The invention relates to the technical field of
drilling fluid plugging materials, in particular to a composite plugging agent and a preparation method thereof.According to the composite plugging agent, glass fibers and walnut shells serve as raw materials, the walnut shells and the glass fibers are pretreated through the composite plugging agent, and a walnut shell-
iron chelate and a
glass fiber-
tannic acid glue solution are obtained; and mixing the walnut shell-
iron chelate with the
glass fiber-
tannic acid glue solution, standing, and
drying to obtain the composite plugging agent. Iron is chelated on the walnut shells,
tannic acid is loaded on the glass fibers, then under the complexing action of the tannic acid and the iron, the glass fibers and the walnut shells are stably combined together, and during plugging, the glass fibers and the walnut shells which are stably combined together form a fixed and stable space structure; therefore, a good plugging effect is achieved.