Abstract

Enhanced oil recovery (EOR) techniques are very expensive processes especially in harsh reservoir environment such as high temperature, pressure and salinity as the applications of classical EOR techniques have been limited to certain reservoirs. This work is aimed to design a cost effective EOR technique utilizing Ethylenediaminetetraacetic acid (EDTA) chelating agent solutions prepared using undiluted seawater (57k ppm).

Chelating agents have been used in petroleum industry as matrix stimulation fluids because of their ability to dissolve calcite and chelate the interlayer cations of clay minerals especially (Fe+3 and Ca+2) and keep them in solution without any significant precipitation. Recently, coreflood tests of sandstone core samples using EDTA solutions revealed significant increase in oil recovery during the tertiary mode. This paper presents a new approach to optimize oil production and minimize the injection pressure needed to flood sandstone reservoirs by injecting chelating agent solutions prepared in seawater without dilution with moderate to high pH levels and optimized concentrations in a sequential form after conventional waterflooding starting with small concentration followed by higher concentrations. The main objective of this approach is to optimize the concentrations and pH of the EDTA chelating agent solutions prepared in undiluted seawater for better oil recovery and improved injectivity using sandstone core samples. Coreflood tests at 100°C were conducted using Gray Berea sandstone core samples.

Coreflood results showed incremental oil recovery of about 15% of OOIP when the samples were flooded by the 5wt% chelating agent solution. The pressure drop during the flooding sequence confirmed that there was no damage due to clays detachment and migration or calcite dissolution at the experiments conditions of pH higher than 9.75 and EDTA concentration of 5wt% or less in undiluted seawater for Gray Berea sandstone samples.

A cost effective EOR fluid system having optimum chelating agent concentrations and pH have been designed to function as surface chemistry agents for alteration of sandstone rock wettability to a more water-wet conditions, and hence, can be used as EOR fluids.

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