Core-Shell Systems for Delayed Delivery of Concentrated Mineral Acid

Abstract

Acid stimulation, for both oil and gas wells, greatly supports the industry as a versatile means of enhancing production. Although acids enhance carbonate reservoir permeability to hydrocarbons, the reactions rates of the acid (e.g., HCl) with the rock often occur too rapidly at high temperatures, leading to a reduction in acid penetration. Several methods exist to improve the effectiveness of acidizing in high temperature reservoirs (i.e., greater than 250°F), including the use of emulsified acid, mixtures of hydrochloric acid (HCl) and organic acids, and gelled acids. Many of the aforementioned techniques are effective forms of treatment; however, they hold significant limitations such as reduction in acid efficiency, poor control over penetration depth and the requirement of corrosion inhibitors. Acc ordingly, encapsulated HCl holds potential as an attractive alternative to address these shortcomings since its prolonged release profile would permit transport of acid deep within the reservoir. In addition, when successfully encapsulated, this technology could completely eliminate the use of corrosion inhibitors. Herein, we demonstrate the design and preparation of highly modular core-shell particles comprising concentrated HCl encapsulated within an acrylate-based thermoset polymer shell. We show that the shell generation mechanism (i.e., photopolymerization of acrylate monomers) is compatible with concentrated HCl and further detail the encapsulation process. Our results demonstrate that acid release profiles are dictated by the properties of the shell material, enabling a prolonged delivery of HCl in laboratory studies. This is a first step towards the design of particle shell systems that can tolerate the harsh reservoir conditions, including high temperatures, pressures, and salinity of mixing water. A tunable core-shell delivery system that encompasses a sufficient amount of strong mineral acid is well-poised to address the unmet need of deeper penetration of HCl into the reservoir enabling greater stimulation efficiency.

Streamline-Based Simulation of Nanoparticle Transport in Field-Scale Heterogeneous Subsurface Systems

“…Nanocapsules ( [11,12]) are a promising new technology for controlled delivery in the subsurface. A species of interest (e.g., acid, crosslinker, surfactant, etc.)…”

“…Additionally, density differences can make NPs respond to gravity or inertial flows in ways that solutes do not ( [10]). Finally, engineered behaviors such as payload release or triggered responses add a more complex reaction component to the modeling, compared to traditional advective-dispersive-reactive transport ( [11,12]).…”

A reservoir-damage-free encapsulated acid dually controlled by hydrogen ion concentration and temperature

“…However, when the H + concentration was below 8%, the residual mass rate of the EA decreased quickly. Compared with the existing encapsulated acids, [18][19][20][21][22] the encapsulating material in this paper is completely dissolved in neutral solution, avoiding damage to the reservoir by the residue.…”

“…14 Although these acid systems have a certain slow chemical reaction rate performance, they are in direct contact with the acid fracturing pipelines and therefore must be treated with corrosion inhibitor additives. [15][16][17] The concept of encapsulated acids, which use encapsulating materials to cover solid hydrochloric acid, 18 nitric acid 19 and citric acid, [20][21][22] has been researched, as has the isolation of solid acids by means of encapsulation methods. The penetration depth of acids has been increased by the temperature and time-controlled dissolution performance of different encapsulating materials.…”

“…The acidic solution has two functions; carrying the EA and also etching the surface of the rock in the near-well region. Unlike other EAs, [18][19][20][21][22] the release of the proposed EA is dual controlled by the H + ion concentration and the temperature. With low temperatures (<95 C) and high H + ion concentrations of the carrying uid (>14%), the encapsulating material should maintain its structural integrity, isolate the carrying uid from the solid hydrochloric acid (SHA), and prevent the solid hydrochloric acid from being dissolved.…”