Effects of Acid Additives on Spent Acid Flowback through Carbonate Cores
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Matrix acidizing is a well stimulation technique used to remove formation damage in the near wellbore region. But it comes with an associated set of challenges such as corrosion of the tubulars and iron precipitation in the formation. To counter these challenges, different chemicals, or additives, are added to the acid solution such as corrosion inhibitors and iron control agents. These additives may change the relative permeability of the spent acid, and formation wettability, and may either hinder or improve spent acid clean-up. Such effects of additives on the spent acid clean-up have not been documented. The aim of this research effort was to document the aforementioned change in the spent acid concentration (by using one additive at a time) before and after gas flowback. This was achieved by acidizing cores and creating wormholes halfway through them, then CT scanning them to observe the spent acid region. Later on, gas was flown through the core opposite to the direction of acid injection for 2 hours, and another CT scan was taken. The difference between the two CT scans was documented. Using a different additive each time, a series of such CT scans was obtained to develop an idea about whether the said additive was beneficial or detrimental to spent acid clean-up. It was found that the corrosion inhibitor FA-CI performed the best in terms of spent acid recovery after gas flowback for both Indiana Limestone and Texas Cream Chalk cores. Moreover, the corrosion inhibitor MI-CI was the worst for Indiana Limestone and the non-emulsifying agent M-NEA the worst for Texas Cream Chalk for spent acid recovery after gas flowback.
Nasir, Ehsaan Ahmad (2012). Effects of Acid Additives on Spent Acid Flowback through Carbonate Cores. Master's thesis, Texas A&M University. Available electronically from