAGS in the process of sol-gel was measured,and the visco-elastic properties of HAGS were evaluated under different conditions.The flowing performance of HAGS was evaluated by man-made cores and sandpack models using the Core Flowing System.Experiments of profile control and oil displacement were also carried out by HAGS. Experiments of HAGS preparation show that the properties of HAGS are effected by the concentration of HPAM,the mass ratio of HPAM to AlCit,temperature,salty and the gellation time.The viscosity of HAGS increases with the increase of HPAM concentration and the gellation time,decreases with the increase of NaCl concentration and temperature.It is also related to the mass ratio of HPAM to AlCit.With the increase of HPAM concentration,the gellation time is getting shorter. Experiments of HAGS Size distribution analysis present that the size of HAGS is in the level of nanometer in the early stage,the mininum peak size is 17.9nm.It is becoming larger with the time going.When it is diluted by distilled water,its size is getting larger and its size range is getting wider. Experiments of HAGS visco-elasticity evaluation show that HAGS is a pseudoplastic fliud,its viscosity changes differently with the shear rate.The loss angle of HAGS also changes with the shear rate.The consistency factor decreases with temperature increase.Most of the HAGS is shear thinning and some HAGS is shear thicking. Core flowing experiments of HAGS present that the fluidity of HAGS in the early stage is better,the residual resistance factor(RRF) after gellation is much higher than that of HPAM with the same concentration.The plugging behavior of HAGS is selective and it can be moved forward in the water-flooding process.With the increase of flow rate,the RRF decreases,On the contrary,the breakthrough pressure grads increases.The viscosity of HAGS decreases after it is adsorbed and sheared in the cores.It is effective for repeated HAGS plugging,and the breakthrough pressure grads is becoming larger. Experiments of profile control and oil displacement by HAGS present that HAGS can improve oil recovery factor on the basis of water-flooding,the oil recovery increment is from 8.62% to 22.95%,and the average oil recovery increment is 14.10%.The result of EOR becomes worse with the times of HAGS injection.The gellation behavior has great effect on oil recovery factor.In order to achieve greater oil recovery factor,the matching and combination of HAGS to core permeability must be considered.HAGS can increase oil recovery by adjusting the permeability variation through plugging the higher permeability layer and forcing the injected water to flow into the lower permeability layer.