Acidizing is a form of rehabilitation done on reservoir rocks to check their absorbency and also improve it. It is a simulation treatment carried out on rocks in order to stimulate and improve permeability. This process entails pumping acids, usually hydrochloric acide HCl into the rocks so that they can be dissolved.
The goal of acidizing is to open up channels in rocks that will accommodate the flow of oil and natural gas into the rocks without any blockage. Acidizing also aims to restore the natural permeable state of rocks.
A Little More on What is Acidizing
Acidizing is a rock rehabilitation process that entails the use of acid treatment in restoring permeability in rocks. This method has been used by operators for more than 120 years and it has proven to be an effective way of improving production in rocks.
This stimulation treatment requires the use of acid such as hydrochloric acide HCl. However, in the 1930s, there was a shortage of lack of effective acids and this caused a decline in the use of acidizing before it witnessed a turnaround afterwards. Acidizing is an effective treatment used in the oil and gas industry as it is essential for the restoration of energy resources in the industry. Acids are however not used in their raw forms, they are diluted with water alongside other chemicals to reduce hazards.
Advantages of Acidizing
In the oil and gas industry, acidizing is a popular stimulation treatment for wells and even reservoir rocks. One of the advantages of acidizing is that it creates channels in rocks for oil and natural gas to penetrate. Unlike fracking that uses high pressures before channels are created, acidizing depends on the potency of the acid to dissolve reservoir rocks and create channels and pathway for oil and natural gas.
Also, acidizing improves the permeability of rocks to a large degree. The types of acidic chemicals that are used for this purpose are not made public to prevent hazards that are associated with its misuse.
Reference for “Acidizing”
Academic research on “Acidizing”
Alternative stimulation fluids and their impact on carbonate acidizing, Fredd, C. N., & Fogler, H. S. (1996, January). Alternative stimulation fluids and their impact on carbonate acidizing. In SPE Formation Damage Control Symposium. Society of Petroleum Engineers. Conventional matrix acidizing treatments rely on hydrochloric acid to stimulate carbonate formations. However, the success of these treatments is often limited because of rapid acid spending at low injection rates and asphaltic sludge precipitation. This study investigated ethylenediaminetetraacetic acid (EDTA) as an alternative stimulation fluid. Results show that EDTA can effectively wormhole in limestone, even when injected at moderate or non-acidic pH values (4 to 13) and at low flow rates where only face dissolution would occur with HCl. Stimulation with EDTA at low injection rates is consistent with the dependence of the wormhole structure on the Damkohler number for flow and reaction. Sludge tests show that EDTA does not induce the precipitation of asphaltic sludge from crude oil, even in the presence of 3000 ppm of ferric iron. This result is attributed to EDTA being able to form stable chelates with ferric and ferrous iron.
Development of a Matrix Acidizing Stimulation Treatment Evaluation and Recording System (MASTERS), Montgomery, C. T., Jan, Y. M., & Niemeyer, B. L. (1995). Development of a Matrix Acidizing Stimulation Treatment Evaluation and Recording System (MASTERS). SPE Production & Facilities, 10(04), 219-224.
Stimulating carbonate formations using a closed fracture acidizing technique, Fredrickson, S. E. (1986, January). Stimulating carbonate formations using a closed fracture acidizing technique. In SPE East Texas Regional Meeting. Society of Petroleum Engineers. Many carbonate formations cannot be successfully fracture acidized at pressures above the formation fracture pressures above the formation fracture pressire using standard fracture acidizing pressire using standard fracture acidizing techniques. This situation exists because standard techniques rely on acid etched, uneven removal of the fracture face to produce fracture flow channels or fracture produce fracture flow channels or fracture Many times the etched fracture face is either too smooth, softens with acid, or the formation strength itself is insufficient to prevent closure due to overburden pressure, as in chalk formations. The “closed” fracture acidizing technique is designed to allow acid to flow through existing “closed” fractures below fracturing pressure in a channelling manner. Wide grooves or channels in the fracture face are then formed as acid is pumped at low rates and allowed to pumped at low rates and allowed to dissolve large flow channels. These grooves tend to remain open with good flow capacities under severe closure conditions and also allow fines or emulsions to be more easily produced. The initial fractured system can be natural fractures, previously created fractures, or fractures created previously created fractures, or fractures created and etched just prior to the “closed” treatment.
Fracture acidizing: history, present state, and future, Kalfayan, L. J. (2007, January). Fracture acidizing: history, present state, and future. In SPE Hydraulic Fracturing Technology Conference. Society of Petroleum Engineers. The first observation and description of hydraulic fracturing, by Grebe and Stoesser (1935), involved injecting acid to stimulate oil production from a carbonate formation. With the advent of hydraulic propped fracturing of sandstones with oil and sand in the late 1940s, fracture acidizing has been generally confined to carbonate formations; its advancement did not match that of propped fracturing. By the 1970s, propped fracturing of carbonates (in addition to sandstones) gained popularity through the greater understanding and ease of modeling fracture stimulation with non-reactive (non-acid) fluids. After the 1970s, however, advancements occurred in modeling fracture acidizing and in fracture acidizing stimulation theory. Thus, entering the 1980s and into the 1990s, fracture acidizing in carbonates increased, with development of a variety of fluid systems and multi-step procedures that are still in use today. Nevertheless, fracture acidizing continues as the less-preferred alternative to propped hydraulic fracturing in carbonates – and it has never been seriously considered as a stimulation method for sandstones. With approximately 70% of worldwide hydrocarbon reserves in carbonate formations, and the need to simplify sandstone stimulation treatments in general, the merits of fracture acidizing and its greater possibilities – for both carbonates and sandstones – must be considered.
This paper endeavors to briefly review the historical milestones leading to fracture acidizing, and their bearing on present methods and on the imposed rules. The paper touches on the types, purposes, benefits and limitations of present technologies and methods with a focus on the propped fracturing versus fracturing acidizing decision – and with a view to future possibilities and opportunities.
Matrix acidizing, McLeod, H. O. (1984). Matrix acidizing. Journal of Petroleum Technology, 36(12), 2-055.
Corrosion inhibition of Tubing steel during acidization of oil and gas wells, Migahed, M. A., & Nassar, I. F. (2008). Corrosion inhibition of Tubing steel during acidization of oil and gas wells. Electrochimica Acta, 53(6), 2877-2882. Acidization is an oil reservoir stimulation technique for increasing well productivity. Hydrochloric acid, HCl, is used in oil and gas production to stimulate the formation. The acid treatment occurs through steel tubes. The process requires a high degree of corrosion inhibition. The present study deals with the evaluation of the effectiveness of the new synthesized compound namely; 6-methyl-5-[m-nitro styryl]-3-mercapto-1,2,4-triazine as corrosion inhibitor for mild steel in 12% HCl solution at 50 °C using various chemical and electrochemical techniques. The results showed that anodic dissolution of mild steel was remarkably decreased. The strong adsorption ability of this new synthesized compound can be attributed to the presence of multiple adsorption centers of nitrogen as well as π-donor moieties.