Preparation And Properties Of Polymer Gel Temporary Plugging Agent For High Temperature Reservoirs

With the gradually development of the oil field,water content in the produced fluild is continuously rising,which causes a sharp decline of the oil recovery rate.Enhanced oil recovery has become an urgent concern for the petroleum field.Oli well plugging technology is a very effective means to enhance oil recovery,in which water shutoff treatment by polymeric gels has been widely used in the field of water plugging.Currently,the polymeric gel materials used in oil field have a short gelation time under high temperature,and this will lead to a complete gelationization before injecting into the formation,which will seriously affect the oil recovery process.In order to improve the problem of poor salt-tolerance and short gelation time for polymeric gel temporary plugging agent prepared by monomer synthesis method under the high temperature condition,two kinds of oil-soluble high temperature initiator,tert-butyl peroxy benzoate?TBPB?and dicumyl peroxide?DCP?,were used as the initiation system instead low/middle temperature initiator which were commonly used,such as persulfate and oxidation-reduction initiator.A kind of salt-toleration and temperature-resistance plugging agent with long gelation time was synthesized by solution copolymerization of acrylamide?AM?,functional monomers acrylic acid?AA?and 2-acrylamido-2-methyl-propane sulfonic acid?AMPS?,thickening agent xanthan gum?XG?and strengthening agent sodium montmorillonite?MMT?with high temperature initiator,crosslinking agent N,N-methylenebbisacrylamide.The effects of reactant contents in these two systems on polymeric gel's gelation time,swelling degree and compressive strength were studied,such as solid content,monomer ratio,the contents of initiator,crosslinking agent,XG and MMT.The optimum preparation program of polymeric gel plugging agent was obtained.The result showed that under the condition of 125?,the gelation time of DCP system gel?DMAS?was 138min,which was longer than TBPB system gel's?TMAS?102min,and both of them were better than the traditional system's gelation time?<1h?.These two systems had a swelling degree of about 9 g·g^-1 in the simulation formation water with the mineralization degree of 2.2×10⁵ mg·L^-1.The compressive strength of TMAS polymer gel before and after swelling were respectively 1.70MPa and0.73MPa,which were greater than the value of 0.91MPa and 0.47MPa for DMAS.In addition,the intensity of these two systems can reach to I level.In contrast,the polymeric gels prepared by DCP initiation system possesses longer gelation time and the intensity is also within the applicable range,so it was more suitable for practical application.The structure and properties of polymeric gel temporary plugging agent were characterized by infrared spectroscopy?IR?,thermogravimetric analysis?TG?,and rotational rheometer.By the means of X-ray diffraction?XRD?and scanning electron microscopy?SEM?,the mechanism of MMT enhancement was explored.The result showed that the prepared product was the target product,thermal decomposition was not observed at the temperature of 330?,storage modulus?G'?remains much higher than loss modulus?G"?,which indicated that the polymeric gel had three-dimentional network formed inherently and possessed perfect swelling properties.After adding MMT,the polymeric gel network structure became denser,the polymer macromolecules interspersed into the layered structure of MMT,and MMT was uniformly dispersed in the internal network structure of polymeric gel,which gave a support to the network structure.This mechanism of action could result in the increase of the compression strength for the polymer gel.