Study On The Synthesis Of Tri-axial Swellable Water-plugging Agent

At present, most oilfields have stepped into high-aquifer stage in our country. Owing to the presence of anisotropy strata, water plugging of oil well and injection well profile controlling had been the important methods for high and stable production of oilfields. A new tri-axial swellable water-plugging agent was developed which was synthesized by acrylic acid (AA), acrylamide (AM), bentonite and N,N-methylene-bis-acrylamide which swelled in water, and can be used to enhance the sweep efficiency of injecting water and improve the injection profile of the stratum to steady yield. Bentonite was used for a functional monomer to crosslinking copolymerize with the expensive monomer AA, which reduced the cost, strengthened the property and improved the combined properties of water-plugging agent.The tri-axial swellable water-plugging agent was synthesized by aqueous solution polymerization and inverse suspension polymerization reaction respectively with acrylic acid, acrylamide and bentonite as start material, N,N-methylene-bis-acrylamide as crosslinking agent and potassium persulfate/sodium acid sulfite as initiator. The influence factors of absorbency properties synthesized by aqueous solution polymerization, such as the concentration of initiator and crosslinker, initial monomer concentration, reaction temperature, pH of system, ratio of monomers, and the amount of bentonite were investigated by the series of single factor tests. By orthogonal experiments, the optimum technological parameters were fixed. The concentration of initiator was 0.3%,crosslinker concentration was 0.05%;initial monomer concentration was 20%, ratio of monomers(AA/AM)was 3:1, the amount of bentonite was 10%, pH of system was 7.0, reaction temperature was 50℃.In the inverse suspension polymerization, with kerosene as the continuous phase, Span80/Tween80 as composite dispersing agent, the conditions for stability of the system and absorbency of the water-plugging agent were investigated, like dispersant concentration, HLB value, the ratio of water to oil (O/W), and the reaction temperature. The result shows: when the dispersant concentration was 5%, HLB value was 4.8 and the ratio of water to oil was 1:1, stability of the system and absorbency properties was better.By the core flooding experiment, anti-washing capability, blocking rate and breakthrough pressure of core were investigated. The water shutoff agent have better performance of anti-washing capability , selection and high blocking rate. Washed by 50 PV water, blocking rate over 85%. Water-plugging efficiency was 95.12%, oil-plugging efficiency was 20.45% and the breakthrough pressure of core was 112.2MPa/m, which can modify the water profile well.