EDTA chelating agent/seawater solution as enhanced oil recovery fluid for sandstone reservoirs

Abstract

Experimental investigations and field applications showed noticeable increase in the oil recovery when low salinity water flooding is used. The mechanisms leading to the increase in oil recovery by low salinity water injection are debatable. Furthermore, low salinity water injection requires relatively huge amount of fresh water to dilute seawater which is not available in many areas around the world especially in the Arabian Gulf region. Using low salinity water as an enhanced oil recovery fluid is a costly process because it requires a lot of fresh water to dilute the seawater.In this paper we introduced EDTA (Ethylene Diamine Tetra Aceticacid)/seawater system for enhanced oil recovery in sandstone reservoirs. This fluid can be used in the secondary or tertiary flooding modes. EDTA/seawater enhanced oil recovery fluid utilizes high pH chelating agents at low concentrations prepared in seawater. Coreflooding experiments were performed using Berea sandstone cores at 100°C to investigate the effectiveness of EDTA/seawater EOR fluid system. In addition, Zeta potential measurements were performed for the EDTA/seawater and crushed Berea sandstone cores to examine the effect of EDTA/seawater on the rock surface charge. Also the effects of the chelating agent on the surface and interfacial tension (IFT) and oil recovery were evaluated. The effect of iron content on the sandstone rock charge was investigated using high iron content sandstone (Scioto sandstone). The effects of EDTA concentration and pH on oil recovery were also investigated. Also the effects of EDTA salt and chelating agent type on the oil recovery were investigated.The results of the coreflooding experiments showed that the EDTA/seawater fluid system was able to recover additional oil recovery up to 30% from the initial oil in place after seawater flooding when injected in the tertiary mode. The results of zeta potential revealed more negative values for the EDTA/seawater system more than the seawater and low salinity water, confirming that the rock wettability was altered towards a more water-wet condition due to the high negativity of the rock surface. The EDTA/seawater yielded low interfacial tension values with the crude oil used in the flooding experiments. Inductively coupled plasma (ICP) analysis for the coreflooding effluent samples showed increase in various cations concentration. The increase in cations concentrations confirmed the rock dissolution during the flooding process. EDTA chelating agent eliminated the iron effect on the surface charge in high iron content Scioto sandstone. Coreflooding experiments showed that EDTA should be used at concentrations higher than 5wt% to yield high oil recovery. Also EDTA should be used at pH higher than 12 to obtain high oil recovery. Sodium salt EDTA performed better than the ammonium salt EDTA in the oil recovery experiments. EDTA chelating agent was better than the HEDTA chelating agent in terms of oil recovery.Based on the experimental results, the possible recovery mechanisms when using EDTA/seawater system at pH 12.2 could be: IFT reduction, rock dissolution, and wettability alteration.