Development And Evaluation Of High-efficiency Salt-tolerant Drag-reducing Agents For Fracturing

In this paper,according to the actual needs and conditions of TH oilfield in Northwest China,a set of drag reducer system is developed,which can be used to prepare drag reducing liquidby using high salinity formation water or back drainage.Firstly,the development of drag reduction mechanism was investigated,and the drag reduction characteristics of polymer were analyzed.At the same time,the application and development of drag reducer at home and abroad,especially the research progress of salt resistance drag reducer,were summarized,and the demand of developing high efficiency the salt resistance drag reducer was put forward.Then,the mechanism of salt resistance of the polymer drag reducer was analyzed in this paper,including electrostatic shielding,reduction of thickness of hydration film,compression of double layer compression of the hydration shell,and complexation effect with high valence ions.The micro-effects of inorganic salts on the solution of drag reducer,including structure network and morphology,were also analyzed.On this basis,the design idea of molecular structure of salt resistance drag reducer is put forward,acrylamide(AM)unit is the main structure,acrylic acid(AA)unit is added to increase water solubility of the polymer,a salt-tolerant monomer 2-acrylamide-2-methylpropionic sulfonic acid(AMPS)is introduced to increase salt-tolerance of molecular chains,and two long-chain nonionic hydrophobic monomers N-dodecyl methylacrylamide(C12AM)/N,N-dodecyl methylacrylamide(DiC12AM)are introduced respectively.Hydrophobic association effect of alkyl long chain in aqueous solution can support each other in high salinity water and reduce the crimp degree of the drag reducer molecular chains.By comparing the salt resistance of two polymer solutions with different hydrophobic groups to Na+,Ca2+ and Mg2+,it is concluded that the polymer with DiC12AM structural unit has better result.So,the structure of the drag reducer is AM/AA/AMPS/DiC12AM quaternary copolymer.After determining the molecular structure of drag reducer,the reaction conditions of the drag reducer were optimized by inverse emulsion polymerization,and the best reaction conditions were obtained(O/W ratio 0.85?0.87:1,HLB value 5.7,monomer content 32%,reaction temperature 33?,emulsifier content 10%,redox initiator to BPO ratio 0.5:1,total content of initiator 0.03%),a stable drag-reducer emulsion can be obtained under this reaction condition.Combining with drag reduction property test,AMPS and DiC12AM contents were optimized and determined to be 9.8%and 0.2%respectively.The drag reduction effects were measured under four different salinity conditions(5?20×104mg/L).With proper adjustment of the concentration,the drag reduction rates reached 68.28%,69.62%,67.50%and 64.68%respectively.According to the test results,the amount of drag reducer added under different salinity water quality conditions was determined.