This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 172640, “Sodium Gluconate as a New Environmentally Friendly Iron- Controlling Agent for HP/HT Acidizing Treatments,” by Ahmed I. Rabie, SPE, and Hisham A. Nasr El-Din, SPE, Texas A&M University, prepared for the 2015 SPE Middle East Oil & Gas Show and Conference, Manama, Bahrain, 8–11 March. The paper has not been peer reviewed.

Iron precipitation is a serious problem in acidizing treatments, causing formation permeability damage by restricting flow channels. Solutions have included buffers, reducing agents, and chelating agents. Experience has shown that chelating agents are the most effective; however, limitations of current chelating agents include poor stability at elevated temperatures, higher cost, low solubility in acidic medium, tendency to precipitate calcium products, and negative health and environmental effects. This work introduces sodium gluconate as an efficient and environmentally friendly iron-chelating agent.

Introduction

Corrosion is a major challenge in any acidizing treatment. The scale of such a problem depends on the acid type; acid concentration; temperature; and the presence of corrosion inhibitor, intensifier, or undesirable corrosion accelerator. In cases where hydrochloric acid (HCl) is used, the effect of the corrosion is magnified and can hinder the success of the treatment, especially at elevated temperatures and higher acid concentrations. Acid corrosion not only destroys storage and mixing tanks, piping, fittings, coiled tubing, and wellbore tubing, but the corrosion products are also carried out with the acid flow and enter the formation. When the acid is in a live condition, these corrosion products are readily soluble. However, when the acid reacts with the formation and the pH increases, the corrosion products show a high tendency to precipitate and plug the pores.

Inhibitors are often used to mitigate the effects of corrosion, and special additives such as corrosion intensifiers are required to compensate for the degradation loss in the inhibitors at elevated temperatures, which results in a substantial increase the treatment cost. In addition, excessive corrosion inhibitors may enter the formation, become adsorbed on the reservoir rock, and subsequently change the wettability. Another limitation is the low health-and-environmental profile of most current corrosion inhibitors.

Several attempts, therefore, have aimed to maintain corrosion inhibitors and intensifiers at a minimum and effectively reduce the potential of iron precipitation by use of buffers, reducing agents, and chelating agents. Laboratory and field experiences concluded that chelating agents are the most effective remedy for controlling iron precipitation.

Gluconic acid and its sodium and calcium salts (Fig. 1) exhibit attractive physical and chemical properties and, hence, are used in several applications and industries. The acid and its salts are noncorrosive, nonvolatile, nontoxic, nonodorous, and readily biodegradable.

The US Food and Drug Administration has assigned sodium gluconate a status of “generally recognized as safe,” and its use in the food industry is permitted without limitation.

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