Synthesis and Evaluation of High-Temperature Resistant Polymer Plugging Agent for Water-Based Drilling Fluids.

As the exploration and development of deep wells have emerged as a key option to extract more oil and gas resources trapped underneath, high-temperature formations impose stringent requirements on the thermal stability of plugging agents used in water-based drilling fluids. In this work, β-cyclodextrin, with its unique conical toroidal rigid stable structure and internal hydrophobic and external hydrophilic special adsorption capacity, was first grafted with maleic anhydride to prepare a silicone polymer and then copolymerized with dimethyldiallylammonium chloride (DMDAAC) in the presence of coupling agent vinyltriethoxysilane (A151) and cross-linking divinylbenzene (DVD) to finally obtain a high-temperature resistant plugging agent (AMMD). Subsequently, the molecular structure was evidenced and the performance of AMMD was examined in the polysulfonate-base fluid via a series of tests including high-temperature high-pressure filtration loss, sand tray plugging, and drilling fluid displacement, and the results were compared with the counterpart Soltex under the same conditions. The optimal synthesis conditions for the plugging agent were found as total monomer concentration of 25%, initiator mass fraction of 1% (based on the mass of monomers), monomer feed ratio of m (DVD):m(A151):m(DMDAAC):m(MD) of 15:3:2:15, pH value of 10, reaction temperature of 75 °C, and reaction time of 4 h. FT-IR spectra indicated that the monomers used to prepare AMMD were successfully involved in the reaction for the design of the plugging agent structure. TGA showed that AMMD has a total weight loss of about 35.98% in the range of 284 to 453 °C. Moreover, the addition of 3%AMMD into the base fluid produced a 4.38-fold and 3.8-fold filtration loss control over 60 min at 200 °C using 400 and 800 mD sand trays, respectively, which were comparatively higher than the commercially available Soltex (ca. 3.72-fold and 3.14-fold, respectively, using 400 and 800 mD). This then contributed to AMMD's superior plugging performance in drilling fluid based on the drilling fluid displacement experiment, implying that AMMD could find potential use as a plugging agent in polysulfonate drilling fluid under severe geothermal conditions.