One of the principal methods of enhancing oil and gas recovery is physical-and-chemical treatment of productive formations using acid and alkali solutions. In most oil and gas fields in Western Siberia on cessation of drilling operations or during prolonged idling of well stock, acid bottom-hole treatment is used following which the well is brought in [1].

However, for physical-and-chemical formation treatment to be highly efficient it is necessary to take into account the material composition of the reservoir formation and to perform technical operations in the well in accordance with the techniques developed specifically for such fields and productive formations. Failure to observe those conditions leads to low efficiency of this type of operations and can even bring about adverse results.

In oilfields, acid spotting involves the use of hydrochloric acid (HCI), hydrofluoric (fluoric) acid (HF) or their mixture – mud acid, and sodium hydroxide solution (caustic soda – NaOH) is used during alkaline soaking. A 15% solution of HCl is used in acid spotting and a 15% solution of NaOH is used in alkaline soaking. Acid spotting lasts from 2 to 6 hours while alkaline soaking takes up to 24 hours.

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