(126c) A New Acid System for Matrix Stimulation of Deep Oil and Gas Wells

Matrix acidizing is used in carbonate formations to create flow channels from the formation to the well bore, whereas in sandstone formations the goal is to dissolve materials that impair the well production. However, the use of acids in deep wells has some major drawbacks including high reaction rate and corrosion to well tubulars.

A new stimulation fluid was developed 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 chelate-based fluid effectively dissolves CaCO3 and it is less corrosive to the equipment.

This paper discusses the reaction of the new GLDA chelate with calcite and will compare its performance with other available chelates, including EDTA, HEDTA, NTA and 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 2 where HEDTA solubility is limited to ~ 10 wt%. A mole of GLDA acid with a natural ~ pH 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 HCl, GLDA is as effective as HEDTA in preventing precipitation of moderate levels of Fe in spent acids. At high Fe concentration GLDA is slightly less effective than HEDTA on a molar basis – but to deal with high Fe GLDA may be better as 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. As a replacement for HCl acid, GLDA is significantly safer and is less corrosive.   GLDA was successfully applied to stimulate a deep gas well, and the results were above expevtations.