Influence of Oilfield Chemicals on the Surface Tension of Stimulating Fluids

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSurface tension plays a very important role in the stimulation of gas wells. A low surface tension is required to reduce capillary forces that trap the aqueous phase in the formation. Accumulation of the aqueous phase near the wellbore area, known as water blockage, leads to a significant reduction in gas production.An experimental study was conducted to examine the effects of various acids and stimulation additives on surface tension. A Krüss tensiometer (Model K-12) was used to conduct surface tension measurements. Acids examined included: HCl, acetic, citric, formic, and combinations of these acids. Stimulation additives tested included: mutual solvent, shortchain alcohols, corrosion inhibitors, hydrogen sulfide scavengers, iron-control agents, and clay stabilizers. In addition, the effects of three classes of surfactants (nonionic, cationic and anionic) on surface tension of acid solutions were investigated. The surface tension of acid stimulating fluids is a complex function of acid type, concentration, and additive type and concentration. Acetic and formic acids had lower surface tension values than HCl, especially at high acid concentrations. The surface tension of the organic acids examined depended on the pK a value of the acid. Organic acids with high pK a values had low surface tension values. The surface tension of hydrochloric acid can be reduced by mixing with acetic acid. EGMBE lowered the surface tension of acetic, formic and hydrochloric acids up to 10 wt%. Increasing the concentration of EGMBE above 10 wt% had no significant effect on the surface tension of these acids. The effect of organic acid strength on surface tension diminished in the presence of EGMBE. Short-chain alcohols reduced the surface tension of 15 wt% HCl with the greatest reduction obtained with n-butanol. Citric and erythorbic acids, which are usually used as iron control agents significantly reduced the surface tension of 15 wt% HCl. Ionic surfactants reduced the surface tension of hydrochloric acid more than the two nonionic surfactants tested. The three corrosion inhibitors examined reduced surface tension up to a critical concentration beyond which they had no effect on surface tension. An aldehyde-based H 2 S scavenger lowered the surface tension of 15 wt% acid solutions at very low concentrations. Clay stabilizers (cationic polymers) did not significantly affect the surface tension of 15 wt% HCl. Addition of a hydrogen sulfide scavenger, a nonionic surfactant or a corrosion inhibitor into solutions of 15 wt% HCl and EGMBE had a small effect on the surface tension of the acid.