Sandstone acidizing origins

Soil acidity originates from parental material (quartz, granite, sandstone, etc.), from organic matter (fulvic and humic acids, etc.), and from the pedogenetic evolution. In fact, acidity occurs not only from the presence of H+ ions but also from Al3+ ions. Roots exchange some H+ ions by Ca2+ and Mg2+ ions and acidify the medium. 

Sandstone acidizing is, for practical purposes, a method for removing acid-removable damage s) only. Except in rare cases, the production rate from an imdamaged well producing from a sandstone formation could be increased up to perhaps twice the original rate, at best. Acid-removable skin, discussed in detail in chapter 6, may manifest itself in the wellbore, in the perforations, or within the formation. 

This matrix acidization process consists of injecting hydrochloric acid (for limestones) or a hydrochloric acid-hydrofluoric acid mixture (for sandstones) into the formation pore space. The acid reacts with and dissolves portions of the original rock matrix and thus increases permeability. The depth that the acid penetrates into the formation is one of the factors that determines the effectiveness of the treatment. 

Plate 11. Carbonate cement in sandstones which suffered intense solution by acids. Note that the carbonate cement in photo c undergoing dissolution is of secondary authigenic origin... 

It is considered that the average nickel content of the lithosphere is about 100 ppm recent investigations confirm this value. More specifically the nickel content varies according to the origin of the rocks ultrabasic igneous and their metamorphic forms, 500 to 1200 ppm basic forms, 150 ppm acidic forms, 5-10 ppm. The metamorphic and sedimentary rocks present intermediate values clays and materials of various textures from 20 to 30 ppm sandstone 90 ppm limestone from 10 to 20 ppm and certain particular rocks as little as 2 ppm. 

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