Abstract: The present invention provides a modified starch, preparation method and use of the same, also provides a drilling fluid comprising the modified starch which contains bi-substituted starch structural units and tri-substituted starch structural units, wherein, the tri-substituted starch structural units are represented by the following formula (1), the bi-substituted starch structural units are the structural units represented by the following formula (2) and/or the structural units represented by the following formula (3), and the total content of the bi-substituted starch structural units and tri-substituted starch structural units accounts for 20 wt % or more of the modified starch, preferably 20-30 wt %, the weight-average molecular weight of the etherified starch is 50,000-600,000, preferably 80,000-580,000, wherein, R1, R2, and R3 are C1-C5 alkylene respectively, and M1, M2, and M3 are H, alkali metal element, or alkaline earth metal element respectively.

Abstract: A copolymer and preparation method and application thereof are disclosed. The copolymer is random copolymer obtained from monomers consisting of acrylamide, acrylic acid, alkenyl sulfonate, 2-acrylamido-dodecyl sulfonate, p-styrene sulfonate or isoprene sulfonate and so on. The copolymer of present invention can be used as fluid loss additive and has good fluid loss properties, which would not make the drilling fluid thicken at high temperature of 200° C. and high salt conditions of saturated brine. It has a medium-pressure fluid loss after aging and rolling for 16 h at high temperature of 200° C., as measured in accordance with the American Petroleum Institute Standard Test at room temperature, and has good properties of high temperature-resisting and salt-resisting.

Abstract: A copolymer and preparation method and application thereof are disclosed. The copolymer is random copolymer obtained from monomers consisting of acrylamide, acrylic acid, alkenyl sulfonate, 2-acrylamido-dodecyl sulfonate, p-styrene sulfonate or isoprene sulfonate and so on. The copolymer of present invention can be used as fluid loss additive and has good fluid loss properties, which would not make the drilling fluid thicken at high temperature of 200° C. and high salt conditions of saturated brine. It has a medium-pressure fluid loss after aging and rolling for 16 h at high temperature of 200° C., as measured in accordance with the American Petroleum Institute Standard Test at room temperature, and has good properties of high temperature-resisting and salt-resisting.