Evaluation of Synthetic Acid for Wells Stimulation in Carbonate Formations

Abstract

Acid treatments of carbonate formations are usually carried out using mineral acid (HCl), organic acids (formic and acetic), mixed acids (HCl-formic, HCl-acetic), or retarded acids. The major challenges when using these acids are their high corrosivity, fast reaction rate and health hazard. The improvement in corrosion inhibitors makes the use of a strong acid as high as 28 wt% HCl possible. The acid reaction rate can be controlled by increasing acid viscosity using gelling agent or emulsifying acid droplets, acid-in-diesel emulsion. While the issues of stimulation acids reaction and corrosion rates are relatively controlled, these acids health hazard rating of 3 by the National Fire Protection Association (NFPA) is a major concern. A health hazard rating of three is defined as an extreme danger where short exposure could cause serious injury. An acid replacement chemical that has no or minimum health hazard rating while still has the ability to dissolve carbonate rock would be a major forward step in stimulation technology. This paper presents the results of the study conducted on a synthetic stimulation acid (Syn-A) chemical, with health hazard rating of one and dissolving power similar to 15 wt% hydrochloric acid (HCl). An extensive experimental scheme including: thermal stability, dissolving power, acidity, compatibility, corrosion rate & inhibition and coreflooding on carbonate formation core plugs was conducted. The Syn-A was found to be thermally stable with similar dissolving power to 15 wt% HCl and lower corrosion rate. In addition, the Syn-A developed a breakthrough on core plugs with an average pore volume (PV) of 2.7 and approximately 3 folds increase in permeability.