Oil well cementing slurry inhibiting gas channelling - even at high temp., by including styrene!-butadiene! latex and latex stabiliser

摘要

Cement slurry for use in oil wells comprises (a) a cement; (b) a latex, pref. of a styrene/butadiene copolymer; (c) a latex stabiliser; (d) water; and opt. (e) particulate SiO2. The cement is pref. hydraulic (Portland, aluminous or special), opt. with sec. constituents such as fly ash. The latex pref. contains styrene and butadiene in the wt. ratio (70-30):(30-70), esp. 50:50 or 66:33. The latex stabiliser inhibits the latex's film-forming properties, except in response to gas channelling. It is pref: (ci) an anionic polyelectrolyte, e.g. a melamine-formaldehyde resin, modified by a sulphonic acid or sulphite; or (cii) a sulphonated formaldehyde-naphthalene resin; or (ciii) a condensation prod. of a 2-ring sulphonated phenol and formaldehyde. Esp. pref. is the Na salt of the condensation prod. of mononaphthalene sulphonic acid and flromaldehyde. At high temps. of use, certain anionic cement setting retarders, e.g. lignosulphonates or a polyhydroxycarboxylic acid, can partially replace the stabiliser. Inhibition of gas channelling (arising from gas pockets in the formation) during the setting of the slurry in the annular space being cemented is obtd. Inhibition occurs even at temps. up to 270-300 deg.C, and at corresp. great depths. Rheological and other properties of the slurry are improved.