Sodium Gluconate as a New Environmentally Friendly Iron Controlling Agent for HP/HT Acidizing Treatments

Abstract

Iron precipitation is a serious problem in acidizing treatments which can damage the formation permeability by restricting the flow channels. Solutions introduced in the past included the use of buffers, reducing agents, and chelating agents. Laboratory and field experiences concluded that chelating agents are the most effective remedy for controlling the iron precipitation. However, substantial limitations hinder the effectiveness and the application of several of the current chelating agents in the industry. These limitations include poor thermal stability at elevated temperatures, higher cost, low solubility in acidic medium, tendency of precipitating calcium products, and serious negative health and environmental impacts.This work introduces sodium gluconate as an efficient and environmentally friendly iron chelating agent. The chemical exhibits an excellent sequestering property for iron over a wide range of pH values, with a chelation power comparatively closer to those reported for EDTA and NTA. The salt is readily dissolved in the acids with a solubility of 600 gm/l.The objectives of this study are to: (1) investigate the ability of sodium gluconate to prevent iron precipitation at different iron loading, (2) examine the efficiency of the new chelant in hydrochloric acid solutions (5, 10, and 15 wt%) at a temperature of 200 and 250°F and chelant to iron molar ratios of 1:1, 2:1, and 4:1, and (3) determine the optimum chelant to iron molar ratio that results in the highest chelation capacity. The effectiveness of the new chemical was examined by determining the percentage increase/ reduction in core permeability.In stirred reactor experiments, iron precipitation was observed at a pH above 2 with the absence of the chelant at iron loading at 5,000 and 10,000 ppm at 77°F. The presence of Na gluconate at an equimolar ratio of the iron loading prevent the precipitation over the investigated range of iron load and temperature.Coreflood results showed that at low injection rates of 0.5 cc/min, 200°F, and 5 wt% HCl with 10,000 ppm Fe 3ϩ the core was damaged and the acid was not able to enter the core due to iron precipitation on the core inlet. At a higher injection rate (2 cc/min) the presence of 5 wt% Na-gluconate enhanced the permeability by 74% (versus 50% when no chelant was added) after injecting 0.75 PV of the acid with a load of 5,000 ppm Fe 3ϩ . At a load of 10,000 ppm of iron (III), the permeability increased to 165% compared to 70% for a controlled experiment. The results of another set of experiments at 250°F and 15 wt% HCl with a load of 10,000 ppm indicated that a 1:1 molar ratio of chelant to iron concentration is the optimum for the maximum chelation capacity compared to the results obtained for other experiments in which the molar ratio of sodium gluconate to iron was 2:1 and 4:1. These results were confirmed by fluid analysis, which showed a significant increase in both ion concentrations at this molar ratio in the effluent samples.

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“…Gluconic acid derivatives such as D-glucono-δ-lactone are important as leavening agents for preleavened products, for reducing fat absorption in doughnuts, for the coagulation of soybean proteins in tofu manufacture, and for improving the heat stability of milk [ 118 , 119 ]. Gluconic acid salts (sodium gluconate, calcium gluconate, ferric gluconate) have a broadened industrial potential from metallurgy where they can act as alkaline derusting agents and anticorrosive agents to use as additives to cement [ 120 , 121 ]. Calcium and iron salts of gluconic acid have important biomedical potential, being used for calcium therapy for osteoarthritis [ 122 ] and the treatment of anaemia [ 123 ], and they also can be used in animal feed [ 124 ] or in agriculture as foliar feed formulations [ 118 ].…”

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