The invention discloses modified composite barite for a
drilling fluid. The barite is prepared from composite barite, a modifier
sodium hexametaphosphate, an acrylic
copolymer, octylphenol ethoxylate-30 and
polyethylene glycol 400. According to the modified composite barite, on the basis that ultrafine barite and baryto
calcite are compounded, an acrylic
copolymer hyperdispersant is prepared fromsodium hexametaphosphate and
phthalic anhydride,
acrylic acid and n-butyl
alcohol as monomers to improve the surface property of
a weighting agent, furthermore, surfactants octylphenol polyoxyethyleneether-30 and
polyethylene glycol 400 are used as auxiliary materials to further enhance the hydrophilic dispersion performance, and thus the modified composite barite is prepared, the modified composite barite is suitable for a water-based drilling and completion fluid, the suspension property is excellent, and the
density reduction rate of a weighted
drilling fluid system is lower than 3%; the acid
solubility is greater than or equal to 45%; the
viscosity coefficient of a
drilling fluid system filter cake is lower than that of conventional barite by 30% or above; and the
apparent viscosity change rate before and after the
calcium sulfate is added is less than or equal to 3mPa*S.