Additive for well cement.

摘要

A hydraulic cement additive which controls gel strength and fluid loss consists of a tannin backbone portion having grafted thereto a graft portion consisting of at least a first vinylamide derivative and a second vinylamide derivative selected from compounds of the general formula
<Chemistry id="chema01" num="0001"><Image id="ia01" he="36" wi="27" file="IMGA0001.TIF" imgContent="chem" imgFormat="TIFF" /></Chemistry>
wherein R₁ is -H or -CH₃, R₂ is -H or CH₃, and R₃ is -H, -CH₃ or
<Chemistry id="chema02" num="0002"><Image id="ia02" he="41" wi="36" file="IMGA0002.TIF" imgContent="chem" imgFormat="TIFF" /></Chemistry>
said first and said second vinylamide derivatives being different, and wherein R₃ in said first derivative is
<Chemistry id="chema03" num="0003"><Image id="ia03" he="39" wi="38" file="IMGA0003.TIF" imgContent="chem" imgFormat="TIFF" /></Chemistry>
and R₂ and R₃ in said second derivative are both -CH₃.