Recently there has been a growing interest in utilizing amino-polycarboxylic acid (APC) for the treatment of limestone or sandstone formation having high bottom-hole temperatures. One of the main benefits of utilizing APC for matrix acidizing is lowered reactivity compared to HCl or organic acids, making it ideal for high temperature conditions. Other benefits include, incorporated chelation chemistry, enabling it to function as an effective iron control agent, and better tubular protection even at higher temperatures, compared to conventional acid systems.

Recent experimental works confirmed that reducing concentration or pH of polycarboxylic (PC) or amino-polycarboxylic acid (APC) can result in local permeability enhancement rather than wormhole creation. Also, reducing the active material concentration and injecting a larger volume of diluted polycarboxylic or aminocarboxylic acid result to a lower skin because of increased unreacted acid in the flushed zone.

Reported in this paper is a patent pending injection process to treat sandstone or limestone formation with high bottomhole temperature using PC or APC such as GLDA, MGDA, DTPA, etc. This process involves: Injection of high concentration of dicarboxylic or amino-polycarboxylic acid to create wormholes accompanied by injection of low active material concentration of PC or APC to improve the permeability of the flushed zone. Alternatively, the second step involve injection of larger volume of low concentration PC or APC after the injection of high concentration with less volume of acid to enlarge the stimulated matrix area.

Also discussed in this paper are laboratory tests to support the high temperature well injection technique such as carbonate solubility, core flood tests, computed tomography scan of treated cores, corrosivity of acid with metals. Skin factor computations as a function of distance penetrated by acid from well bore will also be discussed in this paper.

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