Various modification methods for lignosulfonates have been decribed, for example, by condensation with formaldehyde or modification with iron salts. It has been found that chromium-modified lignosulfonates, as well as mixed metal lignosulfonates of chromium and iron, are highly effective as dispersants and therefore are useful in controlling the viscosity of drilling fluids and in reducing the yield point and gel strength of the drilling fluids. Because chromium is potentially toxic, its release into the natural environment and the use thereof is continuously being reviewed by various government agencies around the world. Therefore less toxic substitutes are desirable. The lignosulfonates are prepared by combining tin or cerium sulfate and an aqueous solution of calcium lignosulfonate, thereby producing a solution of tin or cerium sulfonate and a calcium sulfate precipitate.
Oil-based muds are being replaced now by synthetic muds. Diesel oil is harmful to the environmental, particularly the marine environment in offshore applications. The use of palm oil derivative could be considered as an alternative oil-based fluid that is harmless to the environment. Hydrated castor oil can be used as a viscosity promoter instead of organophilic quaternized clays.
An oil-based drilling mud can be viscosified with maleated ethylenepropylene elastomers. The elastomer are ethylene-propylene copolymers or ethylene-propylene-diene terpolymers. The maleated elastomers are far more effective oil mud viscosifiers than the organophilic clays used. On the other hand, specific organophilic clays can provide a drilling fluid composition less sensitive to high temperatures. PAOs are biodegradable and nontoxic to marine organisms; they also meet viscosity and pour point specifications for formulation into oil-based muds. The hydrogenated dimer of 1-decene can be used instead of conventional organic-based fluids, as can n-1-octene.
Polyethercyclicpolyols. Polyethercyclicpolyols possess enhanced molecular properties and characteristics and permit the preparation of enhanced drilling fluids that inhibit the formation of gas hydrates; prevent shale dispersion; and reduce the swelling of the formation to enhance wellbore stability, reduce fluid loss, and reduce filter-cake thickness. Drilling muds incorporating the polyethercyclicpolyols are substitutes for oil-based muds in many applications. Polyethercyclicpolyols are prepared by thermally condensing a polyol, for example,glycerol to oligomers and cyclic ethers.
Electric conductive nonaqueous mud. A wellbore fluid has been developed that has a nonaqueous continuous liquid phase that exhibits an electrical conductivity increased by a factor of 104 to 107 compared with conventional invert emulsion. 0.2% to 10% by volume of carbon black particles and emulsifying surfactants are used as additives. Information from electrical logging tools, including measurement while drilling and logging whiledrilling, can be obtained.