Effect of Spent Acids on the Wettability of Carbonates at High Temperature and Pressure
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Accumulation of spent acid in the wellbore area after acidizing causes severe formation damage that would result 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 trapping of spent acid in the formation. This work provides a comprehensive study of the effect of acid additives in spent acid on contact angle in tight gas carbonates. All experiments were conducted using the Drop Shape Analysis (DSA) at high temperature and pressure. Different types of commonly used additives including corrosion inhibitors, iron control agents, mutual solvents, methanol, acetic acid and formic acid were tested at different concentrations. Experiments were conducted at temperature of 100°C and pressure of 1000 psi. Acid additives such as methanol, corrosion inhibitors, formic and acetic acids reduced the contact angle. Both iron control agents showed no impact on contact angle at concentration of 0.3 wt.% while at the lower concentration of 0.03 wt.% they decreased contact angle. A study was also done on the effect of temperature on contact angle of spent acid. The results showed that increasing temperature up to 100°C increased contact angle, while beyond this temperature contact angle was decreased. This work would help to better understand the ability of acid additives in altering wettability of carbonate rocks, which would consequently result in better designing the acid formulae and enhancement in well productivity by minimizing capillary forces. Copyright 2011, Society of Petroleum Engineers.
author list (cited authors)
Saneifar, M., Nasralla, R. A., Nasr-El-Din, H. A., Fahes, M., & Hill, A. D.