Innovative Method to Mix Corrosion Inhibitor in Emulsified Acids
Authors: Al-Zahrani Ali A. 
Published: May 2016

Acid in oil emulsions stimulate carbonate formation of limestone and dolomite. These emulsions consist of internal inhibited acid phase and an external hydrocarbon phase mixed with an emulsifier. In this current technology, the corrosion inhibitor is dissolved in the acid phase and encapsulated by hydrocarbon in the outer phase. The facts that the corrosion inhibitor is inside the emulsion will retard it from dispersing on metal surface of the tubing to create a metal protective film.

In this paper, a method is proposed where the corrosion inhibitor is replaced from being in the internal phase to be in the external phase of the emulsion. This situation will allow the corrosion inhibitor to directly disperse onto the tubing metal surfaces to form the protective film required to prevent the tubing from any acid attack. Acid in oil emulsion with corrosion inhibitor being in the external phase of emulsion was successfully created in the lab and resulted in a much better thermal stability at room and reservoir conditions.

In this lab study, thermal stability of emulsion with corrosion inhibitor in the external phase resulted in more stable emulsion than those with corrosion inhibitor in the internal phase. At reservoir temperature of 248oF emulsions with corrosion inhibitor in the external phase acid start to separate after 60 minutes and at 150 minutes was completely separated. Emulsions at same conditions with corrosion inhibitor in the internal phase acid start to separate after 30 minutes and at 110 minutes were completely separated from hydrocarbon phase. When corrosion inhibitor removed completely from the emulsion, it start to separate at 140 minutes and at 180 minutes separation was only 20%.

Corrosion inhibitor being in the external phase will enhance emulsions retardation and hence deeper penetration in the reservoir. In addition this new method will protect the well tubing and stimulation equipment much better than before.

Introduction

This paper provides a method of enhancing the corrosion inhibition of well tubing while using an acid-in-oil emulsion downhole in a hydrocarbon recovery or delivery system. In addition, this paper provides a method for acid stimulation of a carbonate formation while simultaneously protecting the well tubing more efficiently.

Acid-in-oil emulsions are typically used to stimulate or enhance hydrocarbon production in existing carbonate reservoir rock formations, such as limestone, dolomite or calcareous-magnesium. Typically, the emulsified acid enters the formation and where employed successfully creates a barrier causing the acid to release slowly at a distance from the wellbore. The reaction of the released acid with the formation rock takes place simultaneously at different places inside the formation, resulting in channels that are joined together to form continuous wormholes. When pumping the acid-in-oil emulsions through steel tubing and piping, a corrosion inhibitor is usually added to reduce the corrosive effects of the acid. In operation, the corrosion inhibitor coats the steel surfaces as the emulsion is pumped into the wellbore and the surrounding rock.