High-Temperature Acidizing: Advantages of Inhibitor-Intensifier Synergy

Abstract

High-temperature acidizing operations are challenging because of the highly corrosive nature of acids. Hydrochloric (HCl) acid has an especially high reaction rate, which increases the rate of tubular corrosion. In addition to the type and concentration of acids, factors such as temperature and metallurgy influence the rate of corrosion. To meet increasing demand for deeper stimulation at high temperatures, emulsified acid is predominately used. It contains acid in the internal phase and oil in the external phase, forming an invert emulsion. The outer oil phase creates a barrier for acid, allowing its slow release for reaction with reservoir rock. Emulsified acid systems provide several advantages compared to plain acid. The oil barrier especially helps with preventing corrosion by significantly reducing the contact of acid with the metal tubular. High fluid viscosity helps reduce fluid loss, distributes the acid more uniformly in the formation, and reduces the rate of corrosion. Selection of the proper corrosion inhibitor(s) is one of the most important criteria for high-temperature acidizing. The use of intensifier(s) with the inhibitor enhances the corrosion inhibition significantly. This makes it possible to use a higher concentration of HCl acid at temperatures as high as 350°F, thus enhancing the fluid efficiency. In this work, several corrosion inhibitors and intensifiers are studied at varied acid strengths and temperature conditions. To achieve good corrosion control, a synergy is required between corrosion inhibitors and corrosion inhibitor intensifiers. At the same time, they should not negatively impact the emulsion stability. A new emulsified acid system was developed using HCl acid strength up to 28%. High corrosion control imparted by inhibitor-intensifier synergy coupled with the slow reaction rate of emulsified acid makes this blend unsurpassed for use in extreme high-temperature conditions up to 350°F. This emulsified acid system has the potential for use in the Khuff formation of Saudi Arabia with the addition of a H2S scavenger. Testing with a commercially available scavenger exhibited good compatibility with the blend.

Barium Sulfate Scale Removal at Low-Temperature

“…Tetrakis hydroxymethyl phosphonium salt (THPS) was studied to be added to the ethylenediaminetetraacetic acid (EDTA) to develop a chemical scale dissolver with a pH of 8 to enhance the alkalinity base for the solution [28]. Organic and inorganic acids are commonly utilized in the oil and gas field for scale removal purposes [34]. Commonly, a surfactant is added to the chemical solution to remove the hydrocarbon layer from the scale solids to increase the interaction between the scale body and the chemical solution to provide a higher dissolution rate.…”

Perspective Chapter: Downhole Corrosion in the Oilfield

“…The test methods follow the ASTM G31 standard for corrosion immersion tests. If the corrosion rate of the tested solution exceeds 0.05 lb/ft 2 for lowcarbon steel or 0.03 lb/ft 2 for corrosion-resistant alloys, it is too corrosive to be used [51,52]. However, this standard may be lowered in lieu of other factors such as the cost of the metal used or ease of replacement and material transportation [53,54].…”

Development of a Unique Organic Acid Solution for Removing Composite Field Scales

“…Calcium sulfate is a scale type that was found to have low solubility with high pH dissolvers . Also, dissolvers that have low pH will increase the tubular corrosion and therefore damage the facilities’ integrity. , Recent research studies − are directed to provide chemical dissolvers with high pH to sustain the well downhole and surface equipment, processing units, and facilities; also, this will save the corrosion inhibitor and intensifier cost that is commonly added to the treatment operations for low pH dissolvers. , Ahmed et al added tetrakis hydroxymethyl phosphonium salts (THPS) to ethylenediaminetetraacetic acid (EDTA) to formulate a slightly alkaline chemical solution with about pH value of 8. Another recent research was executed and provided a chemical dissolver with a 12.5 pH value for composite sulfate/sulfide scale removal at low temperatures, and the results showed scale solubility efficiencies of 91.8% at 45 °C and 79% at 35 °C …”