###### Abstract  
In this paper, Chelating agents were introduced as standalone fluids for enhancing the oil recovery from carbonate and sandstone reservoirs. Chelating agents such as glutamic acid di-acetic acid (GLDA), ethylene-diamine-tetra acetic acid (EDTA), and hydroxyl-ethylethyl-diamine-tri-acetic acid (HEDTA) were used. Chelating agents can be found in different forms such as sodium, potassium, or calcium salts. There is a significant gap in the literature about the influence of salt type on the hydrocarbon recovery from carbonate and sandstone reservoirs. In this study, the impact of the salt type of GLDA chelating agent on the oil recovery was investigated. Potassium-, sodium-, and calcium-based high-pH GLDA solutions were used. Coreflooding experiments were conducted at high-pressure high-temperature (HPHT) conditions using carbonate and sandstone cores. The used samples had porosity values of 15-18%, and permeability values were between 10 and 75 mD. Seawater was injected as a secondary recovery process. Thereafter, a GLDA solution was injected in tertiary mode, until no more oil was recovered. In addition to the recovery experiments, the collected effluent was analyzed for cations concentrations such as calcium, magnesium, and iron. Moreover, dynamic adsorption, interfacial tension, and contact angle measurements were conducted for the different forms of GLDA chelating agent solutions. The results of this study showed that incremental oil recovery between 19% and 32% of the Original Oil in Place (OOIP) can be achieved, based on the salt type and the rock lithology. Flooding carbonate rocks with the calcium-based GLDA chelating agent yielded the highest oil recovery (32% of OOIP), followed by that with potassium-based GLDA chelating agent, and the sodium-based GLDA chelating agent yielded the lowest oil recovery. The reason behind that was the adsorption of the calcium-based GLDA on the rock surface was the highest without reducing the rock permeability, which was indicated by the contact angle, dynamic adsorption, and flooding experiments. The outcome of this study will help in maximizing the oil recovery from carbonate and sandstone reservoirs by suggesting the most suitable salt type of chelating agents. enhanced oil recovery; GLDA chelating agent; salt type; carbonate and sandstone reservoirs +
Footnote †: journal: Applied Sciences  
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or altering the rock wettability [10; 11; 12; 13; 14]. Glutamic acid di-acetic acid (GLDA), hydroxyl-ethylethylene-diamine-tri-acetic acid (HEDTA), and ethylene-diamine-tetra acetic acid (EDTA) are used for EOR treatments [15; 16; 17; 18; 19]. [PERSON] and [PERSON] [10] studied the oil recovery from carbonate and sandstone reservoirs during HEDTA, DTPA, and EDTA. The efficacy of chelating solutions was assessed using interfacial tension, coreflood, and zeta-potential measurements. They concluded that an injection of a 5 wt % chelating agent can enhance the oil recovery by around 20% for carbonate and sandstone rocks. In addition, they reported that no formation damage was induced during the chelating agent flooding. Instead, rock dissolution took place in the carbonate samples due to the chemical reaction between the carbonate matrix and injected fluids. Analyzing the produced effluent from coreflooding experiments using inductively coupled plasma (ICP) analysis showed high concentrations of calcium, iron, and magnesium ions. [PERSON] and [PERSON] [11; 12] studied the efficiency of EDTA, a chelating agent for enhancing the hydrocarbon recovery from carbonate reservoirs. An optimization study was conducted to estimate the best fluid volume and concentration that can minimize the treatment cost and increase the oil production. They concluded that injecting 3 wt % of an EDTA solution can increase the recovery by around 20% with a minimum operational cost. [PERSON] et al. [20] examined the efficacy of several chelating agents' solutions for changing the wettability conditions.