Evaluation of Synthetic Acid for Wells Stimulation in Carbonate Formations

Al-dahlan, Mohammed N (Saudi Aramco PE&D) | Al-Obied, Marwa Ahmad (Saudi Aramco PE&D) | MARSHAD, KHALID Mohammad (Saudi Aramco PE&D) | Sahman, Faisal M (Saudi Aramco) | Al-Yami, Ibrahim Saleh (Saudi Aramco PE&D) | AlHajri, Abdullah (Saudi Aramco PE&D)


Description of the material
This paper presents the results of the study conducted on HCl-Replacement-Acid (HRA), a synthetic HCl replacement chemical, with health hazard rating of one and dissolving power similar to HCl. An extensive experimental scheme including: thermal stability, dissolving power, acidity, compatibility, corrosion rate & inhibition and coreflooding on carbonate formation core plugs was conducted.
Acid treatments of carbonate formations are usually carried out using mineral acid (HCl), organic acids (formic and acetic), mixed acids (HCl-formic, HCl-acetic), and retarded acids. The major challenges when using these acids are their high corrosion rate, fast reaction rate and health hazard. The improvement in corrosion inhibitors makes the use of strong acid as high as 28 wt% HCl possible. The acid reaction rate can be controlled by decreasing diffusion rate of hydronium ions (H+) to the rock surface where reactions take place by increasing acid viscosity using gelling agent or emulsifying acid droplet in a hydrocarbons liquid, 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 major concern. A health hazard rating of 3 is defined as an extreme danger where short exposure could cause serious injury
Results, Observations, and Conclusions
Based on this study results, the HRA was found to be thermally stable with similar dissolving power to 15 wt% HCl and lower corrosion rate. In addition, the HRA developed a breakthrough on core plugs with average pore volume (PV) of 2.7 and approximately 3 folds increase in permeability.
Significance of subject matter
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.