Technology Focus: Acidizing (June 2021)
Authors: Chang Frank 
Published: August 2021

Hydraulic fracturing technologies propagated from North America outward to other oil- and gas-producing regions in the world. In earlier days, the main technology developments were mostly related to the materials, such as fluids and proppants, and their characterizations. In recent years, more advancements have been made in tools, engineering processes, and analyses. In a cased-hole fracturing treatment, perforating plays a critical role to the success of the job, though it is often overlooked because perforations are visualized as holes with empty tunnel behind the pipe. Any damage is irrelevant because fracturing will simply bypass the damage. In fact, a shaped charge is made of metal liner and case with explosive loaded in between. The metal material is pushed into the formation under extremely high pressure from the detonation of the explosive. Without backflow of reservoir fluid to flush out the debris, the perforation tunnels are very likely plugged. In tight formations, the backflow is not efficient because the permeability is too low and the time scale of the surge is very short. Obtaining information about perforation before pumping the fracture treatment allows the engineers to adjust the job design, adding perforations or other means to deliver a more-desirable outcome for the fracturing treatment.
Not all the wells or zones are suitable for hydraulic fracturing. Concerns over the well completion rating, nearby water layers, equipment and water availability, and other environmental and infrastructure constraints can limit the selection of stimulation method. Matrix chemical injection has often been the preferred or sometimes the only option. More-advanced technologies, however, are needed to extend reservoir access beyond the distance of matrix stimulation. Mechanical tunneling tools have been developed in recent years. They can bridge the gap between matrix and fracturing treatment very well. When combined with chemicals, this process can add efficiency in certain carbonate reservoirs.
Hydrochloric acid continues to be the most effective and low-cost material for carbonate stimulation. Though exotic chemistries such as chelating agents and organic acids have been promoted for being less corrosive at high temperatures, the cost and dissolving capacity limit their use to large-scale implementation. The ability to inhibit the corrosion tendency of hydrochloric acid can prove to be beneficial in the economics of acidizing. New technologies in corrosion prevention, both in acid stimulation and production processes, should always be beneficial.
During the tough year of 2020, and for the foreseeable future, implementation of engineering ingenuity will become more critical to maintain economical energy delivery in our industry.
Recommended additional reading at OnePetro: www.onepetro.org.
SPE 202369 Novel High-Effective Component for Acidizing Corrosion Inhibitors: Indolizine Derivatives of the Quaternary Quinolinium Salts by Zhen Yang, China University of Petroleum, et al.
SPE 203086 First Successful Fishbone Stimulation Completion in Onshore Oil Field in the United Arab Emirates by Fernando Quintero, ADNOC, et al.