Abstract

Alkaline-Surfactant-Polymer (ASP) flooding has shown incredible successes for enhancing oil recovery for both sandstone and carbonate reservoirs. However, the main constraint of ASP flooding in carbonate reservoirs is the presence of undesired minerals either within the reservoir rock or reservoir brine. These minerals could react with the added chemicals to form their insoluble salts as precipitations. In this paper, the performance of the acrylic acid was evaluated in the presence of sodium metaborate as an alkaline, alpha olefin sulfonate as a surfactant and AN-125 SH as a polymer. The effect of various acrylic acid concentrations on alkalinity, interfacial tension reduction and polymer viscosity were investigated using hard brine with a total salinity of 59,940 ppm. Fluid-fluid compatibility test indicates that acrylic acid has the potential to prevent any precipitation when hard brine is used. The acrylic acid to alkali ratio of 0.6:1 was found to be the optimum ratio for keeping the solution without precipitations for 30 days at 80oC. It was also observed that the combination of ASP with acrylic acid has a positive effect on interfacial tension and solution viscosity. This makes the new system more flexible for offshore application in which hard brine or sea water could be used to prepare ASP slug without any negative effects.

Highlights

  • Alkali-surfactant-polymer (ASP) flooding has been proven as the most effective and easiest method in sandstone reservoirs [1,2]

  • The sodium metaborate employed in this study was incompatible with the synthetic hard brine

  • Sodium metaborate showed some resistance against water hardness at the ambient temperature, precipitations were formed immediately at 80°C

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Summary

Introduction

Alkali-surfactant-polymer (ASP) flooding has been proven as the most effective and easiest method in sandstone reservoirs [1,2]. These rocks exhibit immense variation in properties that include porosity, permeability, and flow mechanism. These rocks can be naturally fractured and preferentially oil-wet [4,5]. Carbonate formations contain large amounts of calcium and magnesium ions in the form of calcite (CaCO3) and dolomite These rocks have small quantities of calcium sulphate minerals that are anhydrite and gypsum [4,6]. Alkali reacts with divalent cationic minerals, resulting in an insoluble salts known as precipitations. These precipitates can cause significant formation damage and pore plugging in the reservoir formation [6]

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