Abstract: Iron oxide particles having a high surface area, a high kinetic K value and composed substantially of amorphous Fe.sub.2 O.sub.3 and crystalline Fe.sub.2 O.sub.3 are drilling mud additives suitable for scavenging hydrogen sulfide. Such particles do not adversely affect the rheological properties of the mud and when reacted with hydrogen sulfide form reaction products which are acid stable. Upon completion of drilling, the drilling mud containing these iron oxide particles and their reaction products with H.sub.2 S may be left in place between the inner casing and the formation wall or the outer casing as a packer fluid.

Abstract: An iron oxide having the ideal composition Fe.sub.3 O.sub.4 has a unique high porosity, substantially spherical particle structure. Used in oil and gas well drilling muds, it scavenges hydrogen sulfide. It also improves the rheological properties of the mud, maintains its stability under high temperatures, and functions as a mud weighting material. Upon completion of drilling, the drilling mud containing the porous Fe.sub.3 O.sub.4 additive may be left in place between the inner casing and the formation wall or the outer casing as a packer fluid.