| The formation environment in formation is complex,water plugging and profile control operation requires the polymer with all kinds of excellent performance in order to achieve the profile control effect,at the same time reducing the cost and the pollution to the environment as much as possible.The most widely used water shutoff agents in reservoirs is the acrylamide polymer gels,which usually using chromium acetate,potassium dichromate,citric acid aluminum and chromium derivatives or phenolic and aldehyde derivatives as crosslinking agents,existing the poor performance of temperature resistance and salt tolerance,easily degradation and a series of shortcomings.Natural macromolecule humic acid sodium is cheap and easily to get,widely in source,and friendly to the environment,the water plugging and profile control agents based on it also have good stability of temperature resistance and salt resistance,thus can be applied to various types of reservoirs.Therefor there is a broad prospect to develop water plugging and profile control agent based on natural macromolecule humic acid sodium.In this paper,two new types of water plugging and profile control agents were synthesized by free radical polymerization through water solution with acrylic acid(AA)and acrylamide(AM)as monomers,humic acid sodium(NaHA)as grafted monomers,N,N'-methylene bisacrylamide(BIS)as crosslinking agents potassium persulfate(KPS)as initiators.The expansion rate and gel strength of water plugging and profile control agents were tested in order to optimize the formula.The structure characterization(including analysis of infrared spectroscopy,thermal analysis and microscopic analysis)and performance characterization(including the tests on heat resistance,salt tolerance and sealing performance)of formula optimized water shutoff agents were carried out for proving them with good effects on water pluggings and profile controls.The main achievements are as follows:(1)The optimal synthesis conditions of AA/NaHA water plugging and profile control agents are as follows:reaction temperature of 75?,NaHA concentration of 3.0×10~3mg/L,BIS concentration of 3.0×10~2mg/L,KPS concentration of 2.0×10~3mg/L,monomers concentration of 10×10~4mg/L,AA neutralization degree of 60%.The optimal synthesis conditions of AM/NaHA water plugging and profile control agents are as follows:reaction temperature of 70?,NaHA concentration of 1.3×10~3mg/L,BIS concentration of 2.0×10~2mg/L,KPS concentration of 1.0×10~3mg/L,monomers concentration of 6.8×10~4mg/L.(2)The product of AA/NaHA water plugging and profile control agents and AM/NaHA water plugging and profile control agents were analyzed by infrared spectroscopy and thermal gravimetric analysis.The successful preparation of NaHA grafted copolymers was verified.(3)The microscopic morphology observation on the products before and after adding NaHA was performed,comparative analysis found that adding NaHA introduced many hydrophilic functional groups,at the same time increased the crosslinking density of polymer and the gel strength.The two water plugging and profile control agent systems both maintain a certain strength during swelling,which meets the plugging requirements.(4)Through the test of temperature resistance,it was found that the AA/NaHA and AM/NaHA water plugging and profile control agent systems both have good temperature resistance because they can maintained a high expansion rate even at 150?.Both systems are applicable in the formation temperature range of 100-150?.But the strength of AA/NaHA water plugging and profile control agent system is very low after water absorption,thus it is easily broken under the action of the formation shear force and the stratum erosion,while the AM/NaHA water plugging and profile control agent system not only maintains a certain expansion rate,but also has the considerable strength at high temperature,being more suitable for long-term profile control operation.(5)Through the test of salt resistance,it was found that AA/NaHA and AM/NaHA water plugging and profile control agent systems both have good salt resistance because they can maintain a good expansion rate even in 25×10~4mg/L brine.Both systems are applicable for the formation mineralization of 0-25×10~4mg/L.In brine,the presence of a small molecule electrolyte caused the contraction of polymer network,which leads to the increase of the strength of the gel,which makes the water plugging and profile control agents with more excellent plugging performance.It was also found that the effect of the addition of inorganic salts on the expansion rate of AA/NaHA water plugging and profile control agent system was relatively large,but was not great on the other system.(6)Through the test of absorption rate,it was found that AA/NaHA water plugging and profile control agent system need more time to achieve the rapide expansion period which can enter the deeper strata and block the larger pores with a higher expansion rate,and the products can meet the requirements of water shutoff and profile control in the far stratum;AM/NaHA water plugging and profile control agent system need less time to achieve the rapide expansion period which can block the smaller pores near the wells with a certain expansion rate,and the products can meet the requirements of water shutoff and profile control in the near stratum.(7)Through the test of plugging performance,it was found that both two systems have good plugging rate.The plugging rate of AM/NaHA water plugging and profile control agent system is in the range of 90%-95%,the plugging rate of AA/NaHA water plugging and profile control agent system is in the range of 80%-85%,and the plugging rate of AM/NaHA water plugging and profile control agent system is more excellent. |
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