Evaluation of a New Environmentally Friendly Chelating Agent for High-Temperature Applications

Abstract

Summary Matrix acidizing is used in carbonate formations to create wormholes that connect the formation to the wellbore. Hydrochloric acid (HCl), organic acids, or mixtures of these acids are typically used in matrix-acidizing treatments of carbonate reservoirs. However, the use of these acids in deep wells has some major drawbacks, including high and uncontrolled reaction rates and corrosion to well tubulars, especially those made of chromium-based tubulars (Cr-13 and duplex steel); and these problems become severe at high temperatures. To overcome problems associated with strong acids, chelating agents were introduced and used in the field. However, major concerns with most of these chemicals are their limited dissolving power and negative environmental impact. L-glutamic acid diacetic acid (GLDA), a newly developed environmentally friendly chelate, was examined as a replacement for acid treatments in deep oil and gas wells. The solubility of calcium carbonate (CaCO3) in the new chelate was measured over a wide range of parameters. Coreflood tests were conducted using long Indiana limestone cores 1.5 in. in diameter and 20 in. in length, which allowed better understanding of the propagation of this chemical in carbonate rocks. The cores were X-ray scanned before and after the injection of chelate solutions into the cores. The concentration of calcium (Ca) and chelate was measured in the core effluent samples. To the best of our knowledge, this is the first study to examine the fate and propagation of chelating agents in coreflood studies. GLDA has a very good ability to dissolve Ca from carbonate rocks over a wide pH range by a combination of acid dissolution and chelation. The addition of 5 wt% sodium chloride (NaCl) did not affect the GLDA performance at pH = 13 but significantly accelerated the reaction at pH = 1.7. Compared with other chelating agents, GLDA dissolved more Ca than ethanoldiglycinic acid (EDG) but less than hydroxyethyl ethylenediamine triacetic acid (HEDTA) at high pH values. GLDA of pH = 1.7 was able to form wormholes at 2 and 3 cm3/min. GLDA was found to be thermally stable at temperatures up to 350°F.

Thermal Stability of Oilfield Aminopolycarboxylic Acids/Salts

“…Venezky and Moniz (1970) reported that EDTA started to decompose at 390 F because of hydrogen bridging. They also concluded that the half-life of Na 4 EDTA at 390 F was 15 hours, which is in disagreement with the results of the work that was performed by Martell et al (1975) and Motekaitis et al (1982). Both studies showed that the EDTA started to decompose to iminodiacetic acid (IDA) and 2-hydroxyethyliminodiacetic acid (HEIDA) at 390 F by means of hydrolysis with a half-life of 0.5 hours.…”

“…Both studies showed that the EDTA started to decompose to iminodiacetic acid (IDA) and 2-hydroxyethyliminodiacetic acid (HEIDA) at 390 F by means of hydrolysis with a half-life of 0.5 hours. Moreover, Motekaitis et al (1979) illustrated the split of 0.15 M EDTA molecules to HEIDA and IDA by means of hydrolysis at 347 F in alkaline environments (pH ¼ 9.4) with a half-life of nearly 4 hours (Martell et al 1975;Motekaitis et al 1982). The thermal degradation of Cu(II) EDTA and Fe(III) EDTA was also studied, and it was found that Cu(II) reaction is much slower compared with Fe(III) (Motekaitis et al 1980).…”

“…The thermal degradation of Cu(II) EDTA and Fe(III) EDTA was also studied, and it was found that Cu(II) reaction is much slower compared with Fe(III) (Motekaitis et al 1980). NTA did not form a bridge structure or undergo hydrolysis similar to EDTA, which, for these reasons, made NTA more thermally stable than EDTA (Venezky and Moniz 1970;Martell et al 1975). Thermal-degradation products of NTA (pH 9.3) caused by decarboxylation were determined (at 559 F after 4 hours of heating) to be N-methyliminodiacetic acid, methylsarcosine, and trimethylamine (Martell et al 1975).…”

“…NTA did not form a bridge structure or undergo hydrolysis similar to EDTA, which, for these reasons, made NTA more thermally stable than EDTA (Venezky and Moniz 1970;Martell et al 1975). Thermal-degradation products of NTA (pH 9.3) caused by decarboxylation were determined (at 559 F after 4 hours of heating) to be N-methyliminodiacetic acid, methylsarcosine, and trimethylamine (Martell et al 1975). Booy and Swaddle (1977) found that at 390 F and after 17 hours of heating, 0.15 M NTA decomposed to N-methyliminodiacetic acid, IDA, N,N-dimethyl glycine, Nmethyl glycine, and glycine.…”

“…For example, high-pH (8 to 10) solutions of EDTA are used as cleaning fluids in boilers (Motekiaitis et al 1982). Applications of HEDTA and GLDA have high interest because both are highly soluble in acids (Frenier et al 2000;LePage et al 2011;Mahmoud et al 2011). Field applications that use HEDTA chelate show good results (Frenier et al 2004).…”