DETERIORATION INHIBITOR AND DETERIORATION INHIBITION METHOD OF DRILLED MUD

PROBLEM TO BE SOLVED: To provide a deterioration inhibitor of drilled mud capable of achieving inhibition of viscosity increase of the drilled mud and reduction of specific gravity by suppressing hydration swelling of contaminated clay by addition to the drilled mud, and a deterioration inhibition method of the drilled mud using the same.SOLUTION: There are provided a deterioration inhibitor of drilled mud containing a copolymer containing a compound (A) which is (meth)acrylamide, and at least one kind of compound (B) selected from (meth)acrylic acid and a salt thereof as constitutional monomers, and having a ratio of the compound (B) based on total of the compound (A) and the compound (B) of 10 to 90 mol% and inherent viscosity in a solution of the copolymer at 30°C of 0.5 to 10.0 dL/g, and deterioration inhibition method of the drilled mud using the same.SELECTED DRAWING: None 【課題】掘削泥水への添加により、混入粘土の水和膨潤を抑制して、該掘削泥水の粘性上昇の抑制及び比重の低減を図ることができる、掘削泥水の劣化抑制剤、及びこれを用いた掘削泥水の劣化抑制方法を提供する。【解決手段】（メタ）アクリルアミドである化合物（Ａ）と、（メタ）アクリル酸及びその塩のうちから選ばれる少なくともいずれか１種の化合物（Ｂ）とを構成モノマーとして含む共重合体を含有し、化合物（Ａ）と化合物（Ｂ）の合計に対する化合物（Ｂ）の割合が１０〜９０モル％であり、前記共重合体の３０℃の水溶液における固有粘度が０．５〜１０．０ｄＬ／ｇである掘削泥水の劣化抑制剤、及びこれを用いた掘削泥水の劣化抑制方法。【選択図】なし