Applied Research Of Relative Permeability Modifiers

Water production from oil and gas wells is a serious problem for the oil industry. Water production causes several problems to oil wells such as reducing well productivity, increasing the operating costs of separation and the disposal of produced water. It also promotes scale and corrosion of tubular and equipments, causing premature well abandonment, and having a great effect on oil production and transportation. Many water shutoff technologies have been proposed for this problem. Conventional water shutoff technologies not only block the water channel, but also block oil passage, thus decrease the oil production, and affect the economic effect. An option that can be considered when conventional water shutoff agent cannot be applied is the injection of relative permeability modifier (RPM) that selectively reduce the permeability to water and not significantly restrict oil flow. The main advantages of RPM treatments are low cost, low risk and low environmental impact.Cationic polymers and colloidal dispersion gels (CDG) as PRM for water control were studied. Supermolecule cationic polymer MA303 was selected by residual resistance factor through core flooding experiments. Its water solubility and injectivity are suitable for down-hole application. It also has a good property for selective water control with temperature resistance at 90℃and salinity resistance of 50000mg/L.Using CDG as RPM for water control was presented. An amphoteric polymer/AlCit CDG was prepared. The mechanism and influential factor of crosslinking reaction of CDG were studied by several experiments such as viscosity method; microporous filter membrane method and SEM method, etc. The crosslinking reaction of CDG is intramolecular crosslinking, through forming coordination link between AlCit and carboxyl in polymer molecules. The property of selective water control using CDG was studied by core flooding experiments. Its injectivity is suitable for down-hole application. The CDG treatments as RPM for water control reduce permeability to water more than to oil, and its life is long.Adsorption of RPM on rock surface is important in water control by squeezing RPM in oil wells. The concentrations of supermolecule cationic polymer were measured by iodine-starch colorimetric method. The hydrodynamic adsorption and the mechanism of water control were studied by coreflooding experiments. Experimental results show that adsorption of cationic polymers in porous media is affected mainly by electrostatic attraction and hydrodynamic forces. At low polymer injection rates, polymer adsorption is dominated by electrostatic forces, while it is dominated by hydrodynamic forces at polymer injection rates. The adsorbed layer thickness increases linearly with polymer injection rates. The adsorbed layer thickness is also affected by the brine injection rates in back-flush: high brine injection rate can increase the adsorption. Therefore, the adsorption of polymers can be improved using higher rates in squeezing both polymer and back-flush brine solutions, and so the water control efficiency. The mechanism of water control of RPM includes swelling/shrinking effect and segregated flow effect.Where RPM treatments can be successfully applied and candidate selection rules for RPM treatments were analyzed. The RPM treatment is simple to operate, and has been successfully applied in oil well in Gudong oilfield with a water cut decrease of 6.6% and a input output ratio of 1:3.9.In order to controlling scaling and water production, a combined technique of RPM treatment and scale inhibitor squeeze treatment in oil wells is presented, which achieves both water control and scale control purposes and saves treatment cost. The scale inhibitors combined with RPM have been selected based on laboratory experiments, including compatible tests, scale inhibition efficiency and minimum inhibitor concentration experiments and core flooding experiments. The results demonstrated that the combination of SA13 and MA303 is satisfactory for both scale and water control.