Acetic Acid Demonstrates Greater CarbonateDissolution Than Typically Expected

摘要

Stimulation of carbonate formations by acid dissolution ofthe rock has been an efficient and successful method ofimproving production in oil and gas wells. Hydrochloric acidis the normal fluid of choice. However, in high temperatureapplications corrosion issues limit usage, especially in chromecompletions. Acetic acid has been used with some success andwith adequate corrosion protection. But due to its lowreactivity at higher temperatures, the efficiency with which agallon of acid dissolves the formation is perceived as low. Thisperception comes from reaction efficiency of acetic acidreported in the literature ranging in values from 90%at 25 ℃to 40%at 121 ℃ for 2 to 15 wt%, respectively. Acetic acidreaction on calcium carbonate is controlled by its smalldissociation constant, 1.754E-05at 25 ℃ (77 ℉)and therefore islabeled a weak acid. Experimental data presented here illustrates that takingadvantage of the low concentration acetic acid's higherefficiency could give significant advantages to removal ofcarbonate rock under high temperature conditions. Dissolutionof calcium carbonate using 5 molar acetic acid and dilutionusing fresh water has been evaluated at temperatures of 25° to125 ℃ (77° to 257 ℉)to determine what changes in reactionefficiency can be attained. With no shut-in, an 8.5 to 35%increase in efficiency was observed by decreasing the injectionrate. This technique should be exceptionally useful in thepetroleum industry to acid-stimulate wells with carbonate formation at high temperatures and containing chrome tubing. A further application of the technique could be removal ofcalcium carbonate scale under similar conditions.