Acid stimulation for damage removal is performed when a well is expected to produce satisfactorily when the skin is approximately equal to one. Blindly flowing acid into the well is the easiest thing to do and is commonly performed when the exposure length of the well is relatively short (commonly done in vertical wells). However, as wellbore lengths become longer, this approach is not preferred because it can create massive enlargements to sections near the top of the formation and complications could occur, ranging from re-entry issues and lack of treatment coverage to wellbore collapse.
Tubing-conveyed acid, mostly by coiled tubing (CT), would be the logical choice for acid placement because it evenly spreads the acid throughout the wellbore. Spotting acid throughout a long wellbore has been widely accepted as a viable solution for cleaning the surface of the wellbore. Using CT, acid washing is another common process that can improve stimulation without much additional expense. Using a jetting tool with many jets, acid can be sprayed onto the wellbore wall, and the active agitation caused by this acid-wash process increases the chemical reactivity of the acid at the desired locations.
This paper discusses the implementation of an improvement to the process that uses specialized jetting mechanisms which position the jets closer to the target. This process also uses higher horsepower to provide higher jet-impact pressure onto the wellbore wall. This improvement provides several benefits, including effectively penetrating natural fractures and opening them while stimulating them. Moreover, at certain locations, larger fractures can also be created, which can result in even better production. Actual results of such stimulations are presented.