Oil Recovery Mechanisms During Sequential Injection of Chelating Agent Solutions Into Carbonate Rocks

Abstract

Chelating agent solutions have been proposed as effective fluids for enhancing oil production. Different recovery mechanisms are reported for increasing the oil recovery during chelating agent flooding. The aims of this work are to identify the possible recovery mechanisms during chelating agent flooding in carbonate reservoirs and to investigate the in situ CO2 generation as a potential recovery mechanism during the injection of chelating agent solutions into carbonate reservoirs. The contribution of CO2 on enhancing the oil recovery was determined using experimental measurements and analytical calculations. Several measurements were conducted to study the contribution of each mechanism on enhancing the oil recovery. Coreflooding tests, zeta potential measurements, CO2 generation, and interfacial tension (IFT) experiments were carried out. Also, analytical models were utilized to determine the impact of the injected chemicals on reducing the capillary pressure and improving the flow conditions. In flooding tests, two chemicals (EDTA and GLDA) were injected in a sequential mode and the chemical concentration was increased gradually. In addition, a comparative study was performed to evaluate the effectiveness of EDTA and GLDA solutions to enhance oil recovery. Several parameters were investigated in this paper including incremental oil recovery, in situ CO2 generation, hydrocarbon swelling, IFT, wettability alteration, permeability enhancement, productivity index, and chemical cost. The obtained results show that GLDA chelating agent has better performance than EDTA solutions for enhancing the oil recovery when the same concentrations are used. Also, the in situ generation of CO2 shows a significant impact on improving the oil recovery from carbonate reservoirs during chelating agent flooding. In the literature, the reported recovery mechanisms of using chelating agents are the IFT reduction, wettability alteration, and rock dissolution. Based on this work, injecting chelating agent solutions at low pH can lead to involve additional recovery mechanisms due to the CO2 generation, the additional mechanisms are hydrocarbon swelling, viscosity and density reduction, and oil vaporization.

Applications of Chelating Agents in the Upstream Oil and Gas Industry: A Review

“…Injection of the chelating agent led to a considerable decrease in the capillary forces compared to seawater flooding . The reduction in capillary forces was attributed to the low IFT values and the wettability alterations during chelating agent flooding.…”

“…Chelating agents were injected into the reservoir to adjust the wettability conditions. , The reaction between chelating agents and carbonate rocks was represented by eqs –. , H n Y represents the typical structure of the chelating agents. In aqueous solutions, chelating agents reach to the ionized form (Y n – ) by losing protons (H + ) stepwise, as represented by eq .…”

“…Also, the proton ions (H + ), generated as a result of the chelating agent dissociation, could react with the calcite surface and improve the leaching of Ca 2+ from the rock surface. Therefore, the injection of chelating agent solutions into carbonate reservoirs would change the rock wettability as a result of the leaching of calcium ions from the rock surface The alteration of carbonate wettability to more water-wet conditions would result in improving the oil recovery.…”

“…Hassan and Al-Hashim studied the interactions between EDTA and carbonate rocks. Several measurements were conducted, including coreflooding, spontaneous imbibition, ζ potential, NMR, and ion concentration measurements.…”

Novel Solution for Improving the Hydrocarbon Production Utilizing Chemical Injection

“…The main disadvantages of this technology are the availability of natural CO 2 sources, corrosion of wells and field surface facilities environmental and safety problems. In-situ generation of CO 2 at the wellbore condition can be an effective technique that can eliminate the negative impacts of CO 2 injection [5]. This paper presents new techniques of in-situ generation of active agents at downhole condition using environmentally friendly chemicals.…”