Method of acidizing wells

In the method of matrix acidizing subterranean formations penetrated by a well in which a mineral acid-containing fluid is injected through the well and into contact with the subterranean formations at an elevated pressure sufficiently high to enable the mineral acid-containing fluid to penetrate the formation but less than the formation pressure, the improvement which comprises:

• a. injecting a dispersion of from 0.1 to 10 pounds per gallon of spheroidal-shaped, discrete solid, oil-soluble polyvinyl acetate particles having a density above about 1.19 grams per cubic centimeter and a particle size range of from 20 to 180 mesh in a carrier liquid selected from the class consisting of mineral acid-containing fluid, water, brine and aliphatic hydrocarbons, as a slug before, following or between slugs of mineral acid-containing fluid,
• b. subsequently injecting a further slug of a mineral acid-containing fluid which is diverted into less permeable portions of the formation, and
• c. finally contacting the polyvinyl acetate particles with an oil in which they are soluble.

In the method of fracture acidizing subterranean formations penetrated by a well in which a mineral acid-containing fluid is injected through the well and into contact with the subterranean formations at a pressure sufficient to fracture at least one of the formations, the improvement which comprises:

• a. injecting a carrier liquid selected from the class consisting of mineral acid-containing fluid, water, brine and aliphatic hydrocarbons which carrier liquid contains a dispersion of from 1 to 5 pounds per gallon of permanent propping agent particles and from 1 to 5 pounds per gallon of temporary propping agent particles comprising spheroidal-shaped, discrete, solid oil-soluble polyvinyl acetate particles having a density above about 1.19 grams per cubic centimeter and a narrow particle size range of from 8 to 12 mesh or from 12 to 20 mesh, as a slug before, following or between slugs of mineral acid-containing fluid,
• b. subsequently injecting a further slug of a mineral acid-containing fluid which is diverted into less permeable portions of the formation, and
• c. finally contacting the polyvinyl acetate particles with an oil in which they are soluble.

In the method of fracture acidizing subterranean formations penetrated by a well in which a mineral acid-containing fluid is injected through the well and into contact with the subterranean formations at a pressure sufficient to fracture at least one of the formations, the improvement which comprises:

• a. injecting as a diverting agent a dispersion of from 0.35 to 3.0 pounds per gallon of spheroidal-shaped, discrete, solid oil-soluble polyvinyl acetate particles having a density above about 1.19 grams per cubic centimeter and a particle size range of from 2 to 100 mesh in a carrier liquid selected from the class consisting of mineral acid-containing fluid, water, brine and aliphatic hydrocarbons, as a slug before, following or between slugs of mineral acid-containing fluid,
• b. subsequently injecting a further slug of a mineral acid-containing fluid which is diverted into less permeable portions of the formation, and
• c. finally contacting the polyvinyl acetate particles with an oil in which they are soluble.

In the method of acidizing subterranean formations penetrated by a well in which a mineral acid-containing fluid is injected through the well and into contact with the subterranean formation at an elevated pressure higher than the pressure of the formation whereby the mineral acid-containing fluid is forced from the well into the formation, the improvement which comprises:

• a. injecting a dispersion of from 1 to 5 pounds per gallon of spherical-shaped discrete, solid, oil-soluble polyvinyl acetate particles and from 1 to 5 pounds per gallon of permanent propping agent particles in a carrier liquid as a slug before, following or between slugs of mineral acid-containing fluid, which polyvinyl acetate particles filter out and bridge on the face of the formation and form a low fluid permeability filter cake on the face of the formation,
• b. subsequently injecting a further slug of a mineral acid-containing fluid which is diverted into less permeable portions of the formation, and
• c. finally contacting the polyvinyl acetate particles with an oil in which they are soluble.

In the method of acidizing subterranean formations penetrated by a well in which a mineral-acid containing fluid is injected through the well and into contact with the subterranean formation at an elevated pressure sufficiently high to fracture the formation, the improvement which comprises:

• a. injecting a dispersion of from 0.35 to 3.0 pounds per gallon spherical-shaped, discrete, solid, oil-soluble polyvinyl acetate particles, half of the said polyvinyl acetate particles ranging in size from 2 to 20 mesh and half of the said polyvinyl acetate particles ranging in size from 20 to 100 mesh, in a carrier liquid as a slug before, following or between slugs of mineral acid-containing fluid, which particles filter out and bridge on the face of the formation and form a low fluid permeability filter cake on the face of the formation,
• b. subsequently injecting a further slug of a mineral acid-containing fluid which is diverted into less permeable portions of the formation, and
• c. finally contacting the polyvinyl acetate particles with an oil in which they are soluble.