METHOD OF PREPARING MIXED CHROMIUM-METAL-CONTAINING LIGNOSULFONATES REAGENTS FOR TREATMENT OF DRILLING MUDS

oil and gas production. SUBSTANCE: in a method of preparing compositionally and qualitatively stable chromium-metal-containing lignosulfonate reagents for efficiently controlling properties of drilling muds, including stage of oxidation of lignosulfonates with chromium(VI) compounds in acidic medium and interaction of resulting chromium-lignosulfonate with multivalent metal salts followed by alkalinization and drying, after above- mentioned oxidation stage, metal-containing lignosulfonates (products of interaction of multivalent metals with lignosulfonates) are added to reaction mixture. Metal-containing lignosulfonates can be products of interaction of lignosulfonates with aluminum and/or iron salts taken in amount sufficient to achieve Cr/Al, Cr/Fe, or Cr/(Al+Fe) weight ratio in final product 1: (0.05-0.5), preferably 1: (0.05-0.1), summary chromium and aluminum and/or iron content 2.5-3.5%, and Al/Fe weight ratio (0.1- 99.9):(99.9-0.1), preferably (40:60):(60-40). EFFECT: enabled controlled process of acidic polycondensation of lignosulfonates with formaldehyde and cocondensation agent. 6 cl, 3 tbl, 2 ex