Retarded HF systems

Novel acidizing systems come and go. These serve to differentiate service company providers and thus do not necessarily enhance acidizing response. However, certain retarded HF systems can be uniquely benefidal in various appbcations. Such appfications are removal of deep damage, treatment of highly add-sensitive sands (or sands with unusual mineralogies), and treatment of high-temperature formations. Certain retarded (or buffered) systems are less corrosive and easier to mix on-site, as well, and may be considered with those features in mind. 

Main acid stage (seccnd) Retarded HF system (service company specified) 75... 

Main acid stage HCI-HF (variable strength) or service company-specified retarded HF system —... 

In most cases, the reaction of sulfur tetrafluoride with oxygen functions requires the presence of catalytic to molar amounts of hydrogen fluoride or Lewis acid type fluorides. Standard quality sulfur tetrafluoride, unless special precautions are taken, is unavoidably contaminated by trace amounts of hydrogen fluoride. The existence of ionic species SF3+ and HF2 in the SF4/HF system has been documented by spectral and conductometric investigations34 and there is evidence from vapor-pressure measurements of retardation of the reaction by coordination of hydrogen fluorine on the carbonyl oxygen.35... 

Acids commonly used in sandstone formations include hydrofluoric-based acids. Full strength mud acid (12wt% HCl + 3wt% HF) has been used to stimulate sandstone reservoirs for several decades [J]. Beeause of the fast reaction of hydrofluoric acid with clay minerals, various retarded mud acids were introduced. In one system, aluminum ehloride was added to mud acid systems to ensure deep acid penetration [4. In a seeond system, boric acid was used to achieve the same goal [5]. Reeently, LuUo and Rae [6] introduced a new acid system, consisting of phosphonic acid and hydrofluoric acid. For high temperature applications, mixtures of organic acids (formic or acetic) and hydrofluoric acids are used [7]. 

HF laminates, however, require different processing than brominated FR-4s, in lamination, wet processing, and driUing. Also, HF laminates differ from each other based on the flame-retardant system they are not as similar to each other as one FR-4 is to another FR-4.The fabricator needs to work closely with the laminator to develop processes suited to the particular formulation. The engineer specifying the HF material for the product needs to understand both the properties of the specific brand of HF material, and the capabilities of the fabricator to produce quality MLBs given the design s properties and performance requirements. ... 

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