Surface-Modified Nanoparticle Gelled-Acid System Stimulates Without Formation Damage

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 22443, “Surface-Modified Nanoparticle-Based Novel Gelled-Acid System: A Unique Formation-Damage-Free Well-Stimulation Technology,” by Rajendra Kalgaonkar, SPE, and Nour Baqader, SPE, Saudi Aramco. The paper has not been peer reviewed. Copyright 2022 International Petroleum Technology Conference. Reproduced by permission. Gelled-acid systems based on the gelation of hydrochloric acid (HCl) are used extensively in both matrix and fracture acidizing to prevent acidizing-fluid leakoff. However, these systems can lead to formation damage. To mitigate this risk, the authors have developed a self-breaking, formation-damage-free, novel nanoparticle-based gelled-acid system to replace polymer-based gelled-acid systems. Nanoparticle-Based Gelled-Acid System The complete paper showcases a method for gelling up an acid formulation for stimulating a carbonate reservoir. The technique is based on surface-modified nanoparticles. The new gelled-acid system does not contain any polymer-based gelling agents. It consists of inorganic nanoparticles with a gelation-activator material to activate viscosification. The increase in viscosity will lead to a slowdown of the reaction rate of the acid with the carbonate formation. Suitable functionalities are used to surface-modify the nanoparticles to stabilize them in acidic media. The treatment fluid can be pumped downhole as a single homogeneous fluid system in the same pumping stage. The nanoparticles are easily miscible with the acid formulation without any need for the batch-mixing processes that may be required for a polymer-based gelled-acid system to account for polymer hydration. Thus, this formulation can be mixed easily while pumping the acidic fluid downhole. This ensures that the new gelled-acid system can increase operational efficiency by reducing operational time substantially. Nanoparticle gelation takes place in situ in the acid fluid and does not require a separate pumping stage to introduce the activator. The gelation of nanoparticles is predominantly a pH-based phenomenon. The gelation rate can be influenced also by temperature. As the fluid’s temperature increases, the treatment fluid viscosifies, thus diverting the tail-end acid to less-permeable zones in the reservoir. As the acid spends after reacting with the carbonate formation and the pH of the system increases beyond a pH of 4, the nanoparticles lose their ability to further viscosify the acid, thus reducing the viscosity of the fluid system. This enables easy flowback of the fluid post-treatment. Because the viscosifying material used in the present invention is a nanoparticulate, it will be potentially nondamaging to the formation because of effective flowback and no residual deposition inside the formation.