Single-step sandstone acidizing

The simplicity of a single-step treatment is possible because buffered HF solutions (with pH as high as 3.2-4.8) are essentially nonreactive with carbonate minerals. Calcium fluoride precipitation is thus prevented. Therefore, a conventional acid preflush is not required, even in carbonate-containing sandstones. HF, in the absence of HCl, experiences minimal reaction with iron. Hence, with the elimination of the mineral acid (HCl) preflush and a low concentration of HCl in the HF acid solution, reaction with iron (tubulars) is largely mitigated. HF reacts primarily as a compound. 

It is expecting a lot of the service companies to ask them to enthusiastically endorse the idea of on-the-fly minimum-volume acid treatment, especially offshore or in remote locations. Any acid that was not pumped (because it was not needed) must be taken back. Understandably, service companies do not embrace this requirement. Nevertheless, in locations where they are not totally impractical, such treatments are viable and agreeable. 

Despite this estabHsbed reluctance on tbe part of service companies, BJ Services, for example, bas developed Process Controlled Acidizing for HF appbcations, in wbicb all additives and acid fluids are mixed on tbe fly. This enables tbe use of only those volumes of acid and chemicals needed, thereby providing a much smaller, safer, and more environmentally favorable operational footprint. Process Controlled Acidizing was introduced in southeast Asia.  

The basis of this method is that any acid is wasted when it is pumped beyond the point at which skin damage is completely removed. This is because acidizing an imdamaged sandstone formation or treatment interval cannot be expected to significantly increase production potential. 

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