Organic Acids for Stimulation Purposes: A Review

Abstract

Summary Hydrochloric acid (HCl) is the acid of choice for acidizing operations in most carbonate formations, and is the base acid that is commonly paired with hydrofluoric acid (HF) in most sandstone applications. However, high dissolving power, high corrosion rate, lack of penetration, and sludging tendency coupled with high temperature (HT) can make HCl a poor choice. Alternatively, weaker and less-corrosive chemicals, such as organic acids, can be used instead of HCl to avoid these issues. The objective of this paper is to provide an intensive review on recent advancements, technology, and problems associated with organic acids. The paper focuses on formic, acetic, citric, and lactic acids. This review includes various laboratory evaluation tests and field cases that outline the use of organic acids for formation-damage removal and dissolution. Rotating-disk-apparatus (RDA) results were reviewed to determine the kinetics for acid dissolution of different minerals. Additional results were collected from solubility, corrosion, coreflooding, inductively coupled plasma, X-ray diffraction, and scanning-electron-microscope (SEM) diffraction tests. Because of their retardation performance, organic acids have been used along with mineral acids, mainly a formic/HCl mixture, or as a standalone solution for HT applications. However, the main drawback of these acids is the solubility of reaction-product salts. This challenge has been a limiting factor of using citric acid with calcium-rich formations because of the low solubility of calcium citrate. However, the solubility of the salts associated with formic, acetic, and lactic acid can be increased when these acids are mixed with gluconic acid because of the ability of gluconate ion to chelate calcium-based precipitation. In terms of formation-failure response, organic acids are in lower risk of causing a failure compared with HCl, specifically at deep formation treatments. Organic acids have also been used in other applications. For instance, formic acid is used in HT operations as an intensifier to reduce the corrosion rate caused by HCl. Formic, acetic, and lactic acids can be used to dissolve drilling-mud filter cakes. Citric acid is commonly used as an iron-sequestering agent. This paper shows organic acid advances, limitations, and applications in oil and gas operations, specifically in acidizing jobs. The paper differentiates and closes the gap between various organic acid applications along with providing researchers an intensive guide for present and future research.

Combination of Mollase and Glucose as Substrate for The Production of Biosurfactant by Bacillus subtilis BK7.1

“…The decrease in surfactin micelle micropolarity could be caused by an increase in pH due to the dissolution of a large number of fluorescence probe molecules into the surfactin micelle core. Additionally, Ca 2+ binding to the head group region of surfactin micelles causes an increase in micropolarity, thereby inhibiting the solubilization of the fluorescence probe into the micelle core [23].…”

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“…Biosurfactants produced by Bacillus to be more susceptible to changes in temperature affect the interactions between surfactin molecules, causing the formation of intra-hydrogen bonds within the surfactin molecules and inter-hydrogen bonds between them. One type of biosurfactant produced by these bacteria, surfactin, tends to form a flat structure and horse saddle conformation when temperature increases [23].…”

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“…It mainly involves injecting an acid solution into the formation, reacting with minerals in the formation, dissolving formation rocks, and forming long-distance acid corrosion fractures to increase oil and gas well production [4]. However, with the increasing temperature of the reservoir, conventional acidizing and stimulation fluids based on hydrochloric acid have problems such as fast reaction speed, high corrosion rate, and high environmental pollution, which cannot adapt to the acidizing and fracturing transformation of high-temperature carbonate reservoirs [5].…”

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