An Environmentally Friendly Stimulation Fluid for High-Temperature Applications

Summary Matrix acidizing is used in carbonate formations to create flow channels from the formation to the wellbore; in sandstone formations, however, the goal is to dissolve materials that impair well performance. However, the use of acids in deep wells has some major drawbacks, including high reaction rate and corrosion to well tubulars. We have discovered a new stimulation chemical that can be used as a replacement for or in combination with acid treatments in deep wells. A polyacid whose structure allows for acidification is described. The polyacidic chelate L-glutamic acid, N, N-diacetic acid (GLDA) is manufactured from L-glutamic acid (MSG). The chelate-based fluid very effectively dissolves CaCO3, and it is less corrosive to the equipment and easy to handle. This paper discusses the reaction of the new chelate, GLDA, with calcite and compares its performance with other available chelates, including ethylenediaminetetraacetic acid (EDTA), hydroxy-ethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), and ethanoldiglycine (EDG). GLDA dissolves calcite over a wide pH interval, although it is less effective than HEDTA at pH > 5. A unique property of GLDA is its high solubility; solutions exceeding 40 wt% can be achieved at a pH of approximately 2, whereas HEDTA solubility is limited to approximately 10 wt%. A mole of GLDA with a natural pH of approximately 1.5 is capable of dissolving up to two moles of CaCO3. Throughout the pH range, GLDA appears to be as thermally stable as HEDTA. As an additive to hydrochloric acid (HCl), GLDA is as effective as HEDTA in preventing precipitation of moderate levels of Fe3+ in spent acids. At high Fe3+ concentrations, GLDA is slightly less effective than HEDTA on a molar basis; but, to deal with high Fe3+ levels, GLDA may be better because significantly higher concentrations of it are possible in various acids. In 28 wt% HCl, HEDTA has limited solubility while GLDA's solubility exceeds 40 wt%. From an environmental standpoint, GLDA is readily biodegradable and is made from a renewable raw material, monosodium glutamate. GLDA has low toxicity and aquatic toxicity characteristics. As a replacement for HCl, GLDA is significantly safer and less corrosive.