METHOD FOR SELECTIVE ACID TREATMENT OF NON-UNIFORM CARBONATE FORMATION Russian patent published in 2019 - IPC E21B43/27 E21B43/22 E21B33/138 C09K8/72 C09K8/42 C09K8/40 

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the oil-producing industry. Method of selective acid treatment of non-uniform carbonate formation includes determination of coefficient of specific intake of treatment interval, cyclic successive pumping of buffer liquid into it, portions of viscoelastic composition (VEC) and acid composition in form of an aqueous solution of hydrochloric acid, which contains substances which improve filtration characteristics, followed by fluid pumping, which preserves reservoir properties of the formation. VEC is prepared from components in the following ratio, wt%: thallous amdo-propyl dimethylamine oxide 3.0–4.0; sodium hydroxide 5.0–15.0; sodium chloride 6.0; water – balance. At that in VEC fiber lactide with dosage of 10.0–30.0 kg/m³ is added. Amount of portions VEC and the fiber dosage is determined depending on the specific permeability coefficient on the basis of test works. Before punching portion VEC buffer fluid is pumped with lactide fibers in form of formation or fresh water with surfactant in amount of 0.5–1.0 m³, after which a portion VEC with fiber lactide is forced into formation through portion of formation or fresh water with surfactant acid composition in amount of 0.5–2.0 m³ per running meter of treatment interval for vertical wells or 0.05–0.2 m³ – for horizontal wells. Number of cycles of sequential pumping of formation or fresh water with surfactant, portions VEC with fibers of lactide, formation or fresh water with surfactant and acid composition is 2-3 depending on radius of distribution of acid. Volume of the portion of the acid composition is increased by 10–30 % with each subsequent cycle, after which the compositions are pumped with a liquid which preserves reservoir properties of the formation, in the volume of the tubing cavity plus 3–8 m³ with subsequent well shutdown for 6–8 hours to react acid composition and destruction of lactide fiber.

EFFECT: temporary blocking of formation intervals with high specific intake capacity more than 2 m³/(MPa⋅h), effective action of the acid composition on the rock, alignment of the treatment front, increase of the oil flow rate to 50 %.

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