In carbonate reservoirs, hydrochloric acid (HCl) is commonly used for stimulation purposes. The main disadvantage for using HCl is its high and rapid reactivity allowing for less control on acid reaction with formation. In addition, HCl may react with the tubing causing severe corrosion and damages. Several slow-reacting acid systems, though HCl-based, have been developed to retard the HCl reaction and control its reactivity. Therefore, the emulsified acid can flow deeper inside the formation before it breaks out and reacts with formation rock. However, the selection of the hydrocarbon phase of emulsified acid is critical to the creation and stability of the emulsified acid system. Diesel oil, crude oil and solvents such as xylene have been reported to be successful in the field.
In this work, alternative and less expensive source of oil is utilized to replace the current practices, known as waste oil. Filtered waste oil is used to prepare the emulsified acid of this work. Extensive work has been carried out to study the chemical composition of the waste oil, namely Gas Chromatography (GC) to select the proper emulsifier. Emulsions are prepared using 15% HCl with emulsifier concentration ranging from 0.5 to 2.0 vol% and 70:30 of acid-to-oil ratio. Later, rheological analyses of the waste oil emulsion are compared to the commonly used diesel-based emulsified acid. Results showed the potential use of waste oil to prepare high temperature emulsified acid. The addition of cationic emulsifier helps to formulate a more stable emulsion. Apart from that, the optimum concentration of the emulsifier was at 1 vol%. The rheological data confirms the stability of the new emulsified formulation at higher temperatures. Moreover, to apprehend the behavior of this emulsion, droplet size distribution is addressed. This paper summarizes the findings of using waste oil emulsion and recommends it for field applications.
The novelty of this work is the viscoelastic properties for waste oil emulsion have never been addressed before. Addressing them, will help to comprehensively apprehend this novel emulsified acid.