SummaryBackground Sodium iron edetic acid (NaFeEDTA) might be a more bioavailable source of iron than electrolytic iron, when added to maize fl our. We aimed to assess the eff ect, on children's iron status, of consumption of whole maize fl our fortifi ed with iron as NaFeEDTA or electrolytic iron.

Summary Illitic sandstone reservoirs are sensitive to hydrochloric-acid (HCl) -based fluids. When HCl contacts illite, it breaks down and causes fines migration and formation damage. The migration of fines through the porous media will block the pores, reduce permeability, and decrease the production rate of oil and gas wells. A thorough literature review showed that all clay minerals are essentially unstable in HCl at temperatures greater than 300°F. In turn, there is a need to search for stimulation fluids other than HCl to stimulate deep sandstone reservoirs. Alternative fluids to HCl/hydrofluoric (HF) mud acids were introduced to stimulate and remove the damage from illitic sandstone reservoirs. These fluids are chelating agents such as hydroxyl ethylene diaminetriacetic acid (HEDTA) and glutamic acid-N,N-diacetic acid (GLDA). In this study, sandstone cores with different illite contents were examined. Illite contents of 1, 10, 14, and 18 wt% of the sandstone cores were used in the coreflood experiments at 300°F. Different combinations of GLDA/HF were tested to determine the optimum ratio of chelate/HF. Computed tomography scans and permeability measurements before and after the treatment were used to assess the effectiveness of each fluid in removing the damage and in the stimulation of the sandstone cores. The results show that 15 wt% HCl caused severe damage to sandstone cores with different illite contents. GLDA and HEDTA solutions showed a good compatibility with the illitic sandstone cores, with up to 18 wt% at 300°F. Permeability measurements showed that GLDA performed better than HEDTA at a pH of 4 and at the same molar concentration. The optimum ratio of GLDA/HF concentration was found to be 20 wt% GLDA/1 wt% HF, which gives the maximum increase in core permeability. No deconsolidation was noted with the two chelates tested. The results obtained from this study will significantly improve the outcome of acid treatments in illitic sandstone reservoirs at high temperatures.

For many decades, chelating agents have been used successfully as an additive in the oil and gas industry, for example during scale removal, iron control and matrix stimulation. More recently, these chemicals have also been used as standalone fluids for the same applications. However, the traditional chelating agents like ethylene diamine tetraacetic acid (EDTA), hydroxyethyl ethylene diamine triacetic acid (HEDTA) and nitrilo triacetic acid (NTA) suffer from slow biodegradability and/or an unfavorable health profile. To better meet the stricter health, safety and environmental requirements of the regulatory bodies and the industry, new environmentally friendly chelating agents have been introduced. The question is whether these new chelating agents have the required properties for a versatile downhole application. This paper compares four commercially available, readily biodegradable amino polycarboxylic acid type chelating agents, including glutamic acid N,N-diacetic acid (GLDA), aspartic acid N,N-diacetic acid (ASDA), methyl glycine diacetic acid (MGDA) and ethanoldiglycine (EDG) on a number of properties relevant for the oil and gas industry. It covers the solubility as a function of pH and in various acids, thermal stability, iron control, corrosion tests with low-carbon steel and Cr-based alloys and coreflood experiments on both carbonate and sandstone cores. The corrosion and coreflood experiments were conducted under realistic temperature and pressure conditions. Although the structural resemblance of the tested chelates is great, the results proof that even the slightest change in the chemical structure can have a significant impact on the properties and hence the use in the oil and gas industry. Furthermore, the results show that the new generation of chelating agents include candidates that have a lot more to offer than the traditional chelates in terms of corrosion, functionality in matrix acidizing jobs, descaling, impact on tubular, completion and environment. Our studies show that GLDA is the most versatile environmentally friendly chelating agent.

Summary Acid treatments of deep wells completed by use of chromium (Cr) -based tubulars represent a real challenge to the oil industry. On one hand, Cr-based tubulars are used to protect against carbon dioxide (CO2) corrosion, but on the other hand, the protective layer [chromium(III) oxide (Cr2O3)] dissolves in hydrochloric acid (HCl). This makes protection of Cr tubulars during acidizing very challenging, especially at high temperatures. At temperatures greater than 200°F, there is a need to add corrosion-inhibitor intensifiers, most of which depend on heavy metals [copper (Cu) or antimony (Sb)] or are not effective at temperatures greater than 300°F [e.g., potassium iodide (KI)]. Over the last decade, a new chelant was developed, glutamic acid N, N-diacetic acid (GLDA), which can dissolve carbonate minerals from both carbonate and sandstone formations. This chelant can form wormholes in carbonates (both calcite and dolomite) and does not destabilize clay particles present in sandstone formations. In the present paper, the corrosion rate of GLDA solutions is compared with that of other chelants and simple organic acids that are used for carbonate dissolution, such as hydroxyethylethylenediaminetriacetic acid (HEDTA), acetic acid, and formic acid. All corrosion tests were conducted at high temperatures and pressures and extended for up to 6 hours at temperature and pressure. The Cr and nickel (Ni) -based coupons representing tubular metallurgy were examined thoroughly after the tests, and the spent fluids were analyzed for key cations [Cr, Ni, molybdenum (Mo), iron (Fe), and manganese (Mn)]. Compared with formic acid, acetic acid, and even HEDTA, GLDA is much less corrosive to Cr-13 alloys. The results of this work show that GLDA at 20 wt% causes almost no corrosion with Cr-13 up to 300°F. Unlike GLDA, HEDTA was found to be corrosive at a pH = 3.8, and requires attention when used in wells completed with Cr-13-based tubulars. On more-corrosion-resistant Cr- or Cr-Ni-based alloys, such as super Cr-13, Duplex-2205, Inconel-625, and Incoloy-925, the corrosion rate of GLDA is still far below the acceptable limit of 0.02 to 0.05 lbm/ft2 up to 350°F. In wells with corrosive sweet and sour gases, tubulars consisting of low-carbon steel, Cr-based steel, or corrosion-resistant Cr-Ni alloys can be effectively protected by a combination of GLDA with a minimal amount of a suitable corrosion inhibitor. Because of its favorable environmental profile, this mixture meets all the Oslo-Paris Convention for the Protection of the Marine Environment of the Northeast Atlantic (OSPAR) requirements for use in the North Sea. On the basis of these results, GLDA solutions can be used to stimulate carbonate and sandstone wells completed with Cr- and Ni-based tubulars, while maintaining the integrity of the tubulars.

Different chelating agents were used as alternatives for HCl in matrix acidizing to remove near wellbore damage and create wormholes in carbonate formations. Previous studies have demonstrated the use of ethylenediaminetetraacetic acid (EDTA), hydroxy ethylenediaminetetraacetic (HEDTA) and glutamic acid-N,N-diacetic acid (GLDA) as an alternative for HCl to stimulate carbonate reservoirs. The main problem with EDTA and HEDTA is the low biodegradability.GLDA was introduced as alternative for HCl for stimulating deep carbonate reservoirs at which HCl will cause corrosion and face dissolution problems. In this study calcite cores, 1.5 in. diameter with 6 and 20 in. length were used to determine the optimum conditions where the GLDA can breakthrough the core and form wormholes. GLDA solutions with pH values of 1.7, 3, and 3.8 were used. The optimum conditions of flow rate and pH were determined using the coreflood experiments. CT scan was used to determine the wormholes length and diameter to determine of optimum Damköhler number. GLDA was compared with chelates that are used in the oil industry such as EDTA and HEDTA. GLDA also was used to stimulate parallel cores with different permeability ratios (up to 6.25) to assess its ability on diversion.GLDA was found to be very effective in creating wormholes at pH = 1.7, 3, and 3.8 at different injection rates at temperatures of 180, 250, and 300 o F. Increasing the temperature increased the reaction rate and less amount of GLDA was required to breakthrough the core and form wormholes. Unlike HCl and EDTA, there was no face dissolution or washout in the cores even at very low rates. Also, an optimum flow rate and Damköhler number were found at which the pore volume required to create wormholes was the minimal. GLDA at pH 1.7 and 3 created wormholes with a small number of pore volumes. Compared with acetic acid the volume of GLDA at pH 3 required to create wormholes was less than that required with acetic acid at the same conditions. GLDA was found to be effective in stimulating parallel cores with different permeabilities.