A new type plugging agent for drilling fluid based on hydrophobic associative polymer

In view of the problem that conventional plugging agent cannot realize effective plugging to heterogeneous permeable reservoirs, based on the association theory of hydrophobic associative polymers and using the method of polycondensation in a solvent and through molecular structure optimization design, a new type of hydrophobic associative polymer (HMP) was synthesized of acrylamide (AM)/octadecyl dimethyl allyl ammonium chloride (C18DMAAC)/acrylic acid sodium (AANa). The infrared spectrum, element analysis and gel chromatography were used to represent and measure the molecular structure and molecular weight of HMP, and it’s feasibility of being the drilling fluid plugging agent was discussed in this paper. Results show that the weight-average molecular weight of the new type of hydrophobic associative polymer (HMP) was less than 100 000, which had small influence on the rheological properties of drilling fluid. When molar content in hydrophobic monomer C18DMAAC in HMP molecules was up to 0.66% and the mass concentration of HMP in drilling fluid was up to 0.6%, then it would have excellent sealing performance, and can realize effective sealing of quartz sand bed and cores of different permeability under the condition of high temperature and high pressure and the resulting sealing layer was thin and tight. Results of particle size distribution measurement show that HMP broadens the scope of particle size distribution of drilling fluid system to a few microns to a few hundred microns, and can significantly increase the average particle size of the system. This is the main reason for its good sealing performance.