Dai-Ichi Kogyo Seiyaku Co., Ltd.

Hiroshi Nishiguchi

Hiroshi Hotta

Kinya Yokota

Akira Yada

Yoshihiro Kawamori

Satoshi Hiratsuna

Akira Kitada

Mineo Sabi

Yoshiyuki Mori

A modified polyvinyl alcohol is disclosed, which comprises the following structural units (I) and (II) and has a weight average molecular weight of from 3,000 to 400,000: ##STR1## wherein R.sup.1 represents H or CH.sub.3 ; and M.sup.1 represents H, an alkali metal, ammonium, alkylammonium, or alkanolammonium. The modified polyvinyl alcohol may be sulfonated. The modified polyvinyl alcohol is used as a dispersant such as a drilling fluid additive.

Modified polyvinyl alcohol

A process for forming a gel by gelling an aqueous solution of a water-soluble polymer with a chromium compound as a gelling agent, in which a copolymer of acrylamide, 0.5 to 40% by mole of an unsaturated sulfonic acid or its salt, and optionally an unsaturated carboxylic acid or its salt having an intrinsic viscosity of at least 10 in 1N-NaNO.sub.3 at 30.degree. C., is used as the water-soluble polymer, and which is availably applied to improvement of water-oil ratio in oil production and to civil engineering for preventing leakage of underground water. The formed gel is very stable in a water system containing salts in high concentrations at high temperatures.

Process for preparing stable aqueous gel

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Shiga, Japan

Hiroshi Nishiguchi