To the Barricades! Using a Self-Assembled Wall to Protect Ordinary Portland Cement from Acidic Corrosion

Abstract

A novel cement additive, capable of creating an insoluble barrier at the first sign of acid attack, is offered. When present in small quantities, it allows ordinary Portland cement (OPC) to protect itself from acid corrosion as shown by laboratory tests. This corrosion resistance is critical especially in regards to attack from carbonic acid produced when CO2 combines with water or from naturally occurring H2S in the well. These acids can turn OPC porous and weak, rendering it incapable of maintaining zonal isolation. CO2 gas can enter the wellbore as part of either a stimulation technique to energize production or to sequester this green-house underground in hopes of reducing global warming. Cement used in a CO2-sequestering well must maintain its integrity for hundreds if not thousands of years to keep the CO2 trapped; otherwise, the CO2 can reenter the atmosphere. Damage to the cement sheath in the short -term can lead to contaminated aquifers or annular leakage of natural gas, both of which can have devastating results. Laboratory testing of this commercially-available additive was performed under temperature and pressure in CO2-saturated brines for weeks. Corrosion of the tested cement samples was measured optically and through a variety of chemical analysis procedures. Samples of OPC containing the additive stopped penetration of carbonic acid near the surface whereas sample without suffered deep corrosion penetration. When it is known in advance that the well will be highly acidic it may be cemented with acidresistant alumina-silicate cement (ASC) rather than OPC. However, this technique requires specially isolated pumping equipment to avoid flash set of the ASC, making the process more expensive and error-prone. Addition of the novel dry-powder, acid-activated, barrier-creating compound is much easier. The additive remains inert in the set OPC until acid corrosion occurs. Release of calcium ions by acid attack triggers the formation of an insoluble barrier which reduces further acid damage.

Comprehensive Review of Sealant Materials for Leakage Remediation Technology in Geological CO2 Capture and Storage Process

“…It showed that conventional Portland cement had a compressive strength decrease of 21.43%, while calcium-aluminate cement was only 5.16%. In addition, weight control agents, such as fly ash, , slag, , nanoparticles (e.g., microsilicon), ,− resins, , polymers, and many other swelling agents , can be added to adjust the CaO percentage, improve the cement density, and obtain better cement strength. In recent years, there have been many CO 2 -resistant additives developed to protect conventional Portland cement from acidic corrosion. − Vorderbuggen et al and Doan et al developed a cement additive (e.g., hydroxyethylcellulose, methyl hydroxyethylcellulose, and carboxymethyl hydroxyethyl cellulose) that can create an insoluble barrier when it encounters an acid attack. Laboratory tests showed that this additive performed well under specific pressure and temperature in brines saturated with CO 2 for weeks.…”

“…In recent years, there have been many CO 2 -resistant additives developed to protect conventional Portland cement from acidic corrosion. − Vorderbuggen et al and Doan et al developed a cement additive (e.g., hydroxyethylcellulose, methyl hydroxyethylcellulose, and carboxymethyl hydroxyethyl cellulose) that can create an insoluble barrier when it encounters an acid attack. Laboratory tests showed that this additive performed well under specific pressure and temperature in brines saturated with CO 2 for weeks.…”