Acid Gas Injection into Petroleum Reservoirs: A Review

Matrix acidizing using acid gases is an under developed phenomenon in the oil and gas industry. For most petroleum engineers the most common acid gases are carbon dioxide (CO2 ) and dihydrogen sulfide (H2S). CO2 is mostly injected into oil reservoirs to achieve full/partial miscibility with the crude oil. In the process, CO2 reacts with formation water to form carbonic acid (a weak acid). Many research papers discuss how carbonic acid reacts with carbonate minerals and causes dissolution. Another popular acid gas in the oil industry is H2 S. H2 S is produced as an associated/dissolved gas in crude oil. H2 S has the ability to react with formation water to form hydrosulfuric acid (a weak acid). This research paper introduces other acid gases that react with formation water and generate strong acids. These gases are: Sulfur Trioxide (SO3 ), Nitrogen Dioxide (NO2 ), Hydrogen Chloride (HCl), Hydrogen Bromide (HBr) and Hydrogen Iodide (HI). It is understood that most reservoirs are water wet or intermediate wet. Acid gas injection would change the pH of the water film around the oil globule in the pore. pH of the water in most reservoirs typically ranges between 5.5 and 8.5. Lowering the pH of the water that coats the pore, will initiate the acid treatment and reduce the presence of carbonates within the rock. This would result in an increase in porosity and permeability within the reservoir. Some visual examples of stimulating the reservoirs using acid gases are also discussed in this research paper. Acid gas injection would be considered a solution to many issues in our reservoirs. It would allow for recovery from vuggy pores (also known as isolated pores) in carbonate formations. It would also enhance unconventional reservoirs such as shale oil reservoirs (knowing that some of those shale oil reservoirs have higher carbonate content). Furthermore, in our conventional reservoirs we produce from the larger pores leaving behind a lot of oil in tight pores, acid gas injection would open up some of those tight pores. Acid gas is matrix acidizing tool, that petroleum engineers need to enhance the reservoir rock properties.