Spent acid accumulation in the wellbore area after acidizing causes severe formation damage resulting in loss of productivity. This would cause reduction of relative permeability to gas, especially in tight gas wells. Capillary forces are the key parameters that affect the trapping of spent acid in the formation. This work provides a comprehensive study of the effect of acid additives in spent acid on surface tension in tight gas carbonates. All experiments were conducted using Drop Shape Analysis (DSA) at high temperature and pressure.

Different types of commonly used acid additives including corrosion inhibitors, iron control agents, mutual solvents, methanol, acetic acid and formic acids were tested at different concentrations. Experiments were conducted at 1000 psi and temperature ranging from 25 to 150 °C.

Acid additives such as methanol and corrosion inhibitors reduced surface tension. However iron control agents, formic and acetic acids had no impact on surface tension. In addition, increasing temperature resulted in reduction of surface tension.

A unique feature of this work is that measurements were conducted at high temperature and pressure. This work contributes to the knowledge of surface tension behavior of different acid additives. Consequently, that would help in better designing the acid formulae used to enhance well productivity by minimizing capillary forces.

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