Hydraulic Fracturing, Acid Fracturing, and Acidizing

These three methods are commonly used to stimulate oil wells and enhance hydrocarbon recovery.
Hydraulic fracturing is mainly applied in sandstone reservoirs and shale gas formations to increase permeability and improve production. In contrast, acid fracturing is performed in carbonate reservoirs.
 Hydraulic Fracturing
In hydraulic fracturing, high-pressure pumps inject large volumes of water into the wellbore (as shown in the video clip).The injection pressure becomes high enough to create fractures in the reservoir rock, thereby increasing its permeability.
A material known as proppant is then placed inside the fractures to keep them open and maintain flow conductivity.
 Acid Fracturing
Acid fracturing is used in carbonate reservoirs and is considered one of the Enhanced Oil Recovery (EOR) techniques. In this method, hydrochloric acid (HCl) is injected into the well at high pressure using powerful pumps. The pressure is increased until it creates fractures in the reservoir rock—without requiring any proppant, since the acid etches the fracture faces and naturally maintains conductivity.
 Acidizing
Acidizing is different from acid fracturing. Here, acid is injected into the well without fracturing the formation. The purpose is to:
dissolve part of the carbonate rock to improve near-wellbore permeability, or
remove formation damage caused by drilling fluids and mud-cake that may have plugged the pore spaces.

References: Miskimins, J., Hydraulic Fracturing Fundamentals and Advancements, SPE, 2019.Williams et al., “Design of Acid Fracturing Treatments,” Journal of Petroleum Technology, Vol. 24, 1972.