Accounting for silica precipitation in the design of sandstone acidizing

Eduardo Da Motta, Benjamin Plavnik, R. S. Schechter, A. D. Hill

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29 Citations (Scopus)


Mud-acid treatments normally are designed by approximating the complex mineralogy of a sandstone with a 'lumping' procedure. Minerals are classified as either fast- or slow-reacting and the rates of their reaction with HF are determined by analysis of the acid effluent from acidized core plugs. For most treatments carried out at modest temperatures and reasonable rates, this approach is satisfactory. In this paper, we show that at higher reaction temperatures, the simple two-mineral dissolution model does not apply because an intermediate product of the HF reaction with quartz, feldspars, and clays (H2SiF6) begins to react further with both clays and feldspars. This new reaction must be included to model data. The additional reaction, not observed at lower temperatures, has important consequences. For example, the acid injection rate is no longer critical. The analysis presented here shows that retarded acids are unnecessary. Contrary to previous concepts, mud acid itself provides a deep-penetrating capability. This surprising result may account for the high percentage of successful treatments even when this treatment is carried out under a wide range of conditions.

Original languageEnglish
Pages (from-to)138-144
Number of pages7
JournalSPE Production and Facilities
Issue number2
Publication statusPublished - May 1993
Externally publishedYes


ASJC Scopus subject areas

  • Fuel Technology

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