The Effect of Hydrogen Sulfide Concentration on Gel as Water Shutoff Agent

Abstract

For drilling and water shutoff of oil and gas reservoirs containing hydrogen sulfide (H<sub>2<sub/>S), the effects of H<sub>2<sub/>S on widely used gel as water shutoff agents are studied. The gels include Na<sub>2<sub/>Cr<sub>2<sub/>O<sub>7<sub/>/Na<sub>2<sub/>SO<sub>3<sub/>/HPAM gel, Na<sub>2<sub/>Cr<sub>2<sub/>O<sub>7<sub/>/(NH<sub>2<sub/>)<sub>2<sub/>CS/HPAM gel, Cr(III)-acetate & Cr(III)-lactate/HPAM gel and phenol formaldehyde resin/HPAM gel. The results show that: for Na<sub>2<sub/>Cr<sub>2<sub/>O<sub>7<sub/>/Na<sub>2<sub/>SO<sub>3<sub/>/HPAM gel and Na<sub>2<sub/>Cr<sub>2<sub/>O<sub>7<sub/>/(NH<sub>2<sub/>)<sub>2<sub/>CS/HPAM gel, the H<sub>2<sub/>S as reducing agent (the reducibility is more efficient than that of Na<sub>2<sub/>SO<sub>3<sub/>and (NH<sub>2<sub/>)<sub>2<sub/>CS) can reduce Cr(VI) into Cr(III) and accelerate crosslinking reaction with HPAM in low concentration of H<sub>2<sub/>S, while it can react with Cr(III) generating Cr<sub>2<sub/>S<sub>3<sub/> precipitation in high concentration of H<sub>2<sub/>S, for which the bulk gel can not form without Cr(III); for Cr(III)-acetate & Cr(III)-lactate/HPAM gel, H<sub>2<sub/>S can prolong the gelation time and reduce the gel strength by decreasing pH value; for phenol formaldehyde resin/HPAM gel, H<sub>2<sub/>S can slightly prolong the gelation time and slightly reduce the gel strength by decreasing pH value. Therefore, according to the comprehensive investigations of the effects of H<sub>2<sub/>S on gel as water shutoff agents, the phenol formaldehyde resin/HPAM gel is recommended as the water shutoff agents suitable for oil and gas reservoir containing H<sub>2<sub/>S.